ML20237D347
| ML20237D347 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 07/31/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20237D202 | List: |
| References | |
| NUDOCS 9808260073 | |
| Download: ML20237D347 (7) | |
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t UNITED STATES s
g NUCLEAR REGULATORY COMMISSION 2
WASHINGTON, D.C. 2066H001 4.....,o g-SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.123 TO FACILITY OPERATING LICENSE NO. NPF-43 DETROIT EDISON COMPANY FERMI 2 l
DOCKET NO. 50-341 i
1.0 INTRODUCTION
By letter dated January 28,1998 (NRC-98-0011) as supplemented March 12 and June S,1998, the Detroit Edison Company (DECO or the licensee) requested an amendment to the Tec.hnical Specifications (TS) appended to Facility Operating License No. NPF-43 for Fermi 2. The proposed amendment would revise Technical Specification 3.4.2.1, " Safety / Relief Valves,"
changing the safety relief valve (SRV) setpoint tolerance from *1 percent to i3 percent. An associated footnote would be revised to indicate that, although the as-found setpoint tolerance is
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13 percent, the as-left settings of the SRVs shall be within 11 percent of the specified set points prior to installation of the SRVs after testing. Bases Section 3/4.4.2 would also be revised. The March 12 and June 9,1998, letters provided clarifying information that was within the scope of the original Federa/ Register notice and did not change the staff's initial proposed no significant hazards considerations determination.
2.0 BACKGROUND
The proposed change does not alter the SRV lift set points, the SRV lift setpoint test frequency, or the number of SRVs required to be operable. Also, the proposed change requires the as-left safety valve function settings to be within 11 percent of the specified nominal lift set points prior to installation after testing. The staff has previously granted plant-specific approval to individual boiling water reactors (BWRs) to increase the as-found SRV tolerance to 13 percent. The bases for the approval of tt ese plant-specific amendments were the plant-specific submittals and a staff safety evaluation (SE) dated March 8,1993, for licensing topical report (LTR)
NEDC-31753P, *BWROG In-Service Pressure Relief Technical Specification Revision Licensing Topical Report" (Proprietary information. Not publicly available.), dated February 1990, evaluating the setpoint tolerance increase. The staff SE included six conditions which must be addressed on a plant-specific basis for licensees applying for the increased SRV setpoint tolerance:
(a)
Transient analysis of all abncrmal operational occurrences as described in NEDC-31753P should be performed utilizing a 13 percent tolerance for the safety mode of spring safety valves (SSVs) and SRVs. In addition, the standard reload methodology (or other method approved by the staff) should tw vied for this analysis.
9808260073 900731 PDR ADOCK 05000341 P.
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2-(b)
Analysis of the design-basis overpressurization event using the 3 oarcent tolerance limit is required to confirm that the vessel pressure does not exceed the American Society of Mechanical Engineers (ASME) pressure vessel code upset limit.
(c)
The plant-specific analysis described in items (a) and (b) should assure that the number of SSVs and SRVs, and relief valves (RVs) included in the analyses correspond to the number of vMves required to be operable in the TS.
(d)
Reevaluation of the performance of high pressure systems (pump capacity, discharge pressure, etc.,), motor-operated valves, and vessel instrumentation and associated piping must be completed, considering the 3 percent tolerance limit.
(e)
Evaluation of the effect of the i3 percent tolerance on any plant-specific operating modes (e.g., increased core flow, extended operating domain, etc.) should be completed.
(f)
Evaluation of the effect of the 3 percent tolerance limit on the containment response during loss-of-coolant accidents (LOCAs) and the hydrodynamic loads on the SRV discharge lines and containment should be completed.
3.0 EVALUATION The safety objective of the SRVs is to prevent overpressurization of the nuclear system. This protects the nuclear system process barrier from failure which could result in the uncontrolled release of fission products. The pressure relief system at Fermi 2 includes fifteen SRVs, arranged into three setpoint groupings of five each: one group of SRVs set at 1135 psig, a second group of SRVs set at 1145 psig, and a third group of SRVs set at 1155 psig. Existing TS require a *1 percent as-found setpoint tolerance and *1 percent as-left setpoint tolerance. The proposed TS changes would require a i 3 percent as found setpoint tolerance and a *1 percent as-left setpoint tolerance. The licensee's submittal was evaluated against the generic SE described above.
3.1 Transient Analvsis/ Reload Methodoloav The licensee must consider the impact of the tolerance increase on abnormal operational transients (AOTs). For Fermi 2, the licensee performed analyses of AOTs using the i3 percent tolerance assuming 11 of the total 15 SRVs in service (the minimum required by TS). The transient that generates the limiting reduction in critical power ratio is the feedwater controller failure with the turbine bypass system and moisture separator reheater out of service and reduced feedwater temperature.
Based on the analysis, the thermal limits of the limiting transient would not be affected by the relaxation of SRV setpoint tolerance because the limiting value of the thermal limit occurs before l
the SRVs open. Further, other transient events remain non-limiting and bounded by the above event. The NRC-approved licensing analysis methodology (as documented in the licensee's October 14,1997, letter forwarding the Fermi 2 Cycle 6 Core Operating Limits Report) was used for the analysis. The staff reviewed the results of these analyses and finds them acceptable.
