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A comparison of two criticality accident alarm system detector locations for the X-700 building at the Portsmouth Gaseous Diffusion Plant. Final report

Description: A previous analysis of the X-700 Building Criticality Accident Alarm System (CAAS) showed that some of the building may not adequately be covered by the one building CAAS detector in its current location. This report compares the results of that analysis with a new analysis where the detector is in a different location. The new detector location (outside of the storage area in the center of the building--near column B-7) showed coverage for all points previously analyzed. The new centralized detector location reduces the distance and shielding between the source points and the detector. This explains the difference in the level of response when compared to the original (actual) detector location in the new annex west of the building.
Date: February 1, 1996
Creator: Skapik, C.W. & Lee, B.L. Jr.
Partner: UNT Libraries Government Documents Department

Validation of nuclear criticality safety software and 27 energy group ENDF/B-IV cross sections. Revision 1

Description: The original validation report, POEF-T-3636, was documented in August 1994. The document was based on calculations that were executed during June through August 1992. The statistical analyses in Appendix C and Appendix D were completed in October 1993. This revision is written to clarify the margin of safety being used at Portsmouth for nuclear criticality safety calculations. This validation gives Portsmouth NCS personnel a basis for performing computerized KENO V.a calculations using the Lockheed Martin Nuclear Criticality Safety Software. The first portion of the document outlines basic information in regard to validation of NCSS using ENDF/B-IV 27-group cross sections on the IBM3090 at ORNL. A basic discussion of the NCSS system is provided, some discussion on the validation database and validation in general. Then follows a detailed description of the statistical analysis which was applied. The results of this validation indicate that the NCSS software may be used with confidence for criticality calculations at the Portsmouth Gaseous Diffusion Plant. For calculations of Portsmouth systems using the specified codes and systems covered by this validation, a maximum k{sub eff} including 2{sigma} of 0.9605 or lower shall be considered as subcritical to ensure a calculational margin of safety of 0.02. The validation of NCSS on the IBM 3090 at ORNL was extended to include NCSS on the IBM 3090 at K-25.
Date: January 1, 1996
Creator: Lee, B.L. Jr. & D`Aquila, D.M.
Partner: UNT Libraries Government Documents Department

Validation of MCNP4a for highly enriched uranium using the Battelle process safety and risk management IBM RS/6000 workstation

Description: This document has been prepared to allow use of the Radiation Shielding and Information Center (RSIC) release of MCNP4a, which has been installed on the Battelle Process Safety and Risk Management (PSRM) IBM RS/6000 workstation, for production calculations for the Portsmouth Gaseous Diffusion Plant (PORTS). This hardware/software configuration is under the configuration control plan listed in Reference 1. The first portion of this document outlines basic information with regard to validation of MCNP4a using the supplied cross sections and the additional MCNPDAT cross sections. A basic discussion of MCNP is provided, along with discussions of the validation database in general. A description of the statistical analysis then follows. The results of this validation indicate that the software and data libraries examined may be used with confidence for criticality calculations at the Portsmouth Gaseous Diffusion Plant (PORTS). When the validation results are treated as a single group, there is a 95% confidence that 99.9% of future calculations of similar critical systems will have a calculated k{sub eff} > 0.95. Based on this result, the Battelle PSRM Nuclear Safety Group has adopted the calculational acceptance criteria that a calculated k{sub eff} + 2{sigma}, {le} 0.95 is safely subcritical. The conclusion of this document is that MCNP4a and all associated cross section libraries installed on the PSRM IBM RS/6000 are acceptable for use in performing production criticality safety calculations for the Portsmouth Gaseous Diffusion Plant.
Date: January 1, 1996
Creator: Negron, S.B.; Lee, B.L. Jr. & Tayloe, R.W. Jr.
Partner: UNT Libraries Government Documents Department

Examination of criticality accident alarm coverage on the operating floors of the X-333, X-330, and X-326 facilities at the Portsmouth Gaseous Diffusion Plant

