Slides for the continuation of Principles of Nuclear Energy

1. Basic Principles
Chapter 10B
Nuclear Energy

2. 1938: Fission discovered in Germany by Otto Hahn Fritz Strassmam
Jan 16, 1939: Lise Meitener & Otto Robert Frisch published a theoretical interpretation of
Hahnd Strassmam experiments in Natare (10 days after Hahn & Strassman
publication)
Apr. 17, 1939: Frederich Isliet, Hans von H, Plutonium bomb, alban, & Lew Kiowarsk
publish paper dealing with possiblility of nuclear chain reaction
Aug 2, 1939: Albert Einstein wrote letter to pres. F. D. Roosevelt drawing attention to the
possiblilty of an atomic bomb
1940: Edwin McMillan & Glenn Seaborg discover Plutonium
Dec. 1942: First Nuclear reactor went critical
-beneath the stands of the Universtiy of Chicago stadium (Chicagoo Pile 1)
-Fermi Chain Reaction
-core was 9m wide. 9.5m long, 6 m high
52 tons of natural uranium & 13,50 tons of graphite
Cadmium rods used for control
0.5W power for a few minutes

3. 1943: Town of Los Angeles constructed for atomic research & weapons
construction
July 16, 1945: 1st Nuclear Explosion, Trinity site in New Mexico
1952: Fusion Weapon,. Hydrogen Bomb (much less radioactive debris)
June 1, 1954: 1st Nuclear Power Plant
* Obninsk Nuclear Power Station, near Moscow (ADS-1 Obninsk)
* rated power 5 MW, 30μωeh
* graphite moderated, water cooled
* shut down April 24, 2002
Jan 21, 1954: USS Nautilus (SSN.571) launched
* Pressurized water reactors (Westinghouse)
* 10 μωm
* decommissioned March 3, 1980

4. Atom of lithium-7 (conventional
representation)
Not to scale - the electrons would be
better regarded as a cloud of
negative charge occupying a volume
around 1/100,000,000 cm across, i.e.
some 10,000 times the diameter of
the nucleus
Proton Positive(+1) 1
In nucleus
Around nucleus
Electric chargeParticle Relative mass
Neutron None 1
Electron Negative (-1) 0.00055

5. -20
-10
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100 120
Atomic number
Packing fraction
Packing fraction = (Isotopic mass/Mass number - 1) x 10,000
Onlythe most abundant isotope is shown for each element
} Mass loss
converted to
to energy
E = m c2
Packing protons and neutrons into a nucleus involves some gain or loss in mass per nucleon,
a quantity represented by the packing fraction. For fission products it is lower than in the
parent nucleus. Fission of heavy elements thus releases some surplus mass as energy.

6. The central nucleus contains practically all the mass
Electrons occupy practically all the volume
The simplest nucleus (of hydrogen) consists of a single proton
Other nuclei have more protons held together by a similar or larger number of neutrons
In a neutral atom the positive protons are matched by negative electrons, each with unit
charge
Chemistry depends on the behaviour of electrons
The number of protons (the atomic number) therefore determines the chemical identity
of the atom

7. Elements in vertical columns have more or less similar chemistry
( VIIIA )
1 (IA) GROUP NUMBER 18 (VIII)
1
H
2
(IIA)
13
(IIIB)
14
(IVB)
15
(VB)
16
(VIB)
17
(VIIB)
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
Mg
3
(IIIA)
4
(IVA)
5
(VA)
6
(VIA)
7
(VIIA)
8 9 10 11
(IB)
12
(IIB)
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104 105 106
Lanthanides
(Rare Earths)
58
Ce
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
Actinides 90
Th
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cf
99
Es
100
Fm
101
Md
102
No
103
Lr
(Alternative designation in parentheses)

8. The number of protons determines chemical identity
Neutrons provide the remaining nuclear mass but may vary somewhat in number
number without other effect on chemistry
Forms of an element with different numbers of neutrons are called isotopes,
distinguished by mass number (sum of protons + neutrons)
e.g uranium-235, uranium-238
Isotopes have identical chemistry (except for usually trivial effects of mass) but
different nuclear properties
Not all nuclear combinations are stable - many decay spontaneously and are
radioactive
Specific combinations of protons and neutrons are generically called nuclides, and if
unstable radionuclides

