ML20151Q379
| ML20151Q379 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/08/1988 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| TAC-R00425, TAC-R425, NUDOCS 8808110138 | |
| Download: ML20151Q379 (11) | |
Text
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8 TENNESSEE VALLEY AUTHORITY CH ATTANOOGA, TENNESSEE 374o1 SN 157B Lookout Place AUS 081988 U.S. Nuclear Regulatory Commission ATTN; Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 SEQUOYAH NUCLEAR PLANT (SQN) - CONTAINMENT ISOLATION SYSTEM - EXEMPTION FROM APPENDIX J. TYPE C, LEAK TESTING - RESIDUAL HEAT REMOVAL (RHR) SPRAY AND CONTAINMENT SPRAY (CS) SYSTEMS
Reference:
TVA letter to NRC dated July 11, 1988, "Sequoyah Nuclear Plant -
Containment. Isolation Syste.n - Exemption From Appendh J, Type C Leak Testing - Residual Heat Removal (RHR) Spray and Containment Spray (CS) Systems" The purpose of this letter is to request an exetuption from 10 CFR 50, Appendix J, Type C, testing of the contaitunent isolation check valves (CVs) in the CS and RHR spray systems for bot.h units 1 and 2.
The referenced letter provided an exemption request for the leak test.ing of these CVs.
It was submitted only for unit 2 through the next. rofueling outogo and, at the NRC Staff's request, included a commitment to monitor CV leakage during performance of scheduled Appendix J, Type A, Containment Integrated Leak Rate Tests (CILRT). However, after further review of the requirements of Appendix J, Sections III.C.2 and III.C.3 and evaluation of the system design, testing, and operation, TVA has concluded that compliance with Appendix J is being satisfied.
The NRC Staff had indicated disagreement with TVA's interpretation of compliance with Sections III.C.2 and III.C.3 but has agreed that the additional informat. ion result 'ing from TVA's review could provide the basis for a permanent exemption with additional leakage testing or monitoring of CV leakage not being warranted. While TVA still believes that, compliance with Appendix J is satisfied by the existing system design, testing, and operation, an exemption from Type C tent.ing of the subject valves is being requested for both units 1 and 2 of SQN in order to expedite resolution of this issue. The exemption request submitted in the referenced letter is hereby withdrawn.
This letter provides the basis for requesting the exemption under the criteria of 10 CFR 50.12.
This submittal replaces the exemption request and associated commitments submitted for unit. 2 by the referenced letter.
A check for the $150 application feo required by 10 CFR 170.12 for the review of our request for the exempt.lon nas been wired in conjunction with the referenced letter.
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8808110138 880808 PDR ADOCK 05000327 P
. An Equal Opportunity Employer
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8 B
' U.S. Nuclear Regulatory Commission
/\\UG 081988 If you have any questions concerning this submittal, please telephone M. A. Cooper at (615) 870-6549.
Very truly yours, TENNESSEE VALLEY' AUTHORITY
/ _)
t R. C diey, Man er Nuclear Licens g and Regulatory Affairs Enclosures cc (Enclosures):
Ms. S. C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. F. R. McCoy, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Ceorgia 30323 Sequoyah Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379
. ~ _. -
j ENCLOSURE JUSTIFICATION FOR EXEMPTION TVA requests an exemption to the requirements of Appendix J Type C, leak rate testing for the containment isolation CV in the CS and RHR spray systems.
This exemption is requested in accordance with 10 CFR 50.12(a)(2)(ii),
10 CFR 50.12(a)(2)(iv), and 10 CFR 50.12(a)(2)(vi).
The following provides a discussion of the system operation, which in conjunction with the design features forms the primary basis for an exemption from Type C leak rate testing requirements for the containment isolation CVs 1
in the CS and RER spray systems. A specific discussion of active and passive single failures is provided. Flow diagrams of the CS system and the RHR spray system are provided as reference as Figures 1 and 2 respectively.
RHR SPRAY AND CS SYSTEM OPERATION The CS system is automatically actuated when the containment pressure exceeds 2.81-pounds per-square-inch gauge (psig).
Upon actuation of the CS system, the spray pumps are energized; and the normally closed motor-operated valves (MOVs) automatically open. The RHR spray system is a manually actuated system. The operator initiates this system if the containment pressure exceeds 9.5 psig and more than one hour has elapsed since the start of the accident.
The RHR spray system is designed to supplement the CS system in the event that one train of CS is unavailable.
RHR spray will only be placed in service upon loss of one train of CS, and only one train of RHR spray is ever placed in service.
Both spray systems continue to operate until the containment pressure drops below 2.0 psig at which time they can be manually removed from service.
