ML20212R272

Requests Exemption from Requirements of 10CFR50,App A,Gdc 55 for Penetrations X-43A,X-43B.X-43C & X-43D for Reactor Coolant Pump Seal Water Injection Lines.Fee Paid

ML20212R272
Person / Time
Site:	Sequoyah
Issue date:	01/23/1987
From:	Domer J TENNESSEE VALLEY AUTHORITY
To:	Youngblood B NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
NUDOCS 8702020573
Download: ML20212R272 (12)

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TENNESSEE VALLEY AUTHORITY CHATTANOOGA TENNESSEE 374o1 SN 157B Lookout Place 9~AN 23 s87 10 CFR 50.12 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Office of Nuclear Reactor Regulation Washington, D.C. 20555 Attention: Mr. B. J. Youngblood In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 SEQUOYAH NUCLEAR PLANT - CONTAINMENT ISOLATION SYSTEM - EXEMPTION FROM 10 CFR 50, APPENDIX A, GENERAL DESIGN CRITERIA 55 - REACTOR COOLANT PUMP SEAL INJECTION LINES IE Inspection, Report Numbers 50-327/86-20 and 50-328/86-20, transmitted from J. A. Olshinski to S. A. White by letter dated April 23, 1986, identified unresolved items 50-327/86-20-09 and 50-328/86-20-09, Containment Isolation Design Pertaining to the Chemical and Volume Control System. As TVA moved to close out these unresolved items, NRC requested additional information and detail concerning Sequoyah's containment isolation system design. Our letter of January 2, 1987, summarizes our understanding of the containment isolation system design issues raised by NRC, a chronology of related submittals to and meetings and telephone calls with NRC, a detailed response to containment isolation issues raised by NRC, and list of commitments to be taken by TVA to close out remaininr. open issues with NRC. This letter addresses the commitment made in the January 2, 1987 letter to request an exemption to the requirements of 10 CFR Part 50, General Design Criteria 55, for penetrations X-43A, X-43B, X-43C, and X-43D, which are for the reactor coolant pump seal water injection lines.

TVA has redesignated local manual valves in the seal injection line as containment isolation valves. The seal injection line has redundant isolation l provisions: the inboard check valves, the closed system outside containment, the water seal provided by the centrifugal chstging pumps, and the outboard local manual isolation valve. These redundant isolation provisions provide assurance that no single failure could result in release of containment atmosphere to the environment.

TVA believes that the redundant isolation provisions ensure the protection of the health and safety of the public and that this isolation design is considered acceptable under the provisions of "other defined bases" as allowed by 10 CFR 50 Appendix A General Design Criteria 55. However, NRC has indicated that, while this approach is technically acceptable for Sequoyah, it is not standard practice and that a specific exemption to General Design Criteria 55 would be required. g 3gL 8702020573 870123 l l PDR ADOCK 05000327 sq P PDR An Equal Opporturu y Employer I .{'

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0 0 U.S. Nuclear Regulatory Commission This submittal transmits a brief description of the reactor coolant pump seal injection configuration following a postulated loss of coolant accident, a brief description of the valves and piping, design features of those systems that prevent the escape of containment atmosphere, and a discussion of the applicable basis for requesting an exemption from 10 CFR 50 Appendix A General Design Criteria SS under the criteria of 10 CFR 50.12 for the seal injection system lines. We request that you review our request for exemption and advise us in writing of your determination.

Enclosed is a check for the $150 application fee required by 10 CFR 170.12 for the review of our request for exemption.

Please direct questions concerning this request to Mark J. Burzynski at 615/870-6172.

Very truly yours, TENNESSE{VALLEYAUTHORITY

. a. %

)J.A.Domer,AssistantDirector Nuclear Safety and Licensing Sworn to and subsc bed before me this ,4 5 afday of '/zA

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1987.

