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Title: Application of Nuclear Criticality Safety to Early Earth Age Uranium.


Abstract not provided.

Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
Report Number(s):
DOE Contract Number:
Resource Type:
Resource Relation:
Conference: Proposed for presentation at the American Nuclear Society Annual Meeting held October 29 - November 2, 2017 in Washington, DC.
Country of Publication:
United States

Citation Formats

Schwers, Norman F., and Miller, John A. Application of Nuclear Criticality Safety to Early Earth Age Uranium.. United States: N. p., 2017. Web.
Schwers, Norman F., & Miller, John A. Application of Nuclear Criticality Safety to Early Earth Age Uranium.. United States.
Schwers, Norman F., and Miller, John A. 2017. "Application of Nuclear Criticality Safety to Early Earth Age Uranium.". United States. doi:.
title = {Application of Nuclear Criticality Safety to Early Earth Age Uranium.},
author = {Schwers, Norman F. and Miller, John A.},
abstractNote = {Abstract not provided.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 5

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  • In nuclear criticality safety applications, a number of important uncertainties have to be addressed to establish the required criticality safety margin of a nuclear system. One source of these uncertainties is the basic nuclear data used to calculate the effective multiplication factor of the system. Before criticality safety calculations are performed, the bias and uncertainties of the codes and cross sections that are used must be determined. Cross-section data are measured, evaluated, and tested prior to their inclusion in nuclear data libraries. Traditionally, nuclear data evaluations are performed to support the analysis and design of thermal and fast reactors. Themore » neutron spectra characteristic of the thermal and fast systems used for data testing are predominantly in the low- and high-energy ranges, with a relatively minor influence from the intermediate-energy range. In the area of nuclear criticality safety, nuclear systems involving spent fuel elements from reactors can lead to situations very different from those most commonly found in reactor analysis and design. These systems are not limited to thermal or fast neutron spectra and may have their most significant influence from the intermediate energy range. This requires extending the range of applicability of the nuclear data evaluation beyond thermal and fast systems. The aim here is to focus on the evaluated nuclear data pertaining to applications in nuclear criticality safety.« less
  • Large quantities of low-enriched uranium (LEU) 0.71 to 1.25 wt% {sup 235}U were processed into metallic fuel elements and irradiated in production reactors at the Hanford and the Savannah River sites. Safe processing was ensured by strict adherence to nuclear criticality controls. A criticality control approach emerged for N Reactor fuels that established a k{sub eff} = 0.98 as the safety limit rather than a k{sub eff} = 0.95 used by the commerical power industry for their fuels. This paper demonstrates that the use of k{sub eff} = 0.98 provides equivalent or larger safety margins for N Reactor fuels thanmore » k{sub eff} = 0.95 provides for commercial reactor fuels. Recent accident analyses pertaining to N Reactor spent-fuel storage are used to illustrate compliance with the k{sub eff} = 0.98 limit.« less
  • The US Department of Energy (DOE) Deputy Assistant Secretary of Energy for Environmental Management has issued a challenge to complete DOE environmental cleanup within a decade. The response for Oak Ridge facilities is in accordance with the DOE ten-year plan which calls for completion of > 95% of environmental management work by the year 2006. This will result in a 99% risk reduction and in a significant savings in base line costs in waste management (legacy waste); remedial action (groundwater, soil, etc.); and decontamination and decommissioning (D and D). It is assumed that there will be long-term institutional control ofmore » cascade equipment, i.e., there will be no walk away from sites, and that there will be firm radioactivity release limits by 1999 for recycle metals. An integral part of these plants is the removal of uranium deposits which pose nuclear criticality safety concerns in the shut down of the Oak Ridge Gaseous Diffusion Plant. DOE has initiated the Nuclear Criticality Stabilization Program to improve nuclear criticality safety by removing the larger uranium deposits from unfavorable geometry equipment. Nondestructive assay (NDA) measurements have identified the location of these deposits. The objective of the K-25 Site Nuclear Criticality Stabilization Program is to remove and place uranium deposits into safe geometry storage containers to meet the double contingency principle. Each step of the removal process results in safer conditions where multiple controls are present. Upon completion of the Program, nuclear criticality risks will be greatly reduced.« less
  • The ANSI/ANS 8.12 standard was first approved in July 1978. At that time, this edition was applicable to operations with plutonium-uranium oxide (MOX) fuel mixtures outside reactors and was limited to subcritical limits for homogeneous systems. The next major revision, ANSI/ANS-8.12-1987, included the addition of subcritical limits for heterogeneous systems. The standard was subsequently reaffirmed in February 1993. During late 1990s, substantial work was done by the ANS 8.12 Standard Working Group to re-examine the technical data presented in the standard using the latest codes and cross section sets. Calculations performed showed good agreement with the values published in themore » standard. This effort resulted in the reaffirmation of the standard in March 2002. The standard is currently in a maintenance mode. After 2002, activities included discussions to determine the future direction of the standard and to follow the MOX standard development by the International Standard Organization (ISO). In 2007, the Working Group decided to revise the standard to extend the areas of applicability by providing a wider range of subcritical data. The intent is to cover a wider domain of MOX fuel fabrication and operations. It was also decided to follow the ISO MOX standard specifications (related to MOX density and isotopics) and develop a new set of subcritical limits for homogeneous systems. This has resulted in the submittal (and subsequent approval) of the project initiation notification system form (PINS) in 2007.« less