40 research outputs found
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Plutonium Production Using Natural Uranium From the Front-End of the Nuclear Fuel Cycle
This report explores the potential for producing weapons-grade plutonium using conventional industrial resources, oxides of natural uranium (namely UO{sub 3}), and either heavy water or reactor-grade graphite. Using established codes and data for nuclear analysis, it is demonstrated that physics-based reactor models capable of producing kilogram quantities of weapons-grade plutonium can be readily conceived. The basic assumptions and analysis approach are discussed together with the results of the analysis
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Recommendations for preparing the criticality safety evaluation of transportation packages
This report provides recommendations on preparing the criticality safety section of an application for approval of a transportation package containing fissile material. The analytical approach to the evaluation is emphasized rather than the performance standards that the package must meet. Where performance standards are addressed, this report incorporates the requirements of 10 CFR Part 71. 12 refs., 6 figs., 8 tabs
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Evaluation of shielding analysis methods for spent fuel casks
Accurate results from shielding analyses of spent fuel casks are increasingly important as the desire for optimized designs increases. ALARA concerns also contribute to the need for accurate dose evaluations for casks. Three areas require the attention of cask shielding analysts --- radiation source generation, utilization of cross-section data, and the radiation transport and dose evaluation. This paper reviews recent efforts carried out at Oak Ridge National Laboratory (ORNL) to evaluate the impact of various codes, data, and analysis assumptions on the calculation of radiation doses from spent fuel casks. 9 refs., 1 tab
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Adjoint-based sensitivity analysis for reactor accident codes
This paper summarizes a recently completed study that identified and investigated the difficulties and limitations of applying first-order adjoint sensitivity methods to reactor accident codes. The work extends earlier adjoint sensitivity formulations and applications to consider problem/model discontinuities in a general fashion, provide for response (R) formulations required by reactor safety applications, and provide a scheme for accurately handling extremely time-sensitive reactor accident responses. The scheme involves partitioning (dividing) the model into submodels (with spearate defining equations and initial conditions) at the location of discontinuity. Successful partitioning moves the problem dependence on the discontinuity location from the whole model system equations to the initial conditions of the second submodel
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Issues related to criticality safety analysis for burnup credit applications
Spent fuel transportation and storage cask designs based on a burnup credit approach must consider issues that are not relevant in casks designed under a fresh fuel loading assumption. Parametric analyses are required to characterize the importance of fuel assembly and fuel cycle parameters on spent fuel composition and reactivity. Numerical models are evaluated to determine the sensitivity of criticality safety calculations to modeling assumptions. This paper discusses the results of studies to determine the effect of two important modeling assumptions on the criticality analysis of pressurized-water reactor (PWR) spent fuel: (1) the effect of assumed burnup history (i.e., specific power during and time-dependent variations in operational power) during depletion calculations, and (2) the effect of axial burnup distributions on the neutron multiplication factor calculated for a three-dimensional (3-D) conceptual cask design
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Review of criticality safety and shielding analysis issues for transportation packages
The staff of the Nuclear Engineering Applications Section (NEAS) at Oak Ridge National Laboratory (ORNL) have been involved for over 25 years with the development and application of computational tools for use in analyzing the criticality safety and shielding features of transportation packages carrying radioactive material (RAM). The majority of the computational tools developed by ORNL/NEAS have been included within the SCALE modular code system (SCALE 1995). This code system has been used throughout the world for the evaluation of nuclear facility and package designs. With this development and application experience as a basis, this paper highlights a number of criticality safety and shielding analysis issues that confront the designer and reviewer of a new RAM package. Changes in the types and quantities of material that need to be shipped will keep these issues before the technical community and provide challenges to future package design and certification
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Potential for and consequences of criticality resulting from hydrogeochemically concentrated fissile uranium blended with soil in low-level waste disposal facilities
Evaluations were done to determine conditions that could permit nuclear criticality with fissile uranium in low-level-waste (LLW) facilities and to estimate potential radiation exposures to personnel if there were such an accident. Simultaneous hydrogeochemical and nuclear criticality studies were done (1) to identify some realistic scenarios for uranium migration and concentration increase at LLW disposal facilities, (2) to model groundwater transport and subsequent concentration via sorption or precipitation of uranium, (3) to evaluate the potential for nuclear criticality resulting from potential increases in uranium concentration over disposal limits, and (4) to estimate potential radiation exposures to personnel resulting from criticality consequences. The scope of the referenced work was restricted to uranium at an assumed 100 wt% {sup 235}U enrichment. Three outcomes of uranium concentration are possible: uranium concentration is increased to levels that do pose a criticality safety concern; uranium concentration is increased, but levels do not pose a criticality safety concern; or uranium concentration does not increase
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Bounding criticality safety analyses for shipments of unconfigured spent nuclear fuel
In November 1996, a request was made to the US Department of Energy for a waiver for three shipments of spent nuclear fuel (SNF) from Oak Ridge National Laboratory (ORNL) to the Savannah River Site (SRS) in the US NRC certified BMI-1 cask (CoC 5957). Although the post-irradiation fissile mass (based on chemical assays) in each shipment was less than 800 g, a criticality safety analysis was needed because the pre-irradiation mass exceeded 800 g, the fissile material limit in the CoC. The analyses were performed on SNF consisting of aluminum-clad U{sub 3}O{sub 8}, UAl{sub x}, and U{sub 3}Si{sub 2} plates, fragments and pieces that had been irradiated at ORNL during the Reduced Enrichment Research and Test Reactor Program of the 1980s. The highlights of the approach used to analyze this unique SNF and the benefits of the waiver are presented in this paper
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End effects in the criticality analysis of burnup credit casks
A study to evaluate the effect of axially dependent burnup on k{sub eff} has been performed as part of an effort to qualify procedures to be used in establishing burnup credit in shipping cask design and certification. This study was performed using a generic 31-element modular cast-iron cask (wall thickness 33.1 cm) with a 1-cm-thick borated stainless-steel basket for reactivity control. Fuel isotopics used here are those of the 17 {times} 17 Westinghouse assemblies from the North Anna Unit 1 reactor. Virginia Power (VP) provided detailed spatial isotopics for the fuel assemblies in-core at beginning-of-cycle 5 (BOC-5) as generated from their PDQ analyses. Twenty-two axial planes were defined in the original VP data. The isotopics used in this study were for a 3.41 initial wt % {sup 235}U and an average burnup of 31.5 GWd/MTU
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Review of the international conference on nuclear criticality-issues, discussions, and challenges
The Fifth International Conference on Nuclear Criticality Safety (ICNC`95) was held September 17-22, 1995, in Albuquerque, New Mexico, USA. Organization and support for the conference was provided by the Sandia National Laboratories (SNL), Los Alamos National Laboratory (LANL), the University of New Mexico, and the Organization for Economic Cooperation and Development (OECD). This conference traces its history back to 1981 when a group of select criticality safety specialists (mostly experimentalists) from France, Germany, Japan, the United Kingdom, and the United States participated in a small conference at LANL in the United States. The motivation for the conference had been provided by Dr. J. C. Manaranche of France who had asked D. Smith and G. E. Whitesides of the United States if it would be possible for the French experimentalists to be able to visit the experimental facilities at LANL. This first conference was followed by a similar conference held in Dijon, France, in 1993. Then in 1987 the conference was hosted by the Japanese and opened to much wider participation by criticality safety specialists involved in experiments, methods development and analysis, and operations. With the 1987 conference in Japan and the fourth conference (ICNC`91) held in the United Kingdom, the interest and international participation by the criticality safety community has grown rapidly. With this background, the occasion of ICNC`95 was one of much expectation