Nuclear Energy (Fission and Fusion) Flashcards

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1
Q

When should you treat the neutron and proton as having slightly different masses?

A

Dealing with fusion or fission

(Calculating mass defects, binding energies or mass difference)

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2
Q

Define mass defect (∆m)

A

Mass lost when nucleons (protons and neutrons) come together to form nucleus

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3
Q

Define binding energy

A

Energy released when nucleons (protons and neutrons) come together to form nucleus

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4
Q

How is binding energy related to mass defect (∆m)?

A
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5
Q

Define 1 atomic mass unit

A

Mass of 1/12 of a carbon-12 atom

(1.661x10-27kg)

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6
Q

What’s the next step here?

A

Multiply by 931.5MeV

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7
Q

What’s the next step here?

A

Use E=mc2

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8
Q

Sketch the binding energy per nucleon graph

A
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9
Q

Label the fusion and fission regions

Why are they there

A

Energy only released if binding energy per nucleon increases

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10
Q

Define metastable state in radioactive decay

A

Long-lived excited state of nucleus

Eventually it de-excites emitting γ

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11
Q

How many possible decays are there?

A

2β- and 3γ

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12
Q

What is nuclear fission?

A

Heavy nucleus splits into two lighter nuclei releasing energy and neutrons

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13
Q

What are the 2 main isotopes used as fuel in nuclear reactors?

A

U-235, U-238

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14
Q

How do you calculate the energy released in this fission reaction?

A

Calculate the mass difference (mdiff)

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15
Q

How do you calculate if a reaction is possible?

A

If mass difference is positive reaction is possible

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16
Q

What are the main components of the nuclear reactor?

A
  1. Fuel rods - U-235
  2. Control rods - Boron
  3. Moderator - water or graphite
  4. Coolant - CO2 or water
17
Q

What does the moderator do in a nuclear reactor?

A

Reduce neutrons’ speeds to thermal speeds through elastic collisions

(More likely to be absorbed by U-235)

18
Q

What do the control rods do in a nuclear reactor?

A

Absorb some neutrons

Stop chain reaction occurring

19
Q

What does the coolant do in a nuclear reactor?

A

Transfer heat from fuel rods to the water that spins the turbines

20
Q

What are the main safety features of the nuclear reactor?

A
  1. Reaction happens inside thick walled concrete vessel
  2. Control rods fully inserted if meltdown starts
  3. Reactor flooded with water to remove thermal energy if meltdown starts
21
Q

In nuclear reactors how are spent fuel rods disposed?

A
  1. Removed remotely from reactor
  2. Stored in cooling ponds for up to 1 year
  3. Vitrified by mixing with molten glass
  4. Sealed in barrels
  5. Stored in mountains or deep underground
22
Q

What is nuclear fusion?

A

Two lighter nuclei are combined to form one heavier nuclei and release energy

23
Q

Why is nuclear fusion so difficult to achieve?

A

Requires incredibly high temperatures and pressures

  1. To ionise the isotopes
  2. To bring isotopes close enough to overcome electromagnetic repulsion
24
Q

In fusion how close do the ionised isotopes need to get?

A

Close enough for the strong force to be larger than electromagnetic

(<1fm)

25
Q

What are the two main fusion isotopes in stars (in their main sequence)

A

Deuterium → H-2

Tritium → H-3