ML20095J971
| ML20095J971 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/24/1992 |
| From: | Joshua Wilson TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9205040234 | |
| Download: ML20095J971 (4) | |
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24, 1992 U.S. Nuclear Regulatory Commission ATTN Document Control Desk Washington, D.C. 20555 Gentlemen!
In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 SEQUOYAH NUCLEAR PLANT (SQN) - OPERABILITY OF ICE CONDENSER INLET DOORS
References:
1.
Letter from J. L. Wilson to NRC dated March 27, 1992, "Sequoyah Nuclear Plant (SQN)
Ice Condenser Lower Plenum Floor Movement and Degradation" 2.
NRC Inspection Report Nos. 50-327/92-06 and 50-328/92-06 dated Aptil 9, 1992 3.
TVA Licensee Event Report (LER) 50-327/92007 dated April 15, 1992 4.
Lettet from Bruce A. Wilson to Mark 0. Medford dated April 8, 1992. " Meeting Summary - Sequoyah Ice Condenser and Feedwater Pipe Crackint" 5.
NRC Inspection Report Nos. 50-327/92-10 and 50-328/92-10 da' e d April 23, 1992 In Reference 2, the NRC staff identified for consideration of escalated enforcement -an apparent violation regarding operability _of ice condenser inlet doors at SQN Units 1 and 2, and " provide [d] [TVA) an opportunity for an enforcement conference" to discuss involved issues (Section V of-10 CFR Part 2. Appendix C (1992]). During subsequent discussions between S. D. Ebneter and J. R. Bynum, it was agreed that TVA (1) would submit to
- the staff a letter providing any additional information not addressed in previous communications and TVA's enforcement perspectives, and (2) would be prepared to respond to any ren,ining staff questions regarding this
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Page 3 April 24, 1992 noted in Reference 3, a long-term modification to addresa sealing of the wear slab interfaces, joints, and significant cracks is being evaluated Tor implementation.
As noted in Reference 3, the root cause of this event is the failure to install sealant material in some of the wear slab joints, during initial construction over a decade ago.
This provided an avenue for water intrusion to the floor acsembly and resulted in upward wear slab movement upon freezing. While it is theorized that the conditian may have been progressing slowly over time at SQN, this problem has not been previously identified at SQN or any other ice condenser plant. TVA has alerted other ice condenser plauts to this unexpected phenomenon and has coordinated closely with Westinghouse on this issue.
TVA has evaluated the consequences of the event to determine whether the e
condition of the inlet doors on Units 1 and 2 adversely impacted the ice condenser such that it would not have been able to perform its intended l
function. The evaluation and resultant conclusiors regarding Unit I were previously provided to the staff and are reported in Reference 3.
A separate evaluation, as summarized below, was conuucted for Unit 2 using generally the same approach as for the Unit 1 evaluation.
(This evaluation has also been provided to the staff and, as noted in Reference 3, will be included in a later supplemental LER.)
In sum, evaluations conducted by TVA reflect that the condition would not have prevented the ice condensers from performing their intended functions and
'Se structural integrity and operability of interfacing components were maintained. Accordingly, it is ceneluded that the event was of limited enfety significance.
For the Unit 2 evaluation, it was determined that of the 27 inlet doors
-impac ad by the upward mavement of the wear slabs only six were bound to the extent that they may not have opened duaing al? accident conditions.
Eowever, to be conservative, these six doors were modeled as being closed for all evaluations. Uaing conservative assuupticus and ana? ytical mcthodology, including TVA's containment and subcompartment analysis program, MONSTER TVA determined that in the event of accident conditions
-with the ar.-found ice condenser inlet door configurations, there would have been no iacrease in the peak containment temperature or long-term pressures previously reported in the Updated Final Safety Analysis Report (UFSAR) accident anclyses. There would have been an increase in the'subcompartmant (short-term) pressures over those calculated by Westinghouse and provided in the UFSAR. To de. ermine the imoact of these increases in subcompartment pressures, the containment shell and the critical structures, as defined in Table 3.8.3-10 of the UFSAR, that would be impacted by subcempartment pressure increases were reviewed.
