Allen G. Croff

ORIGEN2: A Versatile Computer Code for Calculating the Nuclide Compositions and Characteristics of Nuclear Materials

AbstractORIGEN2 is a versatile point-depletion and radioactive-decay computer code for use in simulating nuclear fuel cycles and calculating the nuclide compositions and characteristics of materials contained therein. It represents a revision and update of the original ORIGEN computer code, which was developed at the Oak Ridge National Laboratory (ORNL) and distributed worldwide beginning in the early 1970s. Included in ORIGEN2 are provisions for incorporating data generated by more sophisticated reactor physics codes, a free-format input, and a highly flexible and controllable output; with these features, ORIGEN2 has the capability for simulating a wide variety of fuel cycle flow sheets.The decay, cross-section, fission product yield, and photon emission data bases employed by ORIGEN2 have been extensively updated, and the list of reactors that can be simulated includes pressurized water reactors, boiling water reactors, liquid-metal fast breeder reactors, and Canada deuterium uranium reactors. A number ...

Nuclear waste partitioning and transmutation

The long-term (>1000 years) hazard of radioactive waste emplaced in a geologic repository could be reduced by separating the most significant long-lived radionuclides and transmitting them to stable products by bombardment with neutrons in power reactors. A cost-risk-benefit analysis of this concept shows that, while it is technically feasible to partition and transmute the principal long-lived constituents, there are no cost-risk-benefit incentives that can be identified. The cost of partitioning and transmuting the actinide elements is estimated to be

Actinide partitioning-transmutation program final report. III. Transmutation studies

9.2 million/GW(electric) X yr (1.28 mill/kWh(electric)). The short-term radiological risk is increased by 0.003 health-effect/GW(electric) X yr, and the expected long-term benefit (i.e., incremental risk reduction from a repository) is 0.06 health-effect/GW(electric) X yr integrated over 1 million years. The latter is only about 0.001% of the health-effects expected from natural background radiation and is equivalent to

Natural thorium resources and recovery: Options and impacts

32,400 per person-rem saved. If nonradiological risks are included, the short-term risk actually exceeds the long-term benefits.

Comparative Assessment of Thorium Fuel Cycle Radiotoxicity

Transmutation of the long-lived nuclides contained in fuel cycle wastes has been suggested as a means of reducing the long-term toxicity of the wastes. A comprehensive program to evaluate the feasibility and incentives for recovering the actinides from wastes (partitioning) and transmuting them to short-lived or stable nuclides has been in progress for 3 years under the direction of Oak Ridge National Laboratory (ORNL). This report constitutes the final assessment of transmutation in support of this program. Included are (1) a summary of recent transmutation literature, (2) a generic evaluation of actinide transmutation in thermal, fast, and other transmutation devices, (3) a preliminary evaluation of /sup 99/Tc and /sup 129/I transmutation, and (4) a characterization of a pressurized-water-reactor fuel cycle with and without provisions for actinide recovery and transmutation for use in other parts of the ORNL program. The principal conclusion of the report is that actinide transmutation is feasible in both thermal and fast reactors, subject to demonstrating satisfactory fuel performance, with relatively little impact on the reactor. It would also appear that additional transmutation studies are unwarranted until a firm decision to proceed with actinide transmutation has been made by the responsible authorities.

Evaluating the Collective Radiation Dose to Workers from the U.S. Once-Through Nuclear Fuel Cycle

Abstract This paper reviews the front end of the thorium fuel cycle, including the extent and variety of thorium deposits, the potential sources of thorium production, and the physical and chemical technologies required to isolate and purify thorium. Thorium is frequently found within rare earth element–bearing minerals that exist in diverse types of mineral deposits, often in conjunction with other minerals mined for their commercial value. It may be possible to recover substantial quantities of thorium as a by-product from active titanium, uranium, tin, iron, and rare earth mines. Incremental physical and chemical processing is required to obtain a purified thorium product from thorium minerals, but documented experience with these processes is extensive, and incorporating thorium recovery should not be overly challenging. The anticipated environmental impacts of by-product thorium recovery are small relative to those of uranium recovery since existing mining infrastructure utilization avoids the opening and operation of new mines and thorium recovery removes radionuclides from the mining tailings.

