ML20210L175
| ML20210L175 | |
| Person / Time | |
|---|---|
| Site: | Portsmouth Gaseous Diffusion Plant |
| Issue date: | 08/02/1999 |
| From: | Jonathan Brown UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GDP-99-2042, NUDOCS 9908090052 | |
| Download: ML20210L175 (5) | |
Text
I d USEC A Global Energy Company August 2,1999 GDP 99-2042 I
I U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001' Portsmouth Gaseous Diffusion Plant (PORTS)
Docket No. 70-7002 Event Report 99-15 Pursuant to 10CFR76.120(d)(2), Enclosure 1 provides the required 30 day Event Report for an event that resulted from the declaration of an " Alert" emergency classification at the Portsmouth Gaseous
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I Diffusion Plant. An " Alert" was declared as a result of the discovery that plant criticality accident alarm clusters were not calibrated to alarm at the Technical Safety Requirement specified setpoint. is a list of commitments made in the report.
Should you require additional information regarding this event, please contact Scott Scholl at (740) 897-2373.
I Sincerely,
/
Ss J. Morris Brown g
General Manager l
Portsmouth Gaseous Diffusion Plant
Enclosures:
As Stated
'n/
'T cc:
NRC Region III Ofrice
/g NRC Resident Inspector - PORTS 9900090052 990002 PDR ACOCK 07007002 C
()900)2 United States Enrichment Corporation Portsmouth Gaseous Diffusion Plant P.O. Box 628, Piketon, OH 45661 L.
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GDP 99-2042 Page1of3 Event Report 99-15 Description of Event At 0040 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> on July 2,1999, it was determined that Criticality Accident Alarm System (CAAS) cluster alarms were not set _ to activate at 5 mrad /hr as required by the Technical Safety Requirements
. (TSR). All plantsite CAAS clusters were declared inoperable, resulting in the activation of the Emergency Operations Center and declaration of an " Alert" emergency classification. The declaration of an " Alert" is reportable in accordance with 10CFR76.120(a)(4).
On July 1,1999, at approximately 2330 hours0.027 days <br />0.647 hours <br />0.00385 weeks <br />8.86565e-4 months <br />, during preparations to utilize a new radiation calibration neutron source in the Radiation Calibration Facility, an engineer reviewed the basis spreadsheet calculations for the calibration of the CAAS clusters. While performing an evaluation of discrepancies between the calibration calculations and the calculations for the new source, it was determined that the CAAS clusters were calibrated to alarm at a field strength greater than the 5 mrad /hr specified in the TSR.
On July 2,1999, at approximately 0040 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br />, the plant entered the TSR Limiting Conditions for Operation (LCO) for each affected facility. For the cascade and cascade facilities, the applicable LCOs only allow continued operation for a period of 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. On July 2,1999, the plant requested that the NRC issue a temporary Notice of Enforcement Discretion (NOED) to allow plant operations beyond the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> time limit associated with the cascade and cascade facility LCOs. An analysis performed for the NOED determined that the CAAS settings were adequate to detect the minimum credible criticality accident and would alarm to evacuate personnel, if necessary. The analysis determined that the coverage of individual clusters was reduced as a result of the calibration problem, but the clusters would still provide adequate detection coverage.
On July 2,1999, the NRC orally issued an NOED, At 0010 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> on July 3,1999, the " Alert" status was terminated after two clusters were calibrated. At 1709 hours0.0198 days <br />0.475 hours <br />0.00283 weeks <br />6.502745e-4 months <br /> on July 3,1999, the remaining.
affected CAAS cluster alarm setpoints were adjusted to restore compliance with the TSR, removing the need for the NOED and allowing the plant to exit the LCOs.
Cause of Event The' direct cause of the event was that the cluster alarm setpoint was set higher than the 5 mrad /hr required by the TSR. The calibration method in use since CAAS installation in 1985 had resulted in actual alarm setpoints of between 5 and 8.57 mrad /hr.
The root cause for the event was the use of an incorrect instrument span during performance of the CAAS cluster alarm setpoint procedure. CAAS calibration procedure XP4-GP-RI6500 was based on the vendor's manual which recommended an instrument span of 0-120,000 cpm. For this application the instrument alarm.was designed so that a 0-10 volt input signal was equal to
t GDP 99-2042 Page 2 of 3 Event Report 99-15 0-10 mrad /hr. With this span,1 mrad /hr = 12,000 cpm. Based on these requirements, the maximum alarm setpoint was 5 mrad /hr which corresponds to 60,000 cpm. The procedure acceptance criteria required that the detector alarm in the range of 35,000 cpm to 60,000 cpm.
