FCI phenomena uncertainties impacting predictability of dynamic loading of reactor structures (Serena programme)

The paper presents the results of Phase 1 of OECD SERENA programme on fuel-coolant interaction under the aspect of the implications uncertainties on FCI phenomena may have on the predictability of steam explosion induced loads. SERENA, in its Phase 1, made a status of the predictive capabilities of the FCI codes through comparative calculations of most relevant existing experiments and reactor cases. All the codes were able to calculate reactors situations. The way they have been used in the exercise, the calculated in-vessel loads were found far below the capacity of a typical intact vessel and above the capacity of a typical cavity. Confidence in these conclusions are challenged by the large scatter of the results, and by the uncertainties related to the description of the flow patterns in the pre-mixing phase, in particular void fraction evolution, and to the missing physical justification of the reduced energetics observed with corium melts. Addressing these issues as well as considering other reactor situations is required to confirm these conclusions for in-vessel steam explosion and quantify the safety margins for ex-vessel steam explosion. (authors)