ML20101M400
| ML20101M400 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/01/1992 |
| From: | Joshua Wilson TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 91-15, NUDOCS 9207080222 | |
| Download: ML20101M400 (4) | |
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~,a <.n,-# noey t w.i July 1, 1992 U.S. Nuclear Regulatory Commission ATTN: Document Control I'esk Washington, D.C. 20$55 Gentlement In the Matter of
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Docket Nos. 50-327 Tennessee Valley Authority
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50-328 SEQUOYAH NUCLEAR PLANT (SQN) - FACILITY OPERATING LICENSES DPR-77 AND DPR ENVIRONMENTAL QUALIFICATION - Si'ECIAL REPORT 91-15. REVISION 3 i
The enclosed revision to the special report provides the current schedule for completing the necessary qualification documentation revisions. The extended duration has resulted frem identifying an apparent error in the mothrdology being utilized to cciculate the reduction factors.
The program now being utilized is an industry-accepted methodology; results obtained to date continue to support the initial operability basis. The y
original special report was submitted in accordance with Units 1 and ?
License Condition 2.H.
Revisions to the spanial report are annotated by vertical bars in the right-hand margin.
If you have any questions concerning this submittal, please telephone M. A. Cooper at (615) 843-8924.
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Sincerely, b
5 AL J. L. Wilson Enclosure cc:
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U.S. Nuclear Regulatory Commission Page 2 July 1. 1997 cc (Enclosure) i Mr. D. E. LaBarge, Project Manager U.S. Nuclear Regulatory Commission Ona White Flint, Nerth 11553 Reckville Pike Rockville, Maryland 20852 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379 Mr. B. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 I
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^f ENCLOSURE 14-DAY FOLLOW-UP REPORT SEQUOYAH NUCLEAR PLMVT (SQN)
SPECIAL REPORT 91-15, REVISION 3 Deacdrilan_oLCondition on August 1, 1991, with Units 1 and 2 operating in Mode 1, a significant corrective action report (SCAR) was initiated to document that the calculated, free-field Leta radiation doses that were used to environmentally qualify safety-related equipment housed in small unsealed enclosures inside containment-were nonconservative. This condition was subsequently determined to ba reportable on August 12 under License Condition 2.H.of the Units 1 and 2 operating licenses.
The beta radiation input for the environmental qualification of SQN equipment is based on a generic calculai lon generated by TVA corporate Nuclear Engineering in 1986. The calculation determined a reduction factor to be applied to the free-field beta dose to components inside unsealed enclosures utilizing an " effective infinite cloud" reference volume.
This reference volume was based on the possible spectrum of beta energy levels, the associated probabilities of a given beta particle having a specific initici energy, and the range in air that a beta particle can travel at a given energy. SQN-specific calculations then applied the reduction factor from the generic calcu?ation to determine a f ree-field beta radiation dose for that component inside tiae enclosure.
As a result of a recent calculation review, the generic beta radiation doses were recalculated utilizing a state-of-the-art statistical prediction model that utilizes Monte Carlo methodology.
This method
. yleided higher free-field beta radiation doses fer equipment than had the celginal generic calculation. The impacted equipment includes s af ety-related cuales, splices, termin.' blocks, penetrations,
t ransmitters, and safety-related mechanical valve seats.
Cause_of Candition The cause of this condition has been concluded to be the result of the failure of the personnel involved in the original generic beta. dose calculation to realize that the linear reduction methodology used provided nonconservative results.
Personnel involved in the preparation and verification of the calculation had no comparaule methodology readily available tu assess the accuracy or validity of the calculation results.
They primarily relied upon their experience in radiation analyses in reviewing the calculation.
The generic calculation was also reviewed as part of the restart efforts for SQN and Browns Ferry Nuclear Plant (BEN).
These reviews encompassed several aspects, including appropriate reference material, acceptable methodology, numerical correctness, and assurance that results were in y
accordance with the problem statement. As no standard criteria to compare the methodology or the results were readily available, the reviewers relied on industry experience to draw the conclusion that the calculation was acceptable.
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'e CDIrgetive Actions Upon identification of the nonconservative beta dose values, a review of 10 CFR 50.49. equipment qualification records was performed.
Evaluations have been performed for the affected equipment, and it has been concluded that the ~ equipment is qualifiable and capabJe of performing its design function. Site-specific calculations and qualification records to reflect the higher beta doses have not yet been performed.
An assessment of cables and splices was performed by evaluating a detailed Monte Carlo analysis for exposed cables at BFN. This calculation allowed BFN to qualify cables to a much greater airbarne free-field beta dose. By adjui;ing the results of the BrN calculataon to that of SQN (adjusting for SQN's specific containment volume and power
-level), values for the expected beta dose for SQN were determined for unjacheted cables and splices inside unsealed enclosures.
These val *2ec lead to the conclusion that the SQN cables and splices are qualifiable.
For exposed cables, the HRC methodology provided in Inspection and Enforcement Bulletin 79-01B, " Environmental Qualification of Class 1E Equipment" (Enclosure 4. Sectfon 4.1.2), along with credit!ng operating time requirements, supports qualffication.
Terminal blocks-were determined to be qualifiable utilizing the new volume reduction factors computed in the-rcvised generic beta cose calculation.
A review of the calculations performed for the mechanical valve internals shows considerable conservatism in their preparation.
Consideration of the new reduction factors will not change the quali-cation status of the valves affected.
All-other 10 CFR 50.49 components affected by the revised volume reduction methodology are qualifiable considering the revised vclume reduction factors, shielding considerations, required operatinr times, and radiation thresholds of the component material.
Based on the above discussions and engineering judgement, all 10 CFR 50.49 equipment impacted by the new beta dose reduction factors remains qualifiable and continues to remain capable of performing its intended design functions. As such, no operability concerns exist. A detailed corrective action plan has been developed to revise the appropriate 10 CFR 50.49 qualification documentation.
The necessary documentat.an revisions will be completed by August 31, 1992.
l Commitments 1.
The schedule for coepleting these documentation revisions will be provided in a revision to this special report by November 1,199J/
(completed by Revision 1 of this special report).
2.
The necessary documentation revisions will be completed by August 31, 1992.
l PLO90204/1999
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