1
Q
In a non-infinite system, we must account for ________ ________ using the six factor formula
A
neutron leakage
2
Q
Keff is
A
number of neutrons from fission in one generation/neutron absorption + neutron leakage in the previous generation
3
Q
Equation for Keff
A
Keff = Kinfinity PNLf PNLth = e PNLf p f PNLth n
4
Q
what is PNLf called
A
fast non-lekage factor
5
Q
what is PNLth
A
thermal non-leakage factor
6
Q
equation for PNLf
A
PNLf = number of fast neutrons that do not leak from the system/ number of fast neutrons produced by all fission
7
Q
PNLth equation
A
PNLth = number of thermal neutrons that do not leak from the system/ number of neutrons that reach thermal energies
8
Q
PNLf is the probability …
A
a fast neutron does not leak from the core as it slows to thermal
9
Q
tau = T = fermi age and is a measure of
A
average squared distance neutrons travel before slowing down from fast to thermal energies
10
Q
Bg^2 is
A
geometric (critical) buckling
11
Q
Thermal non leakage probability is the probability that
A
a thermal neutron does not leak from the core before it is absorbed
12
Q
L vs L^2
A
Thermal diffusion length vs. thermal diffusion area
13
Q
L is
A
Thermal diffusion length: Neutrons birth point (as a thermal neutron) and its absorption
one half of the average distance a thermal neutron diffuses from the point where it becomes thermal to the point at which it is absorbed in an infinite medium of core material
14
Q
Lm vs L
A
Lm corresponds with the moderator while L corresponds with the entire mixture
15
Q
D is the
A
thermal diffusion coefficient
16
Q
In thermal reactors, the properties of the moderator are generally __________
A
dominant
17
Q
geometric buckling depends only on
A
geometry and size of the reactor
18
Q
The reproduction factor varies by
A
isotope and energy
19
Q
geometric (critical) buckling is
A
a property of the leakage of neutrons related to the shape of the fuel element or core
20
Q
What does SFR stand for
A
sodium fast reactor
21
Q
SFR: following WW2 is was thought that
A
uranium was quite rare
22
Q
SFR: what kind of fuel did the SFR use initially
A
Focus on improved resource utilization
focused on using as much fissile fuel (U235) as possible while breeding more fissile fuel by converting the remaining fertile (U238) into fissile (PU239)
23
Q
Describe the concept of breeding more fissile fuel than you started with
A
1951 the US began this with the experimental breeder reactor 1(EBR-1). In 1965 (EBR-2) formed the basis for the general SFR design used globally
24
Q
Describe the SFR fuel design
A
End plug
Gas plenum: gas fission products, particularly Xe escape into the plenum
Cladding
Sodium bond
Fuel Slug: flexible composition and can include PU239 from weapons or mixed oxide fuel (MOX) from reprocessed LWR fuel
25
Describe the Inner and Outer blanket for the SFR design
The core is the fissile material generated by the blanket. The banket is fertile material, that absorbs fast neutrons and becomes fissile material(for the core). The inner blanket moreso does this and the outer blanket reduces neutron leakage and radiation exposure
26
Advantages of the SFR
-Can be used to consume long-lived transuranic uranium elements (TRUs) from LWR
-great use of fissile fuel
-high output temperature
-possible thermal energy storage option
-can be used to use up stockpiles of weapons grade PU239
- metallic sodium has a low vapour pressure and does not need to be pressurized
27
Disadvantages of the SFR
-sodium ignites when in contact with air and can cause fires that release highly toxic aerosols
- require an intermediate coolant between the primary sodium and the steam cycle
- require 20% fissile material
typically dependent on fuel reprocessing
- generally higher costs than LWRs as long as the price of mined uranium is low
28
Which countries operated small prototype SFR
US, UK, Japan, France, Chine, Russia, and India
29
SFR's were considered as _______ reactors, but were rejected due to _________, __________, and _______ issues
submarine
reliability
proliferation
cost
30
______ and ______ both built full size SFRs but had major issues
France and Japan
31
The USSR/Russia has successfully operated ___, ____, and ___MWe SRFs with a large focus on _______________. They only have ____ capacity factor
350, 600, and 880
waste reduction from their RBMK and PWR fleets
75%
32
2 big SFR that were shut down
280MW japanese Monju
1,242MWe superphenix reactor
33
Describe the current SFR situation
