Activities in the SBL-FPL loops for LMFBR safety studies, (2)

As the first step for the safety study of liquid metal-cooled fast breeder reactors, it is necessary to understand the initial events of potential accidents in LMFBRs. Local faults and sodium boiling are conceivable. The sodium boiling test loop (SBL) and the fuel failure propagation test loop (FPL) were constructed to investigate such phenomena experimentally. The two loops share one sodium dump tank and the purification system, and the whole facility is called ''Sodium installation for experiment of nuclear reactor safety analysis (SIENA)''. In almost all experiments, electrically heated fuel pin simulators were used in the form of pin bundles. The experimental studies using SBL-FPL have been carried out by the ''Core safety sodium behavior experiment group (CSSBEG)''. In addition, the group has operated two water test rigs for the experiments on large bubble behavior during hypothetical core disruptive accidents. A local event may successively cause the failure of adjacent fuel pins by the local worsening of cooling capability. The studies on fuel pin contact, FP gas release, local blockage and anomaly detection were carried out. The cooling of pin bundles by boiling in low heat flux and low flow rate conditions was tested. The behavior of bubbles in HCDA and the behavior of melted claddings were also investigated. (Kako, I.)