Simulation Of CORA&QUENCH Severe Fuel Damage Experiments And Development Of Cladding Oxidation & Hydrogen Release Models

The installed capacity of operational nuclear power units of China is the fourth largest in the world,while the number and capacity of units under construction in China is the first largest in the globe.China is now a big country of nuclear power and is moving towards the goal of a strong country of nuclear power.No matter a big country or a strong country,the nuclear safety is fundamental safeguard for utilizing nuclear power.The 2011 Fukushima nuclear accident has a negative impact on global nuclear power,and the nuclear safety issue has aroused great concern among the world's people.At the same time,the nuclear power severe accident has become the research focus in the nuclear industry again.The occurrence of several hydrogen explosions during the Fukushima accident is very impressive.While the researchers in our country only conduct some preliminary explorations in the field of severe accident in recent years,the Europe and the United States have accumulated nearly 40 years of research experience.The CORA and QUENCH severe fuel damage experiments provide rich data for the research of severe accident phenomenon and the hydrogen source term.These experiments are the cornerstone of severe accident research.Therefore,in this work we use the severe accident analysis program MELCOR to model the series of CORA and QUNENCH experiments,and conduct simulation studies on CORA13,CORA10,CORA29,QUENCH06,QUENCH05 and QUENCH04.And then,it is found that there are several obvious deficiencies in the traditional cladding oxidation and hydrogen generation models.In order to solve those deficiencies,a semi-empirical framework of cladding oxidation model and a semi-empirical hydrogen release model are proposed by this work.Through this work,the system simulation models of the series of CORA and QUENCH experiments are established,which thlay a critical foundation for the development and verification of the subsequent severe accident models.Moreover,the deficiency of a MELCOR-CORA13 model used by Sandia National Laboratories is found.The limitations of traditional parabolic oxidation model are analyzed.The influence of conservatism of oxidation rate correlation is revealed.The reason of unrealistic peak phenomenon of predicted H2 generation rate is found.In this article,several mechanisms during cladding oxidation are proposed,such as surface increase effect,irreversible oxidation between heating and cooling,time-delay effect due to hydrogen generated-released-transported,hydrogen detained by cladding,and asymmetry of hydrogen release rate between heating and cooling.A semi-empirical cladding oxidation model with considering non-parabolic mechanisms of oxide phase transition,loosed oxidation layer,cracked oxide layer,cladding rupture and beta-Zr melting is proposed.A semi-empirical cladding hydrogen release model with considering four hydrogen release mechanisms is proposed.These new findings and models provide new ideas for accurately predicting hydrogen generation and hydrogen release.The semi-empirical oxidation model is verified by CORA7/10/13/29/18/28/31/W1/W2,the results indicate that the model can be used for the rough post-analysis of CORA tests.The hydrogen release model is verified by CORA7/10/13/29/18/28/W1/W2 tests,it is demonstrated that the model has a good performance for correcting the predicted results of H2 generation rate.Moreover,an important hydrogen source term during cladding quenching phase is found,it is the fast release of previously generated hydrogen which detained and/or absorded by cladding.