A new decay heat standard proposition based on a technical specifications guide for computation codes

The existing ISO international decay heat standard provides the basis for calculating the decay heat power of non-recycled nuclear fuel of light water reactors. Computing decay heat with this standard can be really efficient for standard uranium fuels. Though, for Mixed Oxide fuels, high Burn-Up uranium fuels or for non standard irradiation sequences, decay heat can only be estimated by more complex decay heat computation codes. Therefore, a new ISO international standard, a 'Technical specifications guide for decay heat computation' has been proposed to reflect the international way to compute decay heat in light water reactors. The aim of this article is to give the justifications for the methods that lead to simplified modelization of the decay heat and that will be put into this standard. These methods are useful for rapid and precise determination of reaction rates and for nuclide chains simplifications. We propose also a simple method to evaluate the sensitivity of decay heat computations with respect to nuclear data. (authors)