1. Should Nuclear be
Reconsidered?
Nuclear worries surface after Japan
quakes

2. Lurid Headlines
• “Partial meltdown at Japanese reactor likely”
• “US Nuclear Experts Worry About Possible Japan Reactor
Meltdown”
• “Sailors at sea receive month’s dosage in one hour three miles from
plant”
– No mention this is far less that any space launch
• “US Begins Airlift as Japan Battles Nuclear Reactor Leaks”
• “Help Wanted: Save Japan From Nuclear Disaster”
• “Japan’s Nuclear Crisis Stokes Fear In Europe”
• “After Japan Earthquake, Groups Question Nuclear Power”
• “Japan’s crisis: The world rethinks nuclear power”
• “Helicopters drop water on Japan’s troubled reactor”
– False
• “Nuclear power in disarray”

3. What is the truth?
• How does this type of reactor work?
– And how is it designed?
• What are its worse case scenarios?
• How much radiation was released?
– How much of a danger is that?
• Close to the reactor?
• In Japan?
• Elsewhere on earth?
• Was there any danger of “meltdown”?

4. Event timeline
• Quake hits
– Control rods inserted under full cooling conditions
• Reactor powered down 94% and much lower temp
– Loses coolant
• Unclear how long. Over six hours can damage cladding in control rods
• Saturday explosion
– Damaged only most outer containment
– But release of radioactive iodine and hydrogen
• “could” suggest decay of zircaloy cladding in fuel rods (temp > 2000 C)
• But normal small defects in rods could also produce this
• But there is possibility of partial fuel meltdown
– Much confusion calling the fourth level containment building “reactor
containment”

5. Event Timeline 2
• Seawater pumped in
– Actually only pumped in between 2nd (reactor
vessel) and third level (containment building) to
bring overall temperature down
• Core never exposed to sea water or vented to ocean
– Some reports say that seawater was pumped even into core
» Especially as plant was scheduled for 40 yr end of life in
two weeks anyhow.
• Coolant flow is reestablished

6. Japanese Reactor Type
• Boiling Water Reactor (BWR)
– Operating temperature 250 C
– GE BWR reactor
• Fuel uranium oxide or MOX in zircaloy rods
– One or more fuel pellets per rod (1 here)
– Rods melt at > 2300 C
• Control rods mediate the reaction soaking up neutrons
produced by the fuel.
– With fuel rods in only secondary radiation is present
(particularly iodine and cesium)
– Control rods were inserted immediately when quake hit
• Three levels of containment (four in this reactor)

7. Containment Levels
• Level 1 – Cladding
– Zirconium alloy sheath that surrounds fuel pellets keeping
it in bet geometry for management and cooling and
contains fission products
• Level 2 – Reactor Vessel
– Thick steel container housing reactor and its coolant – part
of coolant loop
• Level 3 – Containment building
– Thick steel reinforced concrete to withstand very high
pressure and heat
• Level 4 – Dry-wall outer shell mainly only meant to
protect from elements, not keep anything in.

8. BWR characteristics
• BWR reactor generates steam in the reactor vessel.
• No steam generator and pressurizer are needed.
• Control rods are inserted from the vessel bottom
• BWR has lower operating pressure than PWR does.
• The coolant flow rate of a BWR is smaller than that of a PWR
of equivalent power output.
• The BWR reactor vessel is larger than PWR vessel.
• Its primary coolant system connects to turbine units
• Circulation pump assembly is needed.
• The engineering of a BWR is more difficult than PWR.
• Basic game plan of BWR, keep pouring water on. If pressure
gets to high vent steam into containment building.

12. Reactor Vessel Assembly
Core Thermal Power: ~3,500 MWth
Vessel Diameter (I.D.): ~6 m
Vessel Height: ~22 m
Vessel Wall Thickness: ~14.5 cm to 16.4 cm
Coolant: Water
Coolant Flow Rate: ~13,000 Kg/s
Pressure: ~1,000 psia
Steam Temperature: 551°F
Feed Water Temperature: 420°F

13. Reactor Vessel Assembly
• GE Fuel Rod
– Fuel Pellet Diameter: 1.04 cm
– Fuel Pellet Height: 1.04 cm
– Fuel Material: UO2
– Cladding Diameter (O.D.): 1.23 cm
– Cladding Thickness: 0.81 mm
– Cladding Material: Zircaloy

14. Reactor Vessel Assembly
ABB Fuel Assembly and Control Rod

15. Reactor Vessel Assembly
• GE BWR Fuel Assembly
– Fuel Assembly: 8 ´ 8 array
– Number of Assemblies: 746
– Active length: 3.6 m
– Total Number of Fuel Rods: 46,376
– Fuel Weight: 155,000 Kg
– Number of Control Rods: 177
– Fuel Center Temperature: 3,330°F
– Cladding Temperature: 579°F

16. Reactor Containment
Dry Well:
– Seals the reactor from the rest of the building
Pressure Suppression Pool:
– Store water for emergency use
Containment Shell:
– Steel shell, a sealed barrier against radioactive release
Reactor Building:
– Concrete structure, last barrier.
Negative pressure is maintained between
containment shell and building wall to prevent
radioactive release.

17. Bottom Line
• There was no real danger of major meltdown
• There was very very small local danger from radioactive iodine. No
real immediate danger.
• Actually given a 9.0 quake (very rare)
– The reactors stood up very well even with both power systems down.
No reason for reevaluation of nuclear power from this.
• Much of the world goes into hysteria re nuclear power
– Why?
• Associating with nuclear weapons?
• Creeped by radiation/radioactivity
– And associated confusions?
• Plot to instill fear of some types of energy?
• General reactive clamor so prevalent in hu-mans?
• Lack of understanding of science/technology and fear thereof?

18. Bottom Line 2
• Spent fuel pool in reactor 4
– Much was made of this but..
• Spent fuel doesn’t get dangerously hot even after several days without coolant
• It is sometimes stored for years with only normal airflow cooling in storage
buildings
• At most this was a minor problem not fixed with far less difficulty than claimed
in much of the press.
• Top dose to any worker was about 10 mrem
– Not that high considering normal background dose over year is 250-
500 mrem
• Overall not bad for a once in 300 years event with an older reactor
design.
– Two weeks from its scheduled 40 year decommission.