Plutonium Fuel Technology, Part III: Nuclear Criticality Safety Considerations in LWR (Pu,U)O₂ Fuel Fabrication

The nuclear criticality safety aspects of light water reactor (Pu,U)O₂ fuel fabrication have been reviewed. Conclusions are as follows: 1. Criticality safety limitations will present a major design challenge in those parts of the plant where plutonium and plutonium-uranium solutions are processed. In particular, the requirement of large vessel volume to achieve homogeneous plutonium-uranium blending will be complicated by the restrictive criticality safety limits necessary on vessel dimensions. Special vessel design, such as annular geometry, and fixed nuclear poisons are possible innovations to overcome this problem. 2. Once the PuO₂ and UO₂ are mixed and in dry powder form, plant throughput should proceed at a reasonable rate and criticality safety will not necessarily limit operations. 3. In dry operations, radiation protection limitations are likely to be more restrictive than criticality safety limitations. In other words, criticality safety limits will not be determining factors for process control, since the fuel will be well confined in glove boxes and handled in relatively small batches for radiation protection considerations. 4. The fact that plutonium recycle fuel will be fabricated in sealed glove boxes will make it more feasible to base criticality safety on limits for unmoderated fuel, in certain parts of the plant, than is now possible in UO₂ fuel fabrication plants. 5. The basic critical masses and dimensions applicable to the fabrication of plutonium recycle fuel are expected to be only slightly more restrictive than those for light water reactor UO₂ fuel.