Publications

This presentation titled "Updates on UO₂-BeO Experiment (IER 523)" covers experiment status, experiment motivation, CED-1 summary, current efforts (CED-2), and includes a concluding summary.

The purpose of this proposal is to design a new integral critical experiment to investigate the effects of beryllium oxide and high assay low-enriched uranium fuels. this proposal considers using several existing resources at Sandia: (1) the Critical Experiments (SCX) facility and water tank, (2) spare UO₂-BeO fuel for the Annular Core Research Reactor (ACRR), and 7uPCX fuel rods from previous benchmark experiments.

This lecture is on the design of a Uranium Dioxide-Beryllium Oxide UO₂-BeO Critical Experiment at Sandia. This presentation provides background info on the Annular Core Research Reactor (ACRR). Additionally, this presentation shows experimental and alternative designs and concludes with a sensitivity analysis.

Members of the Nuclear Criticality Safety (NCS) Program at Sandia National Laboratories (SNL) have updated the suite of benchmark problems developed to validate MCNP6 Version 2.0 for use in NCS applications. The updated NCS benchmark suite adds approximately 600 new benchmarks and includes peer review of all input files by two different NCS engineers (or one NCS engineer and one candidate NCS engineer). As with the originally released benchmark suite, the updated suite covers a broad range of fissile material types, material forms, moderators, reflectors, and neutron energy spectra. The benchmark suite provides a basis to establish a bias and bias uncertainty for use in NCS analyses at SNL.

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The intent of this paper is to illuminate the reasons behind the culture of standards involvement by the criticality safety community in the NCSD, and specifically highlight those NCSD activities that build/support this culture. Many NCSD members are currently active in ANSI/ANS-8 and other standards and have been for the last half century. This paper was inspired by a request from ANS’s Professional Divisions Committee concerning how the professional divisions could “increase support to Standards development as Subject Matter Experts”. The healthy level of involvement (i.e., culture) by the NCSD membership in standards was noted. A history of the ANSI/ANS-8 series standards is provided, with roots going back to 1955. The need became apparent during a cluster of nuclear criticality accidents that occurred between 1958-1962. The first NCS related standard was the American Standard N6.1-1964, the parent of ANSI/ANS-8.1, which was prepared in 1958 and adopted in 1964. Thus, the involvement in standards by the NCS community goes back more than 50 years. The NCSD continues to help foster a culture of standards use and development. However, the support provided by the NCSD is frequently not recognized, and standards activities are often viewed as separate from the NCSD. This paper highlights the interaction between the NCSD and the ANSI/ANS-8 standards activities as well as the benefit of this support.

The intent of this paper is to illuminate the reasons behind the culture of standards involvement by the criticality safety community in the NCSD, and specifically highlight those NCSD activities that build/support this culture. Many NCSD members are currently active in ANSI/ANS-8 and other standards and have been for the last half century. This paper was inspired by a request from ANS’s Professional Divisions Committee concerning how the professional divisions could “increase support to Standards development as Subject Matter Experts”. The healthy level of involvement (i.e., culture) by the NCSD membership in standards was noted. A history of the ANSI/ANS-8 series standards is provided, with roots going back to 1955. The need became apparent during a cluster of nuclear criticality accidents that occurred between 1958-1962. The first NCS related standard was the American Standard N6.1-1964, the parent of ANSI/ANS-8.1, which was prepared in 1958 and adopted in 1964. Thus, the involvement in standards by the NCS community goes back more than 50 years. The NCSD continues to help foster a culture of standards use and development. However, the support provided by the NCSD is frequently not recognized, and standards activities are often viewed as separate from the NCSD. This paper highlights the interaction between the NCSD and the ANSI/ANS-8 standards activities as well as the benefit of this support.

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There has only been one naturally occurring reactor region (Oklo) identified historically. There has to have been other factors that prevented uncontrolled nuclear criticality events. There are higher concentration uranium depositions in the earth's crust than the Oklo region, that did not go critical based on uranium enrichment. There are many papers on the Oklo phenomena which do not address why the uranium did not reach criticality prior to the historical point of 2 billion years ago, nor do they specifically address the lack of radiogenic lead in any of the uranium deposits. Consideration of the lack of lead as a potential indicator of the age of the earth as being a possible factor. Reports which address the leaching effect could consider the reactivity effect of moderation associated with higher enrichment uranium. The lack of radiogenic lead associated with the uranium may or may not be due to leaching. Also, the higher concentration uranium deposits (>15%) were discovered in the 1990s, and reevaluation of the overall effect on a natural reactor criticality were not considered. The high reactivity levels and the low quantity of radiogenic lead identified in uranium tailings, tends to favor a significantly shorter time period or a highly efficient naturally occurring leaching process. A shorter time period would reduce uranium mass and enrichment. Given even a small quantity of moderator would allow an uncontrolled nuclear criticality for high concentration uranium deposits for enrichment between 3 and 8 percent 235 U. The evaluation and analysis of the nuclear criticality safety factors should be evaluated further to document the actual uranium ore grade, and Pb constituents. Identification of the macro-scale quantity (PPM) of radiogenic lead coupled with the NCS factors could be a more useful tool for determining the age of the earth. Further calculations could be considered to determine the impact of different rock formations and materials where uranium is located, and evaluation of the natural leaching of uranium and its decay by-products to associate the effect of radiogenic lead or other materials.

During 2016, nuclear criticality safety (NCS) practitioners from SNL and code developers from LANL collaborated in several areas of interest to the DOE/NNSA Nuclear Criticality Safety Program (NCSP). This collaboration involved. Testing of the preliminary release of the MCNP6- Whisper methodology, with feedback to the developers, Sharing of the benchmark catalogs (the collection of MCNP input files and benchmark results), with 1101 cases from LANL and 866 cases from SNL, Comparison and analysis of 357 benchmarks common to both catalogs, Investigation of the impact of the different benchmark catalogs on sensitivity-uncertainty based NCS validation results from MCNP6-Whisper, Investigation of the impact of randomized selections from the benchmark catalog on sensitivity-uncertainty based validation results from MCNP6-Whisper. Investigation of the use of MCNP6-Whisper in selecting benchmarks for use in NCS validation for unique, nonstandard, legacy fuel applications. This paper summarizes the collaboration work and initial results. It must be noted that the results described herein are preliminary and need further research and detailed analysis. However, the initial results are very interesting, and it is important to share them with the NCSP community.

The Nuclear Criticality Safety Program at Sandia National Laboratories has developed a suite of benchmark problems to be utilized for validation of MCNP6 Version 1.0 with ENDF/B-VII Release 1 cross sections. The benchmark suite covers a broad range of fissile material types, material forms, moderators, reflectors, and neutron energy spectra. It is anticipated that this benchmark suite will cover the vast majority of critical safety applications at SNL. The benchmark suite establishes a Bias and Bias Uncertainty for use in criticality safety analyses. In addition, the Bias and Bias Uncertainty value derived from the benchmark suite using the traditional SNL NCS methodology is demonstrated to be equivalent to the more robust statistical techniques used at many DOE sites.