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CIVE40010 - Energy and environmental engineering > Nuclear Energy > Flashcards

Nuclear Energy Flashcards

(79 cards)

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1
Q

What are the criticisms of nuclear energy?

A

Too dangerous, too slow, too expensive

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2
Q

Approximately how many nuclear plants are there in Country US?

A

Country US has about 96 nuclear plants.

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3
Q

Which three countries are the top users of nuclear power?

A

The top three countries using nuclear power are the United States, France, and China.

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4
Q

What percentage of global electricity was generated by nuclear power in 2018?

A

Nuclear power generated about 10% of electricity globally in 2018.

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5
Q

How many nuclear reactors are operating worldwide?

A

420 reactors are operating worldwide.

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6
Q

How many operational reactors are there in the UK, and what is their total capacity?

A

15 operational reactors in the UK at 7 sites, with a capacity of 8.9GW.

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7
Q

What types of reactors are among those operational in the UK and give an example?

A

The UK has 14 Advanced Gas-cooled Reactors (AGR) and 1 Pressurised Water Reactor (PWR), for example, Hinkley Point B

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8
Q

What percentage of the UK’s electricity needs are generated by nuclear power?

A

15%

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9
Q

What are some safety features of the Hinkley Point C PWR?

A
  • Double containment for aircraft impact resistance
  • Core melt spreader to prevent criticality
  • Refueling water storage tank.
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10
Q

Who are the key players in the current status of nuclear power in the UK?

A

EDF and they have plans for subsequent European Pressurised Reactors (EPR) at Sizewell in Suffol

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11
Q

Why do some isotopes release radiation ‘spontaneously’?

A

Some isotopes are unstable and decay ‘spontaneously’, releasing radiation as a part of reaching a more stable state.

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12
Q

What role do neutrons play in the nucleus?

A

Neutrons act like glue within the nucleus, due to the strong force and their interaction with quarks, to hold the nucleus together.

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13
Q

What determines the chemical element of an atom?

A

The number of protons in the nucleus determines the chemical element.

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14
Q

What can a nucleus eject during radioactive decay?

A

A nucleus can eject alpha particles (Helium nucleus), beta radiation (electron), and emit gamma rays, which are waves indicating a change in nuclear energy levels.

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15
Q

How can neutrons induce nuclear processes?

A

Neutrons, having no charge, readily penetrate the atom and can hit the nucleus, leading to neutron scattering (neutron bounces off), neutron absorption (increasing atomic mass, possibly followed by alpha or beta decay), or fission.

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16
Q

What happens during fission?

A

During fission, the nucleus fragments into two or more smaller elements, known as fission products, generating heat and releasing more neutrons. This process typically occurs with large nuclei like Uranium and Plutonium, which are known as fissile materials, and releases between 2 and 3 neutrons.

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17
Q

What is the result of the decay of fission product fragments?

A

Fission product fragments undergo radioactive decay, which further contributes to the release of energy and radiation.

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18
Q

How many neutrons are produced on average in each fission event of U-235 and Pu-239?

A

On average, each fission event produces 2.47 neutrons for U-235 and 3 for Pu-239.

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19
Q

What is necessary for a chain reaction to occur in nuclear fission?

A

For a chain reaction to occur, enough neutrons must cause further fission events, with the potential for the reaction to become self-sustaining if the conditions allow.

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20
Q

What is a cross-section in the context of nuclear fission?

A

In nuclear fission, the cross-section is the probability that fission or any other neutron-induced reaction will occur.

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21
Q

What happens to neutrons during fission?

A

During fission, neutrons could either fly out or scatter, be absorbed, or cause further fission.

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22
Q

What are the two main fissile isotopes of natural uranium used in reactors?

A

The two main fissile isotopes of natural uranium used in reactors are U-235 and U-238.

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23
Q

How can U-238 become a fissile material?

A

U-238 can become fissile by undergoing neutron capture and beta-decay to become Pu-239

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24
Q

What happens to the fission cross-section as neutron velocity is reduced?