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The licensee also evaluated the uncertainty associated with the testing of the SRVs and its effect on the transient analysis to support this TS change. The licensee stated that ANSI /ASME Standard PTC-25.3-1976 requires a setpoint testing uncertainty of less than 0.5 percent and that vendors who perform the testing typically use instruments with accuracies of to.1 percent to ensure that this requirement is met. The licensee further stated that this uncertainty equates to approximately 1 psi of instrument inaccuracy which is small compared to the allowed positive as-found setpoint drift of approximately 34 psi Therefore, the licensee concluded that it is not necessary to account for this uncertainty in the analysis. The staff reviewed the licensee's evaluation and finds that the setpoint testing uncertainty is small compared to both the allowable tolerance and the margin in the analysis and that this is acceptable.
3.2 Analysis of the Desian-Basis Overoressurization Event The licen' ee is required to reevaluate the limiting design-basis pressurization transient using the s
3-percent tolerance limit to confirm that the vessel pressure does not exceed the ASME pressure vessel code upset limit. The ASME Boiler and Pressure Vessel Code Section 111 permits pressure transients up to 10 percent over design pressure (110 percent x 1250 psig =
1375 psig). The limiting pressurization AOT analyzed is a main steam isolation valve (MSIV) closure event occurring at the end of full power life without credit for reactor trip on MSIV position sensing. The licensee analyzed the MSlV closure event with the 3-percent tolerance and calculated the maximum vessel pressure to be 1315 psig. This is within the 1375-psig
~ASME limit and is acceptable to the staff.
3.3 TS Operability Statement for SRVs The licensee has stated that all plant-specific analyses have been conducted with the number of SRVs included in the analyses corresponding to the number of valves required to be operable in TS. The analyses took credit only for 11 of the 15 SRVs required by the TS. This is acceptable to the staff.
As reported in several Licensee Event Reports (LERs), the Fermi 2 SRVs have experienced several occurrences of positive setpoint drift in excess of the *3 percent used in the licensee's analybis to support this TS change. As a corrective action, the licensee has stated that it will install platinum ion-beam bombarded pilot valve disks in the plant SRVs during the next (sixth) refueling outage currently scheduled to begin in August 1998. The licensee believes this modification will allow the plant SRVs to meet the proposed TS setpoint tolerance of *3 percent during future refueling cycles. The licensee a~lso states that, should the TS limits be exceeded, it would be required to analyze the resultant potential overpressurization transient and notify the
. NRC via an LER. The platinum ion-beam bombarded pilot valve disks have significantly reduced the SRV setpoint drift experienced at another BWR plant site having SRVs of the same design as those at Fermi 2. The staff reviewed the licensee's planned near-term corrective action and finds that it is appropriate and consistent with the proposed TS change to the SRV setpoint tolerance.
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4 3.4 Reevaluation of the Perform'ance of Hioh Pressure Systems 3.4.1 System Performance The licensee must also reevaluate performance of high pressure systems (pump capacity, discharge pressure, etc.), coraidering the 3-percent tolerance limit. Fermi 2 has three systems whose performance could be affected by the increased pressure and that are required to inject to the vessel at high pressure conditions: high pressure coolant injection (HPCI), reactor core isolation cooling (RCIC) and standby liquid control (SLC). The most significant impact is the increased reactor pressure specified for system operation. The systems' performances were evaluated for the new reactor pressure of 1169 psig from 1146 psig. The HPCI system was determined to have the capability to inject its design flow of 5000 gallons per minute to the vessel at the new maximum pressure of 1169 psig without any changes. The RCIC turbine / pump maximum speed is increased from 4550 rpm to 4600 rpm in order for the RCIC system to perform at the new maximum reactor operating pressure. The increased speed reduces the overspeed margin from 125 percent to 122.3 percent. The licensee considered the reduction in margin acceptable due to the system modifications made in the turbine start feature.
The licensee also determined that the SLC system was capable of injecting boron into the vessel at its design flow rate.
3.4.2 Evaluation of Motor-ooerated and Air-Ooerated Valves in support of the SRV and SV tolerance increase from *1 percent to 13 percent, the licensee reviewed the motor-operated valves (MOVs) and the air-operated valves (AOVs) in the HPCI, RCIC, and SLC systems. The licensee determined that all such MOVs and AOVs can operate within their performance capability.
l 3.4.3 Evaluation of Pinina l
l The licensee also evaluated the effects of the higher pressures associated with the increased I
setpoint tolerance on the instrumentation and piping for the HPCI, RCIC, and SLC systems. The licensee determined that, with the exception of the calibration change for the increased speed of the RCIC turbine, no changes to instrumentation will be required. The licensee also determined that the impact of the higher pressure on system piping and other components was negligible.
3.4.4 Conclusion for Hiah Pressure Systems The staff reviewed the licensee's evaluation of the effect of the proposed change in SRV setpoint tolerance on high pressure systems and finds that, with the change in the speed of the.
