ML20207A021
| ML20207A021 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/13/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20207A019 | List: |
| References | |
| NUDOCS 9905260087 | |
| Download: ML20207A021 (6) | |
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UNITED STATES p
- r NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. soggHeM
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.1:a TO FACILITY OPERATING LICENSE NO. NPF-10 AND AMENDMENT NO.144 TO FACILITY OPERATING LICENSE NO. NPF-15 SOUTHERN CALIFORNIA EDISON COMPANY SAN DIEGO GAS AND ELECTRIC COMPANY THE CITY OF RIVERSIDE. CAllFORNIA THE CITY OF ANAHEIM. CALIFORNi6 SAN ONOFRE NUCLEAR GENERATING STATION, UNITS 2 AND 3 DOCKET NOS. 50-361 AND 50-362
1.0 INTRODUCTION
By application dated May 8,1996, as supplemented by letter dated January 13,1999, Southem Califomia Edison Company, et al. (SCE or the licensee) requested changes to the Technical Specifications (TSs) (Appendix A to Facility Operating License Nos. NPF-10 and NPF-15) for San Onofre Nuclear Generating Station, Unit Nos. 2 and 3. The proposed changes would rsvise TSs 3.9.4, " Shutdown Cooling (SDC) and Coolant Circulation - High Water Level," and 3.9.5," Shutdown Cooling (SDC) and Coolant Circulation - Low Water Level." These changes would (1) reduce the minimum water level allowed in the reactor cavity when two loops of SDC are required from 23 feet to 20 feet above the reactor coolant pressure vessel flange; (2) increase the time that a required loop of the SDC system may be removed from service from up to 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> per 8-hour period to up to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> per B-hour period, provided the upper guide structure has been removed from the reactor pressure vessel; (3) allow for running only one loop of SDC with additional requirements when the water level in the reactor cavity is less than 20 feet but greater than 12 feet above the reactor pressuis vessel flange; (4) add an action to be taken when operating only one loop of SDC with less than 20 feet of water above the reactor pressure vessel flange when the specified requirements are not met; and (5) restore I
provisions inadvertently deleted by a previous TS amendment.
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The staff also notes that Amendment No.116 for SONGS Unit 2, and Amendment No.105 for SONGS Unit 3, dated February 15,1995, approved similar TS changes (except for item (5)) c.;
a one-time basis. The licensee requested the proposed TS changes to reduce outage l
durations. The required minimum water level during fuel movement will still remain 23 feet above the reactor vessel flange as specified in TS 3.9.10.
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2.0 BACKGROUND
The two low pressure safety injection (LPSI) pumps provide SDC flow through the reactor core and through the SDC system heat exchanges to provide shutdown plant cooling. As the result of a recent design change, the containment spray pumps may also be aligned to be used in place of LPSI pumps in either or both SDC loops to provide SDC flow.
Limiting Conditions for Operation (LCO) in TSs 3.9.4 and 3.9.5 define the o.erability requirements for the SDC system during refueling operations (Mode 6) while the water level above the top of the reactor vessel flange in the reactor cavity is at least 23 feet, and less than 23 feet, respectively. The 23-foot water level was originally chosen to assure a large heat sink was available for core cooling so that in the event of a failure of the operating SDC loop, there would be adequate time to initiate attemate procedures to cool the reactor core.
3.0 EVALUATION 3.1 Proposed Chances to TS 3.9.4 The licensee proposes to reduce the minimum allowable water level in the reactor cavity from 23 feet to 20 feet above the reactor pressure vessel flange for one train of SDC in operation, and increase the time that the required loop of the SDC system may be removed from service from up to 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> per 8-hour period to up to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> per 8-hour period.
The licensee has added the following operational restrictions under these conditions:
Maximum reactor coolant system (RCS) temperature will be maintained s140*F; No operations will be permitted that would cause a reduction of the RCS boron Q
concentration; The licensee will maintain the capability to close the containment penetrations that have direct access to the outside atmosphere within the calculated time to boil; and The licensee will remove the upper guide structure from the reactor pressure vessel during the time that the required loop of the SDC system is removed from service (up to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> per 8-hour period).
