Radioactive waste repository, hazard

In analyzing the safety of a waste repository, it is crucial to know the time period under consideration. A number of geologic processes and events are relevant for the safety analysis only if the time frame exceeds a certain range. As it is obvious that the hazard of a waste repository due to the decrease of its radioactive inventory will eventually approach a level that is no longer significant, it will be feasible to estimate a time frame for the safety analysis. This time frame will be called the significant period of the waste repository hazard. The estimation of... 

The primary issue is to prevent groundwater from becoming radioactively contaminated. Thus, the property of concern of the long-lived radioactive species is their solubility in water. The long-lived actinides such as plutonium are metallic and insoluble even if water were to penetrate into the repository. Certain fission-product isotopes such as iodine-129 and technicium-99 are soluble, however, and therefore represent the principal although very low level hazard. Studies of Yucca Mountain, Nevada, tentatively chosen as the site for the spent fuel and high level waste repository, are underway (44). 

Another desirable attribute of a waste classification system that is a corollary of the system being risk-based is that it treat wastes that pose similar health risks consistently. A chemically hazardous waste estimated to pose a certain risk should be in the same waste class as a radioactive waste that poses an equivalent risk, and similarly for mixed waste. Consistency also implies that wastes posing similar risks could be disposed of using essentially the same technology (municipal/industrial landfill, licensed near-surface facility for hazardous waste, or geologic repository). 

At the present time, a geologic repository is the intended disposal system for most radioactive waste that is not acceptable for nearsurface disposal. Alternatives to near-surface disposal facilities have not been considered for hazardous chemical waste that contains unusually high concentrations of persistent substances (e.g., heavy metals). 

As shown previously, radioactive hazards associated with SF and HLW decrease exponentially over time (see Figure 2). After 10" -10 yr, the risk to the public of a nuclear waste disposal vault approaches that of a high-grade uranium ore deposit and is less than the time invariant toxicity risk of ore deposits of mercury and lead (Langmuir, 1997a). The new ERA standard for nuclear waste repositories seeks to limit exposures from all exposure pathways for the reasonably maximally exposed individual living 18 km from a nuclear waste repository to 0.15mSvyr (15 mrem yr ) (US EPA, 2001). For comparison. 

The most hazardous radioactive wastes are the longer-lived actinides, especially 239Pu and 241 Am. It is also predicted that by the year 2000 there will be 900 metric tons of actinide wastes stored in federal repositories. This would be about 12,000 Megacuries of alpha activity, the exact amount depending on the isotopic composition and age. 

The main objection against nuclear power is the risk of spread of "radioactivity" (radioactive elements) to the environment where it may cause health effects in humans. We have already discussed such effects (Ch. 18). Here, we are concerned with the chemical aspects of the sources of releases and of the migration of the radionuclides in the environment. Their chemical properties, together with hydrology, determine how fast they will move from their point of entry into the groundwater to water resources used by man this is schematically illustrated in Figure 22.1. In particular we discuss actinide behavior as these elements have the most hazardous radionuclides which may be released in the different steps of the nuclear fuel cycle, and, especially, from nuclear waste repositories. 

Moreover, the WIPP repository would be a global first-of-a-kind facility for safe disposal of long-lived and high-energy emitting radioactive waste such as TRUW and HLW. Conceivably, its continued safe operation in compliance with several hazardous waste regulations and one of the strictest environmental radiation protection standards in the world should enhance public confidence in the safety of deep geological disposal of TRUW and HLW both in the USA and abroad. 

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