Russia, chine and india are all building large scale SFR
Russia sells countries the reactors and has an agreement to also sell them the fuel, which they take back and reprocess for their own reactors
34
Both SFR and SMRs will need ________ to start
HALEU
35
Where in canada are they planning on building a SFR-SMR
100MWe in New Brunswick
copy of EBR II
36
Definition of nuclear decay
As mass number (a) increases, the ratio of neutrons to protons increases to maintain stability
37
How do we impart instability on the nucleus
deviation from the line of stability(too many protons or neutrons), excessive mass
38
how can we regain nuclear stability
nuclei undergoes radioactive decay to attain a more stable nucleus
- sometimes require multiple decay processes
39
what are the 4 rules that must be obeyed for nuclear decay
Conservation of electric charge
conservation of mass number
conservation of mass and energy
conservation of momentum
40
describe conservation of electric charge
charges are neither created or destroyed
41
describe conservation of mass number
no net change in the number of nucleons allowed, although they may be interconverted
42
describe conservation of mass and energy
mass can be converted into energy and vise versa but overall be conserved in all decay reactions
43
describe conservation of momentum
available kinetic energy amongst product nuclei, particles, and/or radiation is also conserved
44
What is referred to as the parent nuclide (reactants)
original nucleus/atom
45
what is referred to as the daughter nuclide (products)
resultant nucleus/atom
46
what is the general decay equation format
a + b -> c + d
a(b,c)d
47
Describe spontaneous fission (SF)
occurs when a large nucleus has too much mass
SF is more favorable the larger Z^2/A ratio becomes
rare radioactive decay mode (<1% of all decay reactions)
occurs without an input of energy via quantum tunneling
parent nuclide splits into 2 or 3 smaller nuclei and 1-4 neutrons
releases large amounts of energy - 200MeV/fission
48
describe alpha decay
emission of a helium nuclei (no electrons) from an unstable nucleus
When a nucleus emits an alpha particle, the number of protons decreases by 2, and the atomic mass number decreases by 4
denoted as 4He2, 4a2
49
When alpha decay occurs, how is helium technically emitted
4He2 2+. But it quickly strips electrons from surrounding environment, hence ionizing radiation, becoming 4He2
50
describe beta decay
beta decay results from a nucleus containing too many neutrons or protons
2 forms B- or B+
51
when fission occurs, does B emission or neutron emission come first
B comes first
52
How can a delayed neutron come to be
when beta decay occurs for a highly unstable fission products, the result can be the production of a delayed neutron
53
describe beta decay for B-
Result of too many neutrons
B- is the conversion of a neutron to a proton, accompanied by the emission of an electron and antineutrino from the nucleus
54
describe beta decay for B+
result of too many protons
B+ is the conversion of a proton to a neutron, accompanied by the emission of a positron and neutrino from the nucleus
requires the release of at least 1.022MeV to occur (electron + positron pair mass)
55
what happens to the daughter nuclide Z and A for the 2 types of beta decay
B- = daughter nuclide Z increase by 1, A constant
B+ = daughter nuclide decreases by 1, A constant
56
Describe electron capture
occurs when a nucleus contains too many protons so a proton and a electron(from the innermost electron orbital) converts to a neutron, accompanied by the emission of a neutrino from the nucleus
denoted as e-, e, EC, 0e-1
57
For which decay will a characteristic x-ray be emitted
electron capture
an electron from a higher orbital will move in to fill this vacancy, emitting a characteristic x-ray
58
what happens to Z and A for electron capture
daughter nuclide Z decreases by 1
A is constant
59
describe gamma decay
occurs when a nucleus has too much energy. Results in the emission of a ahigh energy photon containing 0.01-5MeV from the nucleus
Nuclides in this excited state are denoted as metastable with an m or an * beside the atomic mass number A
60
What happens to Z, N and A for gamma decay
The number of protons (Z), neutrons and atomic mass number (A) remain constant
61
what are Decay chain/series
some unstable nuclei require multiple radioactive decays to achieve stability. It typically entails several alpha and beta particle emissions to react stable
