ML17157C529
| ML17157C529 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 10/19/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17157C528 | List: |
| References | |
| NUDOCS 9310280270 | |
| Download: ML17157C529 (9) | |
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UNITED STATES NUCLEAR REGUI ATORY COMMISSION WASHINGTON, D.C, 20555-0001 SAFETY V LUATION B THE OFFICE OF UCLEAR REACTOR REGU TION ATED TO AM DM O. 13 C
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PF-PENNSYLVANIA POWER AND LIGHT COMPANY ALLEGHEN ELECT IC COOP TIVE INC.
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~10 00000 10 By letter dated May 17,
- 1993, as supplemented by letter dated October 7,
- 1993, the Pennsylvania Power and Light Company (the licensee) submitted a request for changes to the Susquehanna Steam Electric Station, (SSES),
Unit 1, Technical Specifications (TS).
The requested changes would reflect a pending modification to Unit 1 that will revise the logic which controls the automatic transfer of the High Pressure Coolant Injection (HPCI) pump suction source on high suppression pool level.
The supplemental letter provided clarifying information that did not change the initial proposed no significant hazards consideration determination.
On July 31,
- 1991, SSES Unit 1 experienced a scram with MSIV closure during which the SRVs were used for pressure control.
During the initial phases of
- cooldown, HPCI was unavailable for pressure control due to high suppression pool level.
Use of the SRVs is consistent with the design basis, but made reactor water level and pressure control difficult for the operators.
The licensee indicated that the use of HPCI for pressure control (i.e. both pump suction and discharge are aligned to the condensate storage tank (CST))
and RCIC for level control allows much smoother control of reactor pressure and level.
Reference 1 documents licensee's plan to enhance the operators'bility to use HPCI in this type of scenario in the future.
The proposed logic will require that the HPCI injection valve F006 be open in addition to the present requirement of a high suppression pool water level in order for the automatic transfer of the HPCI pump suction from the CST to the suppression pool to take place.
This automatically prevents the pump suction transfer when HPCI is not required for injection to the reactor vessel.
The automatic transfer of HPCI pump suction from CST to suppression pool on low CST water level is unaffected by this logic change.
The physical change to the unit involves a relay being added to the HPCI injection valve (F006) control logic to permit transfer of the HPCI pump suction from the CST to the suppression pool on high suppression pool level only when the F006 valve is open.
The relay will be energized by an existing limit switch on the F006 valve that closes as the valve begins to open.
9310280270 931019 PDR
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2 0 KYILNILQH The purpose of the automatic transfer of HPCI.suction on high suppression pool level is to preserve the containment loading assumptions in the existing safety analysis.
Therefore, the impacts on these assumptions as well as HPCI's safety function were evaluated as summarized below:
2.1
~HP 2
The safety function of the HPCI system is to maintain reactor vessel inventory following a Loss of Coolant Accident (LOCA) which does not permit the use'of the low pressure Emergency Core Cooling Systems (ECCS).
The proposed change is designed to ensure that this function will not be affected since the automatic transfer will occur when HPCI injection is required, based on injection valve position.
Various failures associated with the new design were evaluated, and it was determined that failure of the new logic could affect the proper alignment of the suppression pool suction valve (F042) or the F006 valve.
However, in the unlikely event of these failures or previously evaluated
- ones, the Automatic Depressurization System (ADS) will function to ensure that low pressure ECCS can provide adequate core cooling.-
- Further, the new postulated failures wer e evaluated probabilistically,'nd the predicted failure rate of each valve was determined not to change significantly.
In response to a staff question, in their letter of October 7, 1993, the licensee stated that in the event of failure of automatic transfer of suction from the CST to the suppression pool, the transfer can still be performed manually either locally or remotely and failure of the new logic will not interfere with this manual transfer operation.
2.2 Cont inment Anal sis The effect (following an HSIV closure event) of the existing TS is to require suppression pool level control by HPCI if HPCI is used for Reactor Pressure Vessel (RPV) pressure control and suppression pool water level reaches 24 feet.
This is due to the TS requirement that HPCI suction automatically switches to the suppression pool if suppression pool level reaches 24 feet.
Since a high,'suppression pool level is a likely occurrence following an HSIV closure event, the licensee does not use HPCI for pressure control because low quality suppression pool water would thereby be pumped into the reactor.
The result is that in the current configuration, the containment conditions are not impacted by the HPCI system since water is neither taken from the suppression pool nor added.
In the revised configuration, automatic switchover is blocked unless the HPCI injection valve is open.
