ML20054L575

Forwards Submittal Re plant-specific Valve Operability Assessments Per TMI Item II.D.1 & Generic Ltr 81-36, Revised Schedule for Completion of TMI Action Item II.D.1, Relief & Safety Valve Testing

ML20054L575
Person / Time
Site:	Byron, Braidwood, Zion, 05000000
Issue date:	07/01/1982
From:	Swartz E COMMONWEALTH EDISON CO.
To:	Eisenhut D Office of Nuclear Reactor Regulation
Shared Package
ML20054L576	List: ML20054L575 ML20054L579
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.D.1, TASK-TM 4466N, GL-81-36, NUDOCS 8207080259
Download: ML20054L575 (15)

Text

{{#Wiki_filter:/ Commonwealth Edison 14 one First P(ttional Plaza. Chicago, lihnois Address Reply to: Post Office Box 767 v Chicago, Illinois 60690 t Jul y 1, 1982 { Mr. Darrell G. Eisenhut, Director Division of Licensing U.S. Nuclear Regulatory Commission j Washington, DC 20555

Subject:

Zion Station Units 1 and 2 NUREG 0737 Item II.D.1 Plant Specific Submittal Due July 1,1982 NRC Docket Nos. 50-295/304 Reference (a): D. G. Eisenhut letter to All Licensees dated September 29, 1981 (Generic Letter i No. 81-36)

Dear Mr. Eisenhut:

Reference (a) provided the revised implementation schedule requirements for NUREG 0737 Item II.D.1 concerning PWR performance testing of safety and relief valves. The Attachment to this letter provides our Zion Station response to address the July 1,1982 plant-specific submittal requirements. This Attachment provides the final operability assessments for our Zion Station pressurizer safety valves, power operated relie f valves (PORVs), PORV block valves, and the associated piping and support adequacy. In summary, it is our judgement that cach of these valves are capable of performing the operability function required within the criteria set forth in the Attachment, and that l no equipment or analytical corrective actions are warranted. Our assessment of the adequacy of the safety and relief valve piping and supports has resulted in the need for further analytical review. The At tachment discusses our action plan and associated schedule concerning this issue. We believe that this letter along with the Attachment now completes all NUREG 0737 Item II.D.1 submittal requirements. We will inform the NRC Staf f when further conclusions are reached as a result of our piping and supports action plan. oh B2070B0239 B20701 i i PDR ADDCK 05000295 p PDR

. To the bes t o f my knowledge and belie f the statements contained herein and in the Attachment are true and correct. In some respects these statements are not based on my personal knowledge but upon information furnished by other Commonwealth Edison employees and Consultants. Such information has been reviewed in accordance with Company practice and I believe it to be reliable. Please address any questions that you or your staff may have concerning this matter to this office. One (1) signed original and thirty-nine (39) copies o f this letter with Attachment are provided for your use. Howeve r, due to its bound nature, only one (1) copy o f the referenced Appendix A Probablistic Evaluation is attached. Very truly yours, y jr E. Douglas Swartz Nuclea r Licensing Administrato r Attachment cc: J. G. Keppler - Region III D. L. Wigginton - ORB-1 4466N

s ATTACHMENT COMMONWE ALTH E0ISON COMPANY Zion Station Units 1 and 2 NUREG 0737 Item II.D.1 - July 1,1982 Submittal concerning Plant Specific Valve Operability Assessments

