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AQA A-level Physics > Chapter 27 - Nuclear energy > Flashcards

Chapter 27 - Nuclear energy Flashcards

1
Q

What happens to the mass of an object when energy is transferred to or from it?

A

Changes too (due to E=mc2 relationship)

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2
Q

What is the energy of a photon produced in annhilation equal to?

A

E=mc2 where m=mass of the particle or antiparticle

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3
Q

An unstable nucleus that releases a 5MeV gamma photon would lose 8.0x10-13J of energy. What would it’s mass therefore decrease by?

A

Mass change = energy change/c2 = (8.0x10-13/(3.0x108)2 = 8.9x10-30Kg

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4
Q

What is the atomic mass unit (u)?

A

1u = 1.66x10-27Kg

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5
Q

How do you convert from atomic mass units to MeV (energy released)?

A

mass difference in u x 931.3

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6
Q

210Po84 emits alpha particles and decays to form 206Pb82. Write an equation for this and calculate the energy released when 210Po84 emits an alpha particle.

mass of Po-210 nucleus = 209.93667u

mass of Pb-206 nucleus = 205.92936u

mass of an alpha particle = 4.00150u

A

210Po84 -> 206Pb82 + 4He2 + energy released

mass difference = total initial mass - total final mass

= 209.93667 - (205.92936 + 4.00150)

= 5.81x10-3u

energy released (Q) = mass differnce x 931.3 = 5.41MeV

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7
Q

What is the binding energy of the nucleus?

A

Work that must be done to seperate a nucleus into its constituent neutrons and protons (overcoming the strong nuclear force and increasing the potential energy of each nucleon)

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8
Q

Why is energy released when a nucleus forms from seperate neutrons and protons? What is the energy released equal to?

A
  • Strong nuclear force does work pulling the nucleons together
  • binding energy
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9
Q

Since energy is released when a nucleus forms, what happens to the mass?

A

Mass of a nucleus is less than the mass of the seperated nucleons

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10
Q

What is the mass defect (change in m)?

A

Mass defect of a nucelus is defined as the difference between the mass of seperated nucleons and the mass of the nucleus

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11
Q

What’s the equation for binding energy of a nucleus?

A

mass defect x c2

(change in mass) x c2

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12
Q

What is the binding energy per nucleon of a nucleus?

A

Average work done per nucleon to remove all the nucleons from a nucleus

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13
Q

What is binding energy per nucleon also a measure of?

A

Stability of a nucleus

(greater binding energy per nucleon = more stable nuclei)

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14
Q

Draw graph of binding energy per nucleon against mass number (A) for all known nuclides

A
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15
Q

What happens to the binding energy per nucleon in nuclear fission where 2 fragments are formed from one large unstable nucleus?

A

Increases (fragments are more stable)

Change in binding energy per nucleon is around 0.5MeV

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16
Q

What happens to the binding energy per nucleon in nuclear fusion when small nuclei fuse together to form a large nucleus?

A

Increases (provided the nucleon number of the product nucleus is no greater than about 50)

Change of binding energy per nucleon is x10 that of in a fission reaction

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17
Q

What is induced fission?

A

When a nucleus splits into 2 approximately equal fragments. When 235U92 or 239Pu94 is bombarded with neutrons fission occurs

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18
Q

How is a fission chain reaction possible?

A

2/3 neutrons released in a fission event cause further fission events as a result of colliding with another 235U92 nucleus which releases further neutrons, inducing another fission and so on..

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19
Q

Why is energy released in a fission event? What is this energy equal to?

A

Fragments repel each other with sufficient force to overcome the strong nuclear force trying to hold them together. Fragment nuclei and fission neutrons therefore gain kinetic energy.

Changing in binding energy (and Q=(change in m) c2

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20
Q

Write equation for induced fission for 235U92 to 144Ba56 and 90Kr36

A

235U92 + 1n0 -> 144Ba56 + 90Kr36 + 2 1n0 + energy released

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21
Q

What is nuclear fusion?

A

2 nuclei combining at high speed to form a bigger nucleus. Electrostatic repulsion overcame and interact through the strong nuclear force

(binding energy increases and energy released is equalto change in binding energy)

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22
Q

Why is energy released in nuclear fusion?

A

Individual nucleons become more tightly bound together in a bigger nucleus. (binding energy per nucleon increases. Nucleons become more tightly bound together)

(energy released equal to increase in binding energy)

23
Q

Write equation for nuclear fusion of a proton and a deuterium nucleus 2H1 producing a nucleus of 3He2

A

2H1 + 1P1 -> 3He2

24
Q

Briefly describe a thermal nuclear reactor

A

Contains fuel rods spaced evenly in a steel vessel known as the reactor core. The reactor core also contains control rods, a coolant and fuel rods and is connected to a heat exchanger by steel pipes. A pump is used to force the coolant through the reactor core (where it’s heated) and through the heat exchanger where it is used to raise steam to drive turbines that turn the electricity generator.

25
Q

Draw a simple diagram of a thermal nuclear reactor

A
26
Q

What are the reactors called that use water as their coolant?