A

increases particularly in the resonance region

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25
How can a nuclear chain reaction be maintained?
To maintain a nuclear chain reaction, the amount of U-235 can be increased through enrichment, or the neutrons can be slowed down through moderation
26
What distinguishes thermal reactors from fast reactors in terms of fuel and neutron speeds?
Thermal reactors slow down neutrons to thermal energies using a moderator. Fast reactors do not use moderation but require a higher enrichment level, around 20% U-235.
27
Why are most nuclear reactors thermal?
Most nuclear reactors are thermal because the chances of fission occurring are much higher when neutrons are moving at slower speeds, around 10^3 meters per second, which can be achieved by moderating the neutrons to thermal energies.
28
What happens during neutron moderation?
During neutron moderation, the speed of neutrons is reduced to enhance the likelihood of fission. This is typically achieved through elastic collisions with atoms that have low atomic masses.
29
Can you name some examples of moderators used in nuclear reactors?
Examples of moderators used in nuclear reactors include graphite, H2O (light water), and D2O (heavy water).
30
What is the effective neutron multiplication factor, and what does K_eff = 1 indicate?
**Measures the change in the neutron population from one generation** to the next in a reactor. K_eff = 1 indicates a state of criticality, where the reactor is stable and the chain reaction is self-sustaining without increasing or decreasing in intensity.
31
How must a reactor run to sustain a chain reaction with the help of delayed neutrons?
A reactor **must run sub-critical in terms of prompt neutrons but rely on delayed neutrons**, which are released fractions of a second after fission, to sustain the chain reaction.
31
What percentage of neutrons produced in fission are prompt, and what is their significance?
**99.3%** of the neutrons produced in fission are prompt, meaning they are **produced almost instantaneously** (~10^-7 seconds) as the fission occurs. These prompt neutrons are **essential for maintaining the chain reaction.**
32
Under what condition might a reactor need to operate super-critical?
A reactor might need to operate super-critical when an increase in the neutron population per generation is required, such as during startup or when increasing power output.
33
Describe the typical form and configuration of nuclear fuel in a reactor core.
Uranium dioxide (UO2) ceramic pellets, which are stacked in fuel rods. These rods are then installed in fuel assemblies within the reactor core.
34
What are the main components of a nuclear reactor core besides the nuclear fuel?
- Reactor pressure vessel - Liquid coolant - Turbine and generator that convert the heat produced into electricity.
35
What time period do Generation I reactors correspond to, and what was a characteristic of this era?
**1950 to 1970**, characterized by early designs & prototypes and more lax regulations
36
Can you give an example of Generation I reactor designs?
Chernobyl RBMK design
37
What were the main focuses in nuclear reactor development from 1995 to 2010?
- Improved fuel technology - Superior thermal efficiency - Significantly enhanced safety systems - Standardized designs for reduced maintenance and capital costs.
38
Where do uranium mines operate, and which countries are the top producers?
Uranium mines operate in twenty countries, with half of the world's production coming from just ten mines in six countries:** Canada, Australia, Niger, Kazakhstan, Russia, and Namibia.**
39
What kind of uranium do the majority of nuclear power reactors require?
The vast majority of nuclear power reactors require 'enriched' uranium fuel.
40
How much fresh fuel is typically required each year by a 1000 MWe nuclear reactor?
About 27 tonnes
41
Describe the process that enriched UF6 undergoes at a fuel fabrication plant.
Enriched UF6 is transported to a fuel fabrication plant where it is converted to uranium dioxide powder, which is then pressed and sintered into pellets. These pellets are stacked into the reactor.
42
What does VLLW stand for and how is it disposed of?
VLLW stands for Very Low Level Waste. It can be disposed of as ordinary non-radioactive refuse, with each 0.1 cubic meter containing less than 400 kilobecquerels of beta/gamma activity or a single item containing less than 40 kilobecquerels.
43
What is the classification criteria for Low-Level Waste (LLW) in the UK?
- Waste not exceeding 4 gigabecquerels per ton of alpha or 12 gigabecquerels per ton of beta/gamma activity - No shielding needed - Stuck in metal containers and buried on the surface
44
What characterizes High-Level Waste (HLW), and how is it processed?
HLW is significantly **heat-generating and requires extensive shielding.** It is **currently immobilized in glass** due to its high content of fission products.
44
How is Intermediate Level Waste (ILW) managed?
ILW **requires shielding** and is typically **encapsulated in cement** for containment.
45
How much high-level waste does an 80-year lifetime use of electricity generate for one person?
generates a small amount
46
What are the key functions of a deep geological disposal repository?
- Isolate waste from near-surface processes and human activities - Protect the biosphere - Limit the release from progressively degrading waste packages - Disperse and dilute the flux of long-lived radionuclides.
47
What are the current UK stockpile volumes for low, intermediate, and high-level radioactive waste?
The current UK stockpile volumes are 4,200,000 cubic meters for low-level waste, 290,000 cubic meters for intermediate-level waste, and 1,100 cubic meters for high-level waste.