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' Notary Public Mr Commission Expires hO Enclosures cc (Enclosures):

U.S. Nuclear Regulatory Commission Region II Attn: Dr. J. Nelson Grace, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. Joseph Holonich Sequoyah Project Manager U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, Maryland 20814 Mr. G. G. Zech, Director Sequoyah Resident Inspector TVA Projects Sequoyah Nuclear Plant U.S. Nuclear Regulatory Commission 2600 Igou Ferry Road Region II Soddy Daisy, Tennessee 37319 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323

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ENCLOSURE SEQUOYAH NUCLEAR PLANT REQUEST FOR EXEMPTION FROM APPENDIX A GENERAL DESIGN CRITERIA 55 FOR THE SEAL INJECTION LINES BACKGROUND NRC Inspection Report Nos. 50-327/86-20 and 50-328/86-20 identified an unresolved item (URI) concerning four (4) chemical and volume control system (CVCS) containment penetrations. The penetrations involved are X-43A, -43B,

-43C, and -43D, the four reactor coolant pump (RCP) seal injection lines. The URI, identified during an Operational Readiness inspection, identifies the apparent nonconformance of the four penetrations cited to the explicit requirements of 10 CFR 50 Appendix A General Design Criteria (GDC) for containment isolation.

The four subject CVCS penetrations have been evaluated and the design of the seal injection lines, with local manual valves and a closed system designated as providing the outboard isolation barrier, is considered acceptable under the provisions of GDC 55 by employing a design found acceptable on other defined bases.

All valves now designated as containment isolation valves and all associated piping have been purchased to TVA Class B requirements. TVA Class B designation means the valves and piping are ASME Section III Class 2. Seismic Category I or equivalent. Valves and piping procurred before April 1973 are designed in accordance with ANSI standard B 16.5 and B 31.1, respectively, as opposed to Section III of the ASME Code.

All valves now designated as containment isolation valves are protected from both internal and external missiles, pipe whip, or jet impingment that may result from a postulated Loss of Coolant Accident (LOCA).

The local manual valves in the RCP seal injection lines that are now designated containment isolation valves do not have position indication in the main control room; these valves are open for normal plant operation and their closing would be recorded in the plant configuration log.

i TVA believes that the redundant isolation provisions ensure the protection of the health and safety of the public and that the isolation scheme is considered acceptable under the provisions of "other defined bases," as allowed by 10 CFR 50 Appendix A GDC 55. However, NRC has indicated that, while this approach is technically acceptable for Sequoyah, it is not standard practice and that an exemption to GDC 55 would be required. A summary of the evaluations and the basis for requesting the subject exemption from GDC 55 follows.

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SYSTEMS EVALUATIONS Reactor Coolant Pump Seal Injection Lines The provisions for containment isolation relating to the four seal injection lines consist of a check valve inside containment to provide the inboard isolation barrice and a closed seismically qualified, TVA Class B system outside containment which is continuously pressurized postaccident by the high head safety injection pumps. It is desirable for certain transients and accidents that these lines remain in service to protect the RCP seals.

Therefore, these lines are not automatically isolated by an isolation signal.

The system design provides for the following features. A second check valve, which is not missile protected, is provided in series on each line inside containment. Each line has also been provided with a locally operated manual needle valve outside containment. A single supply line feeds the four injection lines.

There are two seal water injection filters in parallel in the seal water injection supply line, as well as a filter bypass line. The valves to isolate the seal water injection filters and bypass line may be operated by reach bars extending from the concrete cubicle housing the valves. (Reference Final Safety Analysis Report (FSAR) figure 9.3.4-1 for TVA flow diagram.)

System Operating Instructions require the valve in the bypass line to be isolated during normal operation, thereby isolating the bypass line frem the supply line. Flow is passed through only one of the filters at a time, with the unused filter being isolated from the flow path by closing valves both upstream and downstream of the subject filter. When the pressure drop across the active filter exceeds 20 psid, or the radioactivity level on the filter exceeds 5 rem, the system is realigned to utilize the previously isolated filter and isolate the used filter. The valve realignment is recorded by the operators in the plant configuration log.

