ML20248K573
| ML20248K573 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 04/13/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20248K567 | List: |
| References | |
| NUDOCS 8904170378 | |
| Download: ML20248K573 (9) | |
Text
1
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'o UNITED STATES I
NUCLEAR REGULATORY COMMISSION o
l r.
E WASHINGTON D. C. 20655
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NOS. 143 -AND 145 TO FACILITY OPERATING LICENSE NOS OPR-44 and DPR-56 PHILADELPHIA ELECTRIC COMPANY PUBLIC SERVICE ELECTRIC AND GA5 COMPANY DELMARVA POWER AND LIGHT CUMPANY_
ATLANTIC CITY EL %IRIC COMPANY PEACH BOTTOM ATOMIC POWER STATIOM. UNIT NOS. 2 AND 3 DOCKET NOS. 50-277 AND-50-278
1.0 INTRODUCTION
By letter dated January 26, 1989, as supplemented with confirmatory information on March 6, 1989, the Philadelphia Electric Company requested an amendment to Facility Operating License Nos. OPR-44 and DPR-56 for Peach Bottom Atomic Power Station, Unit Nos. 2 and 3.
The March 6, 1989 letter submitted voltage regulation studies that had been completed in January 1989. The amendments would modify the Technical Specifications (TS) to correct deficiencies in the degraded voltage protection features that were identified-as a result of revised voltage regulation studies.
The studies were based in part on the consideration that, under certain offsite power emergency conditions, the voltage provided to the station's i
offsite power supply transformers could be lower than previously assumed.
The study also modeled the plant's power distribution system to a greater level of detail.
The proposed changes are grouped into two categories. The Category A changes involve the degraded voltage protection relays. Category B changes address the Emergency Core Cooling System (ECCS) loading sequer.ce.
Specifically these changes to TS section 3.2 are as fol h s:
1.
Provision of separate undervoltage relays with their associated time delay for transfer of the 4.16KV buses to an alternative power supply for conditions involving the presence of a safety injection signal (SIS) and for conditions not involving an SIS. Specifically, at 98%
of rated voltage, a 60 second time delay is actuated; at 89% of rated voltage, with a concurrent SIS, a 9 second time delay is actuated.
Previously there was one undervoltage setpoint at 90% of rated voltage with time delays of 60 seconds for non-SIS conditions and 6 seconds for a concurrent SIS.
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Change the timing of the Emergency Core Cooling System initiations when offsite power (OSP) is available; the timing will not change when offsite power is unavailable.
FORMER ECCS SEQUENCE Time [ seconds]
Components started 0
480V Safety Loads RHR pumps A,B 5
RHR pumps C,0 10 CS pumps A,B,C,0 This starting sequence would be expected to result in voltage dips of sufficient severity to cause transfer of loads to the diesel generators rather than to the remaining offsite power source.
PROPOSED ECCS SEQUENCE Time [ seconds)
Components started 0
480V Safety Loads 2
RHR pumps A,B 8
RHR pumps C,D 13 CS pumps A,C 23 CS pumps B,0 3.
Delete a footnote relating to modifications to the Unit 3 ADS bypass tiner. The footnote is said to no longer be needed because the modifications have been completed.
2.0 BACXGROUND AND DISCUSSION Each Peach Bottom unit has four 4.16kv buses supplied by two offsite power supplies and four emergency diesel generators. Each unit has two safety divisions with two 4.16ky buses each. The alternate or preferred power supply for any 4.16ky bus is, in order of preference, the remaining offsite power source, then the emergency diesel generator (EDG). One preferred power supply (PPS) feeds one 4.16ky bus in each division; the other is supplied by the alternate offsite power supply. For clarification see figures attached. Each diesel generator feeds one 4.16ky safety bus in each unit. Each startup source to each 4.16ky safety bus is equipped with an instantaneous undervoltage protective relay (UVR). These relays were previously set to initiate at.90 pu of nominal voltage on the 4.16ky buses. The undervoltage relay initiates delayed transfers to the alternate power supply and then to the EDG, if the alternate power supply voltage falls below the undervoltage relay setpoint for a time exceeding the time delay relay (TDR) setpoint. The control circuit logic
. to the time delay relay circuitry distinguishes between low voltages with and without a concurrent safety injection signal (SIS). Without an SIS, a 60 second delay allows time for tap changers to recover voltage. With an SIS, another time delay relay will initiate transfer from one preferred power supply (PPS1 to the alternate, after six seconds. The January 1989 voltage regulation study identified an inadequacy in the six second time delay setting, given an SIS and only one of the two preferred power supplies connected.
