TRISO-Coated Fuel Processing to Support High Temperature Gas-Cooled Reactors (2002)

The initial objective of the work described herein was to identify potential methods and technologies needed to disassemble and dissolve graphite-encapsulated, ceramic-coated gas-cooled-reactor spent fuels so that the oxide fuel components can be separated by means of chemical processing. The purpose of this processing is to recover (1) unburned fuel for recycle, (2) long-lived actinides and fission products for transmutation, and (3) other fission products for disposal in acceptable waste forms. Follow-on objectives were to identify and select the most promising candidate flow sheets for experimental evaluation and demonstration and to address the needs to reduce technical risks of the selected technologies. High-temperature gas-cooled reactors (HTGRs) may be deployed in the next -20 years to (1) enable the use of highly efficient gas turbines for producing electricity and (2) provide high-temperature process heat for use in chemical processes, such as the production of hydrogen for use as clean-burning transportation fuel. Also, HTGR fuels are capable of significantly higher burn-up than light-water-reactor (LWR) fuels or fast-reactor (FR) fuels; thus, the HTGR fuels can be used efficiently for transmutation of fissile materials and long-lived actinides and fission products, thereby reducing the inventory of such hazardous and proliferation-prone materials. The ''deep-burn'' concept, described in this report, is an example of this capability. Processing of spent graphite-encapsulated, ceramic-coated fuels presents challenges different from those of processing spent LWR fuels. LWR fuels are processed commercially in Europe and Japan; however, similar infrastructure is not available for processing of the HTGR fuels. Laboratory studies on the processing of HTGR fuels were performed in the United States in the 1960s and 1970s, but no engineering-scale processes were demonstrated. Currently, new regulations concerning emissions will impact the technologies used in processing the fuel. Potential processing methods will be identified both by a review of the literature regarding the processing of similar fuels and by a reliance on the experience and innovation of the authors. The objective is not to generate an exhaustive list of options but rather to identify a number of potentially practical processing options. These options necessarily take into consideration the chemical characteristics of the entire fuel element and its component parts. Once the practical options are identified, a qualitative assessment of the technical merit and maturity, relative costs, and relative quantity of waste generation will be used to rank the various options. Through this form of analysis, a base-case flow sheet will be identified for further study and development. A fallback flow sheet will also be selected to reduce the overall technical risk of the development plan. To support the base-case flow sheet, a technical development plan will be used to identify the key issues for the highest-rated option(s). In this effort the technical uncertainties will be more fully articulated, and research and development activities will be recommended to reduce the technical risks.