Fuel Cycle Utilizing Plutonium-238 as a“Heat Spike” for Proliferation Resistance

The use of a “heat spike” in plutonium product is examined as a possible technical approach to improving the proliferation resistance of the light water reactor (LWR) fuel cycle. The heat spike is achieved by increasing the ²³⁸Pu content in reactor-generated plutonium above the usual levels. Because of the high heat generation rate of ²³⁸Pu, elevated material temperatures would result when significant concentrations of ²³⁸Pu are present. The high temperatures encountered during the fabrication, assembly, and storage of a nuclear device are expected to complicate weapon production. Although the concept would not render the reactor-grade plutonium useless for weapons purposes, it is expected to reduce the attractiveness of such material for this purpose. An important feature of the heat spike concept, as compared to other spiking concepts, is that the spikant (i.e., ²³⁸Pu) cannot be removed by chemical techniques. Among the subjects considered are:

1. reasons why a heat spike may contribute to proliferation resistance
2. means to enhance the production of ²³⁸Pu in reactor-generated plutonium
3. impact of potential future reactor design modifications on the heat spike concept
4. implementation time
5. certain fuel cycle economic penalties resulting from the concept
6. reprocessing considerations.

Results show that the buildup of²³⁸Pu in LWR-generated plutonium can be greatly enhanced by the recovery from spent fuel and recycle of ²³⁷Np and ²³⁶U (in recycle uranium). The penalty in resource utilization introduced by the concept is small, in comparison to that of the “once-through” fuel cycle. The penalty in separative work requirements varies significantly depending on the method selected for recycling spent uranium. Potential future reactor design modifications incorporating higher fuel burn-ups are shown to be advantageous to the concept. Reprocessing flowsheets have been developed to achieve recovery and purification of neptunium from LWR fuels and the subsequent conversion to the oxide. These operations appear to be technically feasible.