Safety performance comparation of MOX, nitride and metallic fuel based 25e100 MWe PbeBi cooled long life fast reactors without on-site refuelling Zaki Su’ud * Nuclear and Reactor Physics Laboratory, FMIPA, ITB, Physics Buildings, Jl. Ganesha 10, Bandung 40132, Indonesia Abstract In this paper the safety performance of 25e100 MWe PbeBi cooled long life fast reactors based on three types of fuels: MOX, nitride and metal is compared and discussed. In the fourth generation NPP paradigm, especially for PbeBi cooled fast reactors, inherent safety capability is necessary against some standard accidents such as unprotected loss of flow (ULOF), unprotected rod run-out transient over power (UTOP), unprotected loss of heat sink (ULOHS). Selection of fuel type will have important impact on the overall system safety performance. The results of safety analysis of long life PbeBi cooled fast reactors without on-site fuelling using nitride, MOX and metal fuel have been performed. The reactors show the inherent safety pattern with enough safety margins during ULOF and UTOP accidents. For MOX fuelled re- actors, ULOF accident is more severe than UTOP accident while for nitride fuelled cores UTOP accident may push power much higher than that comparable MOX fuelled cores. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Long life reactors; ULOF accident; UTOP accident; Reactivity feedback; Natural circulation; External reactivity 1. Introduction After the TMI II and Chernobyl nuclear reactor accidents re- actor scientists and engineers intensively developed inherently safe nuclear power plant which also can solve many problems such as natural uranium utilization efficiency and radioactive wastes. Therefore GEN IV NPP research is now intensively conducted world wide. PbeBi cooled fast reactors are among the important candidates of advanced next generation NPPs. This paper discusses about the safety aspects of such reactors especially we will focus on unprotected reactivity (UTOP) accident and unprotected loss of flow (ULOF) accident. During UTOP accident, Doppler coefficient and other reac- tivity feedback coefficients are important to realize inherent safety capability (Zaki and Sekimoto, 1996; Sekimoto and Zaki, 1995; Zaki, 1998; Zaki et al., 2005). In this case MOX fuelled cores in the above power ranges in general have better performance due to their high Doppler coefficient and rela- tively high coolantefuel temperature difference. Nitride fu- elled cores also have large Doppler coefficient but they have relatively small coolantefuel temperature differences so that they need much larger power increase to overcome external reactivity. Metallic fuelled cores in general meet the severest accident when they experience UTOP accident due to high power increase requirement to compensate external reactivity. However, after some design optimization, in general all the cores have inherent safety capability against UTOP accident for the external reactivity up to 0.3% dk/k. During ULOF accident natural circulation level, coolante fuel temperature difference, and reactivity feedbacks play im- portant role to reach inherent safety capabilities. During this event the temperature increases along with the decrease of coolant flow rate due to the loss of pumping power. In such situation the negative reactivity feedbacks force the power level to decrease so that coolantefuel temperature difference also decreases. In general after reaching peak temperature, the coolant temperature as well as fuel temperature decreases * Tel.: þ62 22 250 0834; fax: þ62 22 250 6452. E-mail address: szaki@fi.itb.ac.id 0149-1970/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.pnucene.2007.10.028 Available online at www.sciencedirect.com Progress in Nuclear Energy 50 (2008) 157e162 www.elsevier.com/locate/pnucene