ML20062E590

Discusses Possible Dangers of LOCA in Containment Purging During Normal Plant Oper.Requests Either Commitment to Limit Purging or Justification for Continuing.W/Encl ANO: 7812080207

ML20062E590
Person / Time
Site:	Hatch
Issue date:	11/29/1978
From:	Ippolito T Office of Nuclear Reactor Regulation
To:	Whitmer C GEORGIA POWER CO.
References
TAC-42603, TAC-42604, TAC-51984, TAC-51985, NUDOCS 7812110035
Download: ML20062E590 (8)

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'p. " ' gfg NUCLEAR REGULATORY COMMISSION g ff g WASHINGTON, D. C. 20556 s ff '

%-*...* 't November 29, 1978 i ,

Docket Nos. 50-321 ,

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Mr. Charles F. Whitmer Vice President - Engineering Georgia Power Company C -P. O. Box 4545 i Atlanta, Georgia 30302

Dear Mr. Whitmer:

RE: CONTAINMENT PURGING DURING NORMAL PLANT OPERATION A number of events have occurred over the past several years which directly relate to the practice of containment purging during normal plant operation. During recent months, two specific events have occurred which have raised several questions relative to potential failures of automatic isolation of the large diameter purge pene-trations which are used during power operation. On July 26, 1978, the Northeast Nuclear Energy Company reported to the NRC such an event at Millstone Unit No. 2, a pressurized water reactor located f- in New London County, Connecticut. On September 8,19/8, the Public

( Service Electric and Gas Company reported a similar event at Salem Unit No.1, a pressurized water reactor located in Salem County, New Jersey.

During a review of operating procedures on July 25, 1978, the licensee discovered that since May 1, 1978, intermittent containment purge operations had been conducted at Millstone Unit No. 2 with the safety actuation isolation signals to both inlet and outlet redundant containment isolation valves (48 inch butterfly valves) in the purge inlet and outlet penetrations manually overridden and inoperable.

The isolation signals which are required to automatically close the purge valves for containment integrity were manually overridden to allow purging of containment with a high radiation signal present.

The manual override circuitry designed by the plant's architect / engineer defeated the high radiation signal and all other isolation signals to these valves. To manually override a safety actuation signal, the operator cycles the valve control switch to the closed position and then to the open position. This action energized a relay which blocked the safety signal and allowed manual operation independent of any safety actuation signal. This circutry was designed to permit reopening these valves after an accident to allow manual operation of certain safety equipment.

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,...- _ , ~ . . _ . . . . ....s.. . m w - m _ , _ _ s. m _ _ l we On September 8,1978, the staff was advised that, as a matter of routine, Salem Unit No. I has been venting the containment through ,

the containment ventilation system valves to reduce pressure.

In certain instances this venting has occurred with the containment high particulate radiation monitor isolation signal to the purge  !

and pressure-vacuum relief valves overridden. Override of the  !

containment isolation signal was accomplished by resetting the j train A and B reset buttons. Under these circumstances, six valves I

( in the containment vent and purge systems could be opened with j a high particulate isolation signal present. This override was performed af ter verifying that the actual containment particulate levels were acceptable for venting. The licensee, after further investigation of this practice, determined that the reset of the particulate alarm also bypasses the containment isolation signal to the purge valves and that the purge valves would not have auto-matically closed in the event of an emergency core cooling system (ECCS) safety injection signal.

These events and information gained from recent licensing actions have raised several concerns relative to potential failures affecting the purge penetration valves which could lead to a degradation in containment integrity and, for PWR's, a degradation in ECCS performance. Should a loss-of-coolant accident (LOCA) occur during purging there could be insufficient containment backpressure to assure proper operation of the ECCS. As the practice of containment k, purging during normal operation has become more prevalent in recent years, we have required that applicants for construction permits or operating licenses provide test results or analyses to demonstrate the capability of the purge isolation valves to close against the dynamic forces of a design basis LOCA. Some licensees have Technical Specifications which prohibit purging during plant operation pending demonstration of isolation valve operability.