. II.D.1 Performance Testing of PWR Safety / Relief Valves Zion Response: Ref. 1: Letter from D. P. Hoffman (Consumers Power) to H. R. Denton (NRC) dated April 1, 1982, transmitting the following EPRI Safety and Relief Valve Test Program Reports: a) Safety & Relief Valve Test Report b) Valve Selection / Justification Report c) Test Condition Justification Report d) Plant Conditions Justification Report 1) Westinghouse Plants 2 Canbustion Engineering Plants 3 Babcock & Wilcox Plants e) Evaluation of RELAP 5 MOD 1 for Calculation of Safety & Relief Valve Discharge Piping Hydrodynamic Loads Ref. 2: Letter from R. C. Youngdahl (Consumers Power) to H. R. Denton (NRC) dated June 1, 1982, transnitting the following EPRI Test Program Report: a) EPRI Safety & Relief Valve Test Program PORV Block Valve Information Package Ref. 3: Letter from 0. Kingsley (Alabama Power) to S. Chilk (NRC) dated July 1,1982, transmitting WCAP-10105, a report performed for the Westinghouse Owners' Group entitled: a) Review of Pressurizer Safety Valve Performance as Observed in the EPRI Safety & Relief Valve Test Program Commonwealth Edison is a participant in the generic EPRI/PWR Safety & Relief Valve Test Program. The reports referenced above document the Test Program results. Commonwealth Edison has performed a final review of the results with regard to valve operability & S/RV piping & support adequacy. We have concluded that the EPRI tests represent the safety, relief, & block valve designs in use at Zion, and that the piping and support load data provided is sufficient to perform a plant unique assessment of the Zion S/RV piping and supports. We have also concluded that the conditions tested envelop and conservatively exceed the range of expected operating and accident conditions that we anticipate for Zion. Safety Valves The Zion pressurizer safety valves are the Crosby model llP-BP-86 6FE type, with loop seal internals. This valve model was tested in the EPRI

Program & the referenced report sections that specifically apply to it relative to its use at Zion are as follows: 1. Safety & Relief Valve Test Report - Section 3.5 2. Valve Selection / Justification Report - Section III-Al 3. Test Condition Justification Report Westinghouse Plants - All Sections related to 4 loop plants. The following is a description of the technical a7proach used in performing the Zion plant specific safety valve operat,ility assessment. Our assessment of the Crosby 6M6 is based on its test performance in response to fluid inlet conditions anticipated for Zion in transient & accident events. Those conditions consist of discharge of the loop seal water immediately upstream of the valve, followed by saturated steam for all such events that may result in safety valve actuation. The technical justification for this inlet condition determination was derived by means of a probabilistic risk study. Documentation of this study constitutes Appendix A to this evaluation. The safety valve operability function considered pertinent to Zion plant safety is mitigation of excessive RCS transient pressure increases. The criteria indicative of the 6M6 valve's capability to perform this function are:

1) Opening to a position where sufficient flow is achieved to prevent exceeding the 2750 PSIA primary system design limit under the highest anticipated transient over-pressure ramp rate, 2) Closure to a position sufficient to curtail reduction of RCS pressure below 88% of the safety valve actuation pressure, ar.d 3) Internal and external structural integrity of the safety valve sufficient to allow subsequent actuations in the event of repeated overpressure transients.

These criteria are considered to be very conservative in regards to Zion plant safety. The express purpose for defining the criteria parameters is to establish a comparison basis by which it can be defensibly stated that performance within the criteria clearly represents no challenge to existing Zion safety margins. As an illustration, the safety valve closure criteria was judged to be a conservative lower limit, above which safety valve liquid challenges are not expected. The absence of such challenges is viewed as a clear indication that no encroachments on present Zion safety analysis margins exist with respect to safety valve closure.

Conclusions Quantitative review of the EPRI 6M6 tests with fluid conditions applicable to Zion have led to the conclusion that this valve is in fact capable of performing the operability function required within the criteria identified. It is therefore also concluded that, since the 6M6 test performance was within the present plant safety analysis margins, no equipment or analytical corrective actions are warranted in the interest of plant safety. The factors providing technical support for these conclusions with respect to each criteria are as follows: Criteria 1 - Opening 1. Regardless of stem lif t delays or upstream piping pressure surges observed in the EPRI test data as a result of loop seal water discharge, in no instance did the tank (pressurizer) pressure exceed the 2750 PSIA criteria. Equally favorable results are anticipated for the Zion plant specific case because: 1.1 Per the analysis shown in Section 4.1 of WCAP-10105, (Reference

3) stem lift delays of up to 2 seconds can be accommodated.

