ML20034C178
| ML20034C178 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/26/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20034C177 | List: |
| References | |
| NUDOCS 9005020139 | |
| Download: ML20034C178 (3) | |
Text
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l 863 Rf 00 UNIT ED STATES i
8' cq NUCLE AR REGULATORY COMMISSION n
,I W ASHING TON, D. C. 20555 r,
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ENCLOSURE, SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION f
REVISED COMMITMENT FOR RIGOROUSLY ANALYZED PIPING PROGRAM 1
TENNESSEE VALLEY AUTHORITY l
SEQUOYAH NUCLEAR PLANT, UNIT 1 DOCKET NO. 50-327 I
1.0 INTRODUCTION
By letter dated November 27, 1989, the Tennessee Valley Authority (TVA) pro-posed a revision to its commitment to complete all post restart modifications _.
resulting from its rigorously analyzed piping program by the end of the Cycle 4 refueling outage for each unit.
The restart modifications were completed before the restart of.each unit in 1988.
TVA proposed to defer up to 40 pipe -
support modifications for only Unit I to the Unit 1 Cycle 5 refueling outage.
An operating cycle between refueling outages is 18 months. The pipe support modifications will be completed for Unit 2 in its Cycle-4 refueling outage because Unit 2 has had an intervening refueling outage between its restart in 1988 and its Cycle 4 refueling outage scheduled to begin in October 1990..
Unit 1 is currently in the Cycle 4 refueling outage.
The rigorously analyzed piping program is discussed in.Section III.4 of the 4
TVA Sequoyah Nuclear Perfomance Plan and evaluated by the staff in Sec-tion 2.3.2 of NUREG-1232, Volume 2 dated May 18, 1988 and its supplement No. 1 dated February 3, 1989.
TVA identified that a'large number (approximately 9,000) of pipe support calculations associated with rigorously analyzed Cate-gory I piping were not retrievable.
Calculations were regenerated to support the restart of each unit. The calculations were done in accordance with TVA Design Criteria SQN-DC-V-24.2.
Supports not meeting this design criteria were l
evaluated for restart in accordance with TVA Interim Design Criteria CEB-Cl-21.89. Supports not meeting the interim criteria were modified to meet the-1 design criteria before restart.
At that time, TVA comitted to upgrade the remaining supports by the end of the Cycle 4 refueling outage for each unit.
This program was reviewed by NRC and the acceptance of the program and the interim design criteria is documented in NUREG-1232, Volume 2, and NUREG-1232, l
Volume 2, Supplement 1, 2.0 DISCUSSION Approximately 930 modifications were identified during the regeneration of the 9,000 calculations.
There were 325 modifications. required for restart, and i
the remaining modifications were deferred to the Cycle 4 refueling outages.
l Since that time, 45 modifications have been eliminated because of plant simplifications being made (i.e., upper head injection [UHI] removal and elimination of the reactor coolant loop bypass lines used for temperature measurement).
9005020139 900426 PDR ADOCK 05000327 P
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To date, all pipe support design calculations have been regenerated and are retrievable. Approximately 530 pipe supptrt modifications have been implemented to date in Units 1 and 2.
Of the remaining 354 modifications, 217 l
can only be worked during Mode 5 or refueliag outages and 137 can be worked I
during nonoutage periods.
Since the time that the commitments were mace for the pipe support calcula-tions TVA has developed an integrated outage scheduling program.
This process considers all factors relevant to sche!uling refueling outages:
NRC i
comitments, necessary plant modifications, pre' erred plant modifications, available resources, available outage periods based on electrical system requirements, and radiological and industrial safety goals.
This process is intended to maximize the utilization of available resources.
l As a result of this process, TVA has identified some constraints to meeting the pipe support commitment for Unit 1.
In particular, the number of people that can work inside containment is limited, and a number of projects are l
competing for that workspace.
The lower containment area is small and compartmentalized in an ice condenser plant.
In addition to the physical i
constraints, the number of people working in the lower containment must also be limited to properly manage the work to meet the radiological dose (as low as reasonably achievable [ALARA]) and industrial safety goals.
l TVA is proposing to defer 40 Unit 1 outage-related pipe support modifications to Unit 1 Cycle 5 (34 known modifications and 6 contingency modifications).
The proposed schedule for the remaining pipe support modifications is as follows:
Period Number to Be Worked Nonoutage (November 1989 to March 1990) 137(completed)
Unit 1 Cycle 4(Spring 1990) 81 Unit 2 Cycle 4 (Fall 1990) 102 Unit 1 Cycle 5 (Fall 1991) 34 with an additional i
6 for contingency It is TVA's intention to work more supports than are currently planned and to take advantage of opportunities that arise. On the other hand, unexpected changes in plant conditions or emergent problems on specific supports may create the need to defer additional modifications.
As a result, TVA has included a contingency of 6 additional supports in this deferral request.
3.0 EVALUATION The deferred modifications remain in compliance with Interim Design Criteria l
CEB-CI-21.89 during the interim period.
These design criteria ensure that the pipe supports with deferred modifications have sufficient capacity to resist the faulted loading condition and maintain system functionality. Adequate protection for accident mitigation and the safe shutdown earthquake is therefore ensured.
. The projected dose for the deferred modifications will be significantly lower when the work is done during the Unit 1 Cycle 5 refueling outage. The removal of the reactor coolant bypass lines is estimated to reduce the dose rate in the lower containment in the area of the steam generators and coolant loops by approximately 50 percent.
It is TVA's assessment that the proposed schedule allows resources to be allocated to the most beneficial safety and reliability improvement modifica-tions without jeopardizing plant safety.
Staff has discussed with TVA the projects to which the resources are being allocated and concurs with TVA's assessment. They include the follow 1 g:
Upper Head Injection (UHI) Removal - This plant simplification is being pursued to improve plant maintainability and to reduce radiation exposure during reactor vessel head disassembly / reassembly during refueling outages.
In addition TVA is pursuing UHI removal as part of an overall NRC-approved plan to resolve a temporary exemption to 10 CFR 50.46 and incorporate best-estimate accident analysis technology.
Resistance Temperature Device Bypass Elimination - This plant simplifica-tion is being pursued to eliminate a source of past reactor coolant leaks and to reduce radiation exposure in the lower containment for future steam generator inspection activities. This modification is being pursued in conjunction with the replacement of the reactor protection system and main control room panel human factors modifications to minimize disruptions to control room activities.
Steam Generator Work - This work involves tube inspections, sludge lancing, and tube plug replacements for Bulletin 89-01.
These activities are all part of the overall steam generator preservation program.
Post-accidentMonitoring(PAM) Instrumentation-Thelowercontainment work primarily involves conduit and cabling to achieve the required train separation for instrument channels.
This work is required to satisfy a license condition to comply with Regulatory Guide 1.97 by the restart from the Unit 2 Cycle 4 refueling outage.
4.0 CONCLUSION
Based on our review we find the TVA proposal to defer modifications of 40 pipe supports inside containment to the Unit 1 Cycle 5 refueling outage, acceptable.
Plant safety is ensured by the interim design criteria to which the supports are presently designed.
The projected doses for the deferred modifications are estimated to be lower.
In addition, the deferral would facilitate the completion of several important safety and reliability improvements which were not actively being considered when TVA made its comitments for its rigorously analyzed program.
Principal Contributor:
J. Rajan Dated: April 26, 1990 l
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