In the pressure control
- mode, however, the injection valve is closed and HPCI takes its suction from the CST and returns the water to the CST.
Therefore, the containment conditions are not impacted in the revised configuration either, since no water is taken or added to the
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suppression pool.
Therefore, the impact of the proposed change on containment is no different than that of the existing TS, if a pipe break is postulated to maximize containment loading during the pressure control mode.
If the suppression pool water level exceeds the limit defined in TS 3.6.2. 1, the action statements require restoration of level within one hour or placing the reactor in hot shutdown within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and cold shutdown within the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
In the pressure control mode, the reactor is already scrammed and the unit is headed for cold shutdown.
No additional operator actions are required due to the logic modification.
The HPCI turbine has a specified limit on exhaust line backpressure and a
vacuum breaker which prevents siphoning water into the exhaust line.
These features preclude turbine operation at water levels above 26'-0".
In their letter of October 7, 1993, the licensee estimated that the highest suppression pool water level that may be reached during the pressure control mode will not exceed 25'.
2 3 e
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e To effect the proposed change to the HPCI pump transfer logic, the licensee proposed the following revisions to the TSs:
l.
In Table 3.3.3-1, Emergency Core Cooling System Actuation Instrumentation, on Page 3/4-28, add a triple asterisk (***)after 3.d. for the HPCI Trip Function when a suppression pool water level-high signal is received.
2.
Table 3.3.3-1,
- above, presently has footnotes on Page 3/4 3-29a clarifying when the various trip functions are applicable.
The licensee proposes to add a new footnote identified by a triple asterisk (***)to read:
"The automatic transfer of HPCI pump suction from the condensate storage tank to suppression pool on high suppression pool water level occurs only when HPCI injection valve is open."
The HPCI system is activated either by reactor vessel low water level or by primary containment high pressure.
Both of these conditions could result from a postulated LOCA.
Either signal starts the HPCI system and opens the injection valve to the primary system.
With the revised logic, if the injection valve gets a signal to open, the HPCI suction will automatically switch to the suppression pool.
Otherwise, the HPCI suction will be aligned to the Condensate Storage Tank (CST) unless the water level in the CST falls below a prescribed level.
3.
Pages 3/4 5-4, 3/4 5-5, and 3/4 5-5a list the surveillance requirements for the Emergency Core Cooling Systems.
Section 4.5. l.c.4 on Page 3/4 5-5 requires that at least once-per-18-months that the licensee verify "that the suction for the HPCI system is automatically transferred from the condensate storage tank to the
4 suppression chamber on a
CST low-level signal and on a suppression chamber-water level high signal."
The licensee proposed to modify this requirement to add the words "when HPCI injection valve is open" after suppression chamber water level-high signal.
The three proposed'hanges to the TSs described above are to permit the HPCI system to stay aligned to the CST unless there is a potential accident condition requiring automatic HPCI injection. If the plant experiences a
pressurization transient such as occurred on July 31, 1991, with rapid closure of the MSIVs, the operators can use the HPCI system for pressure and level control even if SRV discharges have raised the suppression pool water level to 23'".
With the present logic, the HPCI suction automatically switches to the suppression pool when the 23'" level is reached.
The staff has reviewed the design of the proposed logic change (Modification No. 93-9020) and concluded that it adequately meets all regulatory requirements and will accomplish the design intent.
The staff has also concluded that the logic change will enhance plant safety.
The proposed changes to the TSs define when the logic must be functional and describe the necessary surveillance requirements.
Therefore, the staff finds the proposed TS change acceptable.
3.0
SUMMARY
The HPCI system has the capacity in its test mode alignment to control reactor pressure.
This function and the proposed changes to modify HPCI pump suction transfer logic do not conflict with the primary HPCI function as an
- ECCS, do not adversely impact plant design parameters or safe operation of other
- systems, and are not detrimental to the HPCI system components.
The staff, therefore, finds the proposed change to be acceptable.
4.0
~STATE CONBULTA IIIN In accordance with the Commission's regulations, the Pennsylvania State official was notified of the proposed issuance of the amendment.
The State official had no comments.
5.0 ENV RO NT CONSIDE TION The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes a surveillance requirement.
The NRC 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 significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a
proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (58 FR 34085).
Accordingly, the amendment meets the eligibility criteria for categor ical 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.
. 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 or to the health and safety of the public.
Principal Contributor:
H. Razzaque Date:
October 19.
1993
5-1.
PLA-3707, H.
M. Keiser To T. T. Hartin, "July 31, 1991 Scram Issue Resolution Plan," dated Oecember 30, 1993.
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