ML20072A955
| ML20072A955 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 01/20/1983 |
| From: | Hurford W CAROLINA POWER & LIGHT CO. |
| To: | Vassallo D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8301250080 | |
| Download: ML20072A955 (9) | |
Text
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Cp&L Carolina Power & Llejht Company M to 1983 Of fice of Nuclear Reactor Regulation ATTT.:
Mr. D. B. Vassallo, Chief Operating Reactors Branch No. 2 United States Nuclear Regulatory Commission Washington, DC 20555 BRUNSWICK STEAM ELECTRIC PLANT, UNIT NOS.1 AND 2 DOCKET NOS. 50-325 AND 50-324 LICENSE NOS. DPR-71 AND DPR-62 CONTAINMENT PURGING AND VENTING RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION
Dear Mr. Vassallo:
In a letter dated December 15, 1981 f rom Mr. T. A. Ippolito, Carolina Power & Light Company (CP&L) was provided with the status of the NRC long-term review of the containment purge and vent issue for the Brunswick Steam Electric Plant, Unit Nos. I and 2.
The letter also requested additional inforr.ation concerning this issue for five items:
1.
Conformance to Standard Review Plan Section 6.2.4, Revision 1, and Branch Technical Position CSB 6-4, Revision 1.
2.
Valve operability.
3.
Safety actuation signal ovarride.
4.
Containment leakage due to seal deterioration.
5.
Containment isolation pressure setpoint.
In response to the December 15, 1981 request, you will find enclosed CP&L's responses concerning the above five items.
Please note that the response for item 2, valve operability, supersedes the information provided in our November 17, 1981 submittal and addresses the discrepancies discussed in our February 22, 1982 letter.
We will continue to observe the provisions of the NRC's interim position while we are awaiting your concurrence to remove the travel.
limitations on the containment purge and vent valves, and to re-energize those valves that were de-energized due to their inaccessibility for the travel limitation modification.
Please advise us of your concurrence so that CP&L may return all containment purge and vent valves to full operability.
8301250000 830120' ~ ~~
PDR ADOCK 05000324 P
PDR_.
411 Fayettevine Street
- P. O. Box 1551
- Raleigh, N. C. 27G02 p
Mr. D. B. Vassallo Should you have any questions concerning this submittal, please contact our staff.
Yours very tr ly, W.
Hurford l
Manager i
Technical Services WRM/kjr (5967C11T5)
Enclosure i
cc:
Mr. D. O. Myers (NRC-BSEP)
Mr. J. P. O'Reilly (NRC-RII)
Mr. S. D. Mac Kay (NRC)
I
ENCLOSURE RESPONSE TO NRC CONCERNS ON CONTAINMENT PURGING AND VENTING Item 1 - Conformance to Standard Review Plan Section 6.2.4, Revision 1, and Branch Technical Position CSB 6-4, Revision 1 A.
Debris Screens Carolina Power & Light Company (CP&L) agrees to install debris screens on the purge supply and exhaust penetrations for the Brunswick Steam Electric Plant (BSEP) to assure that debris will not prevent the valves from closing.
These screens will be installed on the open end of the penetration in order to prevent materials from entering the system piping, and will be seismically designed.
They will be installed by the end of the next extended outage on each unit (i.e., refueling is presently scheduled for 1984 for Unit No. I and extended maintenance is scheduled for Fall 1983 for Unit No. 2), unless material delivery and outage schedules permit earlier installation.
B.
Protection of Standby Cas Treatment We have evaluated the proposed addition of a Technical Specification that would require the Standby Gas Treatment System to be aligned via the 1/2-inch SGT-V8 and SGT-V9 valves, and have determined that the addition is inappropriate.
This determination is based on the three reasons described below.
Testing was performed while inerting to determine the feasibility of using these valves as described in the proposed Technical Specification. The tests revealed that these valves could not reasonably maintain the flow required for control of oxygen conc entrations.
In addition, a significant increase in the primary containment pressure resulted during nitrogen addition due to the backpressure created.
This increase would greatly l
increase the possibility of a reactor scram during operation due to high drywell pressure since there would be a reduction in the margin between normal operating containment pressure and the scram setpoint during the time when nitrogen was being added.
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In practice, reduced flow greatly lengthens the time these valves I
would have to be open, thus increasing the probability that a LOCA could occur while these valves are open.
1 Secondly, Technical Specifications at BSEP do not specify system j
valve lineups as recommended by the proposed Technical i
Specification, but rather specify operability and surveillance requirements for each system.
The valve lineup required for any l
particular operational mode of a system is provided in the operating procedure for that specific system.