The inadequacy revealed is the excessive accelerating time required for the core spray pumps (CS) to come up to speed with the present worst case low voltage condition on the preferred power supplies namely:.934 pu. The failure to accelerate in time would cause the emergency bus voltage to remain low so that a transfer of the 4.16kv bus to another power supply would unnecessarily, occur.
The licensee has proposed the following Technical Specification changes:
Proposed Changes with SIS 1)
Change settings of undervoltage relay (UVR) from.90 to.89 pu; with SIS present.
2)
Change time delay relay (TDR) setting from six seconds to nine seconds with SIS present.
Under single PPS operation and the previous load sequence scheme, the CS pumps would need in excess of 17 seconds to accelerate. Category A changes 1 and 2 above are plainly insufficient, by themselves to correct the problem. Under the licensee's proposed revised loading scheme, to be completed prior to restart, the CS pump will accelerate in the worst case within nine seconds. The proposed technical specification cnanges also entailed changes to tables 3.2.8 and Bases section 3.2 to correctly describe the new relays and setting changes when an SIS is present.
Undervoltages without an SIS present would also cause safety bus transfers to alternate power supplies, were it not for additional relaying now proposed. The licensee proposes to add a UVR set at.98 pu with an associated TDR of 60 seconds to operate only in the absence of an SIS.
The.98 pu setting is needed to ensure an acceptable voltage level to motor control center (MCC) loads (463 and 120 VAC). The licensee has stated that contactors are the limiting case control components and that, following installation of the proposed protective relaying, the safety system components will be adequately protected and capable of performing their safety function.
In addition ^ > the proo.osed ECCS loading sequence, the licensee will further impre a the vc.1. age reculation of the 480V load centers during a motor starting transient by a combination of plant modifications which revise the load shedding or sequencing of the emergency service water pumps, the emergency cooling water pump, the RHR compartment coolers, the
e
. cooling towers and the diesel generator vont supply fans.
The licensee plans to perform these changes pursuant to 10 CFR 50.59 since none involves an unreviewed safety question or a change to the Technical Specifications.
The Appendix K (ECCS Evaluation Models) analysis was used to determine bounding allowable starting times for the RHR and CS pumps. The licensee concluded that the proposed increases in the core spray timer settings are within the Appendix K analysis. Success of the core spray system requires two factors:
- 1) pump ready for rated flow and 2) injection valve open to permit full flow. The earliest time assumed in the Appendix K analysis that the in.iection valve can be opened is 59 seconds of which 12 seconds is valve stroke time, and the pump 3 must be ready for full flow prior to this time. The series of events contributing to the establishment of the pumps ready for rated flow are the sensor times for detection of the LOCA, the time for power to be available at the emergency bus, the time for power to be available to the pump motor and pump motor acceleration time. Taking into account the above equipment operational time requirements, the CS timer setting must be less than 47 seconds. Thus, the proposed 13 and 23 second timer settings are within the analyzed condition.
The licensee has similarly concluded that the proposed increases in RHR pump timer settings are in accordance with the Appendix K analysis.
Success of the low pressure coolant injection (LPCI) mode of the RHR system recuires three factors:
- 1) pump ready for rated flow, 2) injection valve cpen to permit full flow and 3) full closure of the recirculation discharge valve. Under the limiting scenario, 57 seconds are available for the RHR pumps to start and accelerate to rated speed.