62
how does A and Z change for alpha decay
A decreases by 4
Z decreases by 2
63
what unit is used for radiation intensity
Becquerel (Bq)
64
radiation intensity means
number of nuclei that decay per second
65
what does absorbed dose mean
amount of energy absorbed by a substance of unit mass that received radiation
Unit: gray (Gy) = absorbed energy (J)/mass of the part receiving radiation(kg)
66
what does effective dose mean
unit for expressing radiation doses in terms of effects on the human body
unit: sievert (Sv)
67
In the receiving side, what are the 2 differences
Differences in effects depending on the type of radiation
differences in sensitivity among organs
68
radiation emitted from a a radioactive sample is due to
the collective decays of several independent nuclei
69
each nuclei has a specific probability of decaying within a given unit of time, denoted a
the decay constant λ
70
Describe activity
the activity at a given time t, is given by this probability, λ, times the number of nuclei at time t.
A = λN(t)
71
describe half life
half life is defined ats the time in which the number of radioactive nuclei in a sample has decreased to half its original value
72
Define radionuclide
A nuclide (any nucleus with a specific number of protons (Z) and mass number (A)) that is radioactive
73
Define Radioactive decay
the spontaneous/stochastic transformation of one radionuclide into one or more decay products from the nucleus
74
define radiation
the energy or particles that are released during radioactive decay
75
define radioactivity
property of a given material referring to the rate at which it emits radiation
76
Define Radioactive material
broadly describes a mass, substance, or material containing a radionuclide(s) that emits radioactivity
77
radioactive contamination
spread of radioactive materials or radioactive materials where we don't want it
78
Irradiation
process by which an object is exposed to radiation
79
Neutron activation
The process by which exposure to neutron radiation induces radioactivity in materials
80
Define ionizing radiation
Radiation capable of producing ions. Enough energy is deposited to produce ions by breaking molecular bonds and displacing(or removing) electrons from atoms and molecules. Electron displacement can directly or indirectly cause biological effects and changes within cells
81
Describe the 2 types of ionizing radiation
charged particles: strip off orbital electrons
Neutral particles: scatter or collide with electrons, displacing them.
82
define non-ionizing radiation
radiation capable of causing material heating and other effect, but does not result in ionization
83
examples of ionizing radiation
alpha, beta, gamma particles (high energy photons), and neutrons
84
examples of non-ionizing radiation
low energy photons (infrared, microwaves, etc)
85
Sources of ionizing radiation
Sun/stellar objects
Environment (geological deposits of thorium, carbon 14, potassium 40)
Man made (medical devices for medical imaging, nuclear reactors, smoke detectors)
86
Source of non-ionizing radiation
Sun/stellar objects
man made (communication infrastructure like cell phone towers, radio towers, microwave ovens)
87
what can alpha particles penetrate through
not paper or skin
88
what can beta particles penetrate through
paper and skin, but not aluminum
89
what can gamma particles penetrate through
skin, paper, and aluminum, but not lead
90
what can neutrons penetrate though
paper, sin, aluminum, lead but not concrete
91
describe alpha particle interaction
usually produced by the radioactive decay of heavy nuclides
Big particle with a +2 charge, generally expelled at 4% speed of light
Strips nearby orbital electrons, decelerating and expending its kinetic energy in the process
Deposits large quantities of energy quickly
Has a very short range from incidence to become a stable helium atom
92
Describe Beta- particle interaction
B- is an electron that has been expelled from the nucleus at extremely high velocity
Loses kinetic energy by colliding and displacement of nearby orbital electrons
eventually slows down enough to be captured as an orbiting electron in an atom
More penetrating power than an alpha particle, but still easy to stop
93
describe beta plus particle interactions
B+ decay produces positrons which is very short lived
positrons interact much like a beta minus particle
Positron, once sufficiently slowed down, encounters an orbital electron and the two annihilate.