The initial concern of the NRC inspector regarding the design of these lines was the lack of conformance to the explicit requirements of GDC 55, i.e., no automatic isolation valve is provided outside containment. As previously stated, it is desirable to maintain injection flow to the RCPs following certain transients and accidents to protect the RCP seals. Therefore, these lines are not automatically isolated by an accident isolation signal. GDC 55 allows that certain classes of lines may employ alternate isolation schemes (from those explicitly delineated) if found acceptable on some other defined bases. TVA has previously taken credit for the closed system outside containment as providing the outboard isolation barrier. This originated from the initial design philosophy which considered a closed system alone to be an acceptable isolation barrier inside or outside containment. Following review of TVA's May 30, 1986 submittal, NRC indicated use of the closed system alone outside containment did not constitute an acceptable isolation scheme for these penetrations. The available local manual isolation valves were discussed as additional isolation provisions. NRC requested evaluation of the alternate isolation method proposed--check valve inside containment and closed system with local manual valves outside containment--be discussed in detail to ensure adequate provisions exist for isolation of these lines should the need arise postaccident.

. a Postaccident, these lines will be left in service and will be supplied by the high head safety injection pumps (centrifugal charging pumps) which also provide seal flow and normal charging flow in nonaccident conditions. .Under normal, transient, and accident conditions, at least one of the centrifugal charging pumps (CCPs) will remain in operation providing emergency core cooling system (ECCS) flow and charging flow / seal flow as required.

Therefore, a water seal will be continuously provided on the subject penetrations at a pressure greater than 1.1 Pa to preclude air leakage outside containment through these lines. The closed system piping outside containment meets the requirements for a closed system outside containment as provided in the Sequoyah Nuclear Plant (SQN) FSAR section 6.2.4 and therefore provides a reliable barrier. This piping is leak tested (visual inspection) in accordance with NUREG 0737 position III.D.l.1 and is included in the ASME Section XI inservice pressure test program for SQN. If for some unexpected reason it becomes necessary or desirable to isolate these lines postaccident, the locally operated manual valves are available. NRC requested use of these valves be evaluated, and either the needle valves or seal injection filter valves be redesignated as outboard containment isolation valves. The results of this evaluation follow.

The seal water injection filter valve (filter outlet) is the preferred method of isolation. The seal injection filter outlet valve is located in a concrete block cubicle on elevation 690, approximately 100 feet from the containment wall, and may be operated with a reach bar from outside the cubicle in the auxiliary building general spaces. This valve allows isolation of all lines quickly with a single valve operation (the alternate filter and filter bypass line are normally isolated), and would be accessible postaccident from a dose consideration. The needle valves on the individual injection lines are located in the elevation 690 pipe chase at SQN, approximately two feet from the containment (shield building) wall, in close proximity to many ECCS injection lines, CVCS lines, and the boron injection tank (BIT). For the design basis accident and when in the recirculation mode, this area would be inaccessible from a dose standpoint. Based upon these considerations, the seal injection filter outlet valves and the filter bypass valve will be redesignated as outboard containment isolation valves.

In the unlikely event that a leak should occur in the RCP seal water injection filter valve packing, drains in the floors of the cubicles are provided to duct any potential spillage to the Tritiated Drain Collector Tank, which has a capacity of 24,700 gallons. The drains are sized to accommodate a maximum leak rate of 50 gpm that would be expected from a Residual Heat Removal (RHR) pump shaft seal. Leakage due to failure of valve packing would be substantially less than the 50 gpm design value. Thus, the cubicle drains would provide for the effective removal of any leakage due to valve packing failure and not hinder access to the RCP seal injection line filter valves in the unlikely event that it should become necessary or desirable to isolate the RCP seal injection line.

The RCP seal injection line flow is provided by the CCPs. A leak in either pump room can be associated with the particular pump involved, and appropriate action taken to isolate the affected equipment. From the CCP room, the seal injection line is generally routed through pipe chases that contain a number of other pipes. Local leak detection for the lines running through a common pipe chase is not provided for by the leakage detection system at SQN.

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In the unlikely event that leakage due to a valve packing failure would occur, identification of the affected line by the leakage detection system without operator action is not possible. The operator, however, can sequentially isolate the lines passing through the common pipe chase until the affected line is found. Furthermore, any leakage resulting from valve packing failure, should it occur, would be expected to be considerably smaller than the 50 gpm design valve resulting from a postulated RHR pump shaft seal failure. Thus, it is expected that any unexpected leakage that may occur due to valve packing failure in the RCP seal injection lines can be identified and isolated before the loss of a significant amount of water.

