Radionuclide Screening
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| ANL-NBS-HS-000039_DOC.20070326.0003.pdf (5.04 MB) | 5.04 MB |
The waste forms under consideration for disposal in the repository at Yucca Mountain contain scores of radionuclides. It would be impractical and highly inefficient to model all of these radionuclides in a total system performance assessment (TSPA). Thus, the purpose of this radionuclide screening analysis is to remove from further consideration (screen out) radionuclides that are unlikely to significantly contribute to radiation dose to the public from a nuclear waste repository at Yucca Mountain. The remaining nuclides (those screened in) are recommended for consideration in TSPA modeling for license application. This analysis also covers radionuclides that may not be screened in based on dose, but need to be included in TSPA modeling for other reasons. For example, U.S. Environmental Protection Agency (EPA) and U.S. Nuclear Regulatory Commission (NRC) regulations require consideration of the combined activity of 226Ra and 2 8Ra in groundwater (40 CFR 197.30 [DIRS 173176], 10 CFR 63.331 [DIRS 173176]). In addition, parent radionuclides (e.g. 245Cm and 241Pu) that contribute to the inventory of the screened-in progeny should be included in TSPA modeling.
The radionuclide screening analysis considers two different postclosure time periods: the p~riod up to 10,000 years and the period after 10,000 years up to 1 million years after emplacement. For the purposes of the screening analysis, four modeling cases are considered within the nominal and disruptive scenario classes: (1) nominal, which entails long-term degradation of disposal containers and waste forms, (2) human-intrusion, (3) intrusive igneous, and (4) eruptive igneous. Because the first three cases require groundwater transport, they are called groundwater scenarios below. The screening analysis considers the following waste form types: commercial spent nuclear fuel (CSNF) from light water reactors; U.S. Department of Energy (DOE) spent nuclear fuel (SNF), excluding navy spent fuel, which is not considered in this analysis; and high-level waste (HLW) in the form of borosilicate glass. Within these waste form types, average and outlying (high-bumup, high-initial enrichment, low-age, or otherwise exceptional) waste forms are considered.
