Helium production and behavior in nuclear oxide fuels during irradiation in LWR

Abstract

During irradiation in a LWR, helium is produced in nuclear oxide fuels, particularly in MOX fuels, but also to a lesser extent in UO{sub 2} fuels. In a context of increasing discharge burnup for the fuel rods and use of higher linear heating rates, the impact of He on the behavior of the fuel rod is required. A three-part study has been performed. The first part is related to the review of the main characteristics of the production modes of He, consisting of alpha-decay of some heavy actinides, (n, alpha) reactions on O-16 and ternary fissions. The modeling of each production mode was carried out and a computer code named PRODHEL, applicable to the calculation of He production either in PWR or in BWR conditions, was developed and qualified. The second part is related to a synthesis of the mechanisms involved in the behavior of He in the fuel pellet during irradiation. One of the most significant difference between helium and fission gases like xenon and krypton is the small solubility of He in oxide ceramics, leading to 'infusion/effusion' mechanisms. In the third part of the study, an illustration of the He behavior during an irradiation of a (U, Pu)O{submore » 2} pellet is given. Two types of modeling were developed at two different scales. The first type considers an effective behavior of He at the pellet-fragment scale (millimeter scale). The second type focuses more closely on the fragment, down to the grain scale (micrometer scale). (authors)« less