ML20055G510
| ML20055G510 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 07/18/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20055G509 | List: |
| References | |
| NUDOCS 9007230264 | |
| Download: ML20055G510 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF HUCLFAR REACTOR REGULATION RELATED TO AMENDMENT NO. 32 TO FACILITY OPERATING LICENSE NO. NPF-58 THE CLEVELAND ELECTRIC ILLUMINATING COMPANY, ET AL, PERRY NUCLEAR POWER PLANT, UNIT NO. 1 DOCKET NO. 50-440
1.0 INTRODUCTION
By letter dated May 20, 1988, the Cleveland Electric Illuminating Company, et al. (licensees)~, requested a license amendment for the Perry Nuclear 3
Power Plant, Unit No. 1.
The proposed amendment would modify the control rod scram accumulator alarm setpoint of Technical Specification (TS) 4.1.3.3.b.2 from 1535 + 15 psig to greater than or equal to 1520 psig. The licensees' request was submitted following recommendations from General Electric r
- Company (GE) as contained in GE Service Information Letter (SIL) -429 Revision 1 dated January 18, 1988, "HCU Accumulator Pressure Switches." The SIL documents problems experienced with significant low-side instrument j
drift experienced for the subject pressure switches beyond the margin j.
provided by the current TS alarm setpoint. The purpose of the alarm setpoint is-to maintain sufficient nitrogen pressure in the HCU accumulator for required' control rod scram performance.
l 2.0 DISCUS $10N The-control rod scram accumulators are used to provide the driving force for inserting control rods following a scram signal. The scram accumulators are hydraulic cylinders with an internal free floating piston. The piston L
separates the water on top from the nitrogen gas underneath. The scram-accumulator is precharged-with Nitrogen gas, and charging water pressure l
compresses the gas.to a nominal pressure of approximately 1720 psig. When a scram signal is generated, water in the scram accumulator.and charging line is L
admitted under the Control Rod Drive-Mechanism (CRDM) drive piston, and the L
water above the piston is vented to the scram discharge volume (SOV). The l
large differential pressure between the accumulator and the SDV produces a l'
large upward force on the index tube of the CROM.
This force gives the rod a high initial acceleration and provides a large margin of force to overcome L
friction and the weight of the rod.
After the initial acceleration is achieved, the CRDM insertion continues at a nearly constant velocity. -This characteristic provides a high initial rod insertion rate. As the drive piston nears the top of its stroke, the piston seals close off the large passage (buffer shaft orifices) in the buffer shaft, and the drive slows.
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.,.. In addition to the accumulator, reactor pressure can also be used to scram the control rods. Upon a scram, the accumulator provides the initial pressure to insert the control rod. As the accumulator discharges, its pressure drops rapidly. When_the accumulator pressure drops below the reactor pressure, reactor pressure-forces a ball check valve in the CRDM to unseat, blocking accumulator pressure and allowing reactor pressure to complete the drive stroke. At reactor pressure greater than about 600 psig, reactor pressure alone is capable of scramming the drive. At low pressures (less than 600 psig), the accumulator is necessary to scram the drive.
The accumulator pressure is verified weekly in accordance with the surveillance requirements of TS 3.1.3.3. -In addition, pressure switch alarms are provided to monitor the accumulator pressure between weekly surveillances. The pressure switch detectors are presently set to alarm at 1535 + 15 psig on decreasing pressure in accordance with TS surveillance requirement 4.1.3.3.b.2.
- However, the upper setpoint limit of 1550 psig has not provided sufficient-flexibility to assure that the pressure switch alarms at an accumulator pressure of greater than or equal to 1520 psig. This is because the present TS setpoint does not always provide sufficient instrument drift margin.
The licensees have stated that at initial startup, the calibrated setpoint range for the pressure switches was between 1520-1550 psig.
