Improving the reactor safety aspects by the implementation of (Th-U 233-Pu) fuel in a PWR assembly

The aim of this work is not only to demonstrate how to introduce thorium as an alternative nuclear fuel into pressurized water reactors, but also to examine the several advantages that (Th, U 233 , Pu) has over (Th, U 233 ) and (Th, Pu) fuels when (U 233 O 2 ) is mixed with (Th-Pu)O 2 fuel. To investigate these advantages, three thorium fuels, (Th, U 233 ), (Th-U 233 -Pu) and (Th-Pu) are simulated and analyzed by the MCNPX 2.7 code. The reactor safety aspects of these fuels are compared with those of the reference UO 2 fuel. The concentration of Th-233 and fissile isotopes is adjusted to obtain criticality (Keff = 1.03) at the same burnup value (35 GWd/ tonne) for all fuel types. Based on the predicted results, the author revealed that: 1) 56 % of plutonium (238-242) is depleted in the case of (Th-U 233 -Pu), while 41 % of plutonium is depleted in the (Th-Pu) at 60 GWd/tonne. This result indicates that (Th-U 233 -Pu) is more proliferation -resistant than (Th-Pu). 2) In terms of improving the quantity of radioactive waste, (Th, U 233 , Pu) model produces 0.6 and 0.9 times the amount of Am (241-243) and Cm (242-244) in UO 2 , respectively. On the other hand, (Th, Pu) fuel produces about 7 times the amount of Am and 8 times the amount of Cm in UO 2 fuel. 3) The fuel temperature coefficient (FTC) and moderator temperature coefficient (MTC) of (Th-U 233 -Pu) are more negative than that of UO 2 and (Th-U 233 ) at the early stages of fuel burnup (0 - 5) GWd/tonne.4) the total mass of fissile isotopes in (Th-U 233 -Pu) is greater than that of UO 2 and (Th-U 233 ) and as a result, the fuel life time is longer in the case of (Th-U 233 -Pu). 4) The conversion ratio provided by (Th-U 233 -Pu) is greater than that provided by UO 2 and (Th-U 233 ).This behavior is expected owing to the hardening of neutron spectrum in (Th-U 233 - Pu). 5) The peaking factors are lower in the case of (Th-U 233 -Pu) compared to (Th-Pu). 6) The concentration of xenon and samarium is noticeably lower for (Th-U 233 - Pu) in comparison with (Th-Pu) and consequently, the time required for restarting the reactor is accelerated.