Benchmarking of the FIBWR2 transient BWR (boiling water reactor) core hydraulics code

The FIBWR code has been widely used for boiling water reactor (BWR) steady-state core flow, pressure, and void distribution calculations. The code models the complex flow paths in a BWR core, including water tubes and leakage flow to the bypass. FIBWR results are used to calculate flow-weighted equivalent loss coefficients for geometrically more simplified codes such as SIMULATE and RETRAN. In the 9 years since the original development of FIBWR, BWR fuel designs have become more complex, and computer speed and memory have greatly increased. In mid-1988, several utilities formed a support group to extend FIBWR's capabilities. The resulting transient version of FIBWR, referred to as FIBWR2, can model new fuel designs and perform multichannel BWR core thermal-hydraulic transient analysis using a fast, fully explicit numerical method, referred to as the BRAN method. This paper discusses the model enhancements and addition in the FIBWR2 code and preliminary results of the ongoing benchmark studies.