The safety analysis of a small pressurized water reactor utilizing fully ceramic microencapsulated fuel

Abstract

For post-Fukushima nuclear power plants, accident-tolerant fuel (ATF) is strongly desired in order to prevent radioactive release in the event of a severe accident. The Fully Ceramic Microencapsulated (FCM) fuel is one of these materials. The neutronics and thermal hydraulics analysis of small pressurized water reactor (PWR) utilizing FCM fuels needs to be carried out to demonstrate this fuel performance. In this study, first, a three dimensional full core model of a small PWR design is developed to assess the cycle lengths and power distribution. In order to achieve the acceptable cycle lengths, some design optimizations are taken, including higher TRISO particle packing fraction, higher enrichment and using higher density fuels. The results demonstrate that the acceptable cycle lengths can be achieved after this design optimizations. The results reveal that the cycle lengths can be improved to about 550days after using the 19.9w/o enrichment fuels with UO2 fuel kernel, and the cycle lengths can be maintain about 800days with UN fuel kernel due to the higher density than UO2 fuel kernel. Then, suppressing the excess reactivity, the core power distributions and reactivity coefficients are performed to prepare for thermal hydraulics analysis.The steady state and transient state analysis for LOCA is carried out using the best estimate system code RELAP5. For the conventional UO2 fuel, fission product releases simultaneously when the cladding fails. But for the FCM fuel, the radioactive material can be contained in the fuel pellet even after the cladding failure since enveloping the TRISO particles within a dense SiC matrix provides multiple barriers to fission product release. Consequently, although the Zircalloy cladding fails, there is still 3500s available for operator actions before the start of FCM fuel melting occurs even through the SB-LOCA occurring without ECCS, and there is still 1443s available even through the LB-LOCA occurring without ECCS. The results of the accident analysis without ECCS would be useful in understanding cladding and fuel failure progression and could provide guidelines in establishing detailed accident management procedures to design the proper ECCS in the future.