Nuclear propulsion pushes against diminishing returns


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Nuclear propulsion pushes against diminishing returns

  1. 1. Chapter 2 Nuclear Propulsion Pushes Against Diminishing Returns 'IWo propulsion revolutions made the modem combat submarine possible, and both remain in production. The filst was the Gemtan combination of a diesel·driven gcmerator and banks of batteries we now cal! the diesel-electric submarino. The second revolution was the ADlerican application of nuclear power. Both innovations were widely copied, as their attributcs were immediately recognized. A third revolution is in the making, combining thc best of both systems. It ls certain also to be adopted wídely in the next century's submarines. Thls revolutioo is nonnuclear, air·independent propulsion. A variety of schemes have been proposed, just as a variety of submarino propulsion schemes were tried in the early part of the 20th century, including gasoline, steam and battery-oinly power. The diesel motor displaced ali others, and it is likely the fuel cell wm emerge as the devíce of choice for AIP. But not without a struggle. At least three other AIP systems are under development, and two of thosc have been through serious sea trials. Nuclear power gives total independenco from the surface, meaning submarinos can operate under lhe polar ice cap, circurnnavigate lhe globe submerged, and in ali respects except communication - remain hidden under tho sea. Diesel-electric propulsion, when operating submerged on batteríes, provldes mechanical quietness and compact mechanical spaces, but eveotually must come to the surface for battery recharge. AIP promises a maniage o{ advantages - independence from lhe surface, reduction in radiatcd no.ise and smaller size. AIP is in its infancy, and ooly threo active-duty submarinos in the world use the system, ali Swedish, host AIP. The Gennans have announced a four·ship AlP program, the Italians will build two of the Germao design, and lhe French are exporting three AIP submarinos to Pakistan. By the tum ofthe century, at leastlO AIP submarinos will be i.n some stage of consttuction. More will follow, and by mid-century, h is likely ali non, nuclear submarines will feature AIP. Submariners use the tonn "indiscretioo rate" when talking about submerged endurance. It ls a ratio of the time lhe ship spends underwater and the time it must protrude a snor)cel above the surface. The snorkel, a Dutch invention adopted by the Gonnans lato in WW ll, is a pair of pipes pushed tO the surface from a submerged submarino. lt allows a diesel engine to run underwater by drawing air down one pipe, with the exhaust blown out the second. · In WW I and WW n, submarinos surfaced, usually at nigbt, to run their diesels and recharge their batterics. But the invention of ain:raft-mounted, surface-search radars made the níght as dangerous as the day for recharging. The answer was the snorkel, whlch presonted a far smaller radar cross-section than did the cntire submarine on the surface. Today's snorkels 13
  2. 2. Submarine Technology for the 2 7st Century are e~uipped with radar-absorbing coatings, infrared defeating materiais and other stealth assistance. Modem diesels can run at higher speeds, cutiing charging time to perhaps a haJf. hollf jn every 12 hours. However, the need to malntain a battery charge has been the dieselclectric submarine's Achilles' Hed, for eventually the ship must regain contact with the surface or it - and the men inside - must die. Nuclear submarines do oot need to recharge their baneries. But they too must "poke a pipe" above the surface porlodically. In their case, the pipe is a communications anteMa. While smaller in size than a snorlcel head, the anteMa also can be detected And unlike a snorkel. the antenna often transmits a signal with a range of hundreds or thousands of miJes. While frequency-hoppíng and low~probability-of-intercept procedures will be used to mini· mize the vulnerability to radio direction-finding, the simple fact remains that ali submarinos must occasionally "póke a pipo'' above the sllfface, stripping away if even momentarlly the stealth that is the ship's only armor. ln order to fight, a ship must move. In order to move, it must float, or in the case or submarinos, have control of its ballast. In this chapter, we look at advances in nuclear propulsion. The following two cbapters will examine the rapid progress in non-nuclear propulsion. PROPULSION PUSHES SIZE •• ''Submarines are getting bígger and bigger, and it's not an especially good thing from an active acoustic point of view," says Thomas Taylor, the man who once headed the Defense Advanced Research Project Agency's Naval Technology office. 1The primary reason for growth is the quieting of propulsion technology. The sizc of submarinos today is driven by lhe size and weight of its quiet powerplant, which reduces the volume available for payload. In 40 years of evolution in American nuclear submarino design, displacement rose from the 3,075-ton Skipjack to the 6,927-ton LosAngeles to the 9,200-ton Seawolf. A similar growth can be scen in succeeding classes of other navies' nuclear subuwines as well Tbe increased displacement requires increases in borsepower, a larger powerplant in tum requires more masslve silencing equipment, which clrlves up the size of the ship, and a self-sustainíng cycle of growth is established. This ex.pansion of displacement and horsepower has impacted top underwater speed ooly slightly. The top speed of modem Westem submarlnes is only a bandful of knots faster than theír brethren of 40 years ago. Russian designers have produced ·two higber-speed submarinos- the 4Í-knot-plus Alfa and Papa classes - but their clllTent generation of submarines is notas quick. Unli1 the mid~l990s, nuclear submarine propu1sion plants barely kept pacc wilh lhe additional displacement required Tbe U.S. Navy's New Attack Submarine design has rcverscd this trend to ever-lacger ships, with officials saying it wiU maintain the quieting levei of the 9,200-ton Seawolf in a 7,50(}-ton paclcage. However, the NAS sacrlfices both spced, depth and magazine size in comparison to the Seawolf. Thc advantage of nuclear power for submarine propulsion is complete independence from the sllfface coupled with enonnous high-speed endurance. The penalty is complexity 8lld cost. Crew tralning and retention are vital to successful operatlon. And while the procureDICJII cost of a nuclear submarino may be but twice- or three-times that of a comparable non-nuclear vessel, when training, crew salaries, lífe-cycle suppon and decommissíoning costs are added. 14
  3. 3. Nuclear Propulsion Pushes Agoinst Diminishing Returns lhe multiple jumps higher. This kind of accounting led the Canadians to back away from switclting to a nuclear submarine fleet In the late 1980s. Atouúc propulsion research got under way in the United States immediately afttr WW n, but the roots ofthe effort go back to 1939. "ln March 1939, nuclear scientists at Columbia University arranged through Asslstant Secretary of the Navy Charles Edison for Nobel Laureate Enrico Fenni to give a briefing at the Navy Dept. on the potential of nuclear fission. Rear Adm. Stanford C. Hooper (now technicaJ asst to the CNO) assembled an audience of naval officers, Army ordinance officers and two NRL [Naval Research Labora· tory] scientists. Permi sensed condescension and the brush-off. but one of the NRL scientists, Dr. Ross Ounn, already interested in fission, was impressed by Fenni's informatlon. ''Dr. Gunn, a physicist and technical advisor to the director of the NRL, also was concerned with submarlne propulsion. lt says a lot for NRL and BeEng [Bureau of Engineer· ing) that Dr. Gunn was able to quickly lead the Navy into the nuclear field, the first govemment agency to conduct sucb research. Less than two monlhs later, he got lhe chief of the burcau (again the progresslve Rear Adm. Harold Bowcn) to allow $1,500 to conduct exploratory resea.rch into the use of nuclear energy as a power source. In June, NRL submítted a memorandum on the use of atomic power in submarincs.' 