Severe reactivity injection accident simulations for safety assessment of research reactor

In the frame of safety assessment of research reactor, IRSN studies the consequences of reactivity transient so-called BORAX, more precisely it has appeared necessary to transpose experiments results to new concept of research reactor. For that purpose, the code SIMMER-III, devoted to severe accident simulation, has been adapted and validation work on SPERT experiment has been done in collaboration with FZK/IKET. The results show that SIMMER is accurate to simulate BORAX in a thermal reactor and will be a very convenient tool to transpose experimental results to reactor case. Especially the effects of neutronics feedbacks will be precisely focused on. Furthermore, specific simulations of the steam explosion are computed by a dedicated code developed by IRSN, MC3D. First example of MC3D application to BORAX transient is shown. These two main tools will allow IRSN to deeply analyse the safety demonstration of JHR reactor as far as severe reactivity injection accident is concerned. (author)