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Analysis of criticality accident alarm system coverage in the X-700, X-705, and X-720 facilities at the Portsmouth Gaseous Diffusion plant

Description: Additional services for the uranium enrichment cascade process, such as maintenance and decontamination operations, are provided by several ancillary facilities at the PORTS site. These facilities include the X-700 Maintenance Facility, the X-705 Decontamination Facility, and the X-720 Maintenance and Stores Facility. As uranium operations are performed within these facilities, the potential for a criticality accident exists. In the event of a criticality accident within one of these facilities 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-700, X-705, and X-720 facilities. The analysis has determined that the X-705 and X-720 facilities have complete CAAS coverage; the X-700 facility has not been shown to have complete CAAS coverage at this time.
Date: December 1, 1995
Creator: Skapik, C.W.; Dobelbower, M.C. & Woollard, J.E.
Partner: UNT Libraries Government Documents Department

Determination of the response function for the Portsmouth Gaseous Diffusion Plant criticality accident alarm system neutron detectors

Description: Neutron-sensitive radiation detectors are used in the Portsmouth Gaseous Diffusion Plant`s (PORTS) criticality accident alarm system (CAAS). The CAAS is composed of numerous detectors, electronics, and logic units. It uses a telemetry system to sound building evacuation horns and to provide remote alarm status in a central control facility. The ANSI Standard for a CAAS uses a free-in-air dose rate to define the detection criteria for a minimum accident-of-concern. Previously, the free-in-air absorbed dose rate from neutrons was used for determining the areal coverge of criticality detection within PORTS buildings handling fissile materials. However, the free-in-air dose rate does not accurately reflect the response of the neutron detectors in use at PORTS. Because the cost of placing additional CAAS detectors in areas of questionable coverage (based on a free-in-air absorbed dose rate) is high, the actual response function for the CAAS neutron detectors was determined. This report, which is organized into three major sections, discusses how the actual response function for the PORTS CAAS neutron detectors was determined. The CAAS neutron detectors are described in Section 2. The model of the detector system developed to facilitate calculation of the response function is discussed in Section 3. The results of the calculations, including confirmatory measurements with neutron sources, are given in Section 4.
Date: March 1, 1997
Creator: Tayloe, R.W. Jr.; Brown, A.S.; Dobelbower, M.C. & Woollard, J.E.
Partner: UNT Libraries Government Documents Department

An in-phantom comparison of neutron fields for BNCT

Description: Previously, the authors have developed the in-phantom neutron field assessment parameters T and D (Tumor) for the evaluation of epithermal neutron fields for use in BNCT. These parameters are based on an energy-spectrum-dependent neutron normal-tissue RBE and the treatment planning methodology of Gahbauer and his co-workers, which includes the effects of dose fractionation. In this paper, these neutron field assessment parameters were applied to The Ohio State University (OSU) design of an Accelerator Based Neutron Source (ABNS) (hereafter called the OSU-ABNS) and the Brookhaven Medical Research Reactor (BMRR) epithermal neutron beam (hereafter called the BMRR-ENB), in order to judge the suitability of the OSU-ABNS for BNCT. The BMRR-ENB was chosen as the basis for comparison because it is presently being used in human clinical trials of BNCT and because it is the standard to which other neutron beams are most often compared.
Date: January 1, 1998
Creator: Woollard, J.E.; Blue, T.E. & Capala, J.
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

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