Comparisons of Measured and Calculated Neutron Fluxes in Laminated Iron and Heavy Water

Measurements of neutron fluxes have been performed in configurations depicting the regions extending radially and axially outwards from the core of a PHWR Reactor, in order to test the accuracy of the available methods in shield design on thin alternating laminae of Fe and D₂O. The results are compared to fluxes calculated by the British 18-group removal-diffusion method and by the NRN method developed at AB Atomenergi. The results show that the values predicted may be expected to be within a factor of 2 from the true values in most cases. The predicted relative flux distributions follow the observed ones with fairly good accuracy in spite of the apparent misuse of diffusion theory for the thin regions in question. It is also shown that the predicted change in the fast spectrum while penetrating these setups should be confirmable with certain threshold detectors.