Requiring that the maximum RCS temperature be maintained s140'F during all conditions, including the time when the SDC train is removed from service to test the full flow LPSI pump suction header valve, provides adequate time for the operators to take appropriate actions to maintain RCS inventory. It takes approximately 6 days to reach the point in the outage where the reactor head is removed and the cavity is filled with water. The time to boll with initial conditions of 6 days following shutdown and 20 feet of water above the reactor vessel flange is approximately 3.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. The time to core uncovery with these same initial conditions is approximately 77.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. The time to boil assuming 23 feet of water above the reactor vessel flange is approximately 4.0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />. The reduction of water from 23 feet above the reactor vessel flange to 20 feet above the reactor vessel flange has little impact on the time to boil, thus the basis of having a sufficient heat s!nk to provide core cooling and allow time to take other actions to cool the core in the event of losing the operating loop of SDC is still maintained.
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Ot e By prohibiting operations that would cause a reduction in the RCS boron concentration, the likelihood of an inadvertent boron dilution event is minimized. Boron stratification due to temperature gradients will not develop to any significant extent during the time when no SDC i
loop is in operation. The use of adequately borated water for injection into the RCS during the test provides assurance that the test itself will not lead to a boron dilution event. When the SDC system is operating, the minimum SDC flow rate of 2200 gpm imposed by Surveillance Requirement (SR) 3.9.4.1 and SR 3.9.5.2 is sufficient to ensure complete mixing of boron within the RCS.
The capability to close the containment penetrations that have direct access to the outside atmosphere within the calculated time to boil provides assurance that the likelihood of radioactive material releases to the environment is minimized. The licensee stated in its request that containment closure can be achieved within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, even in the event of a loss of offsite power. The safety function of the containment to control possible radioactive release to the environment is, therefore, maintained.
Specifically requiring that the upper guide structure will be removed assures that natural convection heat transfer is not impeded in the reactor vessel during the time that the SDC loop is secured for testing.
1 The time that the SDC system is allowed to be secured is proposed to be increased to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
This is acceptable because of the operational restrictions identified in the second paragraph of Section 3.1, above, which ensure maintaining appropriate operating conditions.
During the short test of the full flow LPSI pump suction header valve, the water level is being increased by approximately 4 to 20 inches with a high flow rate of cool borated water from the refueling water storage tank. The 6-hour period following the test that the SDC system would be required to run is adequate to provide mixhg and prevent boron stratification.
In its January 13,1999, supplemental amendment request, the licensee stated, "[i]n the request for the October 10,1991, waiver of compliance, the.'ncrease in the RCS temperature without SDC in operation due to decay heat was estimated to be e maximum of 2.6*F per hour." This temperature increase rate ss not generally applicable io the conditions covered by the licensee's amendment request, and was not credited by the staff in this evaluation.
Based on the above discussion, the staff finds acceptable the licensee's proposal to lower the minimum allowable water level in TS 3.9.4 to 20 feet above the top of the reactor vessel flange, and increase the time to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> per 8-hour period that a required loop of the SDC Fystem may I
I be removed from service. The staff concludes that the operational restrictions that the licensee proposed will continue to assure that a sufficiently large heat sink will be available for core cooling, so that in the event of a failure of the operating SDC loop, adequate time would be available to initiate attemate means to cool the core. In addition, the staff concludes that the operational restrictions will reasonably assure adequate mixing and prevent boron stratification in the RCS.
3.2 Proposed Chanoes to TS 3.9.5 To maintain consistency with TS 3.9.4, the licensee proposed to change the a,cplicability of TS 3.9.5 to reflect actions required when the water level is less than 20 feet above the top of the
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.4 reactor vessel flange. Currently, TS 3.9.5 is applicable when the water level is less than 23 feet above the top of the reactor vessel flange.
The licensee proposed to add the following operational restrictions to TS 3.9.5 to enhance plant safety under reduced water inventory conditions.
a.
The reactor will be shut down for at least 6 days; b.
The water level above the reactor vessel flange is 12 feet or greater; c.
The associated loop of satt water cooling (SWC) is OPERABLE and operating; d.
The associated component cooling water (CCW) pump and the CCW swing pump are OPERABLE, and the associated CCW loop is OPERABLE and operating; e.
The SDC system is operating using the containment spray pump, and the associated high pressure safety injection (HPSI) pump and the low pressure safety injection (LPSI) pump are OPERABLE and at ambient temperature, available for injections from the refueling water storage tank (RWST);
f.
The RWST contains the volume of water required to raise the refueling water level to 20 feet above the reactor vessel flange; g.
The associated emergency diesel generator is OPERABLE; and h.
The water temperature of the SDC system is maintained less than 120*F.
Requiring the reactor to be shut down for at least 6 days ensures that the time to boil is greater than twice the time it would take to establish containment closure, and significantly more time i
than it would take to commence reactor cavity fill with the required standby equipment.