In light of the above, we request that you provide within 30 days of receipt of this letter your commitment to cease all containment  ;

purge during operation (hot shutdown, hot standby, startup and ,

power operation) or a justification for continuing purging at your j facilities. Specifically, provide the following information:

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(1) Propose an amendment to the plant Technical Specifications ,

based upon the enclosed model Technical Specification, or j (2) If you plan to justify limited purging, you must propose a Technical Specification change limiting purging during operation to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year as described in the enclosed Standard Review Plan Section 6.2.4, Revision 1. Your justification must include a demonstration (by test or by test and analysis (s ', similar to that required by Standard Review Plan 3.9.3) of the ability of the containment isolation valves to close under postulated design basis accident conditions. Within thirty days of receipt of this letter, you are requested to provide a schedule for completion of your evaluation justifying continuation of limited purging during power operation.

(3) If you plan to justify unlimited purgir.; you need not propose a Technical Specification change at this time. You must, however, provide the basis for purging and a schedule for responding to the issues relating to purging during normal operation as described in the enclosed Standard Review Plan Sesion 6.2.4, Revision 1, and the associated Branch Technical Sosition CSB 6-4. As discussed in these documents, purging auring normal operation may be permitted if the purge isolation valves are capable of closing against the dynamic forces of a design basis loss-of-coolant accident. Also, basis for

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unlimited purging must include an evaluation of the impact of purging during operation on ECCS perfomance, an evaluation of the radiological consequences of any design basis accident requiring containment isolation occurring during purge operations, and an evaluation of containment purge and isolation instrumentation and control circuit designs. Within thirty days of receipt of this letter, you are requested to provide a schedule for completion of your evaluation justifying continuation of unlimited purging during power operation.

Pending completion of the NRC staff review of the justification for continued purging in (2) or (3) above, you should commit to either cease purging or limit purging to an absolute minimum, not to exceed 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year.

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i The staff believes that both the Millstone and Salem events resulted from lack of proper management control, procedural inadequacies, and possible design deficiencies. While the containment atmosphere was properly sampled and the purging (venting) discharges at both facilities were within regulatory requirements, the existing plant operating procedures approved by the licensee's management did not adequately address the operability of the purge valves and the need for strict limitations on (or prohibition of) overriding a safety actuation closure signal. The requirements for valve

(- operability were not discussed and the related Technical Specifi-cations were not referenced in the procedures. Design deficiencies probably contributed to the events as the safety actuation bypass condition is not annunciated nor is a direct manual reset of the safety actuation signal available. Consequently, we have developed the position specified below to assure that the design and use of all override circuitry in your plant is such that your plant will have the protection needed during postulated accident conditions.

Whether or not you plan to justify purging, you should review the design of all safety actuation .<ignal circuits which incorporate a manual override feature t Ms.re that overriding of one safety actuation signal does not al;s v3use the bypass of any other safety actuation signal, that sufficient physical features are provided to facilitate avequate administrative controls, and that the use of each such manual override is annunciated at the system

([ level for every system impacted. Within thirty days of receipt of this letter, you are requested to provide (1) the results of your review of override circuitry and (2) a schedule for the development of any design or procedural changes imposed or planned to assure correction of any non-conforming circuits. Until you have reviewed circuitry to the extent necessary to verify that operation of a bypass will affect no safety functions other than those analyzed and discussed on your dockets, do not bypass that signal. Our Office of Inspection and Enforcebent will verify that l

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Mr. Charles F. Whitmer .

you have inaugurated administrative controls to prevent improper manual defeat of safety actuation signals as a part of its regular ,

inspection program.  ;

i Sincerely,  ! ,

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Thomas h olito, Chief

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. Operating Reactors Branch #3 Division of Operating Reactors i Enclosures.