RCIC turbine, the HPCI, RCIC, and SLC systems will remain capable of performing their design functions considering the higher pressures associated with the change in the SRV setpoint tolerance.
l l-3.5 Alternate Ooeratina Modes The licensee must also evaluate the increased tolerance on any plant-specific attemate operating modes (e.g., increased core flow, extended operating domain, etc.) The licensee's
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analyses considered the currently approved operating domains: maximum extended operating domain, increased core flow and single-loop operation. The staff finds that the consideration of these altemate operating modes in the analyses is acceptable.
3.6 Containment Resoonse / Hydrodynamic Loads The licensee must also evaluate the effect of the increased tolerance limit on (1) the containment hydrodynamic loads during LOCAs and (2) the hydrodynamic loads on the SRV discharge lines and the suppression chamber.
The licensee examined the potential effects of the proposed amendment on the containment design limits. The containment design-basis accident is a double-ended break at the suction of a recirculation pump. For this event, the reactor coolant system depressurizes very rapidly and thus, the SRVs are not challenged. Also, the reactor coolant system inventory and primary system heat sources that would contribute to the containment mass and energy are not increased. The setpoint tolerance thus has no effect on the capability of the containment to '
perform its design-basis safety function (i.e., the containment peak temperature and pressure loads would not be adversely affected). The staff notes that small break LOCAs also would not lead to increased reactor coolant system pressure and subsequent SRV challenges.
An increase in SRV setpoint tolerance involves a potential increase in SRV discharge dynamic and hydrodynamic loads on the SRV discharge piping and the torus. The licensee analyzed the loads and compared the increases to the margins determined in the Fermi 2 Plant Unique Analysis Report. The results demonstrated that the increased torus loads are acceptable for all SRVs. Similarly, the increases in the loads on the SRV piping and main steam lines due to the increased SRV setpoint tolerance were evaluated and found to be acceptable.
The staff reviewed the information provided by the licensee concerning the containment response and the dynamic and hydrodynamic loads on the SRV discharge piping and torus and finds that the results are acceptable.
3.7 Emeroenev Core Coolina System (ECCS) LOCA Performance The Fermi 2 LOCA analyses (NEDC-31982P, " Fermi-2 SAFER /GESTR-LOCA Loss-of-Coolant Accident Analysis," July 1991, proprietary information - not publicly available) were reviewed by the licensee to determine the effect of an increase in SRV opening pressures on ECCS performance. The limiting break LOCA, the design-basis accident reactor recirculation line break, the small break and the steam line break outside containment events were evaluated to determine the effects of the increased SRV setpoint tolerance. Peak cladding temperatures for the small break and the steam line break outside containment are not changed significantly and they are non-limiting. Thei increased SRV asipoint tolerance has no effect on the recirculation line break analyses because the SRVs do not actuate in that event. The acceptance criteria given in 10 CFR 50.46 are still satisfied for all break sizes and locations. The staff revMred the information provided by the licensee and concludes that the setpoint tolerance change is acceptable with respect to ECCS-LOCA considerations.
1 6-3.8 Effant on Anticipated Transient Without Scram (ATWS) Events The main steam isolation valve closure under ATWS conditions was reevaluated to support the current condition of 11 of the 15 SRVs operable with the requested relaxation in SRV setpoint tolerance to 13 percent. The results of the analysis, using the ODYN cede, show that the vessel pressure reaches a maximum of 1457 psig, which is within the vessel overpressure criterion of 1500 psig for ATWS events. The staff determined that the use of the ODYN code for this application is acceptable in this case. The long-term effect on suppression pool temperature due to 13 percent SRV tolerance is nyligible because there is little change in the total energy discharged to the pool. The staff concludes that the results of the analyses are acceptable.
3.9 Technical Specification Chanoes in TS 3.4.2.1, " Safety / Relief Valves," the setpoint tolerance for the SRVs is changed from 11 percent to 13 percent. In s,ddition, the following is added to the existing footnote:
Although the as-found lift setting tolerance is 13%, the as-left lift settings shall be within 11% of the specified setpoints prior to installation following testing.
These changes are acceptable to the staff as described in this SE.
In TS Bases 3/4.4.2, the following sentence is added:
1 Although the safety / relief valves are tested to demonstrate that opening pressures are within i3% of the nominal pressure setpoints, they are adjusted to within i1% of the nominal pressure setpoints prior to reinstallation.
This change is acceptable to the staff as described in this SE.
3.10 Conclusion Based on the information provided by the licensee, the staff concludes that the plant will continue to satisfy the acceptance criteria for the limiting pressurization transient, AOTs, and design-basis accidents. The staff concludes that the proposed changes are acceptable.
4.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Michigan State official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to the installation or use of a facility l
component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no j
significant increase in individual or cumulative occupational radiation exposure The
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Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration and there has been no putvic comment on such finding (63 FR 9600). Accordingly, the amendment meets the elioSility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security er to the health and safety of the public.
-l Principal Contributors: G. Thomas C. Hammer Date: July 31,1998 i
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