In the EPRI tests, the stem lift delay in no case exceeded.9 second. In comparing the Zion plant loop seal volume (a 1.5ft)totheEPRItestfacilityvolume(approx 1.05ftgprox.), it 3 can be seen that the Zion stem lift delay would in no case exceed the 2 second limit established by Westinghouse. 1.2 As shown in Section 3.1.1 of WCAP-10105, the transient overpressure ramp rates tested by EPRI were in excess of those for Westinghouse plants. In comparing cases with equal loop seal volumes, the EPRI overpressure ramp rates would clearly result in higher peak pressures than those anticipated for Zion, since it is apparent in the test data that the stem lift delay is not significantly affected by the ramp rate. 1.3 The EPRI test data clearly demonstrates that the tank (pressurizer) pressure is independent of the observed valve inlet pressure surges during loop seal discharges. Based on comparison of the EPRI test facility & Zion plant configurations with respect to tank (pressurizer) volumes, safety valve inlet piping geometry, & downstream backpressure, it is clear that the Zion pressurizer peak pressure would be even less sensitive to safety valve inlet pressure surges than any responses that were observed in the EPRI tests. The Zion pressurizer liquid and steam volumes are much larger than the EPRI facility volumes, and the EPRI backpressures were significantly higher than the Zion backpressures (assuming all 3 safety valves and both PORVs input maximum flow). Concurrently, the 6M6 valve and the upstream piping length and shape is essentially the same between the EPRI and Zion configurations. It can therefore be seen that this is a conservative assessment.

Criteria 2 - Closure 2. Other than two exceptions in the apparent test results, the 6M6 always closed within 10% of the design actuation pressure. Equally favorable results are expected for the Zion plant specific case because: 2.1 The manufacturer's (Crosby) original blowdown ring adjustments provided 10% or less blowdown. The Zion plant specific blowdown ring adjustments have never been varied for service from the manufacturer's recommended positions. They are verified correct by procedure during setpoint verification testing conducted during each refueling outage. From the viewpoint of the safety valve itself therefore, fundamentally the same blowdown performance is expected for Zion as that experienced by EPRI. 2.2 Similarities between the Zion plant configuration and the EPRI test facility regarding upstream piping geometry (length, flow diameter, bend radii) and the downstream backpressures indicate that no significant flow dynamics differences are anticipated between the EPRI and Zion cases that impact blowdown. 2.3 The two exceptions noted (EPRI tests 920 and 1419) are not considered typical of valve closure peformance expected at Zion. The following discussion forms the basis for this assessment. In these tests, the 6M6 reopened at a pressure lower than tha design actuation pressure and subsequently exhibited a rapid cyclic characteristic. The reopening phenomena was the apparent result of an acoustic wave propogated pressure surge in the upstream pipe of sufficient magnitude to exceed what was at that point a distinctly degraded valve actuation pressure. The actuation pressure degradation was precipitated by a significant increase in seat leakage developed by the time of initial closure in these tests. The increased seat leakage effect was pressurization of the huddle chamber (secondary area) within the valve, thus generating a lifting force at an inlet pressure considerably below the design actuation pressure. The subsequent acoustic pressure surge amplitude was then sufficient to apply the necessary additional force to the valve disc and huddle chamber areas to cause full lift at that lower pressure. At the degraded actuation pressure, but clearly not at the design actuation pressure, the acoustic pressure surge also had sufficient amplitude to produce the cyclic characteristic of the valve. This was due to its wave transit time in relation to the particular upstream piping length, such that the surge impact frequency on the valve disc was applied after valve closure had occurred. Key elements in the determination that such a phenomena would not take place in the Zion plant specific case are:

1) seat leakage that could be conservatively anticipated after initial reclosure of the valve, and 2) valve fluid inlet conditions expected during subsequent actuations for repeated overpressure

