EXPANSION OF DOSE RATE COMPLIANCE METHODOLOGIES FOR RH-TRU WASTE SHIPMENTS IN THE RH-72B CASK

Compliance with 10 CFR §71 dose rate limits for shipments of Remote-Handled Transuranic (RHTRU) waste in the RH-TRU 72-B package is accomplished through preshipment radiological surveys and limiting radionuclide activity to that bounded by conservative point-source analyses. The advantage of the preshipment survey/point-source analysis approach is that knowledge of the source response to accident conditions is not required because the source is assumed to redistribute and reconfigure to a point location that maximizes dose. Expansion of the compliance method is required to maximize the shippable source activity, minimize or reduce the source assay requirements, and to allow the shipment of radionuclides for which an activity limit has not previously been determined. The expansion of dose rate compliance methodologies, developed for Revision 3 of the RH-TRU 72-B package Safety Analysis Report (SAR), consists of three primary initiatives: 1) Refinement of the conservative point source analysis for neutron radionuclides, 2) Evaluation of the effect of redistribution, reconfiguration, and loss of self-shielding from Normal Conditions of Transport (NCT) to Hypothetical Accident Condition (HAC) on gamma and neutron dose rates, and 3) Development of a screening methodology for gamma and neutron radionuclides. The Monte Carlo N-Particle (MCNP) analysis of NCT and HAC geometries, for waste forms that meet specific self-shielding criteria, show that the preshipment radiological survey is sufficient to ensure compliance with 10 CFR §71 dose rate requirements. The allowable activity of neutron radionuclides that are defined by the point source analysis is significantly increased through the use of a subcritical neutron multiplication factor that is derived from a MCNP analysis. To ensure the ability to ship waste that does not meet specific self-shielding criteria and that contains radionuclides for which a conservative point source analysis does not exist, the screening methodology provides an option to bound the radionuclide activity limit based on limited assay data. Overall, the compliance methodology expansion will allow many waste forms for which selfshielding properties are known to be shipped with a simple pre-shipment radiological survey. For waste forms that do not meet the self-shielding criteria, use of the MCNP analysis will increase the shippable neutron HAC activity limit by an average factor of 22.5 and use of the screening methodology will allow shipment of radionuclides for which a HAC activity value has not been established a priori.