Fuel

Question 1

What are the main stages of the fuel cycle?

Answer 1

Natural uranium -> Conversion -> enrichment -> fuel fabrication -> Power -> transport -> spent fuel storage -> reprocessing (recycled or waste)

Question 2

What are the methods of enrichment?

Answer 2

Gaseous diffusion and gas centrifugation

Question 3

What is the principle of gaseous diffusion?

Answer 3

UF6 piped through a series of porous membranes, the smaller, lighter U 235 diffusing 0.4% quicker than heavier U 238 – energy intensive

Question 4

What is the principle of gas centrifugation?

Answer 4

standard method 10x more efficient – rotation send heavier to outside of cylinder, lighter remain near the centre

Question 5

What are the different forms of Pu in the fuel cycle?

Answer 5

Pu239 - produced from U238 and burnt
Pu239 can capture additional electrons -> 240(not fissile)-242 which are fissile
239 has proliferation concerns but once enough 240 and other isotopes have been produced the Pu cannot be used for weapons

Question 6

What are alternative fuel cycles?

Answer 6

once-through
modified open
fully recycled

Question 7

How can we reduce the hazard of spent fuel?

Answer 7

By removing Pu, U and minor actinides, the activity of nuclear fuel is dominated by fission products for which the dose is majority beta radiation

Question 8

What is the breeding ratio?

Answer 8

The average number of fissile atoms created per fission event

Question 9

What is the breeding gain?

Answer 9

The net gain in the number of fissile fuel atoms per fissile fuel atom consume

Question 10

What is the burn-up?

Answer 10

Proportion of heavy-metal atoms in the fuel that has undergone fission

Question 11

What are burnable poisons?

Answer 11

atoms within the core that have a high neutron absorption cross section (higher than uranium), which are transmutated into atoms of relatively low absorption cross section as the result of neutron absorption

Question 12

What are common burnable poisons?

Answer 12

Boron, gandolinium

Question 13

What are the main components of fuel rods?

Answer 13

Cladding tube, fuel pellet, plenum spring, helium gas, seal weld

Question 14

Why do we use powder blends?

Answer 14

To maximise the use of U and recycle waste

Question 15

What is involved in press feed preparation?

Answer 15

Powder blending, pore former addition, analysis and testing, granulation then conditioning

Question 16

Why do we sinter the pellets?

Answer 16

To increase the pellet density, creating the true ceramic of correct microstructure and physical properties

Question 17

What conditions are used for sintering?

Answer 17

1750 C for >5 hrs under H2 to prevent oxidation, on molybdenum boats

Question 18

What shape of pellet is used and why?

Answer 18

Cylinders with Dish ends to accommodate the thermal expansion of pellet, and bevelled edges to prevent chipping during handling

Question 19

Which fuels are commonly used in the PWR?

Answer 19

Magnox fuel rod - MOX fuel