transients. The assumption that the anticipated acoustic wave pressure surge dynamics are as severe in the plant as those present in the tests with respect to upstream piping length and flow area, valve closure time, and blowdown percentage is appropriately conservatfve. Tests 920 & 1419 were warm loop seal tests (approx. 350 F), and both were conducted immediately following similar warm loop seal tests (Nos. 917 and 1415, respectively), without benefit of valve seat refurbishment prior to test initiation. Consequently, at the time of initial valve closure in Tests 920 and 1419, the valve seats had been subjected to more structural distress from full actuations and cycling during loop seal discgarges, as well as more severe seat sealing fluid conditions (350 F water ae opposed to saturated steam or cold water), than at any other points during testing. The seat leakage at these points was of apparent greater magnitude than what was present at corresponding times in any other tests. This is supported by the fact that the reopening phenomena at degraded actuation pressures did not occur in any other tests, particularly Tests 917 & 1415. Conservatively assuming similar loop seal water average temperatures, Tests 917 & 1415 are representative of the Zion safety valve configurations that have anticipated acoustic wave pressure surge dynamics as severe as the tests, in terms of initial actuation fluid inlet conditions. It should be noted that two of the three Zion safety valve configurations have considerably shorter inlet pipe lengths than the third as well as the EPRI test facility (approx.11 feet-vs-approx.16 feet), and significantly less severe dynamics are expected in these cases. Initial actuation performance, by virtue of the fact that the Zion valve seat condition is at least comparable to the condition present at the outset of Tests 917 & 1415 (determined during required refueling outage setpoint verification testing), is expected to be esssentially the same as the 917 & 1415 test results. For Zion however, it is not appropriate to expect that inlet fluid conditions for subsequent actuations from repeated overpressure transients would correspond with initial fluid inlet conditions of Tests 920 & 1419. Such subsequent actuations would, in view of the overpressure ramp rates applicable, take place on satu.ated steam without a preceding loop seal dis-l charge. Since seat sealing with steam is expected to be better l than with warm water, & no cyclic behavior from loop seal discharge would take place to further degrade seat condition, no significant lowering of the valve actuation pressure is anticipated following closure of the valve from subsequent actuations. In the absence of a degraded actuation pressure, the acoustic pressure surge is of insufficient amplitude to cause the reopening phenomena or any associated cyclic valve characteristic. For Zion plant specific purposes, it can therefore be distinguished that should an initial safety valve actuation similar to Tests 917 or 1415 occur, subsequent

actuation closure performance would closely resemble Test 903 rather than Tests 920 & 1419. Since the amount of seat leakage present after Tests 917 & 1415 was negligible and the original valve actuation pressure in Tests 920 & 141!L showed no sign of degradation, it is justifiable to conclude'that no initial or subsequent actuation case at Zion would produce the reopening or cycling phenomena observed in these tests. Criteria 3 - Structural Integrity 3. There were no observations in the EPRI tests of structural damage to the 6M6 that impeded its ability to function repeatedly. The same or better results are expected at Zion because: 3.1 As noted in the preceding discussion, subsequent actuations are expected to take place with saturated steam fluid inlet conditions for Zion plant specific situations. This is clearly less severe than repeated loop seal discharges, such as those that EPRI experienced by conducting multiple loop seal tests without overhauling the 6M6 between tests. 3.2 Despite high frequency cycling (other than loop seal discharge) in subcooled water tests and tests such as 920 and 1419, no damage sufficient to freeze.the 6M6 in a stuck-open or stuck-closed position occurred during the_ duration of the tests. AlthoJgh these tests are not actually applicable to Zion, they do demonstrate that the 6M6 is capable of withstanding a highly significant amount of structural distress beyond what is anticipated in the Zion applicatiibn. In summation, this assessment was conducted against criteria that are considered conservative with respect to ' Zion plant safety h.argins. In turn, the Crosby 6M6 test performance was clearly conservative with respect to these criteria. This performance, obtained in response to test conditions considered more severe than comparable conditions anticipated for Zion, have convinced us that the Zion plant specific needs for primary system safety valve operability have been demonstrated. It is therefore felt that the. conclusions reached from this assessment are justified. ~. ~- Power Operated Relief Valves The Zion pressurizer power operated relief valves are Copes-Vulcan 2 inch Model D-100-160 type, with 17-4PH cage and 316SS steilite ' clad plug. We have determined that the EPRI tes s of the 3_ inch Copes-Vulcan 17-4Pli/316SS stellite clad version of this valve are app?icable to the Zion 2 inch PORVs. The referenced EPRI ~ report sections that apply to Zion are as follows: 1. Safety & Relief Valve Test Report - Section 4.6 2. Valve Selection / Justification Report - Section III-B2 3. Test Condition Justification Report - Sections 2.2 & 3_8