ORNL experience and perspectives related to processing of thorium and 233U for nuclear fuel

Abstract This paper compares the radiotoxicity of thorium-based and uranium-based spent nuclear fuels and reprocessing wastes to inform evaluation of whether thorium-based fuels are significantly less radiotoxic than uranium-based fuels, as has been claimed at times in the technical literature. A consistent approach for calculating the radiotoxicity is established for four oxide fuel types in a pressurized water reactor: low-enrichment uranium, uranium with plutonium fissile material, thorium with 233U fissile material, and thorium with plutonium fissile material. The results of the calculations are presented to display the radiotoxicity trends and are analyzed to determine (a) what underlies the indicated radiotoxicity trends for decay times from 1 year to 20 million years and (b) factors that may have led to erroneous conclusions concerning the comparative radiotoxicity of thorium- and uranium-based fuels. The overall conclusion is that the ingestion radiotoxicity of thorium-based fuels containing 233U or plutonium fissile materials is similar to the radiotoxicity of uranium-based fuels containing 235U or plutonium fissile materials but that within this overall similarity there are significant differences in radiotoxicity in specific eras during decay.

Evaluation of the Acceptability of Potential Depleted Uranium Hexafluoride Conversion Products at the Envirocare Disposal Site

The Electric Power Research Institute (EPRI) is sponsoring the development of tools to support long-term strategic planning for research, development, and demonstration and for evaluation of advanced nuclear fuel cycles (NFCs). The EPRI-sponsored work under way at Vanderbilt University (VU) is developing a new, comparative risk assessment tool for NFCs. In the course of conducting a demonstration application of the assessment tool, it was observed that the relative contribution of NFC operations to radiological worker impacts estimated by the assessment tool was substantially different from widely used historical data and conventional wisdom. This paper analyzes these differences by first describing the NFC and the nature of radiological worker impacts. Then, the assessment tool developed by VU is described, along with assessment results; historical data relevant to radiological worker impacts are then summarized, and key differences between assessment results and previously reported impacts are identified. This comparison is followed by an analysis of the major factors causing the differences and an assessment of their validity. Finally, several implications of the differences are discussed.

Historical perspective, economic analysis, and regulatory analysis of the impacts of waste partitioning-transmutation on the disposal of radioactive wastes

Abstract Thorium-based nuclear fuel cycles have received renewed attention in both research and public circles since about the year 2000. Much of the attention has been focused on nuclear fission energy production that utilizes thorium as a fertile element for producing fissionable 233U for recycle in thermal reactors, fast reactors, or externally driven systems. Lesser attention has been paid to other fuel cycle operations that are necessary for implementation of a sustainable thorium-based fuel cycle such as reprocessing and fabrication of recycle fuels containing 233U. This paper first identifies recent literature that has resulted from the renewed interest in thorium-based fuel cycles. Next, differences in the radiation characteristics of nuclear materials associated with thorium-based and uranium-based fuels are discussed, and the generic implications of the differences to nuclear material processing are identified. Then, experience at Oak Ridge National Laboratory concerning processing of thorium and 233U is described in terms of the processing projects and campaigns undertaken and the facilities in which the processing was implemented. This experience then provides the basis for a generalized discussion of processing nuclear materials associated with thorium-based fuel cycles as compared to uranium-based fuel cycles. This comparative discussion focuses on key out-of-reactor fuel cycle operations: reprocessing of metal-clad oxide and graphite-matrix oxide used nuclear fuels (UNFs) including head-end processing (shearing and dissolution), solvent extraction, product conversion, fuel fabrication, and waste management. It is concluded that the recycle of thorium-based UNF constituents (233U and thorium) is more technically challenging than the recycle of uranium-based UNF constituents (plutonium and uranium) based on the radiation, chemical, and physical characteristics of nuclear materials in thorium-based fuel cycles as compared to uranium-based fuel cycles.

ORIGEN2: a revised and updated version of the Oak Ridge isotope generation and depletion code

The purpose of this report is to review and document the capability of potential products of depleted UF{sub 6} conversion to meet the current waste acceptance criteria and other regulatory requirements for disposal at the facility in Clive, Utah, owned by Envirocare of Utah, Inc. The investigation was conducted by identifying issues potentially related to disposal of depleted uranium (DU) products at Envirocare and conducting an initial analysis of them. Discussions were then held with representatives of Envirocare, the state of Utah (which is a NRC Agreement State and, thus, is the cognizant regulatory authority for Envirocare), and DOE Oak Ridge Operations. Provisional issue resolution was then established based on the analysis and discussions and documented in a draft report. The draft report was then reviewed by those providing information and revisions were made, which resulted in this document. Issues that were examined for resolution were (1) license receipt limits for U isotopes; (2) DU product classification as Class A waste; (3) use of non-DOE disposal sites for disposal of DOE material; (4) historical NRC views; (5) definition of chemical reactivity; (6) presence of mobile radionuclides; and (7) National Environmental Policy Act coverage of disposal. The conclusion of this analysis is that an amendment to the Envirocare license issued on October 5, 2000, has reduced the uncertainties regarding disposal of the DU product at Envirocare to the point that they are now comparable with uncertainties associated with the disposal of the DU product at the Nevada Test Site that were discussed in an earlier report.