Conclusions drawn of tritium balance in light water reactors

In the tritium balance of pressurized water reactors, using boric acid and lithium in the cooling water, contribution of the tritium produced by fission, diffusing through the zircalloy of the fuel cladding estimated to 0.1%, was not in agreement with quantities measured in reactors. It is still difficult to estimate what percentage is represented by the tritium formed by fission in the fuel, owing to diffusion through cladding. The tritium balance in different working nuclear power stations is consequently of interest. The tritium balance method in the water of the cooling circuit of PWR is fast and experimentally simple. It is less sensitive to errors originating from fission yields than balance of tritium produced by fission in the fuel. A tritium balance in the water of the cooling circuit of Biblis-A, with a specific burn-up of 18000 MWd/t gives a better precision. Diffusion rate of tritium produced by fission was less than 0.2%. So low a contribution is a justification to the use of lithium with an isotopic purity of 99.9% of lithium 7 to limit at a low value the residual lithium 6