. 4 4. Plant Conditions Justification Report - Westinghouse Plants - All sections related to 4 loop plants. The technical approach used to perform the Zion PORV operability final assessment was fundamentally the same as that used for the Crosby 6M6 safety valve. The only differences were; 1) Operability was assessed in terms of the most severe bounding fluid inlet conditions achievable at Zion rather than for expected fluid inlet conditions only as shown in Appendix A for safety valves, and 2) the criteria used to make the assessment are considered to be significantly more conservative than those used for safety valves, in the interest of mitigating unnecessary safety valve challenges. The PORV operability function considered pertinent to Zion is mitigation of primary system transient pressure increases during cold overpressurization events. The criteria indicative of the Copes-Vulcan valve's capability to perform this function are; 1) full opening on command regardless of fluid inlet pressure or state, within the opening time assumed in the Zion cold over-pressurization system design, 2) full closure on command regardless of fluid inlet pressure or state, within the closure time assumed in the Zicn cold over-pressurization system design, and 3) internal and external structural integrity of the PORV sufficient to allow subsequent actuations in the event of repeated overpressure transients. The purpose for defining these criteria and the application of them are consistent with criteria used for the Crosby 6M6 safety valve. In summa ry, performance within the criteria indicates that no challenge to present Zion safety margins exists. Conclusions Quantitative review of the EPRI Copes-Vulcan tests which bound the range of fluid conditions achievable at Zion have led to the conclusion that this valve is capable of performing the operability function required within the criteria identified. It is also concluded that, since the Copes-Vulcan PORV test performance was within the present Zion cold overpressurization system design margins, that no equipment or analytical corrective actions are warranted in the interest of plant safety. Evidence providing technical support for these conclusions with respect to each criteria is as follows: Criteria 1 - Opening 1. In all the EPRI tests of this PORV, it always achieved full disc opening within a period of.66 seconds, regardless of the fluid inlet conditicos tested. Equally favorable results are anticipated for the Zion plant specific case because: 1.1 The fluid inlet conditions tested are comparable to the range of conditions achievable at Zion in cold overpressurization events, as shown in the following tabalation:

I Zion

• EPRI Test i

Maximum steam pressure 519 PSIG 2700 PSIG Maximum liquid pressure 519 PSIG 600 PSIG** Maximum temperature at 0 maximum pressure 457 F 442 F Minimum temperature at U maximum pressure 100 F 105 F l,

• Zion information was obtained by review of the plant cold overpressurization system design documentation.

i

• • Maximum pressure tested over applicable liquid temperature range (i.e. 100 to 457 F) 1 1.2 The PORV opening time assumed in the Zion cold overpressurization system design is 2.5 seconds, which conservatively exceeds the.66

[ second opening time observed as a maximum in all the EPRI tests. Criteria 2 - Closure i j 2. In all the EPRI tests of this PORV, it always achieved full disc closure within a period of 1.24 seconds, regardless of the fluid inlet conditions tested. Equally favorable results are anticipated for the Zion plant specific case because: i 2.1 As shown in Iten 1.1, the fluid inlet conditions tested are comparable to the range of conditions achievable at Zion in cold overpressurization events. i 2.2 The PORV closure time assumed in the Zion cold overpressurization 1 system design is 5 seconds, which conservatively exceeds the 1.24 i second opening time observed as a maximum in the EPRI tests. L Criteria 3 - Structural Integrity i 3. Upon disassembly inspection of the Copes-Vulcan PORV, conducted only after j all of the EPRI tests had been completed, no evidence of structural damage was observed that could in any way be interpreted as a challenge to operability for repeated overpressure transients. Equally favorable results are anticipated for the Zion plant specific case because: 3.1 EPRI test performance regarding seat leakage, considered to be a 4 j conservative indicator of internal structural distress, never i exceeded.0042 GPM. This is clearly insignificant in comparison to the Zion Technical Specification unidentified RCS leakage limit of 1 GPM. The test results are also consistent with operational observations at Zion, where the PORVs are in service with the 1 l isolation (block) valves open, and no distinguishable contribution to total RCS leakage is in evidence. 3.2 No performance differences were observed in the EPRI tests, regardless of any applied bending moment preloads. t -.. - - _ -.. _.. _ _, - _. _ _ _. - _ _ _, _ _,, _ _ - ~. _. _ _..