9. COMMON DECAY REACTIONS
Alpha () decay and fission are confined to the heaviest elements;
beta () and gamma () decay may occur in any element.
Fission
may be spontaneous
but more likely if
neutron-induced
Alpha decay
(emission of helium nucleus)
Beta decay
(electron emission,
leaving a neutron
converted to a
proton)
Gamma emission
(electromagnetic radiation)
UNSTABLE NUCLEI

10. Atomic number reduced by 2, mass number by 4
(e.g. Pu-239  U-235)
-emission
-emission Atomic number raised by 1, mass number unchanged (e.g.
Ru-106  Rh-106)
-emission Atomic and mass numbers unchanged (generally
accompanies or follows other nuclear reactions)
Fission Nucleus splits into two main fission products and two or
three free neutrons
Further neutron emission sometimes follows after a short
delay
INTERNAL EFFECTS
COMMON NUCLEAR REACTIONS

11. EXTERNAL EFFECTS
Alpha Short range, stopped by a surface film of water, but causes
concentrated damage to material within range
Rather more penetrating, range about a centimetre in water - more
diffuse damage
Beta
Range several metres in water with still more diffuse damageGamma
Also very penetrating, can induce radioactivityNeutron
A high dose of radiation to the body over a short time is likely to cause illness or
death
A low dose (comparable with natural levels) may or may not have adverse effects;
they cannot be identified against the natural background and the likelihood is
subject to dispute

12. RISKS OF HARMFUL EFFECTS (illustrative, not to scale)
Risk
Dose
Risk
Dose
Risk
Dose
RELIABLE EVIDENCE ONLY AT HIGH DOSES;
ESTIMATESAT LOWER LEVELS DEPENDON FORMOF
EXTRAPOLATIONASSUMED
LINEAR HYPOTHESIS
ADOPTED FOR REGULATION
OF OCCUPATIONAL
EXPOSURESAT
INTERMEDIATE LEVELSON
GROUNDSOF CAUTION,
DESPITE NEGLECTING
MITIGATING FACTORS
OTHER RELATIONSHIPS
AT LEAST EQUALLY
PLAUSIBLE

14. (UK PROPORTIONS, 2005)
Average proportions; levels vary widely from place to place
Radon, internal
(e.g. K-40),
terrestrial and
cosmic
contributions are
natural

15. Time
Amount
NUCLEAR DECAYCHARACTERISTICS
Half-life
Decay of radioactive nuclei is a matter
of chance and can be predicted only
statistically
A characteristic proportion of those
present decays in any unit of time
The time taken for half to decay is the
half-life (unalterable for any given
radionuclide)
The longer the half-life, the feebler
the radioactivity
The pattern of decay is identical for
all pure radionuclides but with
different time scales, so for a mixture
can be complex

16. •Excitation
•Emission
•Conversion
•Fission
then loss of energy as gamma-rays but with no further
change;
of one or more neutrons;
of a neutron to a proton with emission of a beta-
particle - transmutation to next higher element in the
Periodic Table (may be repeated);
splitting into two major parts plus some free neutrons.
Any nucleus can absorb a free neutron - likelihood varies enormously
Likelihood and consequence varies widely according to neutron energy and
nuclear composition; exchanging a neutron in the nucleus for a proton can
make an enormous difference
Absorption can have one of 4 possible consequences
(not necessarily immediate):-

17. Neutron flux
The probability that a nucleus will interact with unit flux of neutrons
(1 neutron per sq. cm. per second) in one second has the dimensions of area.
It may be imagined as the area presented by the nucleus to the neutron flow and is known
as the cross-section.
The unit of cross-section is the barn
(from the expression, “as easy as hitting a barn door”);
1 barn = 1/1,000,000,000,000,000,000,000,000 sq. cm (10-24 cm2).
Neutron density in a given space is inversely proportional to speed.
Absorption is in general therefore likelier with slow than fast neutrons.
After absorption, fission is likelier the higher the energy.
Absorption is especially likely at resonance energies.

