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Conference Article: Prospective Studies of HTR Fuel Cycles Involving Plutonium

Abstract

High Temperature Gas Cooled reactors (HTRs) are able to accommodate a wide variety of mixtures of fissile and fertile materials without any significant modification of the core design. This flexibility is due to an uncoupling between the parameters of cooling geometry, and the parameters which characterize neutronic optimisation (moderation ratio or heavy nuclide concentration and distribution).

Among other advantageous features, an HTR core has a better neutron economy than a LWR because there is much less parasitic capture in the moderator (capture cross section of graphite is 100 times less than the one of water) and in internal structures.

Moreover, thanks to the high resistance of the coated particles, HTR fuels are able to reach very high burn-ups, far beyond the possibilities offered by other fuels (except the special case of molten salt reactors).

These features make HTRs especially interesting for closing the nuclear fuel cycle and stabilizing the plutonium inventory.

A large number of fuel cycle studies are already available today, on 3 main categories of fuel cycles involving HTRs :

1. High enriched uranium cycle, based on thorium utilization as a fertile material and HEU as a fissile material;
2. Low enriched uranium cycle, where only LEU is used (from 5% to 12%);
3. Plutonium cycle based on the utilization of plutonium only as a fissile material, with (or without) fertile materials.

Plutonium consumption at high burnups in HTRs has already been tested with encouraging results under the DRAGON project and at Peach Bottom. To maximize plutonium consumption, recent core studies have also been performed on plutonium HTR cores, with special emphasis on weapon-grade plutonium consumption. In the following, we complete the picture by a core study for a HTR burning reactor-grade plutonium. Limits in burnup due to core neutronics are investigated for this type of fuel.

With these limits in mind, we study in some detail the Pu cycle in the special case of a reactor fleet made of a mixture of LWRs and HTRs. It is reasonable to assume that if HTRs are to be deployed on an industrial scale, they will co-exist during a long period of time with already existing LWRs. The present paper investigates the symbiotic behaviour of LWRs producing plutonium, and of HTRs burning it.

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Reference:

Proceedings of the Conference on High Temperature Reactors, Petten, NL, April 22-24, 2002
Organized by HTR-TN in cooperation with the European Nucler Society (ENS) and the IAEA

International Atomic Energy Agency, Vienna (Austria)

HTR-2002, pp:1-12