Coolant radiologic gas production in SP-100 class reactors

Coolant radiologic helium gas production rates were calculated for an SP-100 type reactor using the discrete ordinates code TWODANT. Neutron cross sections were developed from ENDF/B-V data via the MATXS6s master cross section library. Calculations were performed using an S4/P1 approximation and 80 neutron energy groups. Results indicate that the primary helium production reactions in a reactor utilizing 0.1 at. pct Li-6 coolant are (Li-7)(n, n-prime t) (82 percent) followed by (Li-6)(n,t) (16 percent), and (Li-7)(n,gamma) (1 percent). A reactor operating at 2.5 MWt for 7.3 years using 0.1 at. pct Li-6 coolant is predicted to produce approximately 0.16 moles of helium gas in the coolant. For a reactor using natural lithium coolant, gas production is increased to 1.4 moles. A parametric study was conducted which enabled the development of an empirical correlation to predict helium production as a function of coolant Li-6 at. pct and void fraction. 9 refs