[en] Leaks in LMFBR steam generators cannot entirely be prevented; thus the steam generators and the intermediate heat transport system (IHTS) of an LMFBR must be designed to withstand the effects of the leaks. A large-scale leak which might result from a sudden break of a steam generator tube, and the resulting sodium-water reaction (SWR) can generate large pressure pulses that propagate through the IHTS and exert large forces on the piping supports. This paper discusses computer programs for analyzing long-term flow and thermal effects in an LMFBR secondary system resulting from large-scale steam generator leaks, and the status of the development of the codes