Pre-test Analytical Support for Experiments Quench-10, -11 and -12

Pre-test analyses using MELCOR1.8.5, SCDAP/RELAP5 and SCDAPSIM have been performed in collaboration of PSI and FZK to support FZK QUENCH programme of electrically-heated bundle tests on reflood of a degraded core. The experiments include QUENCH-10 and -11, recently carried out in the EU 5 th Framework LACOMERA programme, with analytical support in the 6 th Framework SARNET network of excellence, and QUENCH-12 to be performed in 2006 in support of the project ISTC1648-2. Each test involves novel features that pose challenges in the planning analyses to determine the test protocol and that require code and input changes to accommodate the test conditions. Special versions of the SCDAP codes were developed to simulate the effect of air on Zircaloy oxidation in the PWR air ingress test QUENCH-10, following pre-oxidation in steam. The analyses highlighted potential difficulties during the air oxidation and reflood phases that were avoided by changes in the test protocol. A more gradual thermal excursion could be achieved, facilitating control of the test, interpretation of data, and minimising the risk of a major excursion during quench. QUENCH-11 involved the steady boildown of an initially water-filled PWR bundle. Additional heating and water supplies were needed to give the desired conditions, and these needed to be tightly specified. Data from pre-tests with lower maximum temperatures were used to benchmark the models for defining the main test. QUENCH-12 examines the effect of WWER bundle configuration and cladding on heat-up, oxidation, and quench response. The bundle is significantly modified with changes to cladding material (Zr/1%Nb instead of Zry-4), electrical heating, and geometry, hence to radiative heat transfer, hydraulics and oxidation characteristics. Oxidation correlations for Zr/1%Nb in steam were introduced into special versions of SCDAP. Pre-test calculations suggest that the modified kinetics have only a minor effect on the thermal response, but there are larger uncertainties in the oxidation history, which could impact the quench behaviour. Recommendations have been made for the conduct of a low temperature pre-test, and the main test, to be conducted in the summer and autumn of 2006. The analyses not only support the QUENCH programme, but provide a valuable test of the codes and models. The capability of codes to simulate integral experiments correctly may help to qualify them for reactor purposes in terms of making judgements about accident evolution and management.