ML20086M295
| ML20086M295 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/14/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20086M282 | List: |
| References | |
| NUDOCS 9507240236 | |
| Download: ML20086M295 (5) | |
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J SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0.120T0 FACILITY OPERATING LICENSE NO. NPF-10 t
AND AMENDMENT NO.109 TO FACILITY OPERATING LICENSE NO. NPF-15 SOUTHERN CALIFORNIA EDIS0N COMPANY SAN DIEGO GAS AND ELECTRIC COMPANY THE CITY OF RIVERSIDE. CALIFORNIA THE CITY OF ANAHEIM. CALIFORNIA SAN ONOFRE NUCLEAR GENERATING STATION. UNITS 2 AND 3 DOCKET NOS. 50-361 AND 50-362
1.0 INTRODUCTION
By letter dated September 15, 1993, as supplemented by letter dated September 6, 1994, Southern California Edison Company, et al. (SCE or the licensee) submitted a request for changes to the Technical Specifications (TS) for San Onofre Nuclear Generating Station, Unit Nos. 2 and 3.
The proposed changes would revise TS Table 2.2-1 " Reactor Protective Instrumentation Trip Setpoint limits," Table 3.3-1, " Reactor Protective Instrumentation," Table 3.3-3, " Engineered Safety Feature Actuation System Instrumentation," and Table 3.3-4, " Engineered Safety Feature Actuation System Instrumentation Trip t
Values," and the associated Bases. The revisions to the notes in these tables change the pressure at which the low pressurizer pressure (LPP) trip bypass shall be automatically removed to a consistant value of "before pressurizer pressure exceeds 500 psia (the corresponding bistable allowable value is 472 psia)."
In addition, the wording of the notes is revised to make the notes more consistent with each other.
The September 6,1994, supplemental letter provided additional clarifying information and did not change the initial no significant hazards consideration determination which was published in the Federal Reaister on September 29, 1993 (58 FR 50975).
2.0 DISCUSSION One of the functions of the reactor protection system (RPS) is to initiate a reactor trip whenever the pressurizer pressure falls below the trip setpoint.
The engineered safety feature actuation system (ESFAS) instrumentation initiates a safety injection actuation signal (SIAS) whenever the pressurizer pressure falls below the safety injection setpoint. The reactor trip and the 9507240236 950714 PDR ADOCK 05000361 p
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safety injection actuation functions are provided to mitigate the consequences of an accident such as a main steam line break -(MSLB) or a loss of coolant accident (LOCA).
The LPP trip setpoint may be decreased in a manner prescribed by the TS, with j
the minimum allowed setpoint equal to 300 psia.
Bypass of the LPP trip and actuation of safety injection, namely RPS/ESFAS bypass, is provided to allow for systems testing at low pressure and to allow heatup and cooldown without i
generating an undesired safeguard action. This bypass may be manually l
initiated when pressurizer pressure drops below the bypass permissive setpoint i
and is automatically removed when pressurizer pressure rises above the bypass permissive setpoint.
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The existing Note (2) of Table 2.2-1, in part, states that the LPP trip may be f
manually bypassed below 400 psia and that the bypass shall be automatically removed whenever pressurizer pressure is greater than or equal to 500 psia.
Note (b) of Table 3.3-1, Note (a) of Table 3.3-3, and Note (1) of Tab _le 3.3-4, in part, state that the LPP trip may be manually bypassed below 400 psia and i
that the bypass shall be automatically removed whenever pressurizer pressure is greater than or equal to 400 psia. As r.oted, there is an inconsistency in the existing tables associated with the pressure at which the automatic removal of the LPP trip bypass becomes effective.
l The licensee proposes to remove this inconsistency by revising the TS to state that the LPP trip bypass shall be automatically removed at a pressurizer l
pressure equal to or less than 472 psia.
The pressurizer pressure at which i
the LLP trip may be manually bypassed, below 400 psia, is not being changed by this TS amendment request. The new value of 472 psia is an allowable value which includes total loop uncertainties for the instruments used in the LPP trip circuit and ensures the analytical limit of 500 psia will not be exceeded.
The licensee verified that the analytical limit of 500 psia was acceptable by evaluating all accident scenarios where the pressurizer low pressure setpoint is relied upon to mitigate the consequences of the accident.
In addition to removing inconsistencies in the TS, increasing the value at which the LPP trip bypass must be automatically removed reduces the possibility of inadvertent actuation of the safety injection system during plant shutdown.
This is because the minimum allowed LPP setpoint is 300 psia and, due to an instrument hysteresis of approximately 75 psi, the operators currently have to reduce RCS pressure to 325 psia before the instruments will permit LPP bypass.
This small margin between the LPP trip (300 psia) and the LPP bypass (325 psia) presents an increased chance of inadvertent actuation of i
the safety injection system.
Increasing the pressure at which the LPP trip bypass must be automatically removed from 400 psia to 472 psia will allow the operators to bypass the LPP trip at a pressurizer pressure much closer to the 400 psia TS limit during plant shutdown.
Due to the proposed TS changes, the appropriate sections of the Updated Final Safety Analysis Report (UFSAR) will be revised to incorporate the changes.
These sections include Sections 7.2.1.1.1.6, " Low Pressurizer Pressure,"
7.2.1.1.5, " Bypasses," Table 7.2-2, " Reactor Protective System Bypasses,"
a Table 7.2-7, " Plant Protection System Failure Mode and Effects Analysis,"
7.3.1.1.1, " Safety Injection System," and Table 7.3-4, "ESFAS Bypasses."
3.0 EVALUATION General Design Criterion (GDC) 20, " Protection system functions," of Appendix A to 10 CFR Part 50 states that the protection system shall be designed to (1) initiate automatically the operation of appropriate systems including reactivity control systems, to assure that specified fuel design limits are not exceeded as a result of anticipated operational occurrences, and (2) sense accident conditions and to initiate the operation of systems and components important to safety.
The licensee evaluated the new LPP setpoint to assure that this regulatory requirement was complied with.
The postulated accidents that are affected most by the proposed change are the MSLE and LOCA. The RPS/ESFAS bypass, if in effect, would prevent a reactor trip and safety injection actuation on low pressurizer pressure, to mitigate the consequences of an MSLB or LOCA occurring at these conditions. The consequences of an unmitigated accident could include a potential return to criticality and subsequent approach to the specified acceptable fuel design limits and the potential for exceeding ECCS acceptance criteria.
The higher value (472 psia as opposed to 400 psia) at which automatic removal of LPP trip manual bypass becomes effective has been evaluated by the licensee. An MSLB outside containment with a RCS pressure equal to or less than 500 psia does not require safety injection actuation to mitigate the consequences of the event. At a RCS pressure of 500 psia, the maximum RCS temperature would be less than 467'F (saturation temperature at 500 psia).
In the event of an MSLB at this condition, the total positive reactivity that would be added would be approximately 4.3 percent g as compared to 3.9 percent g that would be added if an MSLB were to occur at 400 psia.
This 4.3 percent g reactivity is the sum of Doppler and moderator reactivity additions and includes uncertainties. The shutdown margin required by the TS in Mode 3 is 5.15 percent g.
Therefore, the shutdown margin is more than sufficient to offset the reactivity insertion due to an MSLB at 500 psia and preclude a return to criticality.
An MSLB inside containment or a LOCA would result in automatic SIAS generated by the ESFAS high containment pressure signal. The high containment pressure actuation of SIAS is maintained during all modes of plant operation.
The high containment pressure SIAS setpoint trip is 3.4 psig (3.7 psig allowable value). As indicated above, an MSLB initiated at 500 psia does not require automatic SIAS to prevent a return to criticality. However, automatic SIAS on high containment pressure would occur for all but the smallest MSLB to provide mitigation for the MSLB inside containment.
The licensee further indicated that the consequences of a LOCA are not sensitive to the initial RCS pressure assumed (either 400 psia, 472 psia, or 500 psia).
At 3.4 psig containment pressure, SIAS would actuate the safety injection equipment that is required to be operable by the TS to mitigate the event.
The rate at which containment pressure increases to the SIAS setpoint
. a following a LOCA is not sensitive to the initial RCS pressure. Automatic SIAS i
on high containment pressure would be expected for all LOCAs except for very small break LOCAs at the small end of tpe break spectrum. Containment i
analysis of the smallest break (0.01 ft ) in the UFSAR indicates that automatic SIAS actuation on high containment pressure would occur prior to core uncovery.
For smaller break sizes, for which a containment high pressure i
signal may not be generated, the time available would be sufficient to credit manual SIAS initiation to mitigate the event.
The licensee has evaluated the consequences of other accidents occurring with the RCS pressure at 500 psia without an automatic SIAS, and determined that these events were not limiting. These events included increased main steam flow, steam generator tube rupture, inadvertent opening of a pressurizer safety valve, primary sample or instrument line break, and loss of normal feedwater.
The staff has reviewed the analyses and assumptions provided by the licensee to justify the new LPP bypass setpoint. The staff has determined that the appropriate accident senerios were considered and that the analytical methodology used to calculate the change in safety limits was correctly l
utilized by the licensee.
The staff concludes that these analyses demonstrate that the new bypass setpoint complies with the regulatory requirements contained in GDC 20.
The staff therefore finds the proposed new bypass setpoint for the LPP to be 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 amendment.
The State official had no comments.
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5.0 ENVIRONMENTAL 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 and change surveillance requirements. 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 Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (58 FR 50975). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR Sl.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
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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 Contributor: Mel B. Fields Date:
July 14, 1995 i
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