01 After WW ll, in a remarkably swift development program, the Unlted States tested prototype reactors, then installed one in a submarino. The atomic secrets were shared with the British, but not the French or Dutch, whlle the Russians quickly followed the American lead. For lower-tier navies, nuclear propulsion presents two significant hurdles. The first. as mentioncd, is cost. A second hurdle is political. Some submarino reactors use weaponsgradc uranium for fuel, mcaning any nation wishing to build a naval nuclear propulsion system must closely gauge its relationship to the Nuclear Non-Prollferation Treaty. Neither of these factorS bave kept Brazil and India from omba.ddng on the independent development o( a nuclear submarino. Neither natioo js a signatory to the trcaty, and India bas tested a "peaceful" nuclear weapon. But progress has been slow, sometimes halting. as thesc nations weigh domcstic needs against obtaining the perqulsite of a major powcr. The Brazilian program, for cxample, has been cut back by lhe cwrent civilian government. Since the 1960s, subrnarlne-producing nations in Europe developed other propulsion schemes which - whlle not giving the top-speed-around-the-world-submerged capability of a nuclear boat- are affordable and silent, givíng an undersea endurance measured in weeks instead of days. Atmospbere-independent combustion (AIC) of Stlrling and diesel engines are two systems under evaluation: fuel cell technology first developed for the U.S. space program is another promising tecbnology under eumination in Canada and West Germany; France is working on a closed-cycle turbine system it calls MESMA. Other countries, Australia. Japan and South Korea among otherS, are monitoring closely these developments. A Canadlan company developed a stand-alone, low-power reactor uslng nonweapons grade enriched uranium to act as a "nuclear banery cbarger." Sucb a system could be retrofitted iato a conventional submarlne to provide unlimited underwater endurance, but without the unlimited high-speed capability of a true nuclear boat. The Canadians teamed with the Outch submarino mak:er RDM to explore the integration further. While the two primary producers of nuclear subtnarines, the Uníted States and Russia, appear satisfied with the basic pressurized water reactor, other more powerful designs have been proposed, which could elirninate sources of both weight and noise in lhe cycle, ' 15 '
  4. 4. 5ubmarine Technology for the 21st Centvry whilc providing significantly more power. For example, Westem rese;u-ch into gas-cooled reactors promises to increase power while reducing size and weight Unlike land combat. undersea watfll(e does not belong to ''the quick or the dead." Speed underwater often means noise and noise means detection. In propulsion the prime factor is now silence, the secondary factor is power denslty and only third is volume a consideration. A variety of underwater propulsion systems lll1! under development today - improve. ments to existing pressure water nuclear reactors, new gas-cooled nuclear systems and direct conversion of reaclor heat to elecnícity, as well as non.nuclear efforts like closed-cycle diesel motors and Stirling engines, Rankinc cycles, BraytOn cyçles and fuel cells, They all mlllit be evaluated by the cri teria of silence, power density and volume. PRESSURIZED WATER REACTORS REACH MATURITY The basic powerplant in an Amerlcan nuclear submarine is fundamentally no different than thc system used aboard the first mass-produced class, the Skipjack. A hlghly pressurlud water loop is passed through thc reactor to exttaot energ)', wbich is transferred via a heat ~changer to produce steam in a. secondacy loop to spin a turbinc. Thc steam ís condensed and retums to lhe beat exchanger. The system is called a PWR - presswized water rea.ctor (see Figure 2· 1). "Fro.m the Skipjack to the Seawolf, it is basically unchanged with larger plants with bigher power densities," said Lt Cmdr. Richard Martin with the Submarine Technology prognun at tbe Dcfence Advanced Research Projects Agency (DARPA). ''However, power density has reachéd a floor where marginal improvements will be very expensive.''3 Adm. Bruce DeMars. director of naval nuclear propulsioo. told Congress much tbe same tlúng in 1990: "Performance gains in a maturing technology are exponentially harder tQ achíeve." DeMars outlincd tive areas under researoh for what he called ''the next-generation reactor beyond SSN 21." They are: • Materiais development - ''I need materiais capa.ble of waintaining their structural and wecbanical inte_grity over long perlods of time in a harsh tuetor envirolllllent" • Heat and fluid transfer equipment - ''The best reactor in the world is useless in a ship without the equipment to convert its energy to propulsive power," • Chemistry- ''We are developing water chemistry methods a.nd controls to signiticantly reduce the need for maintenance, personnol radiation exposure durlng_ maintenance and the over ali cost of maintenance." • Physícs - "Accurate modeling reduces the need for design margins and thereby increases allowable plant operating parameters.'' • Eleotronics and power distributlon- "SSN 21 is being outfitted with adviUlced microprocessor and graphics-based equipment. This devclopment effor:t will have ille same effeot as better core analyses- knowing our operating margins more preci.seJY. will allow us to get more usable power from the reactor.'" What DeMars didn't mention in the open congcessional session was his wm:k tQ devise and produce a nuclear core that didn't require perlodic (and multlmillion dollar) replaéement. His deve!Qpment of a "througb-life core" eliminated not only the downt:!me infrastructure necessary to perform the recore, but also eliminau:d design constraints and 16
  5. 5. Nuclear Propulsion Pushes Against Diminishing Retvrns Figure 2·1 Fundamentais of the PWR Thls schematlc outllnes lhe basic configuralion of the pressurized water reactor used on ali nuclear submarinas. lhe prlmary loop includes the reactor and steam generators, which uses lhe heat from the reactorcore to create steam. This loop is shielded against stray radlation, and is contalned within depth·reslstant bull<heade, The secondary loop accepts the steam and converts 1t into mechanlcal energy through turblnes. These turbinas can be llnked dlrectly to lhe propeller by reductlon gears (as shown) or spln a generator to create electricity driving large electric motors tumlng lhe propeller (called a turbo-electric drlve or TED). TED systoms are quleter but less efflclent, and hence slower. The pressuriier in lhe primary loop creates pressure by malntalnlng a "bubble" of steam at lhe top. Establlshing and malntainlng this bubble ls criticai to lhe safe operation of lhe syslem, and lhe subject of slgnifK:ant tralnlng in naval nuclear power schools. lhe bubble is lhe probable reason submarina reactors, when starting cold, require massive amounts of electrlcity to produce lhe steam bubble by reslstance healing. The bubble cannot be allowed to collapse; thal would depressurlze lhe prlmaty loop and lead to rapid- perhaps unconlrollable - core heatlng. The lon·excnange vessel in lhe primary loop allows lntroductlon of chemlcals to regulale neutron density and speed. Thls nuclear chemlstry is lmportanl in regulating lhe speed of lhe reaction. 11 also allows chemical remova! of undeslrable byproducts. steam generator design ls key to lhe emclent thermodynamic operatlon of lhe reactor, and has gone through severaJ generatlons of development. The steam generator aboard lhe Amerlcan New Attack Submarina uses a different "spatlal orientalion" than previous generators, aJiowing "greater shlp deslgn flexibllity and decreased construction costs" (see text). Power is regulatect 1hrough wa!er density. The cooling loop is under 2,000·2,500 psi pressure. As more power ls required, lhe steam leavlng lhe turbinas ls cooler and absorbs more heat from lhe steam generator. This cools lhe primary loop, lncreaslng lhe density of lhe water. The denser water slows more neutrons anel accelerales lhe nuclear reactlon, producing more heat. Manual lnterventlon wlth manlp1.118tion of lhe control rods ls unnecessary. The reverse process reduces core heat productlon. Reactors have been deployed uslng conveclion for water clrculallon, ellmlnatlng lhe use oi primary loop coolant pumps at low and medium apeeds, reduclng a major source of noise productlon. AI hlgher speeds, the pumps are switohed on but lhe submarlne is making enough nolse at lhls polnt lha! lhe addltion of coolant pump noise is not consldered delrimental. The secondary loop of lhe submarina reactor system uses baslc power generation engineering, wlth lhe exceptlon of acoustic lsolation. The two greatest producers of noise abóard a submarina, assumlng lhe coolanl pumps are shut down, are lhe turbinas and reduction gears. For noise reductlon efforts, designers are using a variety of melhods (see Chapter 6). Diagram source: Royal Navy Subm!lrino Museum exhlblt, Gosport, U.K.
