Fastrap

The FASTRAP code has been developed with the aim of evaluating special transients (STs) and small break loss of coolant accidents (SB-LOCAs) in pressurized water reactors (PWRs) with U-tubes steam generators (SGs). In order to have fast running time, the code simplicity was a main objective of the work and it was obtained by adapting a fixed schematic structure for simulating PWR. The model includes features allowing to perform ST and SB-LOCA best estimate calculations (enthalpy transport, CCFL, HF and HEM models for critical two-phase flow rate evaluation, etc.); particular care has been devoted to the model of the pressurizer, represented by two nodes, whose volumes change during the transient. The FASTRAP code, written in FORTRAN77, has been designed to run on small computers and has a core storage need of less than 600 Kybtes. The code has been tested on IBM-3081 computer. Typical running time is one- hundred times shorter than real time; the set up of input data files is very easy. In order to assess the capability of the code, a number of tests of the LOFT and LOBI researches have been analyzed. Some results are reported in this paper. They clearly show a very promising behavior, although disagreement points suggest further improvements