Taking into account the sensor and acceleration delays, the RHR timer setting must be less than 50.9 seconds. Thus, the proposed 2 and 8 second timer settings are within the analyzed condition. Neither of these changes involves additional loading onto the DC system. All replacement and additional relays resulting from these changes will be located in existing safety-related panels. The control relays provided will equal or exceed the ratings of the existing relays and meet the applicable design requirements for environmental and seismic qualification.
An additional change is proposed to the Unit 3 Technical Specifications only to delete a footnote which is no longer required since the modification associated with the ADS bypass timer (Modification 633) was completed for Unit 3 on February 24, 1986. Removing the footnote will eliminate the need to check the status of the modification to determine the applicability of the specification. Tha licensee proposes this administrative change to enhance safety by reducing the effort required to interpret the specification.
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.. 3.0 ' EVALUATION The' proposed technical specification changes to the undervoltage relay and time delay relay setpoints are acceptable to the staff subject to completion of the following items.
1)
Revision of the UFSAR in the next update to include the new timing sequence, described above, and other associated timing changes (e.g.
cooling tower loads) not documented in the Technical Specifications.
2)
Completion of modifications to ensure the adequacy of.85 pu of rated voltage at MCC contactors with.98 pu minimum voltage on.
4.16kv safety buses prior to the next restart of each unit.
The proposed changes to undervoltage and time delay settings on safety i
buses and changes to ECCS and related system. loading sequences are acceptable: to the' staff because they ' ameliorate the low voltages found in the electrical distribution systems of both units, both in the balance of plant and in the safety system levels, when the preferred power supply j
v'oltage is low ~and when only one preferred power supply can be connected
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to onsite loads. The frequency with which these conditions occur has been low and-is expected to remain so, so that, usually, onsite voltages will be higher than the worst case analyzed. Overvoltage, another concern when the undervoltage relay is set at.98 pu, is a lesser concern if limited in time and voltage as licensee's analysis shows it should be.
The administrative changes are also acceptable because they improve the consistency and implementation capability of the Technical Specification.
4.0 ENVIRONMENTAL CONSIDERATION
S These amendments involve a change to 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 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 Consnission has previously issued a proposed finding that the amendments involve no significant hazards consideration and there has been no public comment on such finding.
- Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b),
no environmental impact statement nor environmental assessment need be L
prepared in connection with the issuance of the amendments.
5.0' CONCLUSION L
The Commission made a proposed determination that the amendments involve no significant hazards consideration which was published in the Federal j
Register (53 FR 40996) on October 19, 1988 and consulted with the State of Pennsylvania.
No public comments were received and the State of Pennsylvania did not have any conenents.
, b The staff has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the p(ublic will not be endangered by operation in the proposed manner, and2) such act regulations, and the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the
- public, i
Principal Contributors: Charles E. Morris, Robert E. Martin Dated: April 13, 1989
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,o FIGURE 3 PHILADELPHIA ELECTRIC COMPANY PEACH BOTTOM ATOMIC POWER STATION DEGRADED GRID PROTECTIVE RELAY 90 +/- 2 %
(0.1 SEC INTERNAL DELAY) l LOCA 60 SEC TIMER 6 SEC TIMER
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I TRIP FEEDER BREAKER EXISTING DEGRADED GRID PROTECTIVE RELAY LOGIC
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DEGRADED GRID DEGRADED GRID PROTECTIVE RELAY PROTECTIVE RELAY 98 +/.3 %
89 +/.3 %
(1 SEC INTERNAL DELAY)
(1 SEC INTERNAL DELAY)
NON LOCA LOCA 60 SEC TIMER 9 SEC TIMER I
TRIP FEEDER BREAKE A PROPOSED DEGRADED GRID PROTECTIVE RELAY LOGIC
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