These redundant isolation provisions--the inboard check valves, the closed system, the water seal, and the seal injection filter isolation valve--provide assurance that no single failure could result in release of containment atmosphere to the environment. Therefore, protection of the health and safety of the public is ensured and'this isolation design is considered acceptable on other defined bases as presented above.

The seal water injection filter outlet and bypass valves have been evaluated with respect to testing requirements for containment isolation barriers in' accordance with 10 CFR 50 Appendix J. SQN Emergency Operating Instructions (E0Is) call for continuous operation of the CCPs postaccident and thereby ensure a guaranteed 30-day water supply and injection pressure greater than 1.1 Pa, even with consideration of a single active failure. Thus, these valves are not subject to Type C leak testing. This seal system satisfies the provisions of Standard Review Plan (SRP) section 6.2.6.

Leakage Detection Components in Safeguards Systems With respect to piping and mechanical equipment outside the containment, considering the provisions for visual inspection and leak detection, leaks will be detected before they propagate to major proportions. A Westinghouse review of the equipment in the system indicates that the largest sudden leak potential would result from the sudden failure of an RHR or containment spray (CS) pump shaft seal. Evaluation of seal leakage assuming only the presence of a seal retention ring around the pump shaf t showed flows less than 50 gpm would result. piping leaks, valve packing leaks, or flange gasket leaks have been of a nature to build up slowly with time and are considered less severe than the pump seal failure. The Westinghouse review also noted the following:

1. The piping is classified in accordance with ANS safety Class 2 and receives the ASME Class 2 quality assurance program associated with this safety class.

2. The piping, equipment, and supports are designed to ensure no loss of function for the safe shutdown earthquake.

3. The system piping is located within a controlled area on the plant site.

4. The piping system receives periodic pressure tests and is accessible for periodic visual inspection.

5. The piping is austenitic stainless steel which, due to its ductility, can withstand severe distortion without failure.

Based on this review, design of the auxiliary building and related equipment is based upon handling of ECCS leaks up to a maximum of 50 gpm. To ensure adequate core cooling, design features are provided to prevent this limiting passive failure from causing any loss of function in the other train of the ECCS equipment due to flooding of redundant components or loss of section head to the ECCS pumps. Three independent means are available to provide information to the operator for use in identifying ECCS leakage into certain locations in the auxiliary building. These means include the auxiliary building flood detection system, the instrumentation and alarms associated with the drainage, and waste processing systems which normally handle drainage into these areas.

A flood detection system utilizing conductivity type water level detector devices is used to monitor and actuate alarms for ECCS and other leakage at locations throughout the auxiliary building. Individual detectors are located in each ECCS pump compartment, in the ECCS heat exchanger rooms, in the pipe gallery for each unit, and in the pipe chase. A common alarm in the main control room will alert the operator indicator panel, located immediately outside the control room, then identifies the exact location of the tripped detector. The detector panel is provided with a test switch which can be used to verify the availability of power to each individual detector. These flood detectors are to be tested to verify initial operability and will be periodically tested as a part of the plant instrument surveillance and maintenance program.

Since each ECCS pump heat exchanger compartment is monitored by a level detection device, the operator may immediately identify leakage into one of these rooms and determine which subsystem must be shut down and secured to terminate the leak. The operator can readily accomplish this action from the main control room by stopping the appropriate subsystem pump and by closing the corresponding sump isolation valves and individual pump discharge valves.

The time necessary for the operator to detect leakage into one of these compartments is dependent on the leakage rate. A limiting 50 gpm leak in the largest ECCS pump compartment can be detected within 30 minutes. Slower leaks will require proportionally longer detection times.

