Public health risks of substituting mixed-oxide for uranium fuel in pressurized-water reactors

The U.S. Department of Energy (DOE) has awarded a contract to the consortium Duke Cogema Stone and Webster (DCS) to dispose of up to 33 tonnes of excess weapons-grade plutonium (WG-Pu) by irradiating it in the form of mixed-oxide (MOX) fuel in four U.S. commercial pressurized-water reactors (PWRs). This paper estimates the increase in risk to the public from using WG-MOX at these reactors and finds that it exceeds recently established Nuclear Regulatory Commission (NRC) guidelines. Therefore, the NRC will have a technical basis for prohibiting the use of MOX at these reactors unless the risk that they will experience a severe accident can be significantly reduced. MOX fuel will displace a fraction of the low-enriched uranium (LEU) fuel that these reactors currently use. Because MOX cores have greater quantities of plutonium and other actinides than LEU cores throughout the operating cycle, the source term for radiological releases caused by severe reactor accidents will be greater for MOX-fueled PWRs. In this paper, the radiological consequences to the public from containment failure or bypass accidents at MOX-fueled PWRs are calculated, and compared to those resulting from the same accidents at LEU-fueled PWRs. This paper finds that compared to LEU cores, the number of latent cancer fatalities (LCFs) resulting from an accident with core melt and early containment failure would be higher by 39%, 81% or 131% for full WG-MOX cores, depending on the fraction of actinides released (0.3%, 1.5% or 6%). Under the DCS plan, in which WG-Pu will be purified using an aqueous process and only 40% of the core will be loaded with WG-MOX, the number of LCFs would be 11%, 25% or 30% higher, respectively. The average LCF risk to individuals within ten miles of a severe accident approximately doubles for a full WG-MOX core, and increases by 26% for a DCS core. These results are of particular concern for the nuclear plants in the DCS consortium, Catawba and McGuire. These plants have ice-condenser containments, which Sandia National Laboratories estimates are at least two orders of magnitude more vulnerable to early failure than other types of PWR containments. The findings of this paper also apply to the proposed use of WG-MOX in VVER-1000 reactors in Russia, which meet less stringent safety standards than U.S. reactors.

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