Geologic repositories

To recovery and recycle or vitrification and disposal in deep geologic repository... 

Grenthe, I. Ferri, D. Proc. OECD/NEA Workshop on Near-field Phenomena In Geologic Repositories for Radioactive Waste OECD/NEA Paris 1981. 

Transport of plutonium from a geologic repository may be considered to involve three processes ... 

I emphasized and seconded what Rai called out - namely the great need for experimental work to determine solubility data for plutonium in its various oxidation states under typical expected geologic repository conditions (e.g., pH, Eh, temperature, etc.). 

The Clinton Administration believes that the overriding goal of the Federal Government s high-level radioactive waste management policy should be the establishment of a permanent geologic repository - essential not only for the disposal of commercial spent fuel, but also for... 

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. 

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. 

Fig. 1. Schematic illustration of the ideal closed nuclear fuel cycle (NRC 2003). In real practice, the reprocessing capacity does not match the generation rate of the spent nuclear fuel. Thus, the excess SNF must be placed in interim storage or disposed of in a geological repository. Under normal circumstances, the SNF will be in interim storage for just a few years. Also, note that excess material from nuclear weapons, e.g.. highly enriched 235U and 239Pu, can be blended down to lower concentrations and used as a reactor fuel.

Fig. 3. Schematic illustration of the interface of the nuclear fuel cycle with geochemical/hydrological cycles. The geological repository is the interface for these two cycles. The principal sources of radioactivity (over the long term) are indicated by the radionuclides listed at the centre of each cycle. Total background exposures to radiation are less than 300 mrem/y. The total radiation exposure that can be attributed to the nuclear fuel cycle is less than 3 mrem/y.

Over 5001 of HLW have been vitrified in France and Germany. In the USA, the HLW at the Nuclear Fuel Services plant in West Valley Plant, New York, have been vitrified (300 two-ton canisters) and vitrification is ongoing at the Defense Waste Processing Facility (DWPF) at Savannah River, South Carolina 1600 canisters by February 2004). A vitrification plant is under construction at Hanford, Washington. Vitrification of all of the HLW in the USA will generate approximately 20 000 canisters, which are destined for disposal at the geological repository at Yucca Mountain. 

Natural systems have been studied to provide data to support the ability of geological repositories to isolate radioactive wastes (e.g.,... 

C on Hanford N (ninth) reactor corroding U-metal fuel particles do not generate studtite. If the fuel in a geological repository is held at temperatures above 60 °C, it is unlikely that there will be significant H202 build-up, and thus there will be little or no studtite formation. 

Tahle 2. Potential U minerals of interest to spent fuel behavior in a geological repository... 

Burns, P. C., Deely, K. M., Skanthakumar, S. 2004. Neptunium incorporation into uranyl compounds that form as alteration products of spent nuclear fuel Implications for geologic repository performance. Radiochim. Acta, 92, 151-159. 

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 isolation and safety functions of HLNW deep geological repositories are based upon the multibarrier concept, where a number of containment and isolation barriers are put in place. A schematic view of the multibarrier HLNW concept is given in Fig. 1. The main barriers of the system are the waste matrix itself a metallic container (either corrosion resistant like Cu or Ti, or based upon stainless steel) a buffer material (normally bentonite) and finally the host rock itself (essentially granite or clay, although salt domes are also being considered). 

Fig. 1. Schematic mullibarrier HLNW concept of deep geological repositories (with permission of SKB).

Once this common thermodynamic framework is established for the solubility of U02 under nominally reducing conditions, we have to ascertain the most probable pathway for the oxidative alteration of U02 spent fuel in geological repository conditions. There is a large body of evidence on the processes involved in the oxidative alteration of natural uraninites and unirradiated U02. Long-term unsaturated tests performed by Wronckiewicz et al. (1992) on groundwater from Yucca Mountain (the so-called J-13 groundwater), indicated that the formation of schoepite, as described by process (20) and (21), occurs, but is a transient event and that the alteration proceeds towards the precipitation of... 

The final design of a geologic repository will employ multi-... 

Risk Assessment. The overall compilation and assessment of the factors that must be considered in designing and siting geologic repositories is pulled together in a general discipline of risk assessment. Risk assessment calculations develop both generic and site specific models and calculate the potential transport times as a result of various phenomena. Calculations are being... 

Mines studies indicate as much as 5.5 million tons of potash product may be presently economic out of the total 13.1 million tons. These resource values are small compared to the total United States reserves but must be considered as a potential target or inducement for future generations. Studies now underway may show that these resources can be developed without jeopardy to the repository. The issue of future penetrations by man is one that cannot, however, be ruled out. This is true for any geologic repository but the probability of such penetration may be somewhat greater for sedimentary and/or salt basins. This eventuality is considered in the repository safety analyses by determining the consequences of such penetrations if they should occur. 

This is not to say that all is doom and gloom. Although many of these tasks are formidable, the earth-science community believes them to be tractable and that a successful geologic repository for radioactive waste can be constructed. We only plead that our ignorance of earth s processes be considered in the development of a repository and that any repository constructed prior to the acquisition of the needed fundamental knowledge contain many independent natural and manmade barriers to radionuclide transport to compensate for our lack of knowledge. 

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