Nuclear

Question 1

Simplified equation for nuclear fission

Answer 1

U(235) +n(slow –> U(236) –> X + Y + vn(fast) + energy release

Releases approximately 200MeV, most of which as kinetic energy to heavy molecules X and Y. This produces an increase in temperature of the material which is the ‘heat source’ for the conventional heat engines

Question 2

Four factor formula

Answer 2

Not all thermal neutrons (n) produce sufficient numbers of neutrons for second generation reactions. Some processes to consider:

Kn = ηεpfn(1-1_f)(1-1_s)

1. K is the multiplication factor in the system; one thermal neutron will produce K thermal neutron during one complete fission cycle
2. η is the thermal to fast neutron fission yield
3. ε is the fast fission factor
4. p is the resonance escape probability
5. f is the thermal utilisation factor

Question 3

Simplified reaction for Fusion

Answer 3

D + T –> He(4) + n + 17.6MeV

Question 4

Conditions for Nuclear Fusion

Answer 4

Temperature has to be extremely high for D-T reaction

D and T become highly ionised charged particles repelling each other by coulomb forces. This necessitates higher pressures and containment times to increase the likelihood of getting them to react

No engineering material is capable of surviving the high temperatures required. Therefore containment is achieved my either magnetic or inertial confinement

Question 5

Of 2.43 neutrons emitted in fission, how many go on to cause fission of another atom

Answer 5

If <1 then reaction closes down to background decay

If = 1 then perfect balance (used up one, use up another one) therefore sustained reaction

If >1 sustained and potentially runaway situation (explosive)

Question 6

Coolants

Answer 6

Fluid use to remove thermal energy from nuclear fuel and surrounding structures

FUNCTIONS
To remove heat and keep nuclear fuel at acceptable temperature

To transfer thermal energy from core to heat engines

Question 7

MODERATOR

Answer 7

To slow fast neutrons down to thermal neutrons as quickly as possible with minimal absorption

Question 8

SHIELDING

Answer 8

To reduce radiation to acceptable levels

Absorbs neutrons, charged particles, beta and gamma radiation

Question 9

FAST + THERMAL NEUTRONS

Answer 9

FAST
Those that have been emitted from a fissile event with a high velocity
THERMAL
Those that have been slowed by continual collisions with other atoms to reach ambient energy levels set by the temperature

Question 10

FISSILE + FERTILE MATERIALS

Answer 10

FISSILE
Those able to directly undergo a fissile event on absorbing a neutron (U235)
FERTILE
Those unable to directly undergo a fissile event on absorbing a neutron but can transmute to an element that can (plutonium, U238)

Question 11

CONTAINEMENT

Answer 11

Barriers to isolate and contain materials eg Reactor Vessel

Question 12

PROMPT NEUTRONS

Answer 12

Released almost immediately following a fissile event

Question 13

DELAYED NEUTRONS

Answer 13

Released some time after the fissile event in which they were created
It would be impossible to have a sustained chained reaction resulting from only prompt neutrons