Shielding Design and Analysis Methods for Pressurized Water Reactors

The S_n discrete ordinates technique is used as a versatile design tool for a number of pressurized water reactor (PWR) shield design problems. This technique has been used for calculation of maximum neutron fluence at the inside wall of a reactor vessel, neutron flux distributions in steam, generators, and neutron and gamma-ray distributions at the outer surface of a reactor vessel. For vessel fluence calculations, comparisons of one-dimensional S_n and removal diffusion techniques with experiment show that the latter technique predicts higher fluences for typical PWR shield configurations. Studies of the effects of the one-dimensional approximation and different fuel management schemes show significant effects on the predicted fluence. The one-dimensional approximation gives a 20% higher fluence than the two-dimensional approximation, and the fluence can vary by as much as a factor of 2 with the type of fuel management scheme studied. Two-dimensional discrete ordinates techniques are used to determine neutron flux distributions in the energy range from 10 to 15 MeV in a steam generator that will be used for maritime reactor applications. These neutron distributions are used to calculate the source of ¹⁶N in the secondary system of the plant.