ML14192A300

Discusses Generic Concerns Re Purging & Venting of Containment Which Were Interrupted by TMI Accident.Results of Recent long-term Review Encl

ML14192A300
Person / Time
Site:	Robinson
Issue date:	12/21/1981
From:	Varga S Office of Nuclear Reactor Regulation
To:	Jackie Jones Carolina Power & Light Co
References
NUDOCS 8201200814
Download: ML14192A300 (20)

Text

DISTRIBUTION Docket

.DfC 21 0NRC PDR L PDR TERA' NSIC ORB#1 Rdg Docket No. 50-261 DEisenhut OELD 9

ECEIVED IE 3 ACRS-10 Mr. J. A. Jones DEC241981 Svarga Senior Vice President US HU runR maoissia CParrish Carolina Power and Light Company ucusanANn 7

EReeves 336 Fayetteville Street INDShum ffros Raleigh, North Carolina 27602 WPasedag s,4,,isCi.)

WRoss

Dear Mr. Jones:

Gray File In our letter of November 28, 1978, we identified the generic concerns of purging and venting of containments to all operating reactor licensees and requested your response to these concerns. Our review of your response was interrupted by the TMI accident and its demands on staff resources. Conse quently, as you know, an Interim Position on containment purging and venting was transmitted to you on October 29, 1979. You were requested to implement short-term corrective actions to remain in effect pending completion of our longer-term review of your response to our November 28, 1978 letter.

Over the past several months we and our contractors have been reviewing the responses to our November 1978 letter to close out our long-term review of this rather complex issue. The components of this review are as follows:

1. Conformance to Standard Review Plan Section 6.2.4 Revision 1 and Branch Technical Position CSB 6-4 Revision 1.

These documents were provided as enclosures to our November 1978 letter.

2. Valve Operability Although the Interim Position allowed blocking of the valves at partial-open positions, this is indeed an interim position. Ear lier we requested a program demonstrating operability of the valves in accordance with our "Guidelines for Demonstrative Operability of Purge and Vent Valves." These.Guidelines were sent to you in our letter of September 27, 1979. There is an acceptable alternative which you may wish to consider in lieu of completing the valve qualifica tion program for the large.butterfly-type valves.

This would be the installation of a fully-qualified mini-purge system with valves 8-inches or smaller to bypass t P-ar,,r.1a U-h asstem change might prove more timely I rgAs

~21e.

TEN4 stel would meet BTP CSB 6-4 item B.1 8201200814 811221 PDR ADOCK 05000261 P

-PDR-

Mr. J. A. Jones

-2

3. Safety Actuation Signal Override This involves the review of safety actuation signal circuits to en sure that overriding of one safety actuation signal does not also cause the bypass of any other safety actuation signal.

4. Containment Leakage Due to Seal Deterioration Position B.4 of the BTP CSB 6-4 requires that provisions be made to test the availability of the isolation function and the leakage rate of the isolation valves in the vent and purge lines, individually, during reactor operations. But CSB 6-4 does not explain when or how these tests are to be performed. Enclosure 1 is an amplification of Position B.4 concerning these tests.

The status of our long-term review of the above items for the H. B. Robinson Unit 2 facility is as follows:

1. Conformance to Standard Review Plan Section 6.2.4 Revision 1 and Branch Technical Position CSB 6-4 Revision 1.

In your response of January 19, 1979 to our letter of November.28, 1978?you stated that you planned to justify unlimited purging during operation of the Robinson plant. We have reviewed the information you have provided in support of your position, but we believe your plant would be inherently safer if the purge/vent valves were-opened only for safety-related reasons. The bases for our position are given in the enclosed Safety Evaluation (Enclosure 2) for use of purge/vent valves and in the restatement of the salient features of Branch Technical Position CSB 6-4 Revision 1 (Enclosure 3).

On the basis of this Safety Evaluation and subject to your satisfying the valve operability criteria (see item 2) purging will be permitted providing you take the following actions:

(1) Commit to a goal representing a limit to the use of the purge/

vent to a specified annual time that would be system commensurate with identified safety needs.