48
How is low-level radioactive waste stored, according to the UK classification?
Low-level radioactive waste is sealed in metal containers for storage.
49
What type of containment is used for intermediate and high-level radioactive waste?
Intermediate-level waste is **encased in concrete or sealed in metal** containers, while high-level waste is **fused with glass and sealed inside stainless steel or copper flasks.**
50
What types of fuel can be used in nuclear reactors?
- natural uranium metal - uranium dioxide - thorium
51
What are the two types of neutron cycles in reactors?
thermal and fast
52
What are some common coolants used in nuclear reactors?
- water (light and heavy) - gases like CO2 and helium - liquid metals such as sodium and lead - molten salts
53
Describe the fuel type and neutron cycle of a Pressurized Water Reactor (PWR).
A PWR uses uranium dioxide as fuel and operates on a thermal neutron cycle, moderated by light or heavy water.
54
What are the main components of a PWR?
- moderator which is water - pressure vessel - heat exchangers - pressurizer
55
What type of coolant does an Advanced Gas Cooled Reactor (AGR) use, and how is it circulated?
An AGR uses gas, typically CO2, as a coolant, which is circulated using a pump.
56
What moderates the neutron cycle in an AGR?
graphite
57
What is unique about the core of an AGR?
The core of an AGR **features graphite** and has **10 layers in the active core** with **2 layers of reflector bricks on the top and bottom**.
58
What type of neutron cycle and coolant does a BWR use?
A BWR uses a thermal neutron cycle, moderated by light or heavy water, and the coolant is also water.
59
How does a Boiling Water Reactor (BWR) differ from a PWR?
- Generates steam directly in the reactor vessel - Operates at lower pressure - Control rods are at the bottom - Radiated water directly drives the turbine
60
What is the fuel type and neutron cycle for a Pressurized Heavy Water Reactor (PHWR)?
A PHWR uses uranium dioxide as fuel and operates on a thermal neutron cycle, moderated by heavy water (D2O).
61
What is the ability of PHWRs such as the CANDU regarding refueling?
PHWRs like the CANDU can be refueled without reducing power, meaning they can undergo online refueling.
62
What are some characteristics of advanced Gen IV reactors?
Gen IV reactors are designed for better sustainability, economics, safety, reliability, and proliferation-resistance, and they work at high temperatures, typically operating at 800˚C.
63
How do small modular reactors benefit the production economy and installation?
Small modular reactors offer production economy through potential mass manufacturing and provide flexibility of location due to their smaller size and modular construction.
64
What is the difference between an open and a closed nuclear fuel cycle?
An open fuel cycle means fuel is used once in a reactor and then discarded. In contrast, a closed fuel cycle involves reprocessing the waste and potentially putting it back into reactors.
65
What does a modified-open fuel cycle entail?
A modified-open fuel cycle involves reprocessing the waste to extract usable material and putting it back into the reactor, reducing the amount of waste.
66
What are Small Modular Reactors (SMRs) and how do they differ from traditional reactors?
SMRs are nuclear reactors that are significantly smaller in size, typically less than 300 MWe, and even considered 'very small' if under 25 MWe. They differ from traditional reactors in terms of **construction time, cost, modularity, and the ability to improve load-following due to lower inertia**.
67
How does 'modularity' benefit a nuclear power plant (NPP)?
'Modularity' allows for multiple small reactors to be installed at a single nuclear power plant site, which can improve operational flexibility and potentially reduce costs.
68
What are the advantages of SMRs over traditional nuclear reactors?
- lower capital cost - reduced risk - easier entry for new market participants
69
What hypothesis is used to evaluate the health effects of radiation exposure?
The Linear No-Threshold (LNT) hypothesis is used, which assumes that the health effects of radiation are directly proportional to the dose, with no safe threshold.
70
What does the 'Linear No Threshold hypothesis' suggest about low levels of radiation exposure?
The Linear No Threshold hypothesis suggests that any amount of radiation exposure, no matter how small, can have a proportional effect on health, implying there is no safe level of radiation.
71
What were the immediate fatalities at Chernobyl?
Two workers died on the night of the Chernobyl accident.
72
How many people died from radiation after Chernobyl?
Twenty-eight people died shortly after the accident, and 4,000 are predicted to die over subsequent decades due to radiation exposure.
73
How long did it take to build Olkiluoto and Flammanville EPRs?
Around 18 years.
74
Why is nuclear considered expensive?
High discount rates due to long build times increase costs.
75
What is cogeneration in the context of nuclear power?
Utilizing waste steam for heating or desalination to increase revenue.
76
Why must storage costs be included when comparing nuclear to renewable energy (RE)?
To accurately compare costs, as storage adds to the total cost of RE.
77
Why do we need nuclear?
-Reliable Energy Supply - Energy Security - Solar and wind getting cheaper - Analysis which doesn’t include grid cost - Storing adds to costs - Discount rate → will go up if it takes long to build, thats why nuclear so expensive

CIVE40010 - Energy and environmental engineering (21 decks)

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