18. Fission cross-section of uranium-233 (typical - no significance in
choice)
1/V
trend
Fission probability rises
above 1/V trend with
increasing energy

19. Activation
n -
e.g. Co-59  Co-60  Ni-60
5.3 years
Transmutation
n - -
e.g. U-238  U-239  Np-239  Pu-239
24 min 2.4 days
Activation and transmutation involve the same processes; the difference lies in the time-scale
of interest.
In activation a stable nucleus is made radioactive, usually with a fairly long half-life
In transmutation a new element is formed more or less quickly (seconds to days)

20. U-239
Pu-239
U-238
Pu-240 Pu-241 Pu-242
14.4 yr

nnn
n
Am-241
2.355 day

23.5 min

Am-242 Am-243 Am-244nnn
16.02 hr
Cm-242
10.1 hr

Cm-244Cm-243 nn
Np-239
Thus fissile Pu-239 is
generated from
non-fissile U-238

21. Once a neutron is absorbed, the likelihood of fission rather than other effects
increases with neutron energy.
Neutrons with energy matching their surroundings are thermal.
Neutrons as released by fission are fast.
Neutrons rather faster than thermal are epithermal.
Nuclei that can undergo fission with thermal neutrons
(e.g. uranium-235) are fissile.
Nuclei that undergo fission only with fast neutrons
(e.g. uranium-238) are fissionable.
U-238, not itself fissile, is converted by neutron absorption to fissile Pu-239 and
so is fertile.

22. Fission in a heavy nucleus may occur spontaneously but is more readily caused
by absorbing a neutron.
Each fission releases several initially fast free neutrons that in principle could
cause a further fission, and so on in a chain reaction.
If on average exactly one neutron from each fission goes on to cause another,
the chain reaction continues indefinitely at a constant rate - criticality - the
condition required in a power reactor.
If less than one causes further fission, the chain dies away more or less rapidly.
If more than one causes further fission, the reaction accelerates until controlled
naturally or artificially.

23. Large mass of fissile material
Low surface/volume ratio to
minimise escape of neutrons
Reflector to return
some escaping
neutrons
Few non-fissioning
neutron absorbers
“Moderating” medium to
slow down neutrons
A nearby fissile
mass

24. FISSION PRODUCT DISTRIBUTION
Fission usually yields
products differing
considerably in mass.
Symmetric fission is
much less common, as
shown here for U-235 in
a thermal neutron flux.
Very fast neutrons lead
to a distribution with a
shallower minimum
FissionYield (%)
0.00001
0.0001
0.001
0.01
0.1
1
10
70 80 90 100 110 120 130 140 150 160 170
Mass number
In terms of elements, fission peaks are roughly from krypton to palladium and iodine to europium

25. 0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120
2 or 3 free
neutrons
Neutrons
Protons
Typical fission
 -decay chain
~ 5 steps from
fission to
stability line
The proportion of neutrons to
protons needed for stability rises
with atomic number.
Thus the primary fission products
have too many.
They therefore convert some of
the excess to protons by emitting
energetic electrons (-particles),
and usually -radiation
Accordingly they rise by one
atomic number unit at each step
but keep unchanged mass
number.

26. Heavy elements are remnants from stars that exploded before the
Earth was formed.
Only the heaviest are subject to fission.
All beyond lead are more or less unstable.
The heaviest to have survived is uranium.
The only natural fissile nuclide on Earth is U-235.
So the very possibility of nuclear energy depended upon the last
element available to us ... or did it?

27. Thank You!
Sebilo, Eugene Paul Brian D.
BS ECE IV
References:
 http://www.peterwilson-seascale.me.uk/Basic.htm
 http://www.classroom-energy.org/energy_09/new-
window/4_nuclear_steam_turbine_plant.html
 http://www.youtube.com/watch?v=hZqA2hZW53o
 http://www.youtube.com/watch?v=H1ckdTlgvlU