The resulting short-tere pressures would still have remained within the design pressures used by TVA to evaluate the containment shell and internal structures and significantly bulow pressures associated with failure of containment and the internal structures.
I m
U.S._ Nuclear Regulatory Commission Page 2 April 24, 1991
- additional information during the scheduled May 1, 1992, enforcement conference.
It is the purpose-of this letter to provide that additional information and enforcement perspectives.
At the outset, TVA agrees with _ the staf f finding that a number of ice condenser inlet doors at SQN (11 of_48 doors on Unit 1 and 27 of 48 doors 1
on Unit 2) would not have met the operability provisions of Surveillance Requirement 4.6.5.3.1.b.1 and/or 3, because of the
-t-rd movement of the ice condenser wear slabs and the resultant interf_rer(
with the associated flashing beneath the doors.
A question regarding binding of some ice condenser inlet doors was first raised by a:TVA Maintenance foreman on March 15, 1992, while he was preparing for Unit 2 ice condenser outcge activities.
(Unit 2 was shut down for a refueling outage.) The condition was promptly ine.tigated leading tola finding on March 17, 1992, that 27 of the 48 Unit 2 ice
- condenser inlet doors were inoperable. As the staff noted in Reference /5,.this conclusion resulted in prompt action to determine if the problem existed'in Unit 1, which was operating at full power. On March 18, 1992, following identification of the problem in Unit 1, TVA entered Limited Condition for Operation 3.6.5.3.
_ Following evaluation of the condition, TVA conservatively began an orderly shutdown of the unit, well :in advance of action required by SQN technical specifications. This type of prompt and conservative action has characterized TVA's response to this event.
'These actions and the facts associated with this event have been thoroughly documented in correspondence with the staff (References 1
- and 3) and were the subject of an. April 3, 1992, meeting with P.egion II and-Nuclear Reactor Regulation management (Reference 4).
(TVA
~
presentation slides were provided to the staff.)
In addition, TVA-investigation reports and evaluations concerning this event have been made available to and reviewed by the staff.
-In Re arences.1 a i! 3, and during the April 3,1992, meeting with the NRC staff, TVA prov!ied detailed discussions of its actions designed to assess _and. correct the problem, monitor for unexpected additional wear slab movement, and prevent recurrence of that upward movement. These corrective actions were prompt, extensive, aggressively implemented, and have in the main been completed. These actions-included not only i
correction of the immediate condition and detailed evaluations regarding impact.of the. condition, but also-(1) installation of. continuous on-line l
- monitoring capability for unexpected upward movement of the wear slabs, l
.(2)' enhancement of work activities to prevent water intrusion into the L
floor assembly, and (3) implementation of more restrictive. operational guidance in the event of future ice condenser door impairment, pending a formal technical specification change on this issue.
In addition, as b
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U.S. Nuclear Regulatory. Commission Page 4 April 24-1992 Based on the circumstances surrounding this event and its limited safety significance, TVA maintains that-escalated enforcement is not warranted.
This-position is-consistent with past hPC staff enforcement precedent regarding blockage of lower ice condenser inlet doors.
In addition, because the root cause of this unexpected phenomenon was based on activities occurring many years ago and its discovery was a direct result of proactive TVA employee actions.TVA respectfully requests that the NRC staff consider the application of enforcement discretion as provided by the Enforcement Policy.
In this regard, TVA believes that the elements associated with discretion, as set forth it ection VII.B(2) of 10 CFR Part 2, Appendix C, are satisfied, i.e.,
(1) the event was identified by TVA;-(2) it was not associated with previous corrective actions from events within the past two years; (3) associated corrective action was o
conservative. prompt, and extensive; and (4) it was not willful.
If the NRC staff has_any questions regarding the information contained-in this letter, TVA requests that these-questions be directed to M. A. Cooper at-(615)-843-8622, in advance of the scheduled May 1, 1992, meeting. TVA will be prepared to respond to the staff's questions at that-time.
Sincerely, 3 A L. Wilson cc (Enclosures):
Mr. D. E. LaBarge, Project' Manager U.S. Nuclear Regulatory Commission One White Flint,' North 11555 Rockville Pike Rockville, Maryland 20852' NRC Resident Inspector Sequoyah Nuclear. Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379.
-Mr. 3. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323