Procedure XP4-GP-RI6500 requires the use of a spreadsheet calculation to calibrate detector voltage.
The spreadsheet calculates the distance from the source in the beam room where the CAAS detector voltage is adjusted. The detector is then adjusted to read approximately 35,000 cpm at the specified distance. The spreadsheet did not identify the fact that the 35,000 cpm reading corresponded to a 5 mrad /hr field. Since 5 mrad /hr is 50% of the instrument span, the voltage adjustment caused the full range instrument span to be 0-70,000 cpm. With a span of 70,000 cpm,1 mrad /hr = 7,000 cpm.
The inconsistency between the procedure and the spreadsheet caused the instrument span to be off by a factor of approximately 1.7 (120,000 cpm / 70,000 cpm = 1.71). With this error, the procedure acceptance criteria actually resulted in calibrating the detectors to alarm between 5 mrad /hr and 8.57 mrad /hr. This is because the detector was actually set up so that 35,000 cpm = 5 mrad /hr and 60,000 cpm = 8.57 mrad /hr (1.71 x 5 mrad /hr = 8.57 mrad /hr).
The error above was due to the incorrect merging of two separate and distinct calibration methodologies. In the vendor manual the cluster design is for the full range setting of 120,000 cpm.
The vendor manual setting was used in preparing the calibration procedure, XP4-GP-RI6500. The span of 70,000 cpm used for the spreadsheet program was derived from the first principle calculation of neutron strength in air developed as part of the original calibration basis of the cluster. Since the spreadsheets generated by the program did not indicate the field strength at which the calibration was to be done, it appears that personnel who developed the calibration procedure believed that the j
procedure and spreadsheet used the same instrument spans.
Additional investigation activities are planned to determine why this error was not detected and corrected during procedure development activities. If the investigation changes our understanding j
of this event or results in significant new corrective actions, this event report will be revised.
Engineering also performed a comprehensive review of the original CAAS detector calibration basis that was established in 1986. This basis was detennined to be acceptable for establishing compliance with the TSR. However, a new setpoint calculation was performed to update the calibration basis to current setpoint program requirements.
A review of this event also deterr6ed that other calibration processes used to meet TSR setpoints or limits are not likely to coMain similar errors. The CAAS calibration process is different from most TSR related calibrat'.ons because several measurement unit conversions are required to establish the setpoint. The measurement units used in calibrating CAAS clusters are given in cpm.
GDP 99-2042 Page 3 of 3 Event Report 99-15 A conversion is required to convert epm units to the mrad /hr units that are specified in the TSR. The error that led to this event was associated with the conversion process. Additional reviewe are -
planned to confirm that if there are other TSR related instruments which require similar conversions as part of the calibration process.
Corrective Actions 1.
On July 3,1999, all cluster alarm setpoints were adjusted to restore compliance with the TSR.
2.
On July 25,1999, a formal setpoint calculation was performed to update the original technical basis for CAAS detector calibration that was established in 1986.
3.
On July 26,1999, procedure XP4-GP-RI6500 was revised to incorporate the technical information contained in the new setpoint calculations.
4.
By August 31,1999, Engineering will perform an evaluation ofinstruments relied on to meet TSR setpoints or limits to determine whether additional calibration processes require calculations to convert measurement parameters to TSR units.
5.
By November 22,1999, Engineering will verify by independent calculation or measurement, as appropriate, that the calibration processes identified in the evaluation to be completed by August 31,1999 are correct.
Extent of Exposure of Individuals to Radiation or Radioactive Materials There was no exposure to radiation or radioactive materials due to this event.
Lessons Learned This event demonstrated the need to ensure, where possible, that the calibration process incorporates 1
an independent means of verifying calibration results. Where there is no direct comparison to a calibration standard, independent verification of the indirect links would provide a means of ensuring calibration process errors do not go undetected.
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GDP 99-2042 Page1of1 Event Report 99-15 List of Commitments 1.
By August 31,1999, Engineering will perform an evaluation ofinstruments relied on to meet
~TSR setpoints or limits to determine whether additional calibration processes require calculations to convert measurement parameters to TSR units.
2.
By November 22,1999, Engineering will verify by independent calculation or measurement, as appropriate, that the calibration processes identified in the evaluation to be completed by i
August 31,1999 are correct.
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- Regulatory commitments contained in this document are listed here, Other corrective actions listed in this submittal are not considered regulatory commitments in that they are either statements of actions completed, or they are considered enhancements to USEC's investigation, procedures, programs, or operations.
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