Furthermore, the time to boil and time to uncover the core increase with each subsequent day following reactor shutdown. With the reactor cavity water level at 12 feet above the flange and 4
at 6 days after shutdown, it takes approximately 2.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> to boil and 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to uncover the i
core. Since containment closure can be achieved within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> even in the absence of offsite power, this will provide a minimum of a 1.3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> margin. If the operating SDC train becomes inoperable, attemate means of providing ccalant to the RCS can be initiated in approximately 09 minutes, and the water level can be raised to the 20-foot level above the reactor vessel flange in approximately 25 additional minutes.
Limiting the water level above the reactor vessel flange to 12 feet or greater provides sufficient coolant inventory to allow time for corrective actions. Although 12 feet will be the absolute lower & nit, the normal lower limit will be closer to the 12-foot 9-inch level needed to support the plannsd outage work. The reactor pressure vessel flange is approximately 11 feet above the top of the fuel. Therefore, the water level will be a minimum of 23 feet above the fuel, thus maintaining a large volume of water to provide a heat sink.
Operational restrictions c. d, e, f. and g assure that the necessary support systems providing cooling to the core are operable end in geration, and assure the availability of backup systems to provide coolant to the RCS. In the event that CCW is lost, cooling flow to all ECCS
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[ emergency core cooling system) pumps is also lost. The LPSI pump can start cold and raise j
the reactor cavity water level from 12 feet above the reactor vessel flange to 20 feet above the reactor vessel flange in approximately 25 minutes without CCW flow. The HPSI pump will also be maintained as a standby pump ready to increase the water volume if needed. In support of j
this contingency, the licensee will maintain the RWST with the volume of water needed to raise the level to 20 feet above the reactor vessel flange.
Operational restriction h. requires that the water temperature of the SDC system be maintained less than 120*F. This provides the operators with sufficient time to react to potential loss of cooling situations. The normal operating temperature for water levels below 20 feet are typically less than 100*F.
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TS 3.9.5 further stipulates that if only one loop of the SDC system is operable with less than 20 feet of water above the reactor vessel flange and any of the required operational restrictions are not met, the licensee will take action immediately to establish greater than or equal to 20 feet above the reactor vessel flange. By taking action to restore the level to 20 feet above the reactor vessel flange, the licensee will place the plant in TS 3.9.4, which requires only one loop of SDC to be operable. Additionally, the core will not heat up while the reactor cavity water level is being raised with cool water from the RWST. This will provide additional time to either restore one loop of SDC or take other actions to provide core cooling as renuired by TS 3.9.4.
The provisions of the operational restrictions supporting this TS change ensure that there is adequate time to take action and provide a method to restore the reactor cavity water level to 20 feet above the reactor vessel flange, taking the plant to a condition bounded by TS 3.9.4.
Based on this evaluation, the staff finds acceptable the licensee's proposal to use 20 feet above the top of the reactor vessei flange as the definition of low watei level in TS 3.9.5. The operational restrictions that the licensee imposed will provide additional assurance that a sufficiently large heat sink will be available for core cooling, and will minimize the possibility of losing the ability to ccal the core.
3.3 Restore Provisions inadvertentiv Deleted by a Previous TS Amendment Amendment No.127 for SONGS Unit 2, and Amendment No.116 for SONGS Unit 3, added a note to the LCO for both TS 3.9.4 and TS 3.9.5. The note reads:
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A containment spray pump may be used in place of a low pressure safety injection pump to provide shutdown cooling flow.
1 Prior to these amendments, the note had included the phrase, "in either or both shutdown cooling loops." The licensee proposed to restore this phrase, which was inadvertently deleted with the issuance of TS Amendment Nos.127 and 116.
The addition of this phrase brings the TS back into conformance with the approved use of the containment spray pumps. The staff, therefore, finds this editorial change acceptable.
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4.0 STATE CONSULTATION
in accordance with the Commission's regulations, the California State official was notified of the proposed issuance of the amendments. The State official had no comments.
5.0 fJiylRONMENTAL CONSIDERATION The amendments change a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve 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 significant increase in individual or cumulative occupational radiation exposure. The
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Commission has previously issued a propiosed finding that the amendments involve no significant hazards consideration, and there has been no public comment on C,uch finding (64 FR 14285). Accordingly, the amendments. meet the eligibility criteria for categorical exclusion j
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 amendments.
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 amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: M. B. Fields W. Lyo::
i Date: May 13, 1999
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