Annihilation produces two gamma particles/rays with equal energy to the rest mass of the electron/positron pair
94
describe gamma particle interactions
form of electromagnetic radiation (photons)
Very similar to x-rays
no mass + no charge = high penetration power
95
how to gamma rays differ from x-rays
gamma rays produced by the decay of an excited nuclei or nuclear reaction whereas x-rays are produced by orbiting electrons moving from higher to lower energy orbital or when a fast moving electron approaches an atom and is deflected/decelerated as it reaches with an atom's electric field ( referred to as bremsstrahlung or braking radiation)
96
what are the 3 ways to attenuate (block or absorb) gamma radiation
1) photoelectric effect
2) Compton scattering
3) pair-production
97
describe neutron interactions
Neutron possess no charge, nearly same as a proton
Difficult to step and has high penetration power
attenuated via down scattering/moderating effects or absorption in materials
98
3 best modes of radiation protection
Time:
Distance:
Shielding
99
shielding materials and consideration for alpha emitters
generally easily shielded against, except gaseous alpha emitters such as radon gas (do ventilation or dilution to reduce radon gas)
Dangerous is inhaled or ingested
samples often contain impurities and daughter products of alpha emitters
100
Shielding materials and consideration for beta emitters
Thin metals materials will stop beta emitters, but can produce bremsstrahlung radiation which is more penetrating
Low Z materials are used to prevent bremsstrahlung radiation but still attenuate beta particles, like plastic and polyethylene
101
Shielding materials and consideration for gamma emitters
gamma and x-ray emitter shielding requirements dependent upon several factors, including energy of the photon itself
High Z material (lead, depleted uranium and tungsten) make for the best gamma attenuators
Tungsten is really bad for Bremsstrahlung radiation when exposed to beta/plasma fields
Also must account for material handling difficulty, cost, availability, etc
102
Shielding materials and consideration for neutrons
Require considerable materials and geometry consideration
1. must slow neutrons
2. absorb neutrons
3. absorb resultant gamma radiation
Best shielded against using material with low z values (as close to hydrogen as possible) and materials with high absorption cross sections. Like water(high moderating, low absorption), concrete and plastic mixed with boron
103
stopping power is defined as
1: rate at which a material absorbs the KE of a charge particle
2. retarding/slowing force acting on charge particles
104
assumption for the shielding calculation for gamma rays
narrow beam of gamma radiation penetrating a thin material so that any interaction removes the ray
105
define relaxation length
the thickness of the shielding that will reduce the intensity of the radiation to 37% of the original intensity
106
define the specific gamma ray constant
for a single radionuclide with multiple gamma ray emissions exposure rates can be combined into a single value
107
What is the assumption for neutron shielding calculations
narrow beam of neutrons penetrating a thin material
108
how does ionizing radiation do to the body
Ionizing radiation causes cellular damage by forming ions and free radicals
109
what are the units for quantifying dose (D)
rad
gray (Gy)
110
what does rad stand for
radiation absorbed dose
111
are all forms of radiation equally damaging and why
No, you must find the equivalent dose - E=QD
112
what does Q account for in the equivalent dose calculation
Q accounts for differences in energy deposition and rate of damage
113
when would we get rem out of the equivalent dose calculation and when would we get sievert
Rem is QxD(rad)
Sievert is QxD(grey)
114
define chronic dose
exposure to a generally small amount of over a long period of time
115
There was ____ correlation between the levels of natural radioactivity an mortality from cancer in areas where natural radioactivity was evaluated
no
116
What is BED
Banana Equivalent Dose (not a real scientific measurement) Due to potassium-40, but we excrete most of the potassium so you would never actually reach this dose from a banana
