OECD CSNI ISP 15: post-test analysis of a split break transient in FIX-II loop performed at Pisa University by RELAP4/MOD6 and RELAP5/MOD1 codes", University of Pisa Report, DCMN - RL 067(83), Pisa (I), Dec. 1983, OECD CSNI Workshop on ISP 15, Nykoping (S), Dec. 15-16, 1983