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Thirdly, a calculation of the probability of unacceptable releases (greater than 10CFR100 guidelines) resulting from a f ailure of the SBGT System during a LOCA yielded a value of 1.2 x 10-8 This probability is the product of:
10-4, the probability of a LOCA (f rom WASH-1400) 8 x 10-2, the probability of venting (for Brunswick 1 and 2) 1.5 x 10-3, the probability of Regulatory Guide 1.3 source terms (from WASH-1400)
Since this probability is less than the threshold probability of 1 x 10-7 for design basis events (per Appendix A of NEDO 2434),
i this event f requency is beyond the range of events which need to be taken into account in the design and operation of nuclear f acilities.
4 In addition, the planned installation of a nitrogen pumpback system will significantly reduce the frequency of venting in the future.
This installation will further reduce the already acceptable probability.
We, therefore, conclude that the Technical Specification proposed for the protection of the SBGT System is not warranted or justified.
We are willing to pursue the feasibility of using intermediate size valves during venting in lieu of the large CAC valves, but need your concurrence to return the 4-inch diameter valves CAC-V49 and CAC-V50 to service. They have been kept closed since December 1979 as a result of NRC's interim position.
Since this action, an analysis has been performed which demonstrated their closing capability during a LOCA.
(Their inaccessibility during operation had prevented limiting their s troke).
Your concurrence in returning them to normal j
service based on the acceptable analysis and their small size is i
requested.
Item 2 - Valve Operability The operability analysis for the BSEP containment purge and vent valves that was submitted by our November 17, 1981 letter was in error in that a design differential pressure of 62 psia (47.3 psig) was used instead of 62 psig.
The seismic analysis for the valves was not affected.
The valves were reanalyzed using a differential pressure of 62 psig, and the results are listed in Table 1 (this table supersedes page 4 of Attachment 1 to our November 17, 1981 letter). With the exception of Item 7, the results demonstrate the ability of the valves to operate against the design differential pressure of 62 psig.
The analysis showed that Item 7 (one per unit) was capable oof operating
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I against a differential pressure of 55 psig, which is 11 percent above the calculated peak pressure of 49.4 psig.
We, therefore, conclude that all the containment purge and vent valves are capable of operation under all operating and accident conditions.
Item 3 - Safety Actuation Signal Override Our letter responding to your August 26, 1981 letter on safety actuation signal override was submitted to Mr. T. A.
Ippolito on December 16, 1981.
1 Item 4 - Containment Leakage Due to Seal Deterioration 1
During the recent 1982 outages, an extensive investigation into the existing condition of the CAC purge and vent system was undertaken in i
an attempt to further increase the overall reliability of the valves.
During this investigation, problems were found that accounted for the poor performance of these valves.
The reasons for these problem areas were determined and the problems corrected.
These areas included:
A.
Insufficient detail in the maintenance instruction (MI) for the installation of the valve seel rings allowed the seal rings to be installed backwards in several valves. This in turn contributed to the rapid deterioration of the seal ring. The MI was revised to provide sufficient detail to install the seal rings l
correctly. All seal rings were subsequently installed correctly.
l B.
Insufficient detail in the MI for the setting of the closed stop l
adjustment bolts allowed the bolts to be set improperly in i
several valves.
Some valves, therefore, did not close completely.
The MI was revised to provide sufficient detail to l
set the adjustment bolts, and all bolts were readjusted properly.
I C.
Inadequate machining tolerances on some of the actuator mounting brackets allowed the bracket and actuator to shif t (rotate) slightly.
This in turn changed the stroke on the valve and, in some cases, kept the valve f rom closing fully. The MI was revised to ensure that the valve fully closes regardless of the actuator bracket tolerances. All valves requiring adju 'tment were corrected.
D.
Corrosion of the carbon steel bodies of the isolation valves ~ on the CAC torus suction and discharge lines allowed corrosion products to become entrapped in the valve seal ring and to degrade both the seal ring and disc.
Modifications are to be l
prepared to replace these valve bodies with stainless steel valve bodies during the next extended outage on each unit (i.e.,
refueling is presently scheduled for 1984 on Unit No. I and extended maintenance is scheduled for Fall 1983 on Unit No. 2).
Plans are also being made to coat these lines up to the isolation valves to prevent futur 2 corrosion of the piping.
f
1 E.
Corrosion of the carbon steel discs greatly increased the rate of seal ring deterioration and also valve disc degradation. The remaining carbon steel discs are to be replaced with nickel plated discs during the next extended outage on each unit (i.e.,
refueling is presently scheduled for 1984 on Unit No. I and extended maintenance is scheduled for Fall 1983 on Unit No. 2).
The above repairs and modifications, along with the more corrosion resistant Tefzel seal rings installed in 1976, will significantly improve the performance and sealing integrity of these valves. This is supported by the repeatability tests run on these valves during i
the 1982 outages. These tests consist of performing local leak rate tests af ter cycling the valves numerous. times following the postrepair local leak rate test.
These tests verified there was no degradation in valve sealing capability. The local leak rate testing currently in progress has tested half of the large CAC valves on Unit No. 1.
The leakage results are acceptable and are not significantly different f rom the previous results.
