Performance Assessment for Geological Disposal of Graphite Waste Containing TRISO Particles

This paper presents a deterministic performance assessment for spent fuel from deep-burn modular hightemperature reactors (DBMHRs) in the proposed Yucca Mountain repository. Typical DBMHR designs utilize fuel elements manufactured from graphite. The fuel itself is made of TRISO particles containing the fissile material. The performance of the DBMHR spent fuel (DBSF) was evaluated in terms of the annual dose to the reasonably maximally exposed individual (RMEI) under various hydrogeological conditions. Part of this evaluation was an analysis of the graphite waste matrix and of the TRISO particles under repository conditions, the result of which indicates that the lifetime of the graphite matrix greatly exceeds that of the TRISO particles and that it is the graphite, not the TRISO particles, that serves to sequester the radionuclides within the fuel matrix. Under all 14 cases considered, DBSF is seen to comply with the annual dose standards set in Part 197 of Title 40 of the Code of Federal Regulations, for exposure via groundwater contamination under current climatic conditions. Parametric studies for the effect of waste matrix lifetime on annual dose received by the RMEI indicate that repository performance is sensitively linked to waste matrix durability because most radionuclides including actinides are likely to be released congruently with the graphite matrix

Management of Heavy Isotope in the DOE Complex

Currently each Department Of Energy (DOE) Program office manages its own nuclear materials through activities such as production, processing, storage, transportation, and disposition. However, recognizing the need to strengthen its strategic approach to the integrated life-cycle management of nuclear materials, DOE established the Nuclear Materials Management Stewardship Initiative (NMMSI) in January 2000. The NMMSI's first visible product was the Integrated Nuclear Material Management Plan in which it was generally recommended that DOE take a cross-cutting look at managing its nuclear materials, and specifically recommended that four Nuclear Material Management Groups (NMMGs) be formed. These groups were established to facilitate management of nuclear materials for which DOE has or may have responsibility, including many presently not in DOE's direct control. One of these NMMGs, the Heavy Isotope Management Group (HIMG) was established at Oak Ridge National Laboratory in Dec ember 2000, to facilitate management of (a) actinide and their decay products (except sealed sources) and (b) isotopically enriched stable and radioactive isotopes except uranium and lithium, but excluding thorium, uranium, spent fuel, and weapons or reactor grade plutonium which are addressed by other NMMGs. Despite its short duration and relatively limited funding, the HIMG has facilitated the disposition of heavy isotopes from Lawrence Berkeley National Laboratory (LBNL), Rocky Flats Environmental Technology Site (RFETS), Pacific Northwest National Laboratory (PNNL), Oak Ridge National Laboratory (ORNL), Lawrence Livermore National Laboratory (LLNL), and Idaho National Engineering and Environmental Laboratory (INEEL). The primary disposition options have been to facilitate reuse of valuable heavy isotopes by matching custodians of unwanted materials with other users that seek such materials for new applications. This approach has the dual advantages of avoiding custodian disposal costs plus cost to the user of obtaining newly produced material. The HIMG has also prepared issue papers on neptunium and americium/curium that identify the resources, potential uses, and disposal pathways for the materials across the DOE Complex. In the future the HIMG expects to comprehensively identify the status of the U.S. heavy isotope inventory, prepare additional issue papers and plans charting the future of this inventory, and to facilitate execution of the plan

Updated decay and photon libraries for the ORIGEN code

Previously existing decay and photon libraries for the ORIGEN computer code were updated by utilizing a variety of sources. Information obtained form the Evaluated Nuclear Structure Data File (ENSDF) at ORNL was used to revise the half-lives, branching ratios, and recoverable heat values for 427 isotopes. Fifty-seven delayed-neutron precursors were included, on the basis of information in ENDF/B-IV. The natural abundances and the Radionuclide Concentration Guide values were updated for all isotopes. The decay heat values predicted by use of the new decay library were found to compare favorably with those given in the proposed 1978 ANS Standard 5.1 (draft ANSI/ANS-5.1, ''Proposed American National Standard Decay Heat Power in Light Water Reactors''). A new photon library was also generated for 427 isotopes, based principally on data presented in ENSDF. The photon library includes decay gamma and x rays, conversion photons, (..cap alpha..,n) gamma rays, prompt and fission product gamma rays from spontaneous fission, and bremsstrahlung. Both of the revised libraries are listed. 1 figure, 9 tables

Evaluation of Five Sedimentary Rocks Other Than Salt for Geologic Repository Siting Purposes

The US Department of Energy (DOE), in order to increase the diversity of rock types under consideration by the geologic disposal program, initiated the Sedimary ROck Program (SERP), whose immediate objectiv eis to evaluate five types of secimdnary rock - sandstone, chalk, carbonate rocks (limestone and dolostone), anhydrock, and shale - to determine the potential for siting a geologic repository. The evaluation of these five rock types, together with the ongoing salt studies, effectively results in the consideration of all types of relatively impermeable sedimentary rock for repository purposes. The results of this evaluation are expressed in terms of a ranking of the five rock types with respect to their potential to serve as a geologic repository host rock. This comparative evaluation was conducted on a non-site-specific basis, by use of generic information together with rock evaluation criteria (RECs) derived from the DOE siting guidelines for geologic repositories (CFR 1984). An information base relevant to rock evaluation using these RECs was developed in hydrology, geochemistry, rock characteristics (rock occurrences, thermal response, rock mechanics), natural resources, and rock dissolution. Evaluation against postclosure and preclosure RECs yielded a ranking of the five subject rocks with respect to their potential as repository host rocks. Shale was determined to be the most preferred of the five rock types, with sandstone a distant second, the carbonate rocks and anhydrock a more distant third, and chalk a relatively close fourth

Assessment of Preferred Depleted Uranium Disposal Forms

The Department of Energy (DOE) is in the process of converting about 700,000 metric tons (MT) of depleted uranium hexafluoride (DUF6) containing 475,000 MT of depleted uranium (DU) to a stable form more suitable for long-term storage or disposal. Potential conversion forms include the tetrafluoride (DUF4), oxide (DUO2 or DU3O8), or metal. If worthwhile beneficial uses cannot be found for the DU product form, it will be sent to an appropriate site for disposal. The DU products are considered to be low-level waste (LLW) under both DOE orders and Nuclear Regulatory Commission (NRC) regulations. The objective of this study was to assess the acceptability of the potential DU conversion products at potential LLW disposal sites to provide a basis for DOE decisions on the preferred DU product form and a path forward that will ensure reliable and efficient disposal

Experiences of sexual stigma by MSM in rural Oklahoma

Concurrent socioeconomic factors, geography, and cultural context are coalescing for sexual minorities living in rural communities resulting in individuals at risk for HIV infection. By the end of the session, participants will be able to assess sexual stigma in rural communities, its manifestations at the individual or societal level, and its correlates with HIV risk