Some theoretical considerations of neutron rethermalization near temperature and poisoning discontinuities in light water

Abstract

A numerical investigation is made of neutron rethermalization effects in light water near physical temperature discontinuities and discontinuities in 1/ν-poisoning. It is shown that calculations of effective neutron temperatures in unpoisoned water systems possessing only temperature discontinuities are insensitive to the details of the scattering model assumed, and that rethermalization occurs within 1 cm of the temperature interface. However, with or without the presence of physical temperature discontinuities but with one region poisoned, effective temperature differences of up to 70 K exist between predictions using the Nelkin model and the Haywood frequency distribution for the water molecule. In this case, rethermalization occurs up to 2 cm into the poisoned region.