On Risk Assessment for Determination of in-Situ Data Requirements

The use of formal risk assessment techniques to determine in-situ data needed for nuclear waste disposal sites is discussed. Considerations of accident sequences, transport pathways to the biosphere, and dose factors lead to identification of the radionuclides which contribute to potential public radiation exposure as a function of time. Generic risk assessments have identified 14C, 90Sr, 99Tc, 129I, 137Cs, 226Ra (from 238u), 237Np, 238pU, 239pu, 240pu, 241pu, and 241Am as nuclides of interest. Site-specific studies can establish the relative importance of each and thus the precision needed for measurement of nuclide inventory and distribution. Instrumentation needs can then be established for measurement of these nuclides. The presence of low-energy beta emitters and several actinides on the list offers considerable challenge for instrument developers.