Description: This report summarizes the results of an evaluation of Criticality Accident Alarm System (CAAS) coverage of the operating floors (first floors) of the X-333, X-330, and X-326 buildings. CAAS coverage of the process cell floors (second floors) has been evaluated in previous reports. Coverage of the roadways around the three processing buildings by the cell floor detectors in these buildings has also been verified in a previous report. In order to evaluate coverage, the facilities were modeled using the Monte Carlo N-Particle Transport Computer Code (MCNP). MCNP was then used to simulate criticality accidents at various locations throughout the operating floors of the buildings and the associated neutron flux at the current detector locations was calculated. The neutron flux was then converted to an absorbed dose rate (in tissue) and compared with the Portsmouth criticality accident alarm set-point of 5mrad/hr. The parameters defining the simulated criticality accidents have been calculated as ``the minimum accident of concern`` as defined in ANSI Standard ANS 8.3-1986. These calculations are documented in Portsmouth report number POEF-SH-31. The results of this evaluation indicate that the X-333 Operating Floor CAAS may not alarm in response to a minimum accident of concern. This is primarily because of shielding provided by the numerous concrete columns used to support the second floor of this building and the large distances between the CAAS detectors. Conversely, the results indicate that the X-326 and the X-330 CAAS systems would alarm in response to a minimum accident of concern occurring on the operating floors of these buildings. It should be noted that the cell floors in these two buildings are supported with steel I-beams instead of the concrete columns used in the X-333 building.
Date: January 1, 1996
Creator: Lee, B.L. Jr.; Dobelbower, M.C.; Woollard, J. & Skapik, C.W.
Partner: UNT Libraries Government Documents Department

An examination of criticality accident alarm coverage of the X-710, X-760 Buildings and the north half of the X-7745-R storage pad at the Portsmouth Gaseous Diffusion Plant

Description: This report summarizes the results of an evaluation of Criticality Accident Alarm System (CAAS) coverage of the X-710 and X-760 buildings and the north half of the X-7745-R storage lot located east of the X-7725 building at the Portsmouth Gaseous Diffusion Plant. In order to evaluate coverage, the facilities were modeled using the Monte Carlo N-Particle Transport Computer Code (MCNP). MCNP was then used to simulate criticality accidents at various locations in the X-710 and X-760 buildings and the north half of the X-7745-R storage lot. The associated neutron flux at current detector locations was calculated. The neutron flux was then converted to an absorbed dose rate (in tissue) and compared with the Portsmouth criticality accident alarm set-point of 5mrad/hr. The parameters defining the simulated criticality accidents have been calculated as ``the minimum accident of concern`` as defined in ANSI Standard ANS 8.3-1986. These calculations are documented in Portsmouth report POEF-SH-31. The results of this evaluation indicate that the X-710 and X-760 buildings and surrounding roads are adequately covered by the CAAS systems that are currently in place in those buildings. The X-7745-R storage pad is also adequately covered by the CAAS in the X-7725 building.
Date: January 1, 1996
Creator: Skapik, C.W.; Dobelbower, M.C.; Woollard, J. & Lee, B.L. Jr.
Partner: UNT Libraries Government Documents Department

Calculated in-air leakage spectra and power levels for the ANSI standard minimum accident of concern. Final report

Description: This document represents Phase I of a two-phase project. The entire project consists of determining a series of minimum accidents of concern and their associated neutron and photon leakage spectra that may be used to determine Criticality Accident Alarm compliance with ANSI/ANS-8.3. The inadvertent assembly of a critical mass of material presents a multitude of unknown quantities. Depending on the particular process, one can make an educated guess as to fissile material. In a gaseous diffusion cascade, this material is assumed to be uranyl fluoride. However, educated assumptions cannot be readily made for the other variables. Phase I of this project is determining a bounding minimum accident of concern and its associated neutron and photon leakage spectra. To determine the composition of the bounding minimum accident of concern, work was done to determine the effects of geometry, moderation level, and enrichment on the leakage spectra of a critical assembly. The minimum accident of concern is defined as the accident that may be assumed to deliver the equivalent of an absorbed dose in free air of 20 rad at a distance of 2 meters from the reacting material within 60 seconds. To determine this dose, an analyst makes an assumption and choose an appropriate flux to dose response function. The power level required of a critical assembly to constitute a minimum accident of concern depends heavily on the response function chosen. The first step in determining the leakage spectra was to attempt to isolate the effects of geometry, after which all calculations were conducted on critical spheres. The moderation level and enrichment of the spheres were varied and their leakage spectra calculated. These spectra were then multiplied by three different response functions: the Henderson Flux to Dose conversion factors, the ICRU 44 Kerma in Air, and the MCNP Heating Detector. The ...
Date: July 1, 1995
Creator: Lee, B.L. Jr.; Dobelbower, M.C. & Tayloe, R.W. Jr.
Partner: UNT Libraries Government Documents Department

Analysis of criticality accident alarm system coverage of the X-744G, X-744H, X-342/344A and X-343 facilities at the Portsmouth Gaseous Diffusion Plant