  6. 6. Submarina Technology for the 2 1st Century equipment within lhe ship necessary for lhe recoring. The through-life-core is planned for lhe NAS design, and may be featured in lhe Seawolf class. The United States is presently decommissioning a large number of Los Angeles-class submarines rather lhan pay lhe SlOO million-$200 million cost of recoring the ships to extend tbeir operationallifetimes another 15 years. Not surprisingly this is a controversial decision, since the money would lceep the ship active for perhaps 15 more years, while lhe cost of a ney, Seâwolfis at $2 billion. DeMars' lífetime core would eliminate thís mid-llfe funding hump in the future because the Seawolf and NAS classes would not require it. Another innovation pioneered by the U.S. Navy is lhe use of natural circulation reactors, beginning with thé Narwhallaunched in 1967. At lower speeds, lhe large and noisy reactor coolant pumps are inactivat.ed and the water circulates naturally by convection. It is noteworthy that researcb on this reactor began in 1961 at the Knolls Atomic Power LaboratOl') when construction began on a land-based test site. Seven years !ater, lhe ship was undenaking sea trials. The Narwllal's SSG natural circulation reactor served as basis for SSG aboard the ultra-quiet Ohio-class SSBNs. Natural circulation reactors are used in the Ohio, lhe Seawolf, the NAS and French SSNs and SSBNs. The new Bótish Vanguard SSaN as well as modem Russian SSBNs presumably use natural circulation as well. The Seawolf power plant will pToduce 45,000 shaft horsepower - half again as mucb as lhe Los Angcles class figure of 30,000 shaft horsepower - but will weigh only 10% more, an assistant Navy secretary told Congress in 1992.' This 50% incré8Se represents a significant gain in power density in Anlerican reactor design. It is J.ikely lhe power denslty of the NAS reactor wiU be in lhe same viéinity, and it too will use natural circulation. It will àlso be a simplified design, wilh ''considerably fewer compo· nents and half lhe piping [compared to Seawolfj under submergence pressure:• DeMars said. "lt could power a 688.' 16 Using the 50% power/10% weight increase given for the Seawolf, and NAS plant wouJd welgh about 67% of the existing 688 reactor but produce lhe same power. However, lhe equation isn't so simple. Jt is likely the top output of the NAS reactor il less than the 688's, because its top specd is lower.7 Tllis is probably dueto the issue of extended core life. Core redesign isn't the only melhod available to extend the service llfe of the reactor core. As Oeoffrey Fuller, a former director of Vickers Shipbuilding and Engineering, noted, "The designer of the conventional power submarioe even with AIP knows that husbandlng energy when submerged is ctitical to a successful design and its subsequent operation. The l advent of nuc. ear energy lifted this coostraint and has allowed the designer to be, perbaps unconsciously. profligate. A major review of energy consumption must be the way to lhe 'fit and forget' core.•tt Submarine nuclear plants reject about 70% of tbeir total energy into the ocean as waste beat. Thus, any increase in efficiency can e,.;tend lhe life of tho core. Energy efficioncy is probably lhe objective of the NAS's other new piece of propulsion equipment -a new steam generator. In enumerating what he called "maJor thrusts," Adm. DeMars said the NAS would receivc a new steam generator "with improved corrosion resistance and reduced lifecycle costs. The new concept steam generator wiU also àllow greater shlp design flexibllity and decreased construction cost-s due to its smàller siz.e, spatiàl oóentation, and improved transfer efficiency which reduces coolant flow requirements... .'19 18
  7. 7. Nuclear Propulsion Pushes Agoinst Diminishing Retvrns The U.S. Navy bistorically ís e~tremely secretive about reactor technology. However, the natural circulation system of the Seawolf featuring a 45% increased power deosity over the forced circulation 688 class, when coupled with the NAS life-of-ship core may represent a peak: of development in the design of the pressurized water reactors, which will be difficult to surpass. Two Russian submarine designers disagree. "We have not reached a plateau," said Anatoly Kuteinikov. "In reality, the power density of our reactors is higher. That's lcnow how."1°Kuteinikov is a dírector of the Malachite design bureau. rcsponsible for Russian SSN design. "There could be some cbanges in lhis picturoe.'' said lgor Spassky. "lt wlli always be nuclear power. but how to get it worldng? Steam or directly into eleotricity? That deponds on whal scientistS will give us for new technologies in the coming years." 11 Spassky beads the Rubin design bureau, responsible for SSBN, SSGN and SSK development. OTHER REACTOR DESIGNS UNDER DEVELOPMENT The Russians and Americans rejected other reactor systems in favor of pressurized water. However, it is worth noting the second American nuclear submarino used sodiurn cooling, and Russían design work began in the mid·1960s on a lead·bismuth-cooled subma· rine reactor. Both types operated successfully at sea. and both provided an increased power density with unsophísticated equipment The powcr density advantage of liquid metal cooling is available at an early stage of nuclear developmeot Ralllcr than climb the curve of pressurl:ted water, countries starting from scratch may want to pursue metal cooling, especially if it is prone to natural clrculation. Gas cooling is another oplion. and both systems offer improved thermodynamic efficiency. Jn tbe early 19SOs. the U.S. Navy pursued not only pressurized water and liquid metal-cooled nuclear reactors but also gas·cooled devices. Whlle the pressurized water reactor (PWR) has proven the mainstay of nuclear submarino propulsion. research continues in gasand metal-cooled reactors because they promise much higher performance with a reduction in weight, The reason is thennodynamic becauso the temperarure range necossary to operate a pressurized water reactor safely is quite llmited. In hjs book Submarln4 Design and Development, Nonnan Friedman cites tho experience of a civilian PWR developed with naval experience. "For example, the prototype civilian power plant at Shlppingport [, Pennsylvania], developed during 1953-57 on the basis of naval expericnce, experiences a ternperatUJ"e rise of only 34 degrees [Fahrenbeit] in the core's coolant with ao inlet temperature of 508 degrces [Fahrenheit] and an outlet temperature of 542 degrees [Fahrenheit). These temperatures correspond to apressure of 2,000 pounds per squllfe inch, at which saturation (boiling) temperature is 636 degrees [Fahrenheit]," wrote Friedman, a physicist by training.12 Reactor design is a complicated art. To avoid the need to constantly regulate reactor operations with the control rods, the core design and enrichmentlevels must be carefuUy matchcd with the physical properties of the coolant. Tho laws of physics are used to regulate ructor activity. For Navy PWRs, demand for more power automatically heats up lhe reactor without human intervention; conversely, a decline in power requirements automatically cools the reactor. 19 11
  8. 8. Submorine Technology for the 21st Century The 34° Fahrenheit difference between outlet and inlet temperatures renders thc naval PWR quite inefficient. Heat engines, such as turbines, operate on thermodynamic principies where low-temperature differences mean Jow efficiency. The only reason the PWR can propel a submarino displacing thousands of tons is because the device produces so much raw power that inefficiency is almost inconsequential. lf the temperature difference can be expanded to hundreds of dcgrees, then a reactor is more efficient and can either produce more power for the same weight, or the same power in a smaller, Ughter package. The U.S. Navy aban.doned the sodium-cooled reactor in 1959. After only two years at sea, the sodium-cooled reactor wa.s removcd and replaced with a PWR. A Navy roemo determined, "[l]n addition to the leakage of the heat transfer units, and associated problems, it now becomes evident that the inherent characteristic of sodium reactors màke the Seawolf propulsion plant ex.pensive to build, comp)el[. to operate, susceptible to prolonged shutdown as a result of even minor malfunctions, and difficult and time consuming to repair.... These facts clearly demonstrate that sodium is less desirable for naval reactors than presswized water."13 ln fact, the experiment wíth sodium was scary. Any leak of sodium had the potential not only to be a radíatíon problem, but also a tire hazard; mixed with water the material is explosive, and it bums on contact with air. The element is also very aclive chemically. "Sodium's tenibly coJTosive effect damaged steam generators and superheater pipiog and required extraordinary measures to ensure safe operatlon of the reactor," naval historiao Gary Weir wrote. 