The first major
-TS required surveillance of the pressure switch setpoints was performed on December 27, 1985. During this surveillance, 48 percent of the pressure switches alarmed outside of the calibrated setpoint range specified by the present TS (11.4 percent alarmed at 1520 psig or below.) TS required surveil-lances were again performed for 86 HCU pressure switches on January 15, 1986.
Twenty-two percent of the alarm setpoints actuated outside of the calibrated setpoint range (12.8 percent alarmed at 1520 psig or below). On August 8,1987 all 177 HCU Accumulator Alarm Pressure Switch.surveillances were performed.
This time 42.9 percent actuated outside of the calibrated setpoint range with 14.7 percent alarming at or below 1520 psig.
Based on this operating experience, it does not appear that tha 30 psig band (1520-1550 psig)has provideri adequate instrument drift margin for certain of the installed.
accumulator pressure switches.
To allow for sufficient instrument drift margin, the requested change proposes to amend the surveillance requirements (TS 4.1.3.3.b.2) to state that the low pressure alarm be set at " equal to or greater than 1520 psig" on decreasing pressure with no upper setpoint limit. This would allow for a sufficiently high setpoint value to be established.
3.0 EVALUATION The HCU accumulator pressura switches are bourdon tube devices manufactured by Barksdale, Inc. with a p(Model No. BIT-GH32SS). roof pressure of 4800 psig and an adju range of 160-3200 psig As stated in GE SIL-429 Revision 1, the major concern associated with the upper setpoint for the low pressure alarm is that the selected alarm setpoint should not be set so high that the alarm fails to reset following accumulator repressurization after a scram. The licensees have indicated that if this were to occur, the affected accur!)aMds) would be declared inoperable and the appropriate action state eu f TS 3.1.3.3 would be taken.
Foilure of the alarm to reset in this manner would also not affect the ability of the accumulators to function
.. - s during a scram.
All that would be lost would be the alarm function.
GE SIL-429 Revision I has recommended a nominal trip setpoint of 1605 psig on decreasing pressure which should provide adequate setpoint drift margin while avoiding the concern of a too-high setpoint mentioned above. The SIL also states that higher settings may require more frequent nitrogen addition during normal operations (due to alarms actuating at a higher pressure than at present time). This does not represent a safety concern since the accumulators are located in containment which is normally accessible during plant operations. Additionally, discussions with the licensees have indicated that occupational radiation exposure as a result of the change is insignificant. The accumulators are located in a low dose rate
-(approximately 2.5 mrem /hr.). See Figure 12.3-3 of the Updated Safety Analysis Report.
It_ takes approximately 30 minutes to recharge an alarming cylinder, back to its normal pressure of 1750 psig. The calculated additional alarms (due to setting the actual alarm setpoint at a higher value as recomended by GE SIL-429 Revision 1) experienced in a given year would be approximately 22. This results in approximately 11 additional-hours in containment in this low dose area or approximately 28 additional mrem of. exposure. This would be spread over six shifts and is considered insignificant.
The staff has determined, based on the above, that the proposed change would provide increased allowance for expected instrument drift and would reduce the likelihood that a given accumulator would be at a lower pressure than the 1520 psig required for performance of its intended safety function.
Further, the staff has determined that approval of the proposed amendment would not other-wise create a safety concern with respect to the ability of the accumulator to perform their safety. function.
Therefore, the staff finds the proposed TS change to be acceptable.
4.0 ENVIRONMENTAL CONSIDERATION
This amendment involves a change to a surveillance requirement. 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 significant increase in individual or cumulative occupational radiation exposure. The Comission has previously issued'a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(o), no environmental impact statement or environmental assessment need be prepared in c.onnection with the issuance of this amendment.
S '. 0 CONCLUSION The staff has concluded, based on the considerations discussed above, that
-(1) there is reasonable assurance that the health and safety of the public L
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'D will not be endangered by operation in the pro >osed manner, and (2) such activities will be conducted in compliance wit 1 the Commission's regