Safety analysis of a small modular reactor using fully ceramic micro-encapsulated fuel

Highlights: • An SMR model using FCM fuel was built in MELCOR by referred to the WSMR. • The difference between FCM fuel and UO₂ fuel was analyzed under a hypothetical extreme accident. • The SMR using FCM fuel has good safety features and delay the melting of the core. -- Abstract: Fully ceramic micro-encapsulated (FCM) fuel has high thermal conductivity and fission product retention capabilities. It can improve the accident tolerance ability of light water reactors (LWRs). Small modular reactors (SMRs) shows a good inherent safety due to their good design and low power density. Combining FCM fuel and SMR may greatly improve the safety of the reactor. In this paper, a SMR model using FCM fuel is built by referring to the Westinghouse Small Modular Reactor (WSMR). Based on this model, we analyzed some accidents associated with SMR using FCM fuel and compare this information with SMR using UO₂ fuel. The results indicate that the steady running temperature of FCM fuel is low and that the temperature increases slowly in accidents. The SMR using FCM fuel has good safety features and delay the melting of the core. Under the conditions of station black-out (SBO) combined with failure of core makeup tanks (CMTs) and ADS automatic depressurization system (ADS), the failure time of the core using FCM fuel is 5.49E4 s, which is 7.10E3 s (1.97 h) longer compared with that of UO₂ fuel. When considering reinvestment in CMTs, the time limit of FCM fuel is 1.33E4 s (3.70 h) longer compared with that of UO₂ fuel, which offers enough time for the restoration of safety system in the accident state. Because of its low temperature, the hydrogen production rate of FCM fuel is reduced compared with that of UO₂. However, given the use of zirconium cladding, the final output of hydrogen is the same as or even more than UO₂ fuel, and hydrogen elimination devices must be considered.