14 The Russian Alfa class carried liquid metal-coolcd (LMR) reactors, but instead of problematic sodium, it used a lead-bismuth coolant. These two elements do not become radioactive with exposure to a reactor core, eliminating the need to shield the primary coola.nt loop. Such a design would provide a higher-densjty powerplant, which could explain the performance c:haracteristics of some Soviet boats. lt has been suggested less shieldíng and greater power density from an LMR is responsible for the 42-knot top speed of Alfa·class submarines. Ccnainly part of the speed came from drag reduc:tion due to the ship's fine strea.mllning and small size (3,700 tons displacement, dived), wruch was made possible by a small crew (40 men) and substantial automation. GAS COOLING OFFERS ANOTHERALTERNATIVE Oas-cooled reactors (GCRs) substituto either helium, argon or another inen gas for the pressutized coolant. Such gases can be heated to thousands of degrees and then, after performing work llke spínnlng a turbine, cooled for a retum cycle. Thls larger tempera· ture differential means gas-cooled reactors can be more efficicnt. Friedman wrote, "In particular, it is oftcn claimed that a nuclear gas turbine (presumably using helium as the worlting fluid) would be the lightest conceivable nuclear plant. Reportedly a lightweight fastneutron nuclear gas turbine was proposed for the 1957-58 U.S. Skate class. A conventional PWR was substituted because of insufficient time for development."u Michael Golay and Neil Todreas, writing in the April 1990 issue of Sciemtjic American say, "Gas-cooled reactors have been built since 1956, at the bcginning of the civilian nuclear power era. Their major advantage lies in thóir thcoretical abllity to o~rate at temperatureS abovC 700 degrees Celsius, conslderably higher than the 330 and 550 degrees [CelsiusJ achieved In [light water reactors] and LMRs, respectively. Because engines that conven heat into other
  9. 9. Nuclear Propulsion Pushes Against Diminishing Retvrns forms of onorgy work more efficiently at higher than at lower temperatures, the OCR typically converts 40% of its heat energy into electricity, compared with 33% for LWRs." The United States and other countries have not given up on LMR or gas-coolod reactor technology and are exploring its use for civilian as woll à1l milltary appllcations. Perhaps tho most interesting researoh comes from the U.S. Strategic Defense Initiative Organization (SOlO), which needs a high-density power source to operate particle beam weapons in space. Not only must these power sources maintain a constant output for years whíle unattended and in orbit. they must be capable of burst operations to boost their output tenfold or more for beam weapons. The SDIO in 1988 awarded Sl milllon fcasibjljty evaluation contracts to: • Westingbouse Electric Corp., Madison, Pa., for a gas-cooled reactor using an open cycle for burst operations; • General Blectric Co., King of Pnlssia, Pa., for an open BraytOn cycle, gas-cooled reactor; • Roc.kwclllntemational, Canoga Park, Calif., for a liquid lithium Rankine cycle reactor; • General Atomics Technologies. San Diego, for LMR with in-core thermionic conversion of heat to elecnicity; • Boeing Aero$paee Co., Kent. Wash., for an opon Brayton cycle gas-cooled reactor; and • Grumman Corp.. Bethpago, N.Y., for an open Brayton cycle gas-cooled reactor. In addition, Vflrlous U.S. nationaJ Jaboratories are looking at gas- and metal-cooled rcactors. At .ArgoMe, Ill., researchers are studying a lithium-<:ooled reactor; lhe Brookhaven lab in New York ís looldng at gas-cooled designs with a closed Brayton cycle; at Oak Ridge, Tenn., lhe focus is on boiling potassium as a coolant; and in the Lawrence Livermore National Laboratory in Califomia. gas cooling of a reactor with a ceramic core is under study In Oermany, a civilian gas-cooled research reactor has been in operation since 1966. Called AVR, it is a one-thlrd scale model of a proposed commercial reactor for electricity generation, and uses a completely different fuel system. lnstead of conventional fuel rods, the AVR uses tiny spheres. A nugget ofuranium is wrapped in concentric shclls of graphite, silicon carbide and otber materiais. The finJshed sphere is 1 mm in diametet Tc:sting of these spheres indicates they wül not leak uranium or other radioactive materials until temperatures exceed 1,800° Centigrade. A paper by Lawrenc~ Lidsky, with the Massachusetts Instituto ofTechnology, delivered on Sept 7, 1988, at lhe Edison Elcctric Instituto indicates these fuel spheres could withstand the most catastrophic reactor accidcnt withdrawal of control rods simultaneous with a loss of ali coolant. "The AVTI.. meets lhe goal easily because of the fuel 's comblnation of high·temperature capability and high thcrmal conductivity, and there is ample margin for somewhat larger commercíal reactors. Depending on details of design, the limíting slze of those reactors. known as Modular Gas-Coolcd Reactors, or MGRs, is on thc order of 200-250 [thermal megawatts]," wrote Lidsky. General ~tomics is working under contract wíth the Dept. of Energy to produce a design called the Modular High·Temperature Gas-cooled R~actor (MHTGR). Their dosign carne under criticism by the Union of Concerned Scientists. A report by the group released in July 1990 says tho MHTGR design would create combustible gases i f water and alr wero to enter the reactor core. A General Atomics document says "The potential reactions of air andl 21 •
  10. 10. Submarine Technology for the 2 1st Century or water wíth the core have been stuwed extensively for lhe MHTGR. ... The anàlysis shows that although there may be li.mited production of combustible gases during severo accident conditions it does not represent a safety hazard to plant or publlc." Linden Blue, General Atomic's vice chainnan, told the House subcomminee on energy research and devolopment of the Space, Scienco and Technology Committee, "As a rcactor which can't melt down and release substantial quantities of radíonuclides, the MHTGR is the best example of this new philosophy. Thc large safety margins are perceptible to the public and will be appreciated." Work on the MHTOR is going forwo.rd, involving Bcchtcl Corp., Combustion Engineering, Stone & Webster and General Atomícs. Experimental programs concenúng the fuel, fission products and other materials is under way at the Oak Rídge as well as in General Atomics' labs. "The Navy has looked at gas cooling for severa! years," said one naval source. ''Bu.t it's not yet appropriate for submarines." THERMIONICS SKIP THE SECONDARY LOOP Nuclear reactors in a gross sensc are no different than a wood-buming fitebox in an old Iocomotive - a source of heat to boil warer to drlve a steam engine. Regardless of how they are cooled for safe operation, reactors are inherenUy wasteful. If thcir heat could be tumed directly into electricity, the entire secondary circuit to produce steam would be ellminated. That is the goal of a tecbnique called thermionics. The phenomenon is not new, patented by that classic American inventor Thomas Edison in 1884. And it is operating today in the most demandlng environment known- outer space, where thermionic generators are used by American and Russian satellites. Iohn Fleming hamessed Edison's discovery to create the electronic age. Certain materials create electricity when heated. The glowing element in a vacuum tube, Flemíng's contribution, produces a cloud of electrons that enabled them to amplify weak radio signals, including the broadcast of Arthur Godfrey's far-away ukelele. Curiously the phenomenon, while well known, is not well understood. Experimental evidence does not match theoretical prediction, despite the use of very complicated mathematical procedures to fit the data to predicted curves. For decades, the Naval Nuclear Propulslon diviSion of thc U.S Navy supported thermionic research. "We are exploring advanced technologies:' Admirai DeMars said in 1993. ''We are looking at energ)' conversion, getting electricity directly from heat. HoweVer, devclopment is no sooner than several dccades away. We will not allow anyone else to get there ahead of us." 16 As DeMars spoke, America was borrowíng Russian research. ''The Energy Dept. has granted Rockwell Intemational permission to award a subcontract to a Russian instituto for suppon ín designiog a 40-ldlowan thermlonic space nuclear power system. The Institute of Physics and Power Engineering (IPPE), based in Obninsk, Russla, developed the Topaz I thennionic space nuclear reactor that the U.S. Aír Force and Strategic Defense Initiative Organiull:ion are now studying," a ttade publication noted in 1993. ''Under the subconttact. IPPE will test advanced thermionic concepts sucb as insulators and in-gap spacers to see they would work in the Rockeydne [a subsidiary of Rockwell) design. General Atomics in Diego is responslble for designing the reactor and thennionic power conversion subsysteiJIS.
