Assessment of RELAP5/MOD3/V5m5 against the UPTF Test No. 11 (Countercurrent Flow in PWR Hot Leg). International Agreement Report

摘要

During the boil-down phase of a small-break loss-of-coolant accident (SBLOCA), an important source of cooling water to the core may come from the steam which, having previously boiled off in the core, condenses in the steam generator tubes and drains back down into the reactor vessel via the hot leg (reflux condensation cooling mode). The condensate and the steam flow through the hot legs in countercurrent; therefore, the possibility that steam flow could patialy or totally inhibit the water back down flow - partial delivery or countercurrent flow limitation (CCFL) respectively - is a potential concern regarding the reflux condensation cooling mode. Test No. 11 conducted in the Upper Plenum Test Facility (UPTF) in Germany was a quasi-steady state, separate effect test involving the UPTF system with blocked pump simulators and broken hot leg open to the containment simulator. The test was designed to investigate the conditions for countercurrent flow of the steam coming from the core and saturated water in the hot leg of a pressurized water reactor.