Joint studies of LOF and TOP incidents for a 1300 MW(e) LMFBR using the computer codes SAS3D/EPIC and FRAX-2

This paper reports the results of joint studies carried out for a 1300 MW(e) LMFBR. The incidents examined were a slow TOP (3c/s) and a LOF (pump rundown with 9s flow halving time), both with failure to trip. For the TOP incident a benign outcome was predicted largely as a consequence of the prediction of clad failure near the top of the core. For the LOF incident highly energetic outcomes were not predicted for the reference case because the incident was terminated by disassembly (by fuel vapour pressure) in voided channels and failures in low-rated flooded channels with MFCI potential were not predicted. In the variant cases where MFCIs were predicted before shutdown, and rapid enough extension of the clad rips was allowed, low energetics were still predicted as a consequence of fuel swerepout. The strength of the MFCIs (as represented by a Cho-Wright treatment) does not appear to be an important factor but the results are dependent on the prediction of negative reactivity addition through fuel sweepout. The physical conditions obtaining at the time of fuel failure are such as to suggest that internal fuel motion following failure should not have an important effect on accident energetics, unless themore » development of the initial rip is delayed by several milliseconds. This is an area where only limited experimental evidence is available. Other areas of uncertainty are associated with the position of failure, of clad rip propagation and the influence of incoherency on the progression of the incident. Clad motion effects were shown not to influence accident energetics significantly for the reactor model considered.« less