Leakage into safety injection pumps or CCP compartments, the pipe chase, or the pipe gallery (all at elevation 669) is piped through the tritiated water drain header to the tritiated drain collector tank at elevation 651. ECCS leakage into the RHR or CS pump compartments or the pipe chase (all at elevation 653) is piped to the auxiliary building floor and equipment drain sump. The floor drain in each of these areas is provided with a standpipe which ensures that the setpoint for the water level detector is reached prior to draining the leakage from the room. However, the standpipes each have two 1/8-inch drilled holes to allow minor normal leakage to drain from the room.

The floor and equipment drain sump is provided with redundant 50 gpm pumps which automatically discharge on high level to the tritiated drain collector tank. Operation of these pumps is indicated in the main control room. Both the floor and equipment drain sump and the Tritiated Drain Collector Tank have high level alarms which indicate in the main control ro'om. If the waste

disposal system is available, the operator can manually initiate processing of the contents of the Tritiated Drain Collector Tank through the waste disporal system. If the waste disposal system is not available the Tritiated Drain Collector Tank will fill and discharge through overflow piping to the auxiliary building passive sump.

Leakage into an ECCS pump or heat exchanger compartment can be detected by the flood detection system as described above. Leakage into areas other than these compartments can be detected by the flood detectors, by indication of sump pump operation, or by a high level alarm from the sump or the Tritiated Drain Collector Tank. However, the exact location of the leak, if from other than an ECCS pump or heat exchanger compartment, may not be immediately identified. Since ECCS leaks other than a pump seal failure are of a nature to develop very slowly and are less severe than a seal failure, the operator has an extended time period to detect and isolate the leak. Isolation of these minor leaks will be acomplished by arbitrarily selecting and isolating an ECCS subsystem and evaluating the response of the flood detector system. A factor which minimizes the probability of leakage into these areas is that the piping and valves in the RHR and CVCS systems are normally operated at temperatures and pressures which are greater than the postaccident conditions. Additionally, the entire ECCS is periodically inspected as a part of the inservice inspection program.

The flood detection system described above is not designed to meet the requirements of IEEE 279. The detectors, indicator panel, and control room alarm are single track and are powered from nondivisional boards. However, the system is designed such that a loss of power to any individual detector will be indicated on the indicator panel and will actuage the control room common alarm. Additionally, the nondivisional boards which supply the flood detection system are powered from a class IE power board which is automatically loaded on the diesel generators. This ensures continued operability of the flood detection system following an accident.

In addition to the flood detection and normal drainage processing systems described above, water level sensor is provided in the auxiliary building passive sump (elevation 643). This sensor is designed to alarm in the main control room at three separate sump levels.

A determination of the time available for corrective operator action before functioning of the redundant train of ECCS equipment would be impaired was made based on the assumed continuous leakage rate of 50 gpm. An evaluation was made of the minimum time required to fill the passive sump, which has a volume of 209,000 gallons, due to overflow of the tritiated drain collector tank. The calculated time of 2.9 days is conservative because no credit was taken for processing of leakage through the waste disposal system. An additional evaluation was made of the time available before the required suction head for the redundant ECCS pumps would be lost due to decreasing water level in the reactor building sump. The calculated time of 5.0 days is conservative because no credit was taken for the volume of water which will be

available due to melting of the ice condenser system ice (approximately 380,000 gallons). These time periods are much longer than the time necessary for the operator to detect and isolate the limiting 50 gpm leakage into an ECCS pump compartment.

With these design ground rules, continued function of the ECCS will meet minimum core cooling requirements. A single passive failure evaluation is presented in Table 1. It demonstrates that the ECCS can sustain a single passive failure during the long-term phase and still retain an intact flow path to the core to supply sufficient flow to maintain the core covered and affect the removal of decay heat. The procedure followed to establish the alternate flow path also isolates the component which failed.

ALTERNATIVES CONSIDERED The tasks that would be required to install remote manual containment isolation valves in the seal water injection lines with provisions for leak testing for each unit at SQN are as follows:

1. Valve Requirements

a. Four motor-operated valves with associated conduit, cabling, and main control room (MCR) indicators. Note: Valves must satisfy ASME Section III, Class 2, requirements and be equipped with 1E operators; all equipment must satisfy applicable environmental qualification (EQ) requirements,

b. Four each of manual block valves and 1/2-inch vent valves to allow for Appendix J leak rate testing of isolation valves.

