REJUVENATION OF LIGHT-WATER REACTOR SPENT FUEL IN FUSION BLANKETS

The possibility of spent nuclear fuel rejuvenation in fusion reactors is investigated for both (D,T) and catalysed (D,D) modes. The analysis is conducted for light water reactor (LWR) spent nuclear fuel which w as used up to a total enrichment grade (fissionable plutonium plus U-2 35) Of 2.174% The behaviour of the spent fuel is observed during 48 mo nths for discrete time intervals of Delta t = 6 months. The cooling of the fissile fuel zone is considered with three different coolants, na mely pressurized helium ('gas'), Flibe (Li2BeF4) ('molten salt') and n atural lithium ('liquid metal'). The best rejuvenation performance is obtained with Flibe, followed by helium and natural lithium. The catal ysed (D,D) mode has a better rejuvenation capability than the conventi onal (D,T) mode. A rejuvenation time of 12 months is evaluated for a f inal fissile fuel enrichment grade of around 3.5% with Flibe coolant i n the fissile zone under a first-wall fusion neutron current load of 1 0(14) (2.45 MeV n cm(-2) s) and 10(14) (14, 1 MeV n cm(-2) s), corresp onding to 2.64 MW m(-2) by a plant factor of 75% for the catalysed (D, D) fusion reactor mode. The rejuvenation time increases to 24 months f or the same fissile fuel enrichment grade using the (D,T) fusion react or mode under a first-wall fusion neutron current load of 10(14) (2.45 MeV n cm-2 s), corresponding to 2.25 MWm(-2) by a plant factor of 75% . This enrichment would be sufficient for reutilization in a LWR. Long er rejuvenation periods (up to 48 months) increase the fissile fuel en richment level of the LWR spent fuel to much higher degrees (> 5% for gas coolant and > 7% for Flibe), opening possibilities for reutilizati on of the spent fuel in compact LWRs and in multiple cycles. Although the nuclear quality of the plutonium increases steadily during rejuven ation, the isotopic percentages of Pu-239 and Pu-240 remain < 70% and > 20%, respectively, during spent fuel rejuvenation, so that the pluto nium component cannot be considered of nuclear weapon grade quality. T his is a positive factor with regard to safeguarding. (C) 1998 Elsevie r Science Ltd. All rights reserved.