During the initial phase of the accident, the CS system takes suction from the refueling water storage tank (RWST).
When the RWST reaches low-low level, the system is realigned to take suction f rom the containment sump.
Because the RHR spray system is not put into operation before one hour after an accident, it only takes suction from the containment sump.
RHR SPRAY AND CS SYSTEM DESIGN As a result of the importance to safety of their operation postaccident, both the RHR spray and the CS systems are TVA Class B systems. The TVA Class B designation means that the valves and piping are American Society of Mechanical Engineers (ASME)Section III Class 2 or equivalent and Seismic Category I.
Valves and piping procured before April 1973 are designed in accordance with American National Standards Institute (ANSI) Standards B 16.5 and 31.1, respectively, which is considered to be equivalent to Section III of the ASME Code. Each system consists of two redundant trains powered from different electrical trains.
Both systems are supplied by the emergency diesel generators and are automatically loaded on the diesels if offsite power is lost.
At the time the operating license was issued, containment isolation for the RHR spray and CS lines penetrating the primary containment was provided by a CV inside the containment and a closed system outside the containment.
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' An MOV that is located outside the containment (one in each line) was not considered a containment isolation valve. Containment isolation for these systems is currently provided by a CV inside the containment and the normally closed MOV located outside the containment. The closed system is no longer considered the outboard containment isolation barrier based on agreements between TVA and NRC in 1986/1987.
In order to ensure that no containment leakage could occur through these penetrations, a water seal is maintained between the MOV and the CV in eact.
line. The MOVs in both the CS and RER spray systems are leak rate tested in accordance with paragraphs III.C.2 and 3 of Appendix J for those penetrations in which through-line leakage is prevented using a seal system.
The leak test ensures that an adequate water inventory can be maintained for 30 days.
To meet the requirements for a water seal in Appendix J, the seal pressure must be maintained at 1.1 P.
This is 13.2 psig at SQN, which corresponds to a
about 30 feet of water.
The MOVs are located at elevation 714.
The water seal is in a vertical section of piping and is normally maintained at approximately elevation 830.
This provides a head of approximately 115 feet of water.
In addition, the portions of these systems located outside the containment are considered to be closed systems in that they do not communicate directly with the environment.
Thus, any leakage past the isolation valves would be retained in the piping systems.
In the postaccident condition, these systems are water-filled and contain additional water seals as a result of the piping layout. As can be seen from the figures, the valves that isolate both spray systems from the RWST are at elevation 660.
The centerline of the piping drops to elevation 656 because the pumps are located on the elevation 653 floor.
The bottom of the RWST is at elevation 707. This provides a seal with approximately 50 feet of head to prevent outleakage. This is well above 13.2 psig (1.1 P ).
Assuming a a
worst case with multiple failures where all pumps were not running and all valves failed open (including CVs), the water leg in the CS and RHR spray piping would be equal to the post-loss-of-cociant-accident (LOCA) water level inside the containment, which is above elevation 693.
This provides almost 40 feet of head to prevent outleakage of containment atmosphere.
Each CS and RHR spray line also has a CV near the pump discharge. This CV is between the pump and the notor-operated containment isolation valves and is designed to prevent the backflow of water through the pump.
Therefore, these valves provide additional help to maintain the water seal on the MOVs.
SPECIFIC EVALUATION OF SINGLE FAILURES The following section provides a case-by-case discussion of the possible single failures in the CS and RHR spray system.
This discussion demonstrates that a seal system, which meets the criteria of Appendix J III.C.2 and III.C.3, is ensured under all potential conditions.
Case 1 describes normal system operation, and cases 2 through 4 deal with active failures.
Cases 5 and 6 deal with passive failures.
While we note that Standard Review Plan 6.2.6 on containment leakage testing states that only active failures need to be consi.dered in maintaining a seal system, the SQN system is available even considering passive failures.
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. Case 1 - No Single Failure In this case, the CS system functions as designed with both' trains operating after an accident. While the system is in operation, no leakage of containment atmosphere will occur because the water flowing through the srtay system is at a pressure greater than the peak containment pressure.
Whe', tne spray system is no longer required, the containment pressure is less than 2.0 psig--well below the containment design pressure of 12 psig.
The system will be water-filled, and any leakage across either the CV or the MOV will be retained in the closed system. The water seal on the MOV will be reestablished when the operator closes the valve.
The waterhead in the system is sufficient to prevent outleakage of containment atmosphere at these low pressures.
For this case, where both trains of CS operate, the RHR spray would not have been used; and the MOVs in the RHR system would have remained closed.
- Thus, the water leg seal would have 5een maintained; and no leakage through penetrations X-49A oc X-49B would occur.