2. Division of Nuclear Engineering (DNE) activities

a. Author and issue an Engineering Change Notice (ECN).

b. Procure all required materials,

c. Perform a seismic analysis of the planned rerouting of piping.

Note: Present configuration would require rerouting of piping to install required valves.

d. Perform electrical design; routing of conduit and cabling, modification of control room panel to allow for MCR indicator of valve position.

e. Generate documentation for preceding activities, including drawing changes and associated calculations to demonstrate flow requirements to RCP seals is not impeded by piping rerouting and valve installation.

3. Modification Activities

a. Generate mechanical workplan.

b. Generate electrical workplan.

c. Review and approve workplans through quality assurance (QA) procedure,

d. Execute workplans with required craft personnel; reroute piping, install hangers and valves, run cabling and conduit.

4. Postmodification Activities

a. Hydrostatic test of seal water injection lines to demonstrate integrity of new piping and valves,

b. Functional test electrical hardware.

c. Appendix J leak rate test motor-operated valves; perform maintenance as required.

d. Change procedures, EQ binder, operator training, technical specifications FSAR, and Surveillance Instructions.

e. Perform a flow balance test to RCP seals to ensure equal distribution of seal injection flow.

Appropriate valves may be located either in stock or warehoused and the preceding engineering tasks may be accomplished in about nine months at a minimum cost of approximately $1,500,000. Implementation could only occur during an outage of sufficient duration. A total exposure to the work crew used to implement the modification using estimated work crew sizes, times required to do similar tasks, and radiological surveys of the area of the plant in which the modification would be implemented is estimated to be about 47 man-rem.

TVA has evaluated this alternative and determined that it is not viable because of the estimated radiation exposure and cost.

BASIS FOR EXEMPTION The description of the RCP seal injection system identified redundant isolation provisions; the inboard check valves, the closed system outside containment, the water seal provided by the CCPs, and the local manual isolation valve outside containment. These provisions ensure that no single failure could result in release of containment atmosphere to the environment.

Therefore, protection of the health and safety of the public is ensured. TVA has evaluated modifications to the RCP seal injection system and determined that they are not viable because of the radiation exposure to the modification crew and the increased plant capital cost. Thus, an exemption from the requirements of 10 CFR 50 Appendix A CDC 55, should be granted for the RCP seal injection lines in accordance with 10 CFR 50.12(a)(2)(li),

10 CFR 50.12(a)(2)(iii), and 10 CFR 50.12(a)(2)(vi).

ENVIRONMENTAL IMPACT EVALUATION The RCP seal injection system is provided with redundant isolation provisions; the inboard check valves, the closed system, the water seal, and the seal injection filter isolation valve. These redundant provisions ensure that no single failure could result in release of containment atmosphere to the environment. Thus, it is concluded that the granting of an exemption from 10 CFR 50 Appendix A GDC 55 will not adversely impact the environment.

SUMMARY

r Based on the description of the RCP seal injection system and the discussion of the basis for granting exemptions from 10 CFR 50 Appendix A GDC 55, it is our conclusion that the requested exemption is authorized by law, will not present undue risk to the public health and safety, and is consistent with the common defense and security.

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Table 1 e EMERG(NCLCOR_E_C0QUE_ SYSTEM RECIRCyt ATION E1211]G PAS $1VE FAILURE EVALUATI0ti Lona-Term Phase f.lDw_fAlb Indication of toss of Flow Path Alternate Flow Path Low .Hg3dlRccir_CylatjQQ From containment sump to low head Acetanulation of water in a residual Via the independent. identical injection header sia the residual heat removal pump compartment or low head flow path utili2ing the beat removal pumps and the residual Auxiliary Building sump second residual heat exchanger heat exchangers tilsh HC3d_ECC1ICillallDD From containment sump to the high Accumulation of water in a residual From containment sump to the high head injection heaJer via residual heat removal pump compartments or the head injection headers via .

heat removal pump, residual heat Auviliary Building sump alternate residual heat removal exchanger and the high head pump, residual heat exchanger injection and the alternate high head charging pump,

.