There is no apparent degradation in the valves. The results to date indicate our efforts have been successful and have resulted in a significant improvement in the reliability of the CAC valves.
We conclude, therefore, that an increase in surveillance f requency and the related Technical Specification change is not warranted.
i Item 5 - Containment Isolation Pressure Setpoint Complete.
Proposed Technical Specifications An evaluation of the sample Technical Specifications (TS) supplied in
! against the BSEP Technical Specifications was performed to determine the applicability of the suggested changes.
i Sample TS 3.6.1.7 stated that the containment purge supply and exhaust isolation valves could be opened for safety-related reasons I
or would be locked closed. The BSEP operating procedure for the CAC System specifies that these valves be closed during normal operation unless opened for inerting, purging, or venting the primary I
containment. These are actions that are necessary to safely control oxygen and nitrogen concentrations, to control drywell pressure, or to restore safe conditions for personnel entry. The s tatus of the CAC System is reviewed at each shif t turnover, and the reason for an abnormal valve lineup reviewed and explained.
Due to the control switch design and location, existing surveillance requirements, and limited accessibility of the valves, locking them closed when not j
open is dif ficult and not justified.
Existing operating procedures, t
shif t turnover practices, valve lineups, and valve position surveillances preclude the need for sample TS surveillance requirement 4.6.1.7.1.
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9 The action statements associated with sample TS 3.6.1.7 address valve operability and not valve position.
Existing BSEP TS 3.6.3 already specifies actions required in response to inoperable valves. These actions are comprehensive and more limiting. Therefore, the proposed new section is unnecessary.
Experience to date has not shown a need to replace the valve seats on a set interval as the problems have not beea the result of wear or aging of the seats.
Evaluation of local leak rate test results provides the best indication of sealing capability.
Evaluation of leakage results will be used to detect deteriorating seals and determine the need for replacement.
It is inappropriate to specify maintenance requirements in Technical Specifications (sample TS 4.6.1.7.2) since TS are intended to specify operability and surveillance requirements.
Sample TS 3.6.1.7 and 3.6.3 state that the containment isolation valves should be operable in Conditions 1, 2, 3, and 4, with the isolation times given in Table 3.6-1.
Condition 4, however, requires that the reactor he depressurized.
Under this condition, the driving force behind the severe effects of a LOCA is removed, and therefore, primary containment is not necessary or required.
Requiring these valves to be operable in cold shutdown would not allow any opportunity for performing maintenance on these valves.
The action statements in BSEP TS 3.6.3 allow eight hours instead of four hours, as allowed in the sample TS, to return an inoperable valve to operable status. This time limit has proven effective in the past for correcting minor problems, thus minimizing the need for penetration isolation. The reduction to four hours would reduce the number of problems that could be corrected without requiring penetration isolation and would, therefore, increase the number of penetrations isolated during operation (creating abnormal valve lineups).
We, therefore, believe that the existing BSEP TS requirement is adequate and reasonable.
Finally, as discussed earlier, a review of the results from local leak rate testing currently in progress on Unit No. I has shown significantly improved results with the proper installation of the nickel plated discs and Tefzel seats and proper adjustments of these valves. An increase in surveillance requirements per sample TS 4.6.3.4 is, therefore, not warranted.
Based on these reviews, the existing BSEP Technical Specifications, procedures, and practices provide adequate requirements such that no TS changes are justified.
_ Summary In summary, CP&L will complete installation of the following changes by the end of the next extended outage on each unit (i.e., refueling is presently-scheduled for 1984 on Unit No. I and extended maintenance is scheduled for 1983 on Unit tb. 2):
1.
Debris screens on the CAC purge supply and exhaust lines.
2.
Installation of stainless steel bodies on torus CAC butterfly valves.
3.
Coat torus CAC purge supply and exhaust lines inside containment to prevent corrosion.
4.
Replace remaining carbon steel valve discs with nickel plated discs.
i Earlier installation may occur should delivery and schedules permit.
In addition, the existing procedures, newly upgraded procedures, and the planned changes, along with the aforementioned evaluations provide sufficient justification for not implementing the proposed Technical Specification additions and revisions.
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TABLE 1 RATED REQUIRED ACTUAT ACTUATOR
)
TORQUE (2)
ITEM VALVE ACTUATION TOROUE 1
18"-150#
732C-SR80 8200 4342 2
20"-150#
733C-SR80 8200 5407 3
20"-150#
732C-SR80 8200 5407 I
4 8"-150#
CB520-S R80 1300 1170 5
20"-150#
732C-SR80 8200 5407 6
18"-150#
732C-S R80 8200 4342 7
24"-150#
732C-SR80 3200 8452 8
4"-150#
CB415-S R80 700 48) 9 4"-150#
CB415-SR80 800 485 (1)
Values in inch-lbs.
(2)
Torque calculated at 62 psig.
Values in inch-lbs.
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