Case 2 - MOV Fails To Open For the case where one train of CS was inoperable because of failure of the MOV to open, the water leg seal would be maintained; and no leakage would occur from the inoperable line. The other train of CS and the train of RHR spray placed in service would be fully functional; and when they were shut down later in the accident, the containment pressure would be less thaa 2.0 psig. The MOVs in the operable systems would then be closed.
Thus, there i
would not be any leakage of the containment atmosphere outside the system.
The other RHR spray line would not have been used, so the water leg on its MOV would still be present. One final note is thac, even after the spray systems are turned off, the RHR pump associated with the RHR spray system used would continue to run. This provides additional protection against the leakage of containment atmosphere from that line.
Case 3 - Pump Fails to Start For the case where one train of CS was inoperable because of the failure of the pump to start, the MOV in that train may have opened. The operator would close the MOV, and the water leg would be maintained by the pump discharge check valve until the MOV is closed.
Even if it is assumed that some leakage past the MOV occurred, the leakage would be retained in the closed system outside the containment.
Because of the water leg maintained by the sump water level and in the RWST injection line, no leakage from the system could The response of the other train of CS and both trains of RHR spray occur.
would be the same as described in case 2.
Case 4 - Loss of One Train of Power This case would be the same as case 2.
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+
e
. General Note to Cases 1 Through 4 g
RHR spray is only placed in service becau e of a single failure of one train of CS.
Thus, single failures in the RHR spray do not need to be evaluated as these would occur only as the result of multiple failures.
In addition, because the RHR spray is initiated manually no earlier than oi.e hour after an accident, the operator would know if both RHR pumps were available or not and would use the cperable train.
Case 5 - Valve Packing Leak The containment isolation MOVs in both systems are backseated gate valves.
When the valve is open, the backseat prevents the packing from being exposed to system pressure. When the valve is closed, once again the packing does not see system pressure.
Thus, if the packing failed, the only time the packing would leak would be when the valve was opening or closing.
This is considered to be insignificant. A packing leak will not result in the loss of the water seal.
Case 6 - Pump Seal Failure l
While the system is in opacation, injected water prevents any leakage of containment atmosphere.
If the SQN leak detection system indicated a leak in one (' the pumps, the operator would isolate the line associated with that pump using the containment isolation MOV and would also close the sump q
isolation valves.
The water leg on the containment isolation MOV will be maintained, and no leakage path for containment atmosphere would result.
The k
pump discharge CV will also help maintain the water seal.
IMPACT OF TESTINC 3
Imoracticality of Local Leak Rate Testing (LLRT) of RHR and CS CVs The design of the RHR spray and CS lines included no provisions for performing an LLRT on the inboard isolation CVs.
The lines were not constructed to provide block valves or other means of sealing the lines inboard of the CVs from the open spray ring headers. This arrangement precludes any possibility of applying test accident pressure against the CV seats in order to perform a Type C seat leakage test as prescribed by Appendix J.
Addition of block valves in this piping would involve costly analysis and modifications as a result of the location and size of the lines. The design engineering work and materials required have an estimated cost of $280,000 per system per unit.
This cost is greatly overshadowed by the cost of lost revenue and purchase of replacement power during the outage (approximately $500,000 per day for each unit). The modification would require an estimated eight weeks to comple'.e (five weeks for engineering work and three weeks for the actual modification work).
In addition to these numbers, the material procurement leadtime could be as long as six months. Costly modifications to these lines to facilitate LLRT would reduce the reliability of these systems through the introduction of an additional manual valve located in a remote part of the flowpath of a safety system and would result in no increase in the safecy of the public.
The leakage rate of the valves could be monitored on a lesser frequency (than specified in Appendix J) during the CILRT sequence.
This would require draining the piping containing the water seal, connecting a flow measuring
. device to a test connection and measuring the leakage, then removing the test rig and tefilling the water leg.
The potential costs associated with testing would be excessive and unjustifiable because of plant status requirements at the only time leakage monitoring could be ptrformed.
If monitoring were to be performed, it would be conducted during the preparatory time leading to actual conduct od the CILRT.
Because the CILRT requires a specific configuration for the entire plant and preparatory time to achieve that configuration requires an intensive effort over a 14-to 21-day time period, it would be imoractical to relinquish configuration and work control during the time period sequired to perform any valve repairs.
As previously discussed, testing of these valves provides no increase in safety because any leakage is precluded from reaching the environment by the seal aystems provided.
Therefore, if testing required repairs, the entire plant would effectively b.: placed in an indefinite "hold" situation while these tepair activities were conducted.
Accordingly, this time could be expected ~to translate directly into day-for-day lost generation time.