  11. 11. Nuclear Propulsion Pushes Against Diminishing Retvrns In 1995, DeMars halted thermionic research. ''Thermionics is dead right cow. There is no money applied to it." said Rear Adm. Robert Frick, program executivc officer for submarines. 11 DeMars foreshadowed his decision in 1992, saying, "About two years ago, we fi_nisbed detailed studies of more than 15 methods of nuclear propulsion, but we're happy where wc are." 19 ' General Atomics was responsible for mucb of the Navy's researcb, using a trial-anderror approach bet:ause theory was lacking. The company developed a therm.jonic element and demonstrated a two-year lifetime inside a reactor core. In 1990, a company spokesman said a seven-year Ufe span for the element "will have bccn verified by the end of the program in 1993. The USSR is developing a comparable capabiUty and two thermionic systems were recently placed by them into orbit" The company's Línden Blue said the thermionic fuel element verification program "is focused on the 500 kilowatt to 5,000 ldlowatt range." This power range is exactly the sort required by small- to medium-sized submarines. ''Their 1994 final test report under a Dept. of Energy contract is included in tbe Bettis April 1996 package of final test reports,'' wrote thermionics researcher French Caldwell. "It seems they were doing in-core testing of individual thermionic fuel elements as part of the TFE [thermionic fuel element] Verification program. Their life ~sts of 8,000 to 14,000 hours would not do for a nuclear submarino, considering present day refueling cycles. However, J thlnk they got bettcr results in the pre-1973 programs. We are just beginning to restart thermionic research, and with present funding limitadons it is a ldnd of shaky restart.'t20 Caldwell is tak:ing a differeot approach than most American resea.rchers. but is paying the price. "I have a slightly different approach to thermionic converter research. Whilc the electronic theory is important, I have also looked at the device from basic heat theory_ It is an uphill battle because the electton tube theory ls so entrenched as the singular basis for research. 1 have yet to meet a scientist who ca.n look at two separate theoretical fields at the same time. On reviewing my findings, NIST [National Institute of Science and Technology] wrote me that I could not analyze beat to electricity conversion using heat laws, because 'heat radiarion and electrica1 radiation are two different things and should not be confused.'l pointed out that Planck derived his heatlaw from Maxwell's electrical equations, and Richardson derived lhe electron tube theory from Boltzman's heat laws- but got no further rcsponse from NIST.'' Despite the lack of a theoretical basis or goverrunent support to improve performance, thermionlcs is a worldng technology available today. ''When the Navy is ready for a silent generator that needs only heat- no turbines, no spinning dynamos, no moving parts thermíonlc conversion is ready and waiting," wrote Caldwell. 21 . LOW-GRADE FUEL IS A POSSIBILITY TOO It should be no surprise ali the nuclear submarlne powers - France, China, Britain, Russia and the United States- are also nuclear weapons powers. is no accident. for the fuel in lheir nuclear submarines ls also lhe substance necessary to build nuclear bombs. The uranium isotope lJZl' must be separated from the more abundant but inert IJ23' and lhen concentrated When Ull' is concentrated to a levei of 90+%. it is called hlghly enriched uranium (HEU). At this point, the materialjs "bomb grade.'' France and Russia use non-bomb-grade material to power íts submarinos. ' 23
  12. 12. r Submarine Technology for the 2 7st Century HEU releases energy in the form of heat when bombarded with neutrons. The lJ23' atom splits wbeo hit by a slow neutron, and releases energy. An uncontrollcd release creares a titanic e~plosion, an abundance of heat comparable for an iostant to the surface of the sun. A cootrolled release creates heat as well; but in a manageable form. Regulation of the number and speed of the neutrons makes the düference. This relationship - HEU versus neutron activity - is key to maláng reactors or bombs. Most natlons start with the atomic bomb, and then devíse the techniques necessary to harness the atom to propel a submarino. Some nations stop at the bomb - Israel and South Africa.. for example - and mâke no effort to create a submarino propulsioo plant. Others and Canada, for example - eschew the bomb but explore nuclear propulsion. Two schemes exist to use non-bomb-grade Uraniwn to crea.te a submarino propulsion system. One is the system adopted in French and Russjan nuclear submarines. Tbe other is Canadian, and came to llght when Canada consiclered. but then rejected, the nuclear ·submarino community. In lhe late 1980s, the ECS Group of Companies in Ottawa, Canada, developed a nuclear system they called tbe Autonomous Marine Power System (AMPS). Instead of using HEU requiring extensivo monitoring, ECS toolc the Jead from lhe Canadian "Siowpoke" reactor design to develop a low-power nuclear reactor using Freon in a Rankine cycle to produce electrlcity. Preon would become a gll$ in a beat exchanger, spin the turbine connected to a generator, and then liquifY in a CO!ldenser to begin the cycle anew. The AMPS system dHfers significanlly from conventional submarine nuclear reactors. WhHe pressure-water reactOrs commonly use highly cnriched uranium, the AMPS deslgn used fuel of lcss than 20% enrichment. And instead of maintaining high output temperarures, AMPS runs at about 160° Centigrade, or about 100° less lhana PWR. Both would use the same pressurlzation of about 2,000 t. 2,500 psi for lhe primary Ioop coolant o Tbree power ranges were targeted: 100 and 400 kW and 1 megawatt. The smallest plant was considercd to provide AIP for the French experimental submersible SAGA- I, but an air·independent Stirling engine was chosen instead. The 400 kW and I MW AMPS systems could be applled to military submarinos. The absence of high temperatUres in the reactor core, combined the with automaric shut-down mecha.nics of the core design means the AMPS is capable of virtual stand-alone operarion. The "Slowpoke" design- dating from the 1950s- is lhe only nuclear reactor authoriud to operate without constant human attendance on the Earth's surface. The ineffi.ciencies produced by thesc factors, Jow fuel enrichment and low operating temperatures, mean.the AMPS in its present configuration cannot by itself provide alÍ lhe power needcd for the fuU anack submarino performance envelope. lnstcad with pówer outputs of 100 kW or 400 kW, the AMPS falls into the same category of air-independent propulsion as today's fuel cells or heat engines - an awdlia.ry, but not primary source of power. But despite the mass óf sbieJding necessary to protect the crew from radiation, an AMPS-equipped submarine would need to carry neithcr diesel fuel nor liqucfied oxygen for its AlP system. A paper presented Underseas Defense 1988 conference in San Diego by two ECS employees, A.F. Oliva a.nd RJ. Gosling, outlined the system's ba.sic design. "The AMPS was conceived as a low-power nuclear reactor embodying features of intrinsic safety, low complexity and extremely high reliability, while requiring minimal operator attentioo to assurc 24