1. Model Technical Specification

2. Standard Review Plan

3. Branch Technical Position CSB 6-4 cc w/ enclosures:

See next page

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Georgia Power Company Oglethorpe Electric Membership Corporation  !

itunicipal Electric Association of Georgia '

City of Dalton, Georgia cc: G. F. Trowbridge, Esquire Shaw, Pittnan, Potts and Trowbridge 1600 M Street, N. W. i Washington, D. C. 20036

' (3 Ruble A. Thomas b-' Vice President j P. O. Box 2625 j Southern Services, Inc.

Bi rninghan, Alabama 35202 Mr. Harry itajors Southern Services, Inc.

300 Office Park Birminghan, Alabama 35202 Mr. C. T. Moore Georgia Power Company Power Generation Department P. O. Box 4545 Atl anta, Georgia 30302 C

s_ Mr. L. T. Gucwa Georgia Power Company Engineering Department P. O. Box 4545 Atlanta, Georgia 30302 Appling County Public Library Parker Street l Baxley Georgia 31413 '

l Mr. R. F. Rogers U. S. Nuclear Regulatory Commission I P. O. Box 710 Baxley, Georgia 31513 '

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/ 'o, y , g U.S. NUCL*.AR REGULATORY COMMISSION i  ! STANDARD REVIEW PLAN OFFICE OF NUCLEAR REACTOR REGULATION SECTION 6.2.4 CONTAINMENT ISOLATION SYSTEM oEVIEW RESPONSIBILITIES Primary - Containment Systems Branch (CS8) 1 Secondary - Accioent Analysis Branch (AAS)

Instrumentation and Control Systen Branch (ICSB) l Mechanical Engineeri a Branen (MEB)

Structural Engineering Branch (SEB)

Reactor Systees Branch (RSB)

Power Systems Branch (PSB)

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1. AREAS OF REVIEW The design objective of the containment isolation system is to allow the norsal or emer- t gency passage of fluids through the containment boundary while preserving the ability of the boundary to prevent or limit the escape of fission products that say result from postulated accidents. This SRP section, therefore, is concerned with the isolation of fluid systees wnich penetrate the containment boundary, including the design and testing requirements for isolation barriers and actuators. Isolation barriers include valves, closed piping systems, and blind flanges.

The CSB reviews the inforination presented in the applicant's safety analysis report (SAR) regarding containment isolation provisions to assure conformance with the requirements of General Design Criteria 54, 55, 56 and 57. The CSB review covers the following aspects of containment isolation:

1 1 The design of containment isolation provisions, includiig:

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a. The number and location of isolation valves, i.e., the isolation valve arrange-ments and the physical location of isolation valves with respect to the containment.

b. The actuation and control features' for isolation valves.

c. The positions of isolation valves for normal plant operating conditions (includ-ing shutdown), post-accident conditions, and in the event of valve operator power failures.

d. The valve actuation signals.

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e. The besis for selection of closure times of tsolation valves.

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connect directly to the contairment atrosphere should be provided with isolation valves as follows:

a. i One locked closed isolation valveE nside and one locked closed isolation ,

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valve outside containment; or

b. One automatic isolation valve inside and one locked closed isolation valve out-side containment; or

c. Onelockedclosedisolationvalveinsideandoneautomaticisolationvalve$

outside containment; or

d. One automatic isolation valve inside and one automatic isolation valveE#

outside containment.

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2. General Design Criterion 57 requires that lines that penetrate the primary contain-ment boundary and are neither part of the reactor coolant pressure boundary nor connected directly to the containment atmosphere should be provided with at least one locked closed, remote-manual, or automatic isolation valve $ outside containment.

3. The general design criteria permit containment isolation provisions for lines pene-trating the primary containment boundary that differ from the explicit requirements of General Design Criteria 55 and 56 if the basis for acceptability is defined.

Following are guidelines for acceptable alternate containment isolation provisions for certain classes of lines:

a. Regulatory Guide 1.11 describes acceptable containment isolation provisions for instrument lines. In addition, instrument lines that are closed both inside and outside containment, are designed to withstand the pressure and temperature conditions following a loss-of-coolant accident, and are designed to withstand dynamic effects, are acceptable without isolation valves,

b. Containment isolation provisions for lines in engineered safety features or engineered safety feature-related systems may include remote-manual valves, but provisions should be made to detect possible leakage from these lines outside containment.  ;

c. Containment isolation provisions for lines in systems needed for safe shutdown of the plant (e.g. ,11guld poison system, reactor core isolation cooling system, and isolation condenser system) may include remote-manual valves, but provision should be made to detect possible leakage from these lines outside containment.

