Nuclear waste repositories

Miscellaneous. Iridium dioxide, like RUO2, is useful as an electrode material for dimensionally stable anodes (DSA) (189). SoHd-state pH sensors employing Ir02 electrode material are considered promising for measuring pH of geochemical fluids in nuclear waste repository sites (190). Thin films (qv) ofIr02 ate stable electrochromic materials (191). 

A general conclusion from the review of the distribution of plutonium between different compartments of the ecosystem was that the enrichment of plutonium from water to food was fairly well compensated for by man s metabolic discrimination against plutonium. Therefore, under the conditions described above, it may be concluded that plutonium from a nuclear waste repository in deep granite bedrock is not likely to reach man in concentrations exceeding permissible levels. However, considering the uncertainties in the input equilibrium constants, the site-specific Kd-values and the very approximate transport equation, the effects of the decay products, etc. — as well as the crude assumptions in the above example — extensive research efforts are needed before the safety of a nuclear waste repository can be scientifically proven. 

Rydberg, J. "Groundwater Chemistry of a Nuclear Waste Repository in Granite Bedrock" UCRL-53155 Lawrence Livermore Lab. Livermore, 1981. 

Selection criterion for radioactive nuclear waste repository site and... 

I have just returned from an International Conference on Geologic Repositories hosted by Secretary Richardson. The joint declaration from this conference committed to continued international cooperation on waste issues and the viability of geologic repositories as one of the preferred options for disposal of nuclear waste. 

Without confronting the complexity of studying and evaluating the TSPAs, one can gain some perspective on the scale of the hazards by considering the protective standards that have been proposed for nuclear waste repositories, in particular for the proposed US. site at Yucca Mountain (Bodansky, 1996). There have been three major proposals in recent years ... 

There is some dispute among analysts as to whether world production of conventional oil will peak before the year 2020 or whether the peak will be delayed by another decade or two (Kerr, 1998), but in either case the current era of relatively cheap oil will end within several decades. A similar scenario is likely to follow for natural gas, although at a slower pace, and at a still slower pace, for coal. If our responsibilities to future generations include the relatively small problems that nuclear waste repositories may create in 10,000 years, they also include preparing for fossil fuel scarcity that will occur very much sooner. 

For nuclear waste disposal, in a site such as Yucca Mountain, if the maximally exposed individual receives the proposed annual limit of 0.15 mSv, present estimates (based on the linearity hypothesis) suggest a 0.00 1 % risk of an eventual fatal cancer. The maximum dose is reached only if the wastes are dissolved in a small volume of water, and therefore only a limited number of people would receive this dose. If this number were as high as 1000, the implied toll for Yucca Mountain neighbors would be one cancer fatality per century per repository site.19 This toll would not start for many centuries, when the waste canisters begin to fail, and it not unreasonable to expect that cancer prevention and treatment will be much improved by then. Ignoring this prospect, and assuming many repositories and some doses above the prescribed limit, it still appears that the expected toll would be well under a thousand deaths per century. 

Proliferation concerns have been and continue to be the basic cause ofthe official US. opposition to reprocessing and plutonium recycle, and have thus led to the official U.S. categorization of spent fuel as nuclear waste which should be permanently buried in geologic repositories. 

In the past, the extraction of Sr and Cs was investigated for some practical applications (heat and gamma ray sources) but the main interest today is for decreasing the thermal power and the potential hazard of nuclear waste in underground repositories. Results of extractions with some... 

Pearcy, E. C., Prokryl, J. D., Murphy, W. M. Leslie, B. W. 1994. Alteration of uraninite from the Nopal I deposit, Pena Blanca District, Chihuahua, Mexico, compared to degradation of SNF in the proposed U.S. high level nuclear waste repository at Yucca Mountain, Nevada. Applied Geochemistry, 9, 713—732. 

Grambow, B. 1991. What do we know about nuclear waste glass performance in the repository near field In Sellin, P., Apted, M. Gago, J. (eds) Proceedings Technical Workshop on Near-Field Performance Assessment for High-Level Wastes, Madrid, Spain. SKB Technical Report 91-59. Stockholm, Sweden, 25-49. 

Jollivet, P., Nicolas, M. Vernaz, E. 1998. Estimating the alteration kinetics of the French vitrified high-level waste package in a geologic repository. Nuclear Technology, 123, 67-81. 

The most usual route of waste classification is by radioactivity and thermal emission, mainly between high-level nuclear waste (HLNW) and low-level nuclear waste (LLNW). Depending on the countries there are other categories, such as intermediate-level nuclear waste (ILNW) and more recently another category has been introduced in order to avoid unnecessary saturation of LLNW repositories these are the so-called very low activity nuclear wastes (VLNW). 

There are inherent scale limitations in the time and space dimensions covered by laboratory studies. The applicability of the near field geochemical models derived from laboratory observations have to be applied to long-term, large-scale situations like the ones involved in the safety assessment of nuclear waste repositories. Hence, there is a need to test the models developed from laboratory investigations in field situations that are related to the ones to be encountered in repository systems. 

Colloid influence on the radionuclide migration from a nuclear waste repository... 

The reliable long-term safety assessment of a nuclear waste repository requires the quantification of all processes that may affect the isolation of the nuclear waste from the biosphere. The colloid-mediated radionuclide migration is discussed as a possible pathway for radionuclide release. As soon as groundwater has access to the nuclear waste, a complicated interactive network of physical and chemical reactions is initiated, and may lead to (1) radionuclide mobilization (2) radionuclide retardation by surface sorption and co-precipitation reactions and (3) radionuclide immobilization by mineralization reactions, that is, the inclusion of radionuclides into thermodynamically or kinetically stabilized solid host matrices. 

Fig. 1. Potential colloid generation processes in a nuclear waste repository near field (for explanation, see text) (HLW, high-level waste EBS, engineered barrier system).

Murphy, W. M. Palauan, R. T. 1994. Geochemical Investigations Related to the Yucca Mountain Environment and Potential Nuclear Waste Repository. Southwest Research Institute, NUREG/CR-6288, San Antonio, TX. 

Werme, L. B., Bjorner, I. K., et al. 1990. Chemical cotrosion of highly radioactive borosilicate nuclear waste glass under simulated repository conditions. Journal of Materials Research, 5, 1130-1146. 

The origin of Aeolian dust from Chinese desert to Japanese islands was studied with ESR of dust, mostly fine grains of quartz.132 Suspended particulate matter (SPM) collected by environmental protection agency was measured with ESR.133 Dust soot of automobiles was also measured to check the motor combustion rate. Adsorption of NO, Mn2+ and Gd3 on clay minerals, bentonite and se-piolite134 has been studied using paramagnetic ions as tracers for radioactive elements. And studies have been carried out on how divalent and trivalent cations diffuse and blocked by surrounding clay minerals, in the context of their leak from nuclear waste repository to the environment.135... 

Information on the interaction of radionuclides with ground-water in deeply-buried, high-level, long-term "waste repositories" is available at only a few locations. One is the OKLO natural reactor in Gabon which has for over 1. 7 billion years retained some of the radionuclides also present in nuclear wastes (5). Another is the Nevada test Site, where radionuclides were first deposited underground on September 19, 1967 during the 1.7 kt... 

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