Nuclear repositories

While the conditions at Oklo differ in a number of aspects from those expected in nuclear repository sites, they frequently were much less favorable to retention of the radionuclides. The lack of migration of the actinides and the much slower release of Tc agree with the predictions of laboratory studies and indicate their value in validating the safety of nuclear repositories. 

For future advanced nuclear systems, minor actinides are considered more as a resource to be recycled and transmuted than to be disposed of directly into a nuclear repository. A key feature of advanced fuel cycles technologies would be to separate M A and ultimately americium from curium. Several countries are investigating the separation of MA from a PUREX/COEX based process raffinate or a modified PUREX process raffinate using new extractant molecules with two potential options for actinide separations ... 

Cost estimates for direcf disposal at a nuclear repository rose sharply and capacity was limited (even if doubled). 

Environmental scientists such as those involved in performance assessment (e.g., for nuclear repositories) would be pleased to be able to predict the interactions of solutes (e.g., radionuclides) with backfill and geologic materials. However, in this area, which in many countries receives much public attention, even the aqueous solution equilibria for the pertaining conditions of a favored repository concept cannot be accurately described (e.g., metal ions in brine solutions, which require Pitzer formalism, or in highly alkaline backfill pore waters, which have traditionally not received much attention in aqueous solution studies because of the limitations of glass electrodes and solid phase formation). Databases for surface complexation applications are also required for many other purposes, but the major drawback of such potential databases is that no agreement exists on the actual surface complexation model to be used. This may ultimately lead to particular difficult situations whenever one of the following occur ... 

Spent nuclear fuel has fission products, uranium, and transuranic elements. Plans call for permanent disposal in underground repositories. Geological studies are in progress at the Yucca Mountain site in Nevada. Until a repository is completed, spent fuel must be stored in water pools or in dry storage casks at nuclear plant sites. 

Transuranic Waste. Transuranic wastes (TRU) contain significant amounts (>3,700 Bq/g (100 nCi/g)) of plutonium. These wastes have accumulated from nuclear weapons production at sites such as Rocky Flats, Colorado. Experimental test of TRU disposal is planned for the Waste Isolation Pilot Plant (WIPP) site near Carlsbad, New Mexico. The geologic medium is rock salt, which has the abiUty to flow under pressure around waste containers, thus sealing them from water. Studies center on the stabiUty of stmctures and effects of small amounts of water within the repository. 

Other fuel besides that from U.S. commercial reactors may be disposed of in the ultimate repository. PossibiUties are spent fuel from defense reactors and fuel from research reactors outside of the United States. To reduce the proliferation of nuclear weapons, the United States has urged that research reactors reduce fuel enrichment in uranium-235 from around 90 to 20%. The latter fuel could not be used in a weapon. The United States has agreed to accept spent fuel from these reactors. 

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). 

Nucleus The nucleus is separated from the cytosol by a double membrane, the nuclear envelope. The DNA is complexed with basic proteins (histones) to form chromatin fibers, the material from which chromosomes are made. A distinct RNA-rich region, the nucleolus, is the site of ribosome assembly. The nucleus is the repository of genetic information encoded in DNA and organized into chromosomes. During mitosis, the chromosomes are replicated and transmitted to the daughter cells. The genetic information of DNA is transcribed into RNA in the nucleus and passes into the cytosol where it is translated into protein by ribosomes. 

Operate the Department of the Army repository of drawing information pertaining to nuclear components received from the Atomic Energy Commission and its contractors... 

Except for large scale accidental releases (e.g. nuclear explosions or catastrophic accidents at nuclear plants), water will be the main transport medium of plutonium to man. Therefore the size and location of plutonium sources, its pathways to man and its behaviour in natural waters are essential knowledge required for the evaluation of its ecological impact. That information, combined with radiological health standards, allows an assessment of the overall risk to the public from plutonium e.g. from a waste repository for spent unreprocessed reactor fuel elements in deep granite bedrock (8, 9). ... 

In 1976 the Swedish government stipulated that no new nuclear reactors should be charged until it had been shown how the radioactive waste products could be taken care of in an "absolutely safe manner" (8). Consequently, the nuclear power industry (through their joint Nuclear Fuel Supply Co, SKBF) embarked on a program referred to as the Nuclear Fuel Safety (KBS) Project (8). In one of the schemes (9) a repository for spent nuclear fuel elements in envisaged at a depth of 500 m in granitic bedrock. The repository will ultimately contain 6000 tonnes of uranium and 45 tonnes of plutonium. The spent fuel elements will be stored in copper cylinders (0.8 m in diameter and 4.7 m in length) with a wall thickness of 200 mm the void will be filled with lead. 

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... 

A permanent geologic repository is also important to our non-proliferation goals an alternative to reprocessing. . . storage for foreign research reactor fuel. . . and an option for the disposition of surplus plutonium from nuclear weapon stockpiles. 

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. 

In the last twenty odd years, almost all nuclear endeavors in the U.S. have run into bureaucratic and litigious delays, making their schedules and costs unpredictable. In addition to reactor construction, there are the bureaucratic delays in the waste repository programs. Another example is the attempt to build a new uranium enrichment plant in the state of Louisiana, a plant which uses advanced technology demonstrated in several countries in Europe. Licensing started over seven years ago and is still held up by issues without relevance to technology or safety. It is approaching the point where the delays, and costs may lead to the abandonment of a potential asset... 

The spent firel issue is central to long-term fuel cycle policy, not simply because large volumes are threatening to clog the arteries of the nuclear power industry but because spent fuel is the repository of most of the worid s plutonium, some 1000 tons at present, and is already dispersed among the 30-odd countries in which nuclear power plants are located. The indefinite accumulation of these dispersed inventories has proliferation implications that are at least comparable in their gravity to the surplus weapons plutonium inventories in Russia... 

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. 

---