Tritium Generation in the Coolant-Moderator of Pressurized Water Reactors

The generation of tritium from the ¹⁰B(n, 2α)³H reaction involving boric acid in the coolant-moderator of PWRs is studied. First, the total amount of tritium produced by this process during a core cycle is calculated for the case of base load operation assuming separability of the neutron flux into space, energy, and time modes as well as a linear decrease of the boric acid concentration in compensation for burnup effects. Subsequently, analytic solutions to this problem are obtained for square-wave load-following assuming both total and one particular mode of partial compensation of the reactivity transients due to xenon poisoning by boric acid. The limitation to load following due to practical limitation of the dilution rate is observed. The solutions are expressed in terms of commonly available plant parameters and are presented in graphical form as a function of characteristics of the load following program. The significance of the analysis is illustrated by means of a numerical example; details of the xenon-transient analysis are included as an appendix.