The inaccessible location of these valves requires erection of a work platform approximately 50 feet above the polar crane bridges or approximately 100 feet above the floor level.
This extreme height not only requires excessive time to erect the required scaffolding but also raises serious industrial safety concerns.
Disassembly, removal, and replacement of the valves is difficult and time consuming (estimated repair time is seven to eight days) because of their location and is further complicated by radiological concerns. This work must be performed in a contaminated area; and because these systems contain radioactive material, face masks must be worn by the workers when the piping is opened.
This represents unnecessary exposure and a departure from radiation exposure goals that are as low as reasonably achievable.
In summary, testing of the subject CVs would result in undue hardship and costs without a compensating increase in protection of the health and safety of the public.
ADDITIONAL CONSIDERATIONS 1.
The CVs that isolate the RWST from the CS and RHR systems, when these systems are in the recirculation mode from the sump, are functionally tested as part of the ASME Section XI in-service test requirements provided by Technical Specification (TS) 4.0.5.
In addition to the CV, each of these lines is equipped with an MOV that is also used to isolate these lines from the RWST.
Both the CS system and the RHR spray system are monitored for excessive external leakage in accordance with TS 6.8.5.a.
The RWST isolation valves and the associated testing and s stem monitoring ensure that these closed systems outside the containment are maintained.
2.
The CVs 8.n both the CS system and the RHR spray system are incl'uMd in the ASME Section XI valve test program.
Each refueling outage, on. 4 these valves is disassembled to check the condition of the valve as 4
4 t3 i
internals, including the condition of the valve seat.
If a yt ;lem with
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one of the valves was discovered, the other three valves would be inspected during the same outage.
Inspections to date have shown the valves are 4.n good condition.
)
. 3.
The MOV is leak tested every 18 months to ensure that the water seal is maintained.
The height of the water leg is verified quarterly during Section XI testing of other valves in the system.
This provides added i
I confidence that the water seal is maintained, l
ENVIRONMENTAL ASSESSMENT Identification of Proposed Action:
The exemption will permit the exclusion from Type C leak rate testing of the inboard containment isolation check l
valves in the CS and RHR spray systems.
10 CFR 50 Appendix J, requires the l
performance of periodic leak rate testing of valves that serve as containment l
isolation valves.
The SQN-designed operation of these systems provides a guaranteed water seal for the penetrations' paths, which precludes any leakage of containment atmosphere to the environment.
Type C testing cannot be performed because of the lack of manual or remote-manual block valves in the lines that are necessary to allow such testing. An exemption is requested
?
from Appendix J specifically for the Type C testing of the inboard check l
l valves.
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The Need for the Proposed Action: The proposed exemption is needed to ensure NRC approval of SQN compliance with 10 CFR 50, Appendix J.
Environmental Impact cf the Proposed Action:
The proposed exemption is for the testing requirements of Appendix J.
This testing ensures that specified limits for postaccident containment leakage are met.
The penetrations associated with the CS and RHR spray systems are protected from through-line leakage by the CVs, an outboard isolation valve, a closed system outside containment, and a guaranteed water seal.
Thus, any leakage past the isolation valves would be precluded from reaching the environment by the water-filled, closed system piping. Consequently, the radiological releases will not be greater than previously determined nor does the proposed exemption otherwise affect radiological plant effluents. Therefore, it is concluded that there are no significant radiological environmental impacts associated with this proposed exemption. With regard to potential nonradiological impacts, the proposed exemption does not affect nonradiological plant effluents and has no other environmental impact.
Therefore, it is concluded that there are no significant nonradiological environmental impacts associated with the proposed exemption.
Alternative to the Proposed Action: The alternative to the proposed action would be to install manual or remote-manual block valves between the inboard CVs and the spray rings. This would result in increased capital costs to the plant and radiation exposure to workers without a compensating increase in protection of the health and safety of the public. Most importantly, the addition of these valves could reduce reliability of the safety system performance.
Alternative Use of Resources:
This action does not involve the use of resources not previously considered in connection with the "Final Environmental Statement Related to the Operation of Sequoyah Nuclear Plant.
Units 1 and 2," dated July 1974.
.=
SUMMARY
IVA concludes that an exemption from 10 CFR 50, Appendix J, Type C, leak rate testing of the CVs in the CS anc' RHR spray systems is justified for SQN units 1 and 2.
Leak rate testing of the CVs vill not reduce the leakage of containment atmosphere to the environment after an accident but would impose an unwarranted burden on the plant.
It is TVA's conclusion that the requested exemptions are muthorized by law, will not present undue risk to the public's health and safety, and are consistent with the common defense and security.
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