THe thermal nuclear reactor Flashcards
1
Q
Where are the fuel rods in a reactor?
A
- steel vessel known as the reactor core
2
Q
What do the fuel rods contain?
A
- contain enriched uranium, consists mostly U-238
- non-fissionable
3
Q
Why is there less of the fissionable U-235 isotope?
A
- natural Uranium is 99% U-238
4
Q
What is the function of the control rods
A
- absorb neutrons
- depth of control rode in the core is automatically adjusted to keep the number of neutrons in the core constant
- so that exactly one fission neutron per fission even on average to produce further fission
- keeps fission energy released constant
5
Q
What is the PWR?
A
pressurised water reactor?
6
Q
What happens in the pressurised water reaction>
A
- coolant (pressurised water)
- heated by reactor
- connected by steel pipes to a heat exchanger
- a pump is used to force the coolant through the reactor core
- and through heat exchanger where is is used to raise steam to drive the turbines that turn the electrictiy generator in the power stations
7
Q
What is the moderator?
A
- fission neutrons need to be slowed down significantly to cause further fission, otherwise they would be travelling too fast to cause further fission
- fuel rods need to be surrounded by a moderator so the neutrons slowed down by repeated collisions with the moderator atoms
- reactor described as a thermal nuclear reactor because fisssion neutrons are slowed down to EKE comparable to the KE of the mdoerator molecules
- water in PWR reactor core acts as coolants and moderator
8
Q
What is critical mass?
A
- for a cjaom reactopm tp pccir. tje mass of the fissile material must be greater than a minimum mass. referred tp as the critical mass
- some fission neutrons escape the fissile material w/o causing fission and some are absorbed by other nuclei without fission
- if the mass of fissile material is less than the cirtical mass needed, too many of the fission neutrons escape because the SA to mass ratio of the material is too high
9
Q
What is a thermal neutron?
A
- slow moving neutron with low KE
- (They are in) thermal equilibrium with the moderator / Are in thermal equilibrium with other material (at a temperature of about 300 K)
