{'fraction_non_alphanumeric': 0.02621502209131075, 'fraction_numerical': 0.02857142857142857, 'mean_word_length': 4.968365553602812, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
SIGNIFICANCE OF 14C AND 228Ra IN TERMS OF THE PROPOSED YUCCA MOUNTAIN HIGH-LEVEL RADIOACTIVE WASTE REPOSITORY

14C and 228Ra are two of the radionuclides that have either been identified as being potentially significant in terms of releases from the proposed Yucca Mountain high-level radioactive waste repository, or are specifically cited for consideration and evaluation in the regulations promulgated by the U.S. Nuclear Regulatory Commission. The purpose of this study was to estimate the concentrations and associated doses for these two radionuclides, if released under conditions of a scenario assumed to apply to a repository containing some of the features of the one proposed at Yucca Mountain, NV, and to compare these estimates to the regulatory limits for that facility. For 14C, the postulated condition was that an annual fractional release of 10−5 of its total remaining inventory occurs beginning at 10,000 y after repository closure. For 228Ra, the same fractional release rate was assumed, but in this case it was presumed to occur when the 228Ra inventory was projected to reach a maximum at more than 108 y after repository closure. The estimated concentrations and doses were, in turn, compared to the concentration limit, specified in the Ground Water Protection Standards (GWPSs) in the case of 228Ra, or derived, in the case of 14C, on the basis of the regulatory dose rate limit. Due to the small inventory of 14C in the waste, and its short half-life relative to the performance period evaluated, its estimated concentration in the ground water would be slightly more than 4% of the derived GWPS. Due to the relatively small initial inventory of 232Th, the precursor of 228Ra, and the correspondingly small quantities of higher atomic number actinides that could, through decay, produce additional quantities of 232Th, its estimated concentration in the ground water would be less than 3% of the GWPS, leaving the remaining portion of the limit for potential contributions from 226Ra. At the same time, however, it must be recognized that, in this case, the regulations require that any contributions of naturally occurring 226Ra and 228Ra already present in the ground water must be included in the determination of compliance. If this is done, the total concentration of 228Ra, combined with the naturally occurring concentration of 226Ra, would be about 10.5% of the limit. In a similar manner, the committed doses due to the annual consumption of each of these two radionuclides in ground water and food, produced in the local biosphere, were evaluated in terms of the Individual Protection Standard (IPS). Based on these analyses, the estimated effective dose for 14C, using the coefficients in Federal Guidance Report (FGR) No. 13, was 4.15 &mgr;Sv y−1, less than 3% of the IPS. For 228Ra, the comparable estimate at the time of maximum inventory, excluding in this case the contributions from naturally occurring 226Ra and 228Ra, was 7.39 &mgr;Sv y−1, representing about 5% of the IPS. Based on the value assumed for the fractional release rate (10−5 y−1), it was concluded that neither 14C nor 228Ra will be significant in terms of either the applicable GWPS or the IPS. While it was recognized that, due to the time spans involved, these analyses were primarily an academic exercise, it is believed that the perspectives and accompanying insights are useful.