In summation, this assessment was conducted against criteria that are considered conservative with respect to Zion plant safety margins. In turn, the Copes-Vulcan PORV test performance was clearly conservative with respect to these criteria. This performance, obtained in response to test conditions considered more severe than comparable conditions anticipated for Zion, have convinced us that the Zion plant specific needs for primary system PORV operability have been demonstrated. We are also convinced that this demonstration extends beyond the considerations of cold overpressurization events only, such that the Zion PORV operability for all overpressure transient functions is assured. This assurance provides an added measure of confidence that the objective of mitigating unnecessary safety valve challenges has been attained. It is therefore felt that the conclusions reached from this assessment are justified. PORV Block Valves Our response regarding PORV block valve operability is that we are in full agreement with the generic PWR utilities' position identified in Reference 2. As noted in the documentation associated with the generic response, the Zion PORV block valves are 3 inch Velan gate valves, model B10-3054B-13MS, with Limitorque model SMB-00-15 motor operators. Having reviewed the EPRI/ Marshall Velan tests, documented in Reference 2, we have determined that the test results are applicable to Zion. We have therefore concluded that the Zion plant specific requirements relative to PORV block valve operability have been satisfied. S/RV Piping & Support Adequacy Our assessment of the Zion S/RV piping and support adequacy is based on a comparison between the thermal-hydraulic forcing function data supplied by EPRI (for Crosby 6M6 safety valve tests applicable to Zion) and predicted forcing r i functions for the EPRI/CE test facility. The forcing functions predicted for this purpose were generated with the same calculation techniques used in the Zion S/RV piping system design, such that the comparison would clearly demonstrate whether or not the adequacy of these techniques could be verified. The ability to demonstrate this verification was considered to be sufficient evidence to justify the conclusion that the adequacy of the forcing function predictions used as basic input to the Zion S/RV piping and support system structural analysis could be clearly established. It would therefore follow that the adequacy of the structural analysis itself, recently upgraded through efforts performed in response to I.E. Bulletin 79-14, could also be demonstrated. The function of the Zion S/RV piping and support system in question regarding plant safety margins is consistent with the concern expressed in fiUREG-0578 and 0737. Specifically, this is the effects of the plant as-built S/RV piping and support system reactions on the operabilty of the primary system safety and relief valves required to insure plant safety. Our position is that this assessment effectively responds to that concern.

.-10 The criterion used in the comparison to determine if this verification could be established was straightforward and conservative. If the predicted forcing functions were more severe than the forcing functions observed in the EPRI test data by a factor of 2 to 1, the desired conclusion was justifiable. This was seen as conservative for two reasons; 1) the present Zion piping and support structural analysis employs a similar factor to insure structural integrity of the system for operational considerations beyond what is considered to be pertinent to Zion plant safety margins, and 2) no credit was assumed for overpressure transient mitigation via operator action or PORV operability. Conclusions 1. The comparison has revealed that the predicted forcing functions are less severe than those observed in the EPRI tests involving cold loop seal liquid discharge followed by saturated steam. These test cases are considered typical of Zion. It was therefore clear that the desired verification could not be achieved, because these results did not fall within the bounds of the identified criterion. t 2. These results justify the need to perform a plant safety margin impact assessment. This assessment is identified in the following section. Safety Margin Impact Assessment 1 ] Our objective is to develop an action plan and associated schedule for development and use of new forcing function predictions that can be i conservatively verified as adequate. This action plan will also identify plant modification alternatives to either reduce these forcing functions to a level of severity within the present Zion S/RV piping and support structural analysis, or upgrade the structural analysis and associated plant hardware to accommodate the new forcing functions, in the event that such modifications are found to be necessary. In our judgment, plant operation during the course of efforts to resolve the Zion S/RV piping and support adequacy is justified. This conclusion was reached on the basis of the following observations from the EPRI tests and their associated generic analytical efforts: 1. As a corollary to the EPRI effort to verify the adequacy of RELAPS M001 (Reference 1e), a typical plant evaluation task was undertaken in which Zion was used as a model. This task revealed that the apparent most severe i thermal-hydraulic forcing functions occurred in the second piping segment downstream of one of the safety valves, in the range of approximately 25-50 kips. Forces in the second downstream piping segments for the other two safety valves, and reaction forces at all of the safety and relief valve flanges were considerably less severe. A qualitative preliminary examination of these results with respect to the discharge piping and the safety valve structures indicates that postulated distortions would not j tend to have the effect of impeding the flow necessary to provide adequate overpressure protection. This is believed to be a conservative l determination for the following reasons: s h