  13. 13. Nuclear Propulsion Pushes Against Diminishing Returns safe and effective plant performance under routine and off-normal plant conditions. The AMPS plant utilizes a Jow-temperature, low·pressure, water-cooled reactor heat source coupled to a low-temperature Rankine cycle engine to generate electrlcal power. The plant electricaJ generation and distribution system converu the AC output of lhe turbine altemators to a DC supply suitable for charging the submarine main batteries. An integrated faulttolerant contrai and monítoring system is employed to automate all routine plant operations." The fuel is a uranium-zirconium-hydride alloy wjth an enrichment levei of 19.7%. The Oliva-Gosling paper notes, ''Tbis fuel type has been used in 63 rescarch reactor installations in 23 countries and has logged over 800 reactor·years of safe operation since 1958." Thcy note the AMPS reactor core ls expected to provido eight to 10 years of service bofore refueling is necessary. closely matches the refit cycle of modem conventíonal submarines. Anolher paper on AMPS, presented ECS employee J.S. Hewitt ata seminar on sma11· and medium· sized nuclear reactors in Lausanne, Switzerland, in 1987, indicates the wodting medium for the Rankine cycle is Freon. "The energy conversion technology cbosen for the continuous conversion of the low-temperature heat to electricaJ energy is that of the organic Rankíne cycle engine in which Freon is used as the lhennodyruunic worlciog med.ium. In this conversion system, the hot water of tbe primary beat transport system is circulated through a heat exchanger of which lhe secondary side serves as an evapora.tor (boiler) ofFreon. The Freon vapor passes through a turbine/altemator for lhe conversion to electricaJ power, following which is passed through a condenser cooled by seawattr, before retuming as liquid to the evaporator," h. explained. e Tbe difference in temperature betwecn the seawater coolant and vaporizcd Freon provides the necessary thermal gradient forthe system's operation. But as is usual with most Rankine cycle engines, lhe lhennodynamic efficiency is small. "The nominal operating thermal parameters of the AMPS reactor are an output power of 1.5 MW and an average core coolant temperature of 90 degrees Cenrlgrade," wrote Hewitt." These figures are consistent with achieving a reasonable thermodynamic efficiency in the energy cooversion unit when lhe seawater temperature is in the 5-15 degrees Centigrade range, and yielding a net electricaJ output of 100 kW after appropriate allowance is made for lhe consumption by plant auxlliary systems." Thus lhe efticiency of the AMPS system in converting heat to electricity is less than 10%. The "auxHlary systems" mentioned by Hewitt include pumps for both the primary cooling loop and the seconda.ry Freon loop. Pumps are inevitably a source of noise aboard a submarine. AMPS never made it out of the starting blocks. The Canadlan govemment rejected it - along with every other nuclear propulsion system, it must be said. Tbe only submarine de.~gner to indicate interest quietly dropped AMPS after investigation. In.weigbt, power density, use of rotating machinery and low efliciency, the system appears to hold littJe advantage for submarine propulsion. But its use of non-bomb-grade uranium and its stand· alone operational capabilitY are notable. The Cariadians also studied the system used by thc French in their Rubis-class submarine, which uses non-bomb-grade uranium too. The French were competing against the British to seU Canada a squadron, or more, of nuclear submarines. Tho British, following lhe American model, use bomb-grade HEU. The French, as a selling point, noted their reactor used LEU - low-enrichment uranium, wilh a concentration of approximately 20% U:'~. 25
  14. 14. Submarine Technology for the 21st Century The French also adopted natural ciroulation for the Rubis. ''For up to two-thirds power, ít uses only natural circulation," Keith Davies, a representative of the French shipbuilder The Rubis' reactor, he said, produces 48 megawatts of thennal power putting about 7,000 horsepower to the propeller shaft. The French reactor ls different in another respect It combines into a single unit the reactor core and steattt generator. The combined uo.ít is about 6.1 meters ta11 and 3 meters in diameter. The steam genera!or sits atop the reactor core (see Figure 2·2), The Rubis uses a turbo-electric drive system, witb the steam spinning turbines connected to generators. The power is dire.ctéd to an electrlc propUlsion motor. The Uni,ted States has twice tried, but rejected, turbo-electric drive.l) By contrast the Trafalgar-class submarine offered by the British uses the split configuration píoneered by the Americans, with a reactor separare from the steam generator: the steam spins turbines, which are geared difectly to the propeller shaft. This system pro-duces about 12,000 sbaft horsepower but required a larger ship because the reactor is much bigger at 9.8 meter.;. Both ships, said Davies, have a top speed of less than 30 knots; for the Trafalgar, it i~ 29 knots and for the Rubis the top speed is 26 knots. Much of Davies' infonruuion was confinned by Yves Girard, with Technícatome of Franoe, during a seminar at the Massacbusetts Institute of Technology (MIT). He said France began studies on nuclear propulsion in 1954, soon after thc American Nautllus - the fiM nuclear powered SUbmatine was launcbed in Ianuary of that yea.r - and received tho. go.ahead in 1958 to build a land-based prototype. '"We asked for U.S. help, but they said no. They did loar us 250 kilos of enricbed uranium;" saíd Girarei. "lUckover was dead [set) against the projecL'ou In thl' late 1960s, France began looking at low~nriéhed uranium, and the French navy !ater ordered eigbt boats in two batches of four. "Tbe trend to low enrichment was due to industrial and economic considerations," said Gíratd. A paper presented at the same conference indicates one disadvantage of LEU versus HEU nuclear fuel is the requirement to recore a LEU reactor mote frequently. Using two hypothetical 50 megawatt reactors - one using HEU, the other LEU - David Lanning and Tbomas Ippolito concluded the LEU-oored reactor would have about 10 years of usefulllfe a consumption rate of 60 full-power-days per year, the HEU-cored reactor would have a 20year usefullife at the same rate of power consumption. They concluded, "As demonstrated by the French submarine reactor, Rubis, the use o f LEU fuel is feasible. The calculated results in this report in dicate that changing from 7% to 20% LEU can give a larger core operarlng lifetime without significant reduction in safetyrelated reactivity effects.... Also the 20% LEU core volume in thls set of examples is a factor of 2 to 2.5 times larger thân tht HEU core. This increase will álter the size of shielding and general reactor compartment arrangement, but the impact is not largt and can be accommodated. For example, an integral reactor design could be used rather than a loop configuration it is desired to design the core with 20% enriched uranium fuel.'~ Girarei said the increa.sed trequency of recorlng is not onerous because the R,ubis class "will ·need electronics and weapons re.fits around every five years. At that tinie, the refueling cost is .negligible." Brazil is embarked on a program to build a nuclear submarino, and apparently will use a LEU-cored reactor. ''There a política! decision to use LEU at around 20% enrich- was 26
