In the European 7th Framework SARNET project, European Commission (EC) co-funded from 2008 to 2013, work package WP8.3 ”Bringing Research Results into Reactor Application”, task “Benchmarking of available codes against integral experiments” the Phébus FPT3 experiment was chosen as the basis for such a benchmark. The aim of the benchmark was to assess the capability of computer codes to model in an integral way the physical processes taking place during a severe accident in a pressurised water reactor, from the initial stages of core degradation, fission product, actinide and structural material release, their transport through the primary circuit and the behaviour of the released fission products in the containment. The FPT3 Benchmark was well supported, with participation from 16 organisations in 11 countries, using 8 different codes. The temperature history of the fuel bundle and the total hydrogen production, also taking into account of the hydrogen generated by the boron carbide control rod oxidation were well captured, but no code was able to reproduce accurately the final bundle state, using as bulk fuel relocation temperature, the temperature of the first significant material relocation observed during the experiment. Total volatile fission product release was well simulated, but the kinetics were generally overestimated. Concerning the modelling of semi-volatile, low-volatile and structural material release, the models need improvement, notably for Mo and Ru for which a substantial difference between bundle and fuel release was observed, owing to retention in the upper part of the bundle. The retention in the circuit was not well predicted, this was due mainly to the boron blockage formation in the rising line of the steam generator, and the volatility of some elements (Te, Cs, I) could be better predicted. Containment thermal hydraulics were are well calculated, while as regards the containment aerosol depletion rate, only the stand-alone cases (in which the input data were derived from experimental data) provided acceptable results, whilst the integral cases (in which the input data came from circuit calculations) tended to largely overestimate the total aerosol airborne mass, due to the propagation of the errors from the previous phases. Calculation of iodine chemistry in the containment turned out to be a major challenge. Its quality strongly depends on the correct prediction of chemistry speciation in the integral codes. The major difficulties are related to the presence of high fraction of iodine in gaseous form in the primary circuit during the test, which is not correctly reproduced by the codes. This inability of the codes compromised simulation of the observed iodine behaviour in the containment. In the benchmark a significant user effect was detected (different results being obtained by different users of the same code) which had to be taken into account in analysing the results. This article reports the benchmark results comparing the main parameters, and summarises the results achieved and the implications for plant calculations which follow. Relevant experimental and theoretical work is under way to resolve the issues raised.

SARNET benchmark on Phébus FPT3 integral experiment on core degradation and fission product behaviour

PACI, SANDRO;
2016-01-01

Abstract

In the European 7th Framework SARNET project, European Commission (EC) co-funded from 2008 to 2013, work package WP8.3 ”Bringing Research Results into Reactor Application”, task “Benchmarking of available codes against integral experiments” the Phébus FPT3 experiment was chosen as the basis for such a benchmark. The aim of the benchmark was to assess the capability of computer codes to model in an integral way the physical processes taking place during a severe accident in a pressurised water reactor, from the initial stages of core degradation, fission product, actinide and structural material release, their transport through the primary circuit and the behaviour of the released fission products in the containment. The FPT3 Benchmark was well supported, with participation from 16 organisations in 11 countries, using 8 different codes. The temperature history of the fuel bundle and the total hydrogen production, also taking into account of the hydrogen generated by the boron carbide control rod oxidation were well captured, but no code was able to reproduce accurately the final bundle state, using as bulk fuel relocation temperature, the temperature of the first significant material relocation observed during the experiment. Total volatile fission product release was well simulated, but the kinetics were generally overestimated. Concerning the modelling of semi-volatile, low-volatile and structural material release, the models need improvement, notably for Mo and Ru for which a substantial difference between bundle and fuel release was observed, owing to retention in the upper part of the bundle. The retention in the circuit was not well predicted, this was due mainly to the boron blockage formation in the rising line of the steam generator, and the volatility of some elements (Te, Cs, I) could be better predicted. Containment thermal hydraulics were are well calculated, while as regards the containment aerosol depletion rate, only the stand-alone cases (in which the input data were derived from experimental data) provided acceptable results, whilst the integral cases (in which the input data came from circuit calculations) tended to largely overestimate the total aerosol airborne mass, due to the propagation of the errors from the previous phases. Calculation of iodine chemistry in the containment turned out to be a major challenge. Its quality strongly depends on the correct prediction of chemistry speciation in the integral codes. The major difficulties are related to the presence of high fraction of iodine in gaseous form in the primary circuit during the test, which is not correctly reproduced by the codes. This inability of the codes compromised simulation of the observed iodine behaviour in the containment. In the benchmark a significant user effect was detected (different results being obtained by different users of the same code) which had to be taken into account in analysing the results. This article reports the benchmark results comparing the main parameters, and summarises the results achieved and the implications for plant calculations which follow. Relevant experimental and theoretical work is under way to resolve the issues raised.
2016
Di Giuli, M.; Haste, T.; Biehler, R.; Bosland, L.; Herranz, L. E.; Fontanet, J.; Beuzet, E.; Torkhani, M.; Davidovich, N.; Klein Heßling, W.; Weber, S.; Dickinson, S.; Horváth, G.; Kruse, P.; Koch, M.; Paci, Sandro; Weber, S. J.; Salay, M.; Bujan, A.; Ivanov, I.; Kalychev, P.; Kim, S. B.; Morandi, S.; Del Corno, A.; Kotouč, M.; Dienstbier, J.; Kim, H. C.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/778418
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