Tritium production within thermal reactor nuclear fuel

Tritium is an important nuclide for environmental assessments of releases from nuclear power plants, fuel storage facilities, reprocessing and waste handling plants. Its half-life of 12.3 years limits concerns about this nuclide to the first hundred years after its generation. The development of new fuels that include significant amounts of lithium, boron or nitrogen will increase the generation of tritium in fuel, the source term for the estimation of the environmental release of tritium. This paper accesses the production routes of tritium in nuclear fuels during thermal reactor operation and assesses where new fuels and fuel cycles will significantly alter its production. In the cases studied, the major component of tritium production is always direct from fission. If lithium is present the neutron induced reaction of 6Li is the second major component in magnitude, otherwise the contributions from the activation of other fission products dominate all other production routes. The JEFF-3.1 tritium yields increases the direct tritium production from fission by approximately 10% over the JEF-2.2 data. For the calculation using JEFF-3.1, the addition of cross-sections for missing ternary fission products increases the fission product tritium production by about 10 per cent. An estimate of the missing fission yields in JEFF-3.1 suggests that a further 10% increase may be possible. The inclusion of (n,t) reaction leads to an approximate additional 0.04% of tritium in the PWR case. Recommendations are made to improve the accuracy of the calculation of tritium within spent fuels from thermal reactors using the recently available JEFF-3.1 data