  15. 15. Nuclear Propulsion Pushes Against Diminishing Returns Figure 2-2 French adopt unified approach to submarlne reactors -ngWater The Frenoh navy - unlike the Brltlsh navy - received no assistance from lhe Unlted States In craatlng its submarina propulsion system. Perhaps as a consequence, it differs from American and Brltlsh practice In two slgnlflcant ways. One ls lhe use of low-onrlchod urantum to power the core. French luel uses a 20% enrlchment levei, compared to tl'le 95% fuel used In the United States and the Únlted Kingdom. There ls evldence the Russian navy also used fuel of lowet enrichmant In lts eartier generatlons of nuclear submarinas. lower enrichmant levais- unlike lower grades of gasolina for automoblles - still produce ample amounts oi heat, but must be refueled with greater frequency because lhey contaln fewer "full-power days.• The sccond difference in the French system Js consolidation of lhe reactor core, steam generator and pressurizer lnlo one unlt. The pressurizer (with I!S "bubblej sits on top of the steam generator whlch in tum ls atop the reactor core. This produces a more compaot unlt wlth slgniflcently fewer pipe runs. lt ls ooe reason the French Rubls-class attack submarinas displacing 2,600 tons submerged are slgnlncantly smaller than their British or American oounterparts. 27
  16. 16. ______ ,. . . _ Submarine Technology for the 21st Century ment,'' said úilberto Gomez. de:~ Andrade at the MlT conference. Asked if a LEU reactor can change power leveis quickly, he said, "lt is no real can be !ncreased by 15% per second, and mop by 20% per second'ou Russian submarines fOO use LEU, which actounts for the requirement to recore mo1 frequently. Because an LEU core contains less ''full power days," it also helps to explain wh Russian submarines spend less time al sea. Sou.rces indicàte the cores of first-generation of Russian nuclear submarinos used a 20% enrlchment levei. This has gwwn to around 40% fo1 the Selrra- and Akula-classes of the third-generation boats. WU.DER IDEAS POSSIBLE The planned through-life core of the American NAS design may be a refinement of existing designs, and very frugal with the neutrons necessary to induce the-tission reaction. It indicates the reactor operates at very close to a break-even point, and may be creating as muc fuel as it consumes. Such a design is called a "near breeder," and is wjtlún the state-of-the-ar "Advanced thermal reactors may be designed to utilize avallable neutrons much more ca.refu11y," wrote Anthony Nero Jr, ''Sufficiently hlgh conversion ratios may be achleved so that, after an inidal running period, little or no additional fissile material need be supplied from the resource base. It is possible to approach or süghtly surpass this break even state with thermal reactors."27 The key, however, is converting a fertile atomk: nucleus into a fissile one. As an atom of tJll' is split by a neutron, it releases on average two more. For a break-even reaction, one free neutron must spllt another atom of U 23' , while the second must seek a feltile nucleus to cooven to a fissile state to achieve a 1; 1 ratio of fuel bumed to fuel created. The ratio falls short for current reactor designs, meaning they must be recored periodically. .For example, the abundant, but non~fissile, isotope (P)1 can be convened to fissile Plutonium with the capture of a neutron. "In current light·watcr reactors, the ratio of only about 0.6 is achieved for two fundarriental reasons: the water moderator and thc reactivity control systems absorb a signifi. cant portion of the neutrons from fission, and the nuclear fuel itself cannot practically sustaio a conversion ratio of 1 because the UD'- {Fl1- Pu139 combinaúon is not good neutrQnically. B ; the latter we mea.n that tr" and Pu:D9 produce such a small eJtcess of neutro os (per neutron absorl>ed) above the 2 required for break-cvcn, that any small unavoidablc Iosses will deprcis lhe conversion ratio below 1," wrote Nero. The SO}UtiOn ÍS a change in fucl from IJ»~ to tr'', anoUter uraniwn isotO~. The would be created from Thorium (chemi~ symbol Th). Instead of using HEU, a reactor be cored wjth a combination of fissile {PJ5 and fertile Th~~ ·were Th~~ used as the tertüe material. the situation would be different rlrSt Thl]J has a higher neutron absorption cross-section than does {P'&. so that more conversion takes place in the former. As a result, more lPl is produced than Pu239 in equivalent circumstances. (11ús means that móre fissile material must be supplied initially to overcome the greater absotpl.ion of the Th~2. ) Furthennore, tr'~ is a much better thennal fuel than .PW19, and is superior to l?'," wrote Nero.::a As usual, there's a hitch. lJU'doesn't occur naturally because its half-life is short. It must be produced by irradialing Thorium in a conventional HEU-fueled real~{ur,, :......
  17. 17. Nuclear.. Propulsion Pushes Against Diminishing Returns then separated out. This would add an additional purification stage to obtain UV3• But it would el.intinate reactor recoring. And finally, there is the Holy Grail of nuclear engineering- fusion power. A fusion reactor rises in the east every moming; and the energy it produces 150 million ldlometers away is responsible for allllfe on this Bringlng thc reaction closer to home and making it perfonn work has proved a chimera, so far. But Donald Davidson, director of the Princeton Plasma Physics Laboratory in New Jersey, thlnks fusion power may come sooner than expected. In 1998, the engi.neering design for the Intemational Thermonuclear Experimental Reactor (ITER) is elt.pected to be finished, jolning the efforts American, Russian, Japílnese and European n:scarcher~. An American follow-along project, called TPX (Tokamalc Physlcs Experiment), would dernonstrate a continuous-operation fusion rea.ction. ;1'aken together, lhe results of lTER and TPX will produce the te-ehnical basís for an electricity-producing fusion demonstration reactor operating by 2025 - or sooner ü America so chooses," Davidson wrote.29 · While the sun gains lts cnergy from the fusion of four normal hydrogen nuclei to form one helium nucleus, the man-made reaction uses exotic isotopes of hydrogen to promote the rcaction. So-called heavy hydrogen atoms of deuterium and tritium are the fuel for man· made fusion. Whilc not ab11ndant, deuterium and tritium occur in seawater as a fraction of the hydrogen component of thc water molecule. Although a "deuterlum sieve" is currently beyond the threshold of research, it could scoop fusion fuel from the sea. Experimental fusion facilities, ca.lled tokam. ks, are huge, and require enormous a amounts of energy. But they have already produced power ín lhe megawan range, and improvements are coming. "In De(:ember 1993, more thao 6 million warts offusion power were generated during lhe historie experlments on the TFI'R Tokamak at Princeton. With these ex.perlmcnts - which used a 50-50 deuterium-tritium fuel mixture for the tirst time America surpassed the European tokamak record ofless than 2 million watts set in 1991," wrote Davidson. "In May 1994, TFI'R produced 9 million watts of fusion power, surpassing its own record sct five mooths earlíer.'>lO lt is conceivable that fusion power will be the energy source of lhe nex.t century, just as easily extracted oi! deposits begin to dry up. li fusion can be tamed, it may be availablo for undersea use. The idea of drawing seawater into a system and extracting heat or electricity is undeniably attractive, and development is certain to continue. CONCLUSION lf evor tbere was an engíncering tale followíng the themc of "if it ain 't broke, don 't fix it," the story of the development of the pressurizcd-water reactor for submarine propulsion is an archetYJ>C. For the Unlted States; one experiment with a metal-cooled reactor was suf:ficient to exclude that technology from any future consideralion. The Russians persisted in their ex.periment wilh metal-cooling, despitc the failure of lhe lead shlp of the Alfa class, whioh was scrapped. But after finíshlng the construction of slx Alfas by 1983, the class was retired in 1989 and the Russians reverted to PWR-only reactors.