(2)

Provide debris screens for the purge/vent systems as noted in the Safety Evaluation.

2. Operability 42-inch Supply-Exhaust and 6-inch Pressure-Vacuum Valves This item is still under review. In order to complete this action we need additional information to confirm that the valve assemblies are seismically qualified. You are requested to provide this information (see Enclosure 4) within 30 days of receipt of this letter.

Mr. J. A. Jones

-3 Item II.E.4.2 Position 6 of NUREG-0737 requires that valves which do not satisfy the operability criteria must be sealed closed above 200 0F coolant temperature. Technical Specifications are provided (Enclosure 5) for your consideration to assure that any unqualified supply/exhaust and/or vaccuum/relief valves are sealed (locked) shut and verified as such every 31 days.

3. Safety Actuation Signal Override This item is still under review. We held several recent discussions between members of the NRC and CP&L staffs. We are now awaiting further information from your staff to supplement the information submitted.in your letter of October 7, 1981. Please provide the promised information within 30 days of receipt of this letter so that our review can be completed.

4. Containment Leakage Due to Seal Deterioration We request that you propose a Technical Specification change that incorporates an acceptable valve surveillance program. Also you should provide the details of your proposed test program for our information. Please provide the requested information within 6!0 days of receipt of this letter.

5. Containment Pressure Setpoint As you are aware, TMI Task Action Plan Item II.E.4.2 of NUREG-0737 includes the long term positions of the November 28, 1978 letter.

In addition Item II.E.4.2 Position 5 requires that the containment pressure setpoint be reduced to the minimum compatible with normal operating conditions. In your letter of December 31, 1980 you provided justification for retention of a setpoint of 4 psi.

We have reviewed this information and find this setpoint to be acceptable. Our Safety Evaluation is enclosed (Enclosure 5).

We have not completed our review of the Technical Specifications (3.6.4 and 4.4.5) related to valve closing time that you proposed in your letter of June 20, 1980. We request that you review existing Technical Specifications related to containment isolation valves and whenever further revision may be needed, that it be proposed within 60 days of.receipt of this letter as a supplement to your June 20, 1980 request. A model Standard Technical Specification relating to this subject is enclosed (Enclosure 7) for your guidance.

Mr. J. A. Jones

-4 The above actions, when completed, will cover all of the requirements of Item II.E.4.2 except Position 7 which is still under review.

Please contact the HRC Project Manager (Mr. W. Ross) for Robinson Unit 2 if you have any questions related to these items.

0MB clearance is not required for this letter. It involves only plant specific safety evaluations and the resulting Technical Specifications for licensee consideration. No generic reporting requirements would result from this letter.

Sincerely, original signed by:

S. A. Varga Steven A. Varga, Chief Operating Reactors Branch #1 Division of Licensing

Enclosures:

1. Purge/Vent Leakage Tests

2. Safety Evaluation for Use of Purge/Vent Valves

3. Salient Features of Branch Technical Position CSB 6-4 Revision 1

4. Questions related to Valve Qualifications

5. Model'Technical Specification for II.E.4.2 Position 6

6. Safety Evaluation for Minimum Containment Pressure Setpoint

7.

Model Standard Technical Specifications for Containment Isolation Valves cc w/enclosures:

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NRC FORM 318 (10-80) NRCM 0240 OFFICIAL RECORD COPY USGPO; 1981-335-960

Mr. J. A. Jones Carolina Power and Light Company cc: G. F. Trowbridge, Esquire Shaw, Pittman, Potts and-Trowbridge 1800 M Street, N.W.

Washington, D. C. 20036 Hartsville Memorial Library Home and Fifth Avenues Hartsville, South Carolina 29550 U. S.. Nuclear Regulatory Commission Resident Inspector's Office H. B. Robinson Steam Electric Plant Route 5, Box 266-lA Hartsville, South Carolina. 29550 Michael C. Farrar,, Chairman Atomic Safety and Licensing Appeal Board Panel U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Richard S. Salzman Atomic. Safety andLicensing.

Appeal Board Panel U. S. Nuclear-Regulatory Commission Washington,D.

D., C., 20555 Dr. W., Reed; Johnson Atomic. Safety and Licensing Appeal Board Panel U. S. Nuclear Regulatory Commission Washington, 0. C. 20555 PURGE/VENT VALVE LEAKAGE TESTS The long term resolution of Generic Issue 8-24, "Containment Purging During Normal Plant Operation," includes, in part, the implementation of Item B.4 of Branch Technical Position (BTP) CSB 6-4.

Item 8.4 specifies that provisions should be made for leakage rate testing of the (purge/vent system) isolation valves, individually, during reactor operation.

Although Item B.4 does not address the testing frequency, Appendix J to 10 CFR Part 50 specifies a maximum test interval of 2 years.

As a result of the numerous reports on-unsatisfactory performance of the resilient seats for the isolation valves in containment purge and vent lines (addressed in OIE Circular 77-11, dated September 6, 1977), Generic Issue B-20, "Containment Leakage Due to Seal Deterioration," was established to evaluate the matter and establish an appropriate testing frequency for the isolation valves. Excessive leakage past the resilient seats of isolation valves in purge/vent lines is typically caused by severe environmental con ditions and/or wear due to frequent use. Consequently, the Teakage test frequency for these valves should be keyed to the occurrence of severe environ mental conditions and the use of the valves, rather than the current require-,

ments of 10 CFR 50, Appendix J.

It is recommended that the following provision, be added to the Technical Specifications for the leak testing of purge/vent line. isolation valves:

"Leakage integrity tests, shall be performed on the. containment isolation valves with resilient material seals in (a) active purge/vent systems (i.e., those which may be operated. during plant operating Modes 1 through 4) at least once every three months and (b) passive purge systems (f.e., those which must be administratively controlled closed during reactor operating Modes 1 through 4) at least once every six months."

By way of clarification, the above proposed surveillance specification is predicated on our expectation that aplant would have a need to go to cold shutdown several times a year. To cover the possibility that this may not occur, a maximum test interval of 6 months is specified.

However, it is not our intent to require a plant to shutdown just to conduct the valve leakage integrity tests.

If licensees anticipate long duration power oper ations with infrequent shutdown, then installation of a leak test connection that is accessible from outside confainment may be appropriate. This will permit simultaneous testing of the redundant valves. It will not be possible to satisfy explicitly the guidance of Item 8.4 of BTP CSB 6-4 (which states that valves should be tested individually), but at least some testing of the valves during reactor operation will be possible.

-2 It is intended that the above proposed surveillance specification be applied to the active purge/vent lines, as well as passive purge lines:

i.e., the purge lines that are administratively controlled closed during reactor oper ating modes 1-4. The reason for including the passive purge lines is that B-20 is concerned with the potential adverse effect of seasonal weather con ditions on the integrity of the isolation valves.

Consequently, passive purge lines must also be included in the surveillance program.

The purpose of the leakage integrity tests of the isolation valves in the containment purge and vent lines is to identify excessive degradation of the resilient seats for these valves.. Therefore, they need not be conducted with the precision required for the Type C isolation valve tests in 10 CFR Part 50, Appendix J.. These tests would be performed in addition to the quantitative Type C tests required by Appendix J and would not relieve the licensee of the-responsibility to conform to the requirements of Appendix J.

In view of the wide variety of valve types and seating materials, the acceptance criteria for such tests should be developed on a plant-specific basis.

ENCLOSURE 2 SAFETY EVALUATION REPORT FOR CONTAINMENT PURGING AND VENTING DURING NORMAL OPERATION OF THE H. B. ROBINSON STEAM ELECTRIC POWER PLANT, UNIT 2 (Docket No. 50-261)

I.

INTRODUCTION A number of events have occurred over the past several years which directly relate to the practice of containment purging and venting during normal plant operation.. These events have raised concerns relative to potential failures affecting the purge penetrations which could lead to degradation in contain ment integrity, and, for PWRs,. a degradation in ECCS performance. By letter, dated November 28, 1978, the Commission (NRC) requested all licensees of op erating reactors to respond to certain generic concerns about containment purging or venting during normal plant-operation. The generic concerns were twofold:

11 Events had occurred. where Ticensees overrode or bypassed the safety actuation isolation signals to the containment isolation valves.

These. events were determined to be abnormal occurrences, and were so characterized in our report to Congress in January 1979.

(2) Recent licensing.reviews have required tests or analyses to show that containment purge or vent valve would shut without degrading containment integrity during the dynamic loads of a design basis loss of coolant accident (DBA-LOCA).

The NRC position of the November 1978 letter requested licensees to cease purging (or venting) of containment or limit purging (or venting) to an abso lute minimum. Licensees who elected to purge (or vent) the containment were

-2 requested to demonstrate that the containment purge (or vent) system design met the criteria outlined in the NRC Standard Review Plan (SRP) 6.2.4, Revi sion 1, and the associated Branch Technical Position (BTP) CSB 6-4, Revision 1.

II.

DISCUSSION AND EVALUATION The licensee for H. B. Robinson Steam Electric Plant, Unit 2 (Robinson 2), Caro lina Power and Light Company (CP&L), responded to the NRC position letter of November 1978, by stating that they planned to justify unlimited purging during power operation.

CP&L reported that plant. conditions require purging in excess of 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year-and that they are-currently developing procedures and pro grams at the plant to be consistent with the philosophy of NRC's ALARA (as low as reasonably achievable) Program.

CP&L indicated that in order to minimize per sonnel exposure during routine inspection and maintenance required inside the containment vessel,,it is essential that containment purging be performed.

Pre cise requirements depend on the size and quantity of minor leaks and other normal sources of airborne activity.

The limiting, of this purge capability would un doubtedly increase the occupational exposure at Robinson and. be inconsistent with the ALARA program. CP&L stated that during hot summer months ambient temperatures within the containment vessel approach 120*F. Under this condition, the contain ment vessel becomes habitable for only short periods of time. It is likely that extended maintenance efforts would be required during this period. In order to reduce-the potential for heat prostration, a significant occupational hazard under these con ditions, the containment purge capability is utilized to reduce the high ambient temperatures. This permits the necessary completion of maintenance/inspec tion of equipment, some of which is vital to reactor protection and safeguards.

CP&L indicated that the impact of open purge valves on ECCS performance has been evaluated. The results show that containment pressure is reduced by 0.13 psi

-3 with the purge valves open. This small decrease in containment pressure results in an increase in the peak clad temperature of 6*F (from 2188*F to 2194*F) which is within the requirement of 10 CFR Part 50, Appendix K. We find the licensee's ECCS analysis to be acceptable.

CP&L indicated that the containment vent valves (vacuum and pressure relief) are 6-inch, series-configured butterfly-type isolation valves.

CP&L believes that because of the size of these valves, sufficient mass flow of air and steam would not exist in their vicinity to create a debris problem.

In the event debris did enter the valve, the two-valve configuration with Penetration Pressurization Sys tem (PPS) air being supplied between them on closure should assure closure of the ventilation penetration line. CP&L reported that the purge air flow path to the two 42-inch series-configured, butterfly-type, containment inlet isolation valves is via a diffuser containing 6-inch openings to disperse the air evenly.

In case of a pressure buildup in containment,, this diffuser-would act as a missile barrier to prevent large debris from entering the valve ducting.

In addition, the re dundancy of the two, valves in series eight feet. apart with PPS air supplied be tween them at closure further minimizesthe probability of valve inoperability due to debris. The air to the outlet purge valves is through the HVH unit's dis charge header ducting and is protected at each inlet/outlet from this header by a diffuser-with similar openings and valve. configuration as for the purge inlet discussed above. CP&L stated that the purge and vent openings inside containment are located several feet above the floor in relatively open areas, which mini mizes the potential for debris near their openings.

CP&L concludes that although screens or other devices specifically for debris are not provided, other provi sions as discussed above are sufficient to assure isolation valve closure. Based on our review of the Ticensee's rationale, we are not able to conclude that iso lation valve closure will not be preveffed by debris which could potentially be come entrained in the escaping air and steam.

-4 We, therefore, recommend that debris screens be provided for the purge/vent systems. The debris screens should be Seismic Category I design and installed about one-pipe-diameter away from the inner side of each inboard isoaltion valve.

The piping between the debris screen and the isolation valve should also be Seis mic Category I design.

CP&L indicated that there are no provisions needed for additional protection of structures and equipment located beyond the purge system isolation valves in the ventilation ductwork path, since none of the equipment in this path is required for safe shutdown. The primary purpose of this equipment is for normal operation of containment purging, and its. sole-safety-related purpose is for containment air purging during reactor refueling operations.

We have reviewed the assump tions made in the licensee's evaluation-and find them to be acceptable.

III CONCLUSIONS We have reviewed the. Robinson-2 Purge System against the guidelines of BTP CSB.

6-4, Revision 1, "Containment. Purging During Normal Operations."

Although the licensee provided information to justify unlimited purging/venting during power operations, our view is that system use should be-limited.

The plant is in herently safer with closed purge/vent valves than with open lines which require valve action to provide containment integrity.

We, therefore, recommend that the licensee commit to limit the use of the purge/vent system to a specified annual time that is commensurate with identified safety needs.

We recommend that debris screens be provided for the purge/vent systems. The debris screens should be Seismic Category I design and installed about one-pipe diameter away from the inner side of each inboard isolation valves. The piping between the debris screen and the isolation valve should also meet Seismic Cate gory I design standards.

-5 In addition, as a result of numerous reports on the unsatisfactory performance of resilient seats in butterfly-type isolation valves due to seal deterioration, periodic leakage integrity tests of the 6-and 42-inch butterfly isolation valves in the purge system are necessary.

Therefore, the licensee should also propose a Technical Specification for testing the valves in accordance with the following testing frequency:

"The leakage integrity tests of the isolation valves in the containment purge/vent lines shall be conducted at least once every three months."

The purpose of the leakage integrity tests of the isolation valves in the con tainment purge lines is to identify excessive degradation of the resilient seats for these valves. Therefore, they need not be conducted with the pre cision required for the Type C isolation valve tests in 10 CFR Part 50, Appen dix J. These tests' would. be performed in addition to the quantitative Type C tests required by Appendix J, and would not relieve the licensee of the respon sibility to conform to the requirements of Appendix J.

Subject to successful implementation of the above recommended actions, we find the purge/vent system design and operating practices' for Robinson 2 to be ac ceptable.

ENCLOSURE 3 SALIENT FEATURES OF BRANCH TECHNICAL POSITION CSB 6-4 REVISION 1

1. Purging/venting should be minimized during reactor operation because the plant is inherentiy safer with closed purge/vent valves (containment) than with open lines which require valve action to provide containment. (Serious ctnsideration is being given to ultimately requiring that-future plants be designed such that-purging/venting is not required during operation).

2. Some purging/venting on current plants will be permitted provided that:

a) purging is needed and justified. for safety purposes, and b) valves are judged by the staff to be both operable and reliable, and c) the estimated amount of radioactivity released during the time required to close the-valve(s:) following a LOCA either

i. does not cause the total dose to exceed the 10 CFR Part 100 Guidelines; then a goal should be established which represents a limit on the annual hours of purging expected through each particular valve, or ii. causes the total dose to exceed the guideline values; then purging/venting shall be limited to 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br />s/year.

3. Purging/venting should not be permitted when valves are being used that are known to be not operable or reliable under transient or accident conditions.

ENCLOSURE 4 VALVE QUALIFICATION QUESTIONS FOR ROBINSON-2

1. Confirm that purge/vent valve assemblies are qualified against seismic loads.

2. Discuss testing and maintenance program for valves and resilent seats.

3. Discuss the capability of one valve to close properly if the other series valve (6-inch or 42-inch) fails partially open.

ENCLOSURE 5 CONTAINMENT SYSTEMS LIMITING CONDITION FOR OPERATION 3.6.1.7 The containment purge supply and exhaust isolation valves may be open for safety-related reasons [or shall be locked closed].

The containment vent line isolation valves may be open for safety-related reasons [or shall be locked closed].

APPLICABILITY:

MODES 1, 2, 3, and 4.

ACTION:

(For plants with valves closed by technical specification)

With one containment purge supply and/or one exhaust isolation valve open, close the open valve(s) within one hour or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

(For plants with valves that may be opened by technical specifications)

1. With one containment purge supply and/or o.ne exhaust isolation or vent valve inoperable, close the associated OPERABLE valve and either restore the inoperable valve to OPERABLE status, within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or lock the OPERABLE valve closed.

2.. Operation may then continue until performance of the next required valve test provided that the OPERABLE valve is-verified to be locked closed at least once per 31 days.

3. Otherwise, be in at least HOT STANDBY within the next six hours and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

4.

The provisions of Specification 3.0.4 are not applicable.

SURVEILLANCE REQUIREMENTS 4.6.1.7.1 The

-inch containment purge supply and exhaust isolation valves and the

-incEFvent line isolation valves shall be determined locked closed at least once per 31 days.

4.6.1.7.2 The valve seals of.the purge supply and exhaust isolation valves and the vent line isolation valves shall be replaced at least one per years.

3/4 6-10.

ENCLOSURE 6 Safety Evaluation Report Minimum Containment Pressure Setpoint (Item II.E.4.2(5) of NUREG-0737)

H, B. Robinson Nuclear Power Plant, Unit 2 Docket No:

50-261 1.0 Introduction As a consequence of the accident at TMI-2, implementation of a number of new requirements has been recommended for operating reactors.

These new require ments are described in NUREG-0660, "NRC Action Plan Developed as a Result of the TMI-2 Accident," May 1980, and NUREG-0737. *Clarification of TMI Action Plan Requirements," November 1980.

The NRC' staff has also requested licen sees to submit information sufficient to. permit an independent evaluation of their response to these new requirements. This report provides an evaluation of the response to Action Plan Item II.E.4.2, position 5, by the desigiated licensee.

2.0 Evaluation Our consultant, the EG&G Energy Measurements Group (a subcontractor to Lawrence Livermore National Laboratory, which has, the TMI Action Plan contract) has.

reviewed the licensee's submittals and prepared the attached technical evaluation report of the licensee's containment pressure setpoint used to isolate nonessential containment penetrations. We have reviewed this evaluation and concur in its basis and findings.

3.0 Conclusions The information submitted by the licensee provided sufficient details of the licensee's containament Isolation pressure for-the staff to conclude that the requirements of Item II.E.4.2(5) of NUREG-0737, with the additional guidelines developed by the staff, have been met.

Energy Measurements Group San Ramon Operations SRO-271 May 193 TECHNICAL EVALUATION OF THE RESPONSE TO POSITION NO.5 OF ITEM II. E. 4.2 OF NUREG-0737 CONTAINMENT ISOLATION SETPOINT FOR THE H.B. ROBINSON NUCLEAR POWER PLANT UNIT 2 (DOCKET NO. 50-261) by W., 0. Wade Approved for Puolication W. R. Ruvalcaca Department Manager This document is UNCLASSIFIED Derivativye Classifier:

-'NicnolasX. drocericK Department Manager Work Performed for Lawrence Livermore NatQn'al Lacoratory under U.S. Department of Energy Centract No. DEACOS-76 NVO 1183.

INTRODUCTION AND BACKGROUND As a consequence of the incident at TMI-2, implementation of a number of new requirements has been recommended for operating reactors.

These new requirements are described in NUREG-U660, "NRC Action Plan Uevel oped as a Result of the TMI-2 Accident," May 1980, and NUREG-0737, "Clari fication of TMI Action Plan Requirements,"

November 1980.

Tne NRC staff has also requested licensees to submit information sufficient to permit an independent evaluation of their response to these new requirements.

Tnis report provides an evaluation of the response to Action Plan Item II.E.4.2, position 5, by the designated licensee.

DESIGN BASIS OR REVIEW CRITERIA Position 5. requires that the containment pressure setpoint that initiates containment isolation for'non-essential system containment vessel penetrations be at, or reduced to,, "....tne. minimum: compatible, with normal operating conditions.."

TECHNICAL EVALUATION Response evaluation is based upon the values provided for tne following parameters:

(1) The maximum observed or expected containment pressure during normal operation..

(2) The-loop error and observed drift in tne pressure, sensing instrumentation providing the isolation signal (see note).

(3) The containment isolation pressure setpo-int.

NOTE: The clarification document (NUREG-0737) provided only the expected margin for instrument error and did not specify acceptable values for instrument drift or atmospneric changes tontributing to the total sensing loop error.

Additional staff guidance established a limit of 3.0 psi for an isolation setpoint margin over the normal containment pressure to account for total loop error.

In addition, for subatmospheric contain

ments, a 3.0 psi setpoint margin over atmospneric pressure is also considered acceptable.

In consideration of tnese.values, the isolation pressure setpoint is to be as low as practical without increasing the probaoility of inadver tent activation of the isolation signal.

CONCLUSIONS The letter of December 31, 1980, submitted by Carolina Power and Light. Company, provided sufficient information to conclude that tne con tainment isolation pressure setpoint for H. S. Robinson Nuclear Power Plant, Unit 2, (4 psi) meets the NURE 0600/0737 requirements and is within the additional limiting guidelines provided by tne NRC staff.

ENCLOSURE 7 CONTAINMENT SYSTEMS 3/4 4.6.3 CONTAINMENT ISOLATION VALVES LIMITING CONDITION FOR OPERATION 3.6.3 The containment isolation valves specified in Table 3.6-1 shall be OPERABLE with isolation times-as shown in Table 3.6-1.

APPLICABILITY: MODES 1, 2, 3 and 4.

ACTION:

With one or more of the isolation valves(s) specified in TabTe 3.6-1 inoperable, maintain at least one isolation valve OPERABLE in each affected penetration that is open and either:

a. Restore the inoper3ble valve(s) to OPERABLE status within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> or

b. Isolate each affected penetration within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> by use of at least one deactivated automatic valve secured in the isolation position, or

c. Isolate each affected penetration within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> by use of at least one closed manual valve or blind flange; or

d.

Be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

SURVEILLANCE REQUIREMENTS 4.6.3.1 The isolation valves specified in Table 3.6-1 shall be demonstrated OPERABLE prior to returning the valve to service after maintenance, repair or replacement work is performed on the valve or its.associated actuator, control or power circuit by performance of a cycling test, and verification of isola tion time.

3/4 6-14

CONTAINMENT SYSTEMS SURVEILLANCE REQUIREMENTS (Continued) 4.6.3.2 Each isolation valve specified in Table 3.6-1 shall be demonstrated OPERABLE during the COLD SHUTDOWN or REFUELING MODE at least once per 18 months by:

a. Verifying that on a Phase A containment isolation test signal, each Phase A isolation valve actuates to its isolation position.

b. Verifying that on a Phase B containment isolation test signal, each Phase 8 isolation valve actuates to its isolation position.

4.6.3.3 The isolation time of each power operated or automatic valve of Table 3.6-1 shall be determined to be within its limit when tested pursuant to Specification 4.0.5.

4.6.3.4 The containment purge and vent isolation valves shall be demonstated OPERABLE at intervals not to exceed months. Valve OPERABILITY shall be determined by verifying that when the measured leakage rate is added to the leakage rates determined pursuant to Specification 4.6.1.2.d for all other Type B and C penetration, the combined leakage rate is less than or equal to 0.60La..

However, the leakage rate for the containment purge and vent isolation valves shall be compared to the previously measured leakage rate to detect excessive valve degradation.

3/4 6-15