J/ Locked closeo isolation valves are defined as sealed closed barriers (see item II.3 f). ,

1/A simple check valve is not nomally an acceptacle automatic isolation valve for this application.

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4. Isolation valves outside containment should be located as close to the containment i as practical, as required by General Design Criteria 55, 56, and 57.

5. The position of an isolation valve for normal and shutdown plant operating conditions and post-accident conditions depends on the fluid system funiction. If a fluid Systes does not have a post-accident function, the isolation alves in the lines should oe automatically closed. For engineered safety feature or engineered safety feature related systems, isolation valves in the lines may remain open or be opened.

The position of an isolation valve in the event of power failure to the valve operator should be the " safe" position. Normally this position would be the post-accident valve position. All power-operated isolation valves should have position indication in the main control room.

6. There should be diversity in the parameters sensed for the irdtiation of containment

(_ isolation.

7. System lines which provide vi open path from the containment to the environs should be equipped with radiation monitors that are capable of isolating these lines upon a high radiation signal. A high radiation signal should not be considered one of the diverse containment isolation parameters.

8. Containment isolation valve closure times should be selected to assure rapid isola-tion of the containment following postulated accidents. The valve closure time is the time it takes for a power operated valve to be in the fully closed position after the actuator power has reached the operator assembly; it does not include the time to reach actuation signal satpoints or instrument delay times, which should be considered in determining the overall time to close a valve. System design capa-bilities shuuld be considered in establishing valve closure times. For lines which provide an open path from the containment to the environs; e.g., the containment purge and went lines, isolation valve closure times on the order of 5 seconds or less may be necessary. The closura tires of these valves should be established on the basis if minimizing the release of containment atmosphere to the environs, to i mitigate the offsite radiological consequences, and assure that emergency core cooling system (ECCS) effectiveness is not degraded by a reduction in the containment backpressure. Analyses of the radiological consequences and the effect on the containment backpressure due to the release of containment atmosphere should be provided to justify the selected valve closure time. Additional guidance on the design and use of containment purge systems which may be used during the normal plant operating modes (i.e., startup, power operation, hot standby and hot shutdown) is provided in Branch Technical Position CSB 6-4 (Ref. 9). For plants under review for operating licenses or plants for wnich the Safety Evaluation Report for construc-tion permit application was issued prior to July 1, 1975, the methods described in Section B. Items B.l., a, b, d, e, f, and g B.2 througn B.4, and B.S.b, c, and d of Branch Technical Position 6-4 should be implemented. For these plants, BTP Items B.I.c and B.S.a. regarding the size of the purge system used during normal plant operation and the justificatrion by acceptable dose consecuence analysis, may be 6.2.4-5 Rev. 1 1

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11. The design of the containment isolation system is acceptable if provisions are made to allow the operator in the main control room to know wnen to isolate fluid systems that are equioped with remote manual isolation valves. Such provisions may include instruments to measure flow rate, sump water level, temperature, pressure, and radiation level.

12. Provisions should be made in the oesign of the containment isolation system for l operability testing of the containment isolation valves and leakage rate testing of the isolation barriers. The isolation valve testing program should be consistent with that proposed for otner engineered safety features. The acceptance criteria for the leakage rate testing program for contairsent isolation barriers are presented in SRP section 6.2.6.

For those areas of review identified in subsection 1 of this SRP section as being the responsibility of other branches, the acceptance criteria and their methods of application are contained in the SRP sections corresponding to those branches.

III. REVIEW PROCEDURES The procedures described below provioe guidance on review of the containment isolation system. The reviewer selects and emphasizes material from the review procedures as may be appropriate for a particular case. Portions of the review may be done on a generic basis for aspects of containment isolation common to a class of containments, or by adopting the iesults of previous reviews of plants with essentially the same containment isolation provisions.

