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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management Background HIGH-LEVEL RADIOACTIVE WASTE IN GENERAL The challenge of HLRW disposal in the United States is dominated by spent fuel from nuclear power plants. At present, about 17 percent (20 percent in the United States) of the world's electricity is generated by some 413 nuclear power plants (111 in the United States). The generation rate is as high as 75 percent in France and 50 percent in Sweden. Each 1,000-megawatt electrical nuclear power plant produces about 30 metric tons of spent fuel each year. In 1990 spent fuel temporarily stored at ground level in pools or dry casks at the 111 nuclear power plant sites in the United States constituted about 21,500 metric tons of heavy metal (MTHM). By 2030, the last year of DOE's Mission Plan, spent fuel is expected to total 86,000 MTHM, provided that no reactor licenses are renewed and no new plants are operating. In addition to spent fuel, a HLRW repository would be licensed to contain some 10,000 metric tons of high-level solid and liquid defense wastes that have been stored pending permanent disposal since the inception of the U.S. nuclear program in the 1940s. (These wastes are present at such sites as Hanford, Idaho National Engineering Laboratory, and Savannah River.) At this time DOE is also looking carefully at the possibility of deep geologic disposal for Greater-Than-Class-C waste from processing of nuclear materials from the U.S. nuclear weapons program. Most countries, including the United States, have concluded that the best means of long-term disposal of HLRW is deep geological emplacement, always including some form of engineered containment or encapsulation and generally with some limited retrieval capability, at least initially. The Nuclear Waste Policy Act of 1982 divides the responsibilities for regulation of HLRW disposal among three federal agencies: the EPA, to pro-
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management mulgate generally applicable standards to protect the environment from nuclide releases off site; the USNRC, to set technical requirements for specific implementation of the Standard and to license the facility; and DOE, to issue general guidelines for recommending and selecting sites, characterizing sites, and ultimately, constructing and operating a geologic repository. In the 1987 amendments to the Nuclear Waste Policy Act, Congress designated the Yucca Mountain, Nevada, site as the single candidate location for a HLRW repository and directed DOE to conduct detailed site characterization. The Yucca Mountain site, by law, may store no more than 70,000 metric tons until a second repository is licensed. The Waste Isolation Pilot Plant (WIPP) in Carlsbad, New Mexico, was authorized as a research and development facility concerned with TRU waste disposal in December 1979 by DOE's National Security and Military Applications of Nuclear Energy Authorization Act of 1980 (P.L. 96–164). THE EPA ENVIRONMENTAL STANDARD—40 CFR PART 191 Promulgated by the EPA in September 1985, 40 CFR Part 191 establishes a set of generally applicable standards for the disposal of spent nuclear fuel, high-level and transuranic radioactive wastes. The Standard does not, by federal law, apply to WIPP, but is being implemented by DOE in accordance with an agreement with the State of New Mexico. Subpart A of 40 CFR Part 191, "Environmental Standards for Management and Storage," covers temporary storage and long-term monitored retrievable storage (MRS). Subpart A establishes dose limits to the "public in the general environment" for exposure during waste management and storage. Subpart A was not included in the court remand of the standard, and the provisions of Subpart A were not discussed at the symposium. As originally promulgated, Subpart B of 40 CFR Part 191, "Environmental Standards for Disposal," applies to disposal-related releases to the accessible environment, doses to the public, and contamination of groundwater. The release limits set forth in Subpart B were established based on generic analyses of the possible performance of hypothetical repositories. EPA's analyses suggest that such a level of performance would ensure that the risk to future generations does not exceed that of a corresponding amount of unmined uranium ore. The rationale of limiting health effects to that of unmined ore is contained in the preamble to the Standard, but there is no goal stated in the Standard itself. The containment requirements in the Standard set total quantitative limits on release of radionuclides into the "accessible" environment during the first 10,000 years following disposal. The EPA derived these limits from a technology-based release standard by determining the amounts of radionuclides, singly or in combination, that would result in 1,000 or fewer cancer
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management deaths during the 10,000-year period for each 100,000 MTHM in spent reactor fuel. Generic assumptions were made about the behavior of various types of repository sites, the pathways by which radionuclides might move through the environment (and be ingested or inhaled by people), and the habits of human populations over the next 10,000 years. Since many radionuclides might be released over time, a weighting procedure is provided to ensure that the calculated total of all effects under the release limits is below the objective of 1,000 cancer deaths in 10,000 years. Some symposium participants criticized the lack of a mechanism within the Standard for basing the distance to the accessible environment on the geologic or hydrologic variability of a specific site or geological medium. The requirements of the Standard also provide two probabilistic distribution requirements: that the cumulative releases of radionuclides should have, first, less than a 1 in 10 chance of exceeding the specified limits and, second, less than a 1 in 1,000 chance of exceeding 10 times those limits. These probability distributions are to be used in performance assessments, to include all elements of uncertainty in the parameters. The assessments examine all credible possibilities for movement of radionuclides from the repository into the accessible environment. In conducting such analyses, DOE will rely heavily on computer modeling of the repository, taking into account the surrounding geological environment and all possible environmental transport pathways. The products of the various performance assessments will then be presented in a complementary cumulative distribution function (CCDF) format, overlaid on the probabilistic standards referred to above. This will indicate whether that particular set of performance assessments exceeds the Standard. With the understanding that absolute assurance is not feasible, the Standard requires only a "reasonable expectation" that compliance would be achieved. The groundwater and individual protection requirements assume an undisturbed site, and are applicable for the first 1,000 years following disposal. One requirement specifies the maximum allowable annual radiation doses to individual members of the public. Other requirements pertinent to groundwater set dose limits for 1,000 years for any nearby irreplaceable sources of drinking water that supply communities (i.e., thousands of persons). THE COURT REMAND In July 1987 the U.S. Court of Appeals for the First Circuit vacated Subpart B of 40 CFR Part 191, remanding it to the EPA for further consideration and substantiation. Three reasons were cited by the court for the remand. The first was that EPA had not given adequate public notice in the proposed rule of the groundwater provisions adopted in the final rule. Sec-
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management ond, the court found the groundwater protection standard invalid because it was not reconcilable with the EPA standards that protect underground sources of drinking water according to the mandates of the Safe Drinking Water Act; the court directed the EPA to reconcile the inconsistency or to explain it. Third, the court found the 1,000-year duration of the individual and groundwater protection standard to be arbitrary and capricious, in part because the EPA had relied solely on general population, not individual, risks in setting it. EPA's reconsideration of these portions of the Standard could result in a revision of the Standard as a whole or merely the insertion of a better justification for the 1985 requirements. THE USNRC REGULATION—10 CFR PART 60 Promulgated by the USNRC in June 1983, 10 CFR Part 60, "Disposal of High-Level Radioactive Wastes in Geologic Repositories" (the Regulation), established procedures and technical criteria for licensing geologic repositories. Under an USNRC license, DOE is responsible for disposing of spent fuel and HLRW, and for implementing the Standard at the future HLRW repository. The most controversial provisions of the Regulation are those that establish subsystem performance standards. The USNRC specifies quantitative criteria for each part of the subsystem: the minimum number of years (300 to 1,000) over which the waste package must provide substantial containment, the maximum release rate (1/100,000 or 0.001 percent of the yearly inventory of each radionuclide after the first 1,000 years of radioactive decay), and the minimum groundwater travel time (1,000 years to the accessible environment). The controversy over these criteria involves the stringency of the limits, the cost-effectiveness of their implementation, and the amount of reliance placed on a site's geology.
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