Canadian reactor shielding

It has been the policy in Canada to build radiation measuring facilities into reactor bulk shields when the reactors are under construction. Radiation attenuation through the NRX shield was measured by means of a special plug. These measurements formed the basis for the design of the NRU and NPD shields. Design calculations and measurements on the NRU shield have been published. The most recent shield measurements were carried out on NPD. Calculation of the radiation fields through the NPD shield is being carried out using removal-age-diffusion theory. Both MAC and a series of programmes written at AECL [6] are being used in this work. Preliminary calculations indicate that while agreement between calculated and measured gamma radiation and fast neutron flux is good, there is lack of agreement in the case of the thermal neutron flux. This work is continuing