Upon request from the primary reviewer, the secondary review branches will provide input for the areas of review stated in subsection 1. The primary reviewer obtains and uses such input as required to assure that this review procedure is complete.

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The CSB determines the acceptability of the containment isolation system by comparing +.he system oesign criteria to the design requirements for an engineered safety feature. The quality standards and the seismic design classification of the containment isolation pro-visions, including the piping penetrating the containment, are compared to Regulatory Guides 1.26 and 1.29, respectively.

The CSB also ascertains that no single fault can prevent isolation of the containment.

This is accomplished by reviewing the containment isolation provisions for each line penetrating the containment to determine that tw isolation barriers in series are provided, and in conjunction with the PSB by reviewing the power sources to the valve operators. l The CSB reviews the information in the SAR justifying containment isolation provisions which differ from the explicit requirements of General Design Criteria 55, 56 and 57.

The CSB judges the acceptability of these containment isolation provisions based on a comparison with the acceptance criteria given in subsection II. ]

6.2.4-7 Rev. 1 r%

l Systems having a post-accident safety function say have remote-manual isolation valves in the lines penetrating the containment. The CSB reviews the provisions made to detect leakage from these lines outside containment and to allow the operator in the main control room to isolate the system train should leakage occur. Leakage detection provisions may include instrumentation for measuring system flow rates, or the pressure, temperature, radiation, or water level in areas outside the containment such as valve rooms or engi-neered safeguards areas. The CSB bases its acceptance of the leakage detection provisions described in the SAR on the capability to detect leakage and identify the lines that should he isolated.

The CSB determines that the containment isolation provisions are designed to allow the l

isolation barriers to be individually leak testad. This information should be tabulated j in the safety analysis report to facilitate the CSB review. l l

The CSB determines from the descriptive information in the SAR that provisions have been j made in the design of the containment isolation systes to allow periodic operability ,

testing of the power-operated isolation valves and the containment isolation system. At the operating license stage of review, the CSB determines that the content and intent of proposed technical specifications pertaining to, operability and leak testing of contain-ment isolation equipment is in agreement with requirements developed by the staff.

IV. EVALUATION FINDINGS The information provided and the CSB review should support concluding statements similar to the following, to be included in the staff's safety evaluation report:

"The scope of review of the containment isolation system for the (plant name) has included schematic drawings and descriptive information for the isolation provisions for fluid systems which penetrate the containment boundary. The review has also included the applicant's proposed design bases for the containment isolation provi-sions, and analyses of the functional capability of the containment isolation systee.

"The basis for the staff's acceptance has been the conformance of the containment isolation provisions to the Commission's regulations as set forth in the General Design Criteria, and to applicable regulatory guides, staff technical positions, and industry codes and standards. (Special problems or exceptions that the staff takes to specific containment isolation provisions or the functional capability of .he containment isolation system should be discussed.)

"The staff concludes that the containment isolation systes design conforms to all applicable regulations, guides, staff positions, and industry codes and standards, and is acceptable."

V. REFERENCES

1. 10 CFR Part 50, Appendix A, General Design Criterion 54, " Piping Systems Penetrating Containment."

6.2.4-9 Rev. I

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CO*f7AIMMENT P'JRGING DURING NORMAL PLAHT OP! RATIONS A. BACKGROUND This branch technical position pertai9s to system lines which can provide an open uth from the containment to the environs during (olantoperation;e.g.,thepuqtand vent lines of the containment purge systesi. gret the position take g in 3RP It supplements 1

section 6.2.4.

While the containment purge systes provides plant operational flexibility, its' design

must consider the importance of minimizing the release of containment ateosphem to tne E, environs following a postulated loss-of-coolant accident. Therefore, plant designs must i not rely on its uso on a routine basis.

. 1 The need for purging has not always been anticipated in tne design of plant /;, and there-fore, design criteria for the containment purge system have not been fully developed.