A

Pressurised water reactor (PWR)

27
Q

What are fuel rods in a thermal nuclear reactor made out of?

A

Contain enriched uranium which consists mostly of U-238 - the non-fissionable uranium isotope, and aout 2-3% of U-235 which is fissionable

28
Q

What is the function of the control rods?

A

Absorb neutrons

29
Q

What does the depth of the control rods control?

A

Keeping rate of release of fission energy constant by keeping the number of neutrons in the core constant. (so that one fission neutron per fission event on average goes on to produce further fission)

30
Q

What happens if the control rods are pushed in further?

A

They absorb more neutrons so that the number of of fission events per second and the rate release of fission energy is reduced

31
Q

What does a moderator do?

A

Slows down fission neutrons by repeated collisions with the moderator atoms. (slowed to a kinetic energycomparible to that of the moderator molecules)

32
Q

Why do fission neutrons need to be slowed down?

A

To cause further fission. Too fast otherwise

33
Q

What acts as the moderator in PWR?

A

Water (both moderator + coolant)

34
Q

What materials are usually used for moderators? And why?

A

Graphite (C-12 atoms) and water due to size of atom close to that of a neutron and transfer of kinetic energy is most effective if this is the case. This and chemical stability

35
Q

What condition must be true in a nuclear reactor for a chain reaction to occur?

A

Mass of the fissile material (e.g. U-235) must be greater than a minimum mass (the critical mass)

36
Q

Why does the mass of a fissile material need to be greater than the critical mass for a chain reaction to occur?

A

Some fission neutrons escape from the fissile material without causing fission and some are absorbed by other nuclei without fission (too many fission neutrons escape because the SA : mass ratio of the material is too high)

37
Q

What does an advanced gas - cooled reactor use as it’s moderator and coolant?

A

Moderator - graphite

coolant - CO2 gas

38
Q

What fuels are used for advanced gas-cooled reactors and pressurised water reactors?

A

AGR - Uranium oxide in stainless steel cans

PWR - uranium oxide in nirconium alloy cans

39
Q

What is the coolant temperature and power output of an AGR and a PWR?

A

AGR - coolant temp = 900K power output = 1300W

PWR - coolant temp = 600K power output = 700W

40
Q

What are the safety features of nuclear features of nuclear reactors?

A
  • reactor core is a thick steel vessel
  • Core is within thick concrete walls
  • Reactor has an emergency shut down system
  • Fuel rods are inserted and removed from the reactor by means of remote handling devices
41
Q

How is having a thick steel reactor core a safety feature?

A
  • Withstands high pressure and temperature in the core
  • Absorbs beta radiation and some of the gamma radiation and neutrons from the core
42
Q

How is thick concrete walls around the core a safety feature?

How can it become radioactive over time?

A
  • Absorbs the neutrons (some) and gamma radiation that escape from the reactor used

neutrons which escape the reactor may enter the shielding nuclei causing them to become unstable/neutron rich and start experiencing beta-minus decay

43
Q

Why is an emergency shut down system for the reactor a safety feature?

A

Designed to insert the control rids fully into the core to stop completely

44
Q

Why are spent fuel rods so dangerous?

A

Contain Pu-239 as a result of absorption of neutrons by U-238 nuclei (plutonium isotope is very active alpha emitter and if inhaled causes lung cancer)

45
Q

What are nuclear power stations hopefully able to provide in the UK?

A

Securing future electricty supply and reducing carbon emmissions

46
Q

What 3 catagories is radioactive waste put in?

A

High level, intermediate level and low level

47
Q

How must radioactive waste be stored?

A

In accordance with legal regulations and approved by disposal companies to ensure wate is stored safely in secure constainers until it’s activity is insignificant

48
Q

What an example of high level radioactive waste?

A

Spent fuel rods (HLW is mostly from nuclear power stations or form specialist users in univerisities and industry)

49
Q

How are spent fuel rods stored?

A
  • Removed by remote control and stored in cooling ponds for up to a year as they release heat due to radioactivity
  • Unused uranium and plutonium can be removed and stored in sealed containers for further use, with the rest (radioactive waste) vitrified (encased in glass) and stored in thick, sealed steel containers in deep trenches in geologically stable areas for centuries. (Long term storage is an issue as no one wants this in their own locality)
50
Q

How is intermediate-level waste stored? Give examples

A
  • Sealed in drums that are encased in concrete and stored in specially constructed buildings with walls of reinforced concrete.
    e. g. radioactive materials with low activity or containers of radioactive materials
51
Q

How is low level waste stored?

A

Sealed in metal drums and buried in large trenches

52
Q

What are some examples of low-level waste?

A

Laboratory equipment and protective clothing

53
Q

What 2 nuclei are most likely to be used in nuclear fusion

A

Deuterium (2H1) anf tritium (3H1)

54
Q

What methods are used to raise the temperature needed for fusion?

A

Electrical heating, electrical discharge, em radiation, inducing a current in plasma

AQA A-level Physics (31 decks)

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