Nuclear Fission
Q9.
(a)
(i) State two physical features or properties required of the shielding to be placed around the reactor at a nuclear power station.
thick
high density
material giving minimal fatigue problems after irradiation
withstands high temperature
any two ![](../../../../graphics/symbols/nuclides/ticksmall.png)
![](../../../../graphics/symbols/nuclides/ticksmall.png)
(ii) Which material is usually used for this purpose?
(reinforced) concrete ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(3 marks)
(b) Describe the effect of the shielding on the γ rays, neutrons and neutrinos that reach it from the core of the reactor. Also explain why the shielding material becomes radioactive as the reactor ages.
γ-rays - the intensity of gamma rays is (greatly) reduced by the shielding![](../../../../graphics/symbols/nuclides/ticksmall.png)
neutrons - there is some absorption
the speed or energy of the neutrons is reduced by collisions with the shielding ![](../../../../graphics/symbols/nuclides/ticksmall.png)
neutrinos - very little effect, most pass straight through![](../../../../graphics/symbols/nuclides/ticksmall.png)
Neutron absorption by nuclei within the shielding produces neutron rich or unstable nuclei by artificial transmutation.
These nuclei become β– emitters and/or γ emitters, and these often decay to produce daughter radioactive isotopes. ![](../../../../graphics/symbols/nuclides/ticksmall.png)
![](../../../../graphics/buttons/SeeNotes.png)
(4 marks)
(Total 7 marks)