  18. 18. Submarine Technology for the 21st Century The same appears true of lhe American experience with turbo-electric drlve. Although used by the French Rubis with success, thc American one·of-a-kinds Upscomb and Tullibcc were considered slow and technically deficient Still they achleved their requirement for quieting. The Lipscomb was retired with half its service life Itmaining, and although som believe the future of suhmarine propulsion Ues in some form of electric drive, there are few serious research efforts under way to examine its requirements. Gas-cooled reactors offer high performance, and if they could be made small, safe and quiet, could lead to a tumabout in the ever increasing size of nuclear submarines. Thenni onic generation of electrlcity without the use of steam and turbines, would further re.duce the space necessary for propulsion equipment. For the last half-century, pressurized water reactors dominated nuclear submarino propulsion. The system steadily has bcen refined. Power densities increased to the point whe1 the next-generation American attack submarine will never need refueling. Other advances have trimmed the size of the equipment set, and reduced thc levei of uranium enrichment necessary to produce effective power. The fundamental liabilities remain. Pressurlzed water reactors are inefficient, and requite a substantial industrial infrastructure behind them. As nuclear submarino production leveis continue to decline, this infrastructure will become even more expensive to maintain. Thc singular advantage of nuclear powcr is undeniable - the abiUty to make high-speed deploymcnts anywherc in the world. However, its olher principal attribute, ext.ended indepen· dence ftom the surface, is under challenge as laboratories worldwide seek to refine nonnuclear alr-independent submarine propulsion. Unless new developments in nuclear science can cut the cost of developing, buildin~ quieting and maintaining a fleet of nuclear submarine propulsion plants, their growing price i certain to cut into the number of new shlps, reducing submarine fleet sizes. A Seawolf costs $2.4 billion to build; its successór, the NAS, is eslimated to cost S1.5 billíon - not including the research costs. In peacetíme econornies, these are shocldng figures. In war there is insufficient time to build replacements for tosses. To pàtaphrase Admirai DeMars, performance gains in a mature technology are expónentially harder to achleve. The PWR reactor is a marure technology. Unless new development.s, thermionics for example, are able to eliminate a1l or part of the thermomechanical cycle, nuclear power is nearing the bitter end of the diminishlng-retums curve. 30
  19. 19. Nuclear Propulsion Pushes Against Diminishing Returns Endnotes For Chapter 2 1Thomas Taylor, actlng director of the Defense Advanced Projects Research Agency's Naval Technology Office at a rneeting of the Marlne Machinery Assn. on Nov. 29, 1989, in Arlington, Va. z Rear Adm. R.W. King (ed.), The Nautical and Avlatlon Publishing Co. of Amerlca, Baltimore, Md., p. 196. "The use of U235 for power was even lhe subject of an article in lhe November 1940 ASNE Joumal 'Uranlu~- Power Fuel of the Futura?' lt discussed sources of uranlum ore, difficulty of isotope separation, neutron bombardment and chain reaction, use for heat in steam generatlon, and factors In power plant operatlon." ' Lt. Cmdr. Richard Martln, USN, manager of the mechanical-electrical element of the Advanced Submarina Technology program of Defense Advanced Research Projects Agency remarks to the Marine Machlnery Assn. on Nov. 29, 1989, In Arllngton, Va. Adm. Bruce DeMars, dlrector of naval nuclear propulsion, In prepared testimony before the House Armed Services seapower subcommittee on March 7, 1990. 4 8 Gerald Cann, assistant Navy secretary for research, development and acquisltlon, in a wrltten response furnished to a questlon posed by the House Armed Servlces research and development subcomrnittee durlng his testimony on March 25, 1992. H.A.S.C. No. 102-441, p. 245. ' Adm. Bruce Oemars, remarks to the annual Naval Submarina League meetlng on June 1O, 1993, In Arlington, Va. 7 Assistant Navy Secretary Nora Slatkin told the House Armed Servlces mllitary acqulsitlon subcommlttee on April 26, 1994, In response to a question frorn its chairman, that "26 knots ls satlsfactory." Her comment carne in a dlscussion of design trade-offs between speed and weapons payload for the NAS. The 26-knot figure could represent the maxlmum deslgn speed of the NAS. Thls number ls less than the 30 knot maximum design speed of the Los Angeles class. However; 26 knots ls approxlmately the top "quiet search speed" of the Seawolf, so deslgners may have opted for a maximum speed for the NAS, whlch ls also lts maximum qulet speed. .. *Geoffrey Fuller, ~submarinas for the 21st Century: Propulsion, the Real Choice," paper to the Chesapeake Section of the Soclety of Naval Architects and Marine Engineers, 1992, p. 1O Fuller is a long-time player In the buslness of designing and . building Britlsh submarinas. 'Adm. Bruce OeMars, prepared testlmony before the House Armed Services mllitary 31
  20. 20. Submarine Technology for the 21st Century applloations of nuclear energy panel on April 28, 1993, p. 1o. lntervfew wfth Anatoly Kutelnfkov, general d~signer and director of lhe Malachite submarine deslgn bureau, St. Petersburg, Russia, on Nov. 13, 1992. 10 ''lntervlew with lgor Spassky, dlrector of the Rubtn submarine design bureau in St. Petersburg, Russta, on Nov. 14, 1992. 2 Norman Friedman, Submarine Desfgn and Dsvelopment, Conway Marttime Press, ' N.Y 1984. ., '~Cited in Gary Weir's Forged In Wàr: The Naval-Industrial Complex and Amerlcan Submarine Construction, 1940-1961, U.S. Govemment Printing Offlce, Washington, 1993, p. 193. 14 lbid 18 p. , 93. Friedman, op cit. 11 Adm. Bruce Demars, director of naval nuclear propulsion, before the Naval Submarina League annuaf meeting on June 1O, 1993, In Arlington, Va. ' 17 "Russian instltute to receive Rockwelf award for Topaz work," Aerospace Daily, Feb. 1, 1993, p. 174. 18 lnterview with Rear Adm. Robert Frick, program executive officer for submarinas on Sept. 13, 1996, in Crystal City, Arlington, Va, 18 Adm. Bruce DeMars, before the Naval Submarlne League annual rneeting on June 11, 1992, at Arlington, Va. 20 Personal correspondence with the author. 21 See Lt. French Caldwell, USNR (ret.), "Looklng Forward, Thermlonic Reactors for-a Revolutionary Electric Boat,• The Submarine Review, January 1996, p. 64. 22Tetephone interview with Keith Davies, DCN representative to Canada on April14, 1988. 23'fhe American attack submarina Glenard P. Llpscomb (SSN 665) used turbo-electric drive. lt was a Sturgeon class hulf with a turbine-electrlc drive of steam turbina· generator-electric motor, instead ot steam turbine-reduction gears. Jt was quieter, and about 5 knots slower than a Sturgeon. The Upscomb was a one-of-a·klnd shlp. One source told the author, "The Llpscomb was one of Rlckover's last hurrahs. A research submarine. Neither General 32
  21. 21. Nuclear Propulsion Pushes Agoinst Diminishing Returns Electric nor Westlnghouse were interested in the technologies involved." Neither was the Navy. The Lipscomb was retired with half it's service llfe remalnlng ~ one week before its 15111 birthday - a.fter the Navy refused to recore the reactor. The Lipscomb was the second turbine·electrlc-drtve submarine tested by the U.S. Navy. The flrst, another one-of-a-kind, was the Tullibee, commissioned in 1960. ~4 Presentation by Yves Girard, Technlcatome of France, conference on the lmplicatlon of Acquisltion of Nuclear-Powered Submarinas by Non-Nuclear Weapons States, March 27, 1989, at MIT. Boston. ~David Lanning and Thomas lppolito, "Some Technical Aspects of the Use of Low· Enrlched vs. High-Enriched Uranium Fuel in Submarina Reactors, n conference on the lmplication of Acqulsltlon of Nuclear-Powered Submarinas by Non-Nuclear Weapons States. 2 DGilberto Gomez de Andrade, technical actvisor to the Brazilian navy, at a conference on lhe lmplication of Acquisition of Nuclear-Powered Submarinas by Non-Nuclear Weapons States. Nero. Anthony Jr., A Gu/dsbook to Nuclear Reactors, London, 1979,p. 145. 27 24 Univ~rsity of California Press, lbid, p. 148. Fionald Davldson, director of the Princeton Plasma Physlcs Laboratory, 8 Fusion Dreams: Plugglng lnto the Planet," The Washington Post, August 14, 1994. 20 lO lbid. 33