.-11. 1.1 The modeling technique used assumes that the entire loop seal volume remains intact at the discharge flange of the safety valve such that no credit is taken for partial flashing of this volume. 1.2 Potential safety valve or discharge piping failures due to distortion are expected to rupture rather than seal off these structures, even though no credit is assumed for plastic deformation. 1.3 No credit is assumed for the low probability of occurrence of an over-pressure transient that may result in a safety valve actuation event, or for mitigation of such transients through PORV operability. 2. No impact on safety valve performance was discernable in the EPRI tests from structural responses. In addition, the valve performance clearly exceeded the operability criteria established for Zion. 3. As shown in Appendix A, safety valve actuation events have a very low probability of occurrence. Also, EPRI tests have shown that the Copes-Vulcan valves, used at Zion, have a high degree of reliability. Because Zion operates with the PORV block valves open, the probability of a safety valve challenges is further reduced. It is expected that the analytical efforts shown in the following action plan will provide the basis to demonstrate that anticipated Zion S/RV piping system thermal-hydraulic forcing functions that exceed the original predictions do not represent a challenge to safe plant shutdown. These analytical efforts will consist of the following: 1. New thermal-hydraulic forcing functions predictions for this system will be generated through use of the RELAP5 M001 computer code. This effort has been initiated and is being performed for us by Sargent & Lundy. 1.1 An element of this effort will be a sensitivity study to determine the effects of elevating the loop seal temperature. Based on a comparison of the EPRI cold loop seal versus warm loop seal test results, it is anticipated that force reduction benefits are likely to be very significant by as much as a factor of 10 to 1. Safety valve inlet temperatures of up to 300 F will be considered. Higher temperatures are specifically excluded in order to avoid potential seat leakage challenges. 2. If the results of this temperature sensitivity study are positive, a feasibility study will be performed to determine what system hardware changes would be required to obtain the maximum achievable increase in loop seal valve inlet temperature. Consideration will be given to loop seal and safety valve insulation, loop seal volume reduction, and loop seal heat tracing. Input to this study is presently being arranged. 3. The maximum feasible safety valve inlet temperature, with a conservative reduction for possible temperature variance, will be incorporated in the RELAPS fl001 analysis. The resultant forcing function predictions will then be compared to the original system forcing function predictions. If the new predictions are uniformly less severe than the originals, verification

.-12 .~ of the system adequacy will be considered complete, pending implementation of the necessary elevated loop seal temperature hardware modifications. 4. If the new forcing function predictions are more severe than the originals, non-conservative differences observed will be used as input to the system structural analysis. The choice of a professional engineering firm to perform this effort will be made if the need to perform the work is confirmed. 5. The results of any warranted structural analysis will be reviewed against the as-built system piping and support hardware. If any modifications are found to be necessary, design of them will be arranged and initiated. 6. Our estimated completion date for the above described analytical efforts is January 1,1983. In summation, the Zion S/RV piping and support system adequacy, in terms of effects on safety and relief valve operability, could not be verified under the prMent thermal-hydraulic forcing function prediction techniques. In our judgment continued operation is justified on the basis of a favorable qualitative review of the EPRI test data and related analytical efforts. It is expected that the adequacy of the Zion S/RV piping and support system in its present form can be demonstrated for purposes of safe plant shutdown. Actions planned to resolve the system adequacy, for operational as well as safety considerations, have been initiated, and completion schedule estimates have been shown. It is therefore believed that the response needed for this aspect of the NUREG-0737 Item II.D.1 requirements have been provided. I L

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