Researches On Thermal Hydraulic Characteristics Of PWR Core Loaded Accident Tolerant Fuel

In March 2011,station blackout accident happened in the Fukushima Daiichi nuclear power plant in Japan,which leaded to the loss of reactor core cooling capacity.As a result,the temperature of reactor core was high enough to trigger vigorous reaction between zirconium and high temperature steam and generate hydrogen.Hydrogen explosion followed,which caused release of radiation.Accident tolerant fuel?ATF?with the stronger severe accident tolerant capacity is regarded as alternative scheme for traditional UO₂/Zr-4 fuel.At present,the design concept of ATF is expected to achieve an equivalent even superior fuel performance compared to traditional fuel.Considering that most of nuclear power units?operating or being built?of our country are pressurized water reactor?PWR?,researches on thermal hydraulic characteristics of PWR core loaded accident tolerant fuel are conducted from the views of large scale?reactor system?and mesoscale?subchannel of reactor core?in this paper.These researches are of great importance and contribute to the further study and development of ATF for the country even the world.Two kinds of ATF pellet materials with different blending ratios?UO₂+10/20/30BeO and UO₂+10/20/30SiC?and three kinds of ATF cladding materials?FeCrAl?HNLS/ML-A and SA3/PyC150-A?are object of this study.Firstly,an CPR1000 system model loaded ATF materials is established using RELAP5/MOD3.4 system codes,and besides,thermal hydraulic characteristics during SBLOCA,SBLOCA with all injection failures accident and LBLOCA is investigated.The study results indicate that,the temperature of each“ATF pellet-cladding”differs little and is below failure temperature during SBLOCA and LBLOCA.However,during the SBLOCA with all injection failures accident,three kinds of ATF claddings are able to extend the time to failure but UO₂+BeO pellet will melt before traditional UO₂ pellet.Secondly,an 1/8 core model loaded ATF materials is built using COBRA-EN subchannel codes,and besides,thermal hydraulic characteristics of different“ATF pellet-cladding”groups during rapid rod ejection accident is investigated.Furthermore,considering the boiling characteristic differences between ATF claddings and Zr-4 cladding,boiling characteristic sensitivity studies and thermal impact analysis induced by boiling enhancement are conducted.We find that ATF claddings decrease MCT but increase MFCT slightly.Conversely,ATF pellet slightly increase MCT but largely decrease MFCT.Cladding temperature is most sensitive to CHF.With 10%boiling enhancement of claddings,MCT is obviously decreased.In the end,based on COBRA-EN codes,a 5×5 bundle model loaded ATF materials is established to conduct thermal hydraulic analysis under 4 transient scenarios.The analysis results show that MCT is little affected by ATF pellets or ATF claddings during these 4transient scenarios,but MFCT is remarkably reduced by the application of ATF pellets.