Description: Additional services for the uranium enrichment cascade process, such as UF{sub 6} feed, sampling, and material storage are provided by several ancillary Uranium Material Handling (UMH) facilities at the PORTS site. These facilities include the X-343 Feed Vaporization and Sampling Facility, the X-744G Bulk Non-Uranium Enrichment Service Activity (UESA) Storage Building, the X-744H Waste Separation and Storage Facility, the X-344A Toll Enrichment Services Facility and the X-342A Feed Vaporization and Fluorine Generation Facility. As uranium operations are performed within these facilities, the potential for a criticality accident exists. In the event of a criticality accident within a process facility at PORTS, a Criticality Accident Alarm System (CAAS) is in place to detect the criticality accident and sound an alarm. In this report, an analysis was performed to provide verification that the existing CAAS at PORTS provides complete criticality accident coverage in the X-343, X-744G. X-744H. X-344A and X-342A facilities. The analysis has determined that all of the above-mentioned facilities have complete CAAS coverage.
Date: September 1, 1995
Creator: Dobelbower, M.C.; Woollard, J.; Lee, B.L. Jr. & Tayloe, R.W. Jr.
Partner: UNT Libraries Government Documents Department

Verification of criticality accident alarm system detector locations for the X-326 process cell floor

Description: Criticality Accident Alarm System (CAAS) detectors on the cell floor of the X-326 process building at the Portsmouth Gaseous Diffusion Plant (PORTS) are located at a height of 5 m above the cell floor. It has been suggested that this height be lowered to I m to alleviate accelerated system failures caused by the elevated temperatures at 5 m and to reduce the frequency of injury to maintenance personnel lifting the approximately 90-lb units into position. Work has been performed which analyzed the effect of relocating the CAAS detectors on the process floors of the X-333 and X-330 buildings from their current height to a height of 1 m{sup 1}. This earlier work was based on criticality accidents occurring in low enriched material (5% {sup 235}U) and was limited to the X-333 and X-330 buildings and the low enriched areas of X-326. It did not consider the residual higher enriched material in the X-326 building. This report analyzes the effect on criticality alarm coverage of lowering the CAAS detectors. This analysis is based on criticality accidents resulting from higher enriched material which may be present as ``hold-up`` in the process equipment within the X-326 building. The criticality accident alarm detectors at the PORTS facility are set to alarm at a neutron absorbed dose rate of 5 mrad/hr. The calculated absorbed dose rates presented in this report show that the detectors examined that produce an alarm for the given criticality event at their current height will also produce an alarm if located at a height of 1 meter. Therefore, lowering the detectors will not result in a loss of coverage within the building.
Date: August 1, 1995
Creator: Dobelbower, M.C.; Woollard, J.; Lee, B.L. Jr. & Tayloe, R.W. Jr.
Partner: UNT Libraries Government Documents Department

Evaluation of coverage of enriched UF{sub 6} cylinder storage lots by existing criticality accident alarms

Description: The Portsmouth Gaseous Diffusion Plant (PORTS) is leased from the US Department of Energy (DOE) by the United States Enrichment Corporation (USEC), a government corporation formed in 1993. PORTS is in transition from regulation by DOE to regulation by the Nuclear Regulatory Commission (NRC). One regulation is 10 CFR Part 76.89, which requires that criticality alarm systems be provided for the site. PORTS originally installed criticality accident alarm systems in all building for which nuclear criticality accidents were credible. Currently, however, alarm systems are not installed in the enriched uranium hexafluoride (UF{sub 6}) cylinder storage lots. This report analyzes and documents the extent to which enriched UF{sub 6} cylinder storage lots at PORTS are covered by criticality detectors and alarms currently installed in adjacent buildings. Monte Carlo calculations are performed on simplified models of the cylinder storage lots and adjacent buildings. The storage lots modelled are X-745B, X-745C, X745D, X-745E, and X-745F. The criticality detectors modelled are located in building X-343, the building X-344A/X-342A complex, and portions of building X-330. These criticality detectors are those located closest to the cylinder storage lots. Results of this analysis indicate that the existing criticality detectors currently installed at PORTS are largely ineffective in detecting neutron radiation from criticality accidents in most of the cylinder storage lots at PORTS, except sometimes along portions of their peripheries.
Date: March 1, 1995
Creator: Lee, B.L. Jr.; Dobelbower, M.C.; Woollard, J.E.; Sutherland, P.J. & Tayloe, R.W. Jr.
Partner: UNT Libraries Government Documents Department