Single U-tube testing and RELAP5 code analysis of PCCS with horizontal heat exchanger

A passive containment cooling sy stem (PCCS) is under planning to use in a next-generation-type BWR for long-term cooling by condensing steam in heat exchangers especially during a severe accident when a containment spray system is in failure. JAER1 and JAPC started a cooperative study to verify the performance of the PCCS using horizontal heat exchange in 1998. Fundamental heat exchanger performance was studied using a horizontal single U-tube test facility under postulated severe accident conditions. Studied phenomena included condensation heat transferin horizontal tube (19, 32 and 43 mm o.d., 8 m long) being degraded by non-condensable gas up to total pressure of 0.7 MPa, pressure loss and discharge behavior of condensate and non-condensable gas. Steam was totally condensed with a small pressure drop across the condenser tube. Condensation degradation was insignificant even at high gas concentration, suggesting that horizontal U-tube heat exchanger is promising for the PCCS purpose. The experimental results were used for verification of RELAP5/MOD3 code in post test calculations. The RELAP5 code was modified by incorporating correlations based on the test results, as the original code underpredicted the data. The modified code predicted the data well under both the pure steam and steam-gas mixture inlet conditions. (author)