The purging ext,erience at operating plants varies considerably from plant to plant. Sont plants do not purge duriqq reactor operation, some purge intermittently fer 58. ort periods and some purge continuoualy. g The containment purge system has been used in a variety of ways, for example, to alleviate certain operational prcblems, such as excess air leakage into the containment from pneumatic l controllers, for reducing the airborne actWity within the containment to facilitate personnel access during reactor power ooJration, and for controlling the containment pressure, temperature and relative hinidity. However, the purge and vent lines provide C an open path from the containment to the environs. Should a LOCA occur during containment purging when the reactor is at power, the calculated accident doses should be witnin 10 CFR 100 guideline values.

The sizing of the purge and vent lines in most plants has been based on the need to control the containment atmosphere during M fueling operations. This need has resulted in very large lines penetwating the containment (about 42 inches in diameter). Since these lines are normally the only ones provided that will permit some degree of control ,

over the containment atmosphere to facilitate personnel access, some plants have used them for containment purging during normal plant operation. Under such conditions, calculated accident doses could be sigaificant. Therefore, the use of these large contain-ment purge and vent lines should be restricted to cold shutdown conditions and refueling I operations.

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6.2.4-11 Rev. 1 l

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d. The Containment isolation provisions for the purge system lines should meet the standards apprcpriate to engineered safety features; i.e. , quality, redundancy, testability and other appropriate criteria.

e. Instrumentation and control systans provioed to isolate the p;rge system lines should be independent and actuated Dy diverse parameters; e.g., containment pressure, safety injection actuation, and containment radiation level, if energy is required to close the valves, at least two diverse sources of energy shall be  !

provided, either of which can affect the isolation function.

f. Purge system isolation valve closure times, including instrumentation delays, should not exceed five seconds.

g. Provisions should be made to ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam.

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2. The purge system should not be relied on for temperature and humidity control within the containment.

3. Provisions should be made to einimize the need for purging of the containment by providing containment atmosphere cleanup systems within the containment.

4. Provisions should be made for testing the availability of the isolatten function and the leakage rate of the isolation valves, individually, during reactor operation.

5. The following analyses should be performed to justify the containment pu ge system design:

C a. An analysis of the radiological consequences of a loss-of-coolant accident.

The analysis should be done for a spectrum of break sizes, and the instrumenta-tion and setpoints that will actuate the vent and purge valves closed should be identified. The source term used in the radiological calculations should be based on a calculation under the terms of Appendix K to detemine the extent of fuel failure and the concomitant release of fission products, and the fission product activity in the primary coolant. A pre-existing iodine spike should be considered in detemining primary coolant activity. The volume of containment in which fission products are mixed should be justified, and the fission products from the above sources should be assumed to be released through the open purge valves during the maximum interval required for valve closure. The radiological consequences should be within 10 CFR 100 guideline values,

b. An analysis which demonstrates the acceptability of the provisions made to protect structures and safety-related equipment; e.g., fans, filters and duct-work, located beyond the purge system isolation valves against loss of function from the environment created by the escaping air and steam.

6.2.4-13 Rev. 1 i

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CONTAINMENT SYSTEMS CONTAINMENT VENTILATION SYSTEM (OPTIONAL *)

LIMITING CONDITION FOR OPERATION 3.6.1.8 The containment purge supply and exhaust isolation valves shall be closed.

APPLICABILITY: MODES .1, 2, 3, and 4. l' ACTION:

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 follow-ing 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

SUR/EILLANCE REQUIREMENTS

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4.6.1.8 The containment purge supply and exhaust isolation valves shall be detennined closed at least once per 31 days.

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CONTAINMENT SYSTEMS i

i BASES 3/4.6.1.8 CONTAINMENT VENTILATION SYSTEM The containment purge supply and exhaust isolation valves are required to be closed during plant operation since these valves have not been demonstrated capable of closing during a (LOCA or steam line break accident). Maintainirig these valves closed during plant operations ensures that excessive quantities of radioactive materials will not be

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