In-containment source term: Key insights gained from a comparison between the PHEBUS-FP programme and the US-NRC NUREG-1465 revised source term

NUREG-1465 was a major change to the preceding figures defining in-containment source term. Since then, the most important research venture in the arena of severe accidents has been the PHEBUS-FP project. Experimental data and interpretations brought in along the course of the project have highlighted similarities and discrepancies with those insights given in the NUREG-1465.This paper sets comparisons between NUREG-1465 and PHEBUS-FP in three key aspects: the release of radionuclides into containment, the in-containment aerosol behaviour and, finally, iodine chemical behaviour in the containment. The experimental basis of discussions is the FPT0, FPT1, FPT2 and FPT3 series, although the latter cannot be openly addressed yet. Similarities have been found regarding qualitative gap and early in-vessel releases, quantitative net release of noble gases and iodine releases, dominance of sedimentation as natural removal mechanism for in-containment aerosols, etc. Nonetheless, PHEBUS-FP data have also drawn attention to major discrepancies with respect to NUREG-1465. Examples are cesium and tellurium releases and possible massive iodine release under specific conditions. But, in addition, PHEBUS-FP has brought new insights, such as potential formation of in-sump iodine precipitates or the need of revisiting NUREG-1465 element grouping.