ELSEVIER www.elsevier.com/locate/pnucene Progress in Nuclear Energy; Vol. 47, No. 1-4, pp. 212-221,2005 Available online at www.sciencedirect.com © 2005 Published by Elsevier Ltd. s e ~ E N e E ~ ) D, ~ E e T ° Printed in Great Britain 0149-1970/$ - see front matter doi: 10.1016/j.pnueene.2005.05.021 THE PROSPECT OF MOX FUEL BASED Pb-Bi COOLED SMALL NUCLEAR POWER REACTORS ZAKI SU'UD 1, BAKRIE ARBIE 2 and SEDYARTOMO S. ~ 1) Reactor Physics Lab., Department of Physics ITB, J1. Ganesha 10 Bandung, Indonesia. E-mail ' szaki@fi.itb, ac.id 2)National Atomic Energy Agency (BATAN), J1. Abdul Rochim, Jakarta, Indonesia ABSTRACT Safety performance of MOX fuel based Pb-Bi cooled small fast power reactors has been analyzed and discussed. Though the thermal conductivity of MOX fuel is not large relative to that of nitride or metal fuel, but by proper combination of relatively small power density and relatively large natural circulation it can compensate fuel temperature decrease with coolant temperature increase smartly during unprotected loss of flow accident. Under such condition, accident analysis discussed in this paper show that under unprotected total loss of flow (ULOF) accident the reactor can survive inherently using combination of reactivity feedback. For unprotected rod run out transient over power (UTOP) accident the MOX reactor can overcome external reactivity by smaller power increase compared to that of nitride fueled reactors case. In this case doppler feedback plays much more important role compared to radial expansion component. So the MOX fueled small power reactors discussed here can survive both UTOP and ULOF accident with still enough temperature margin. © 2005 Published by Elsevier Ltd. KEYWORDS Pb-Bi cooled; MOX fuel; UTOP; ULOF; Reactivity feedback 1. INTRODUCTION TMI-2 and Chernobyl accidents have pushed the safety paradigm of nuclear reactors toward inherent/passive safety. For liquid metal cooled fast reactors, proper combination of reactivity feedback will results in inherent safety capability against unprotected rod run out transient over power (UTOP) accident and unprotected loss of flow (ULOF) accident (Su'ud and Sekimoto, 1995; Su'ud and Sekimoto, 1996; Su'ud, 1998; Su'ud, 2003; Su'ud, 2004a; Su'ud, 2004b; Su'ud, 2004c; Su'ud, 2004d). During unprotected rod runout transient over power (UTOP) accident, reactor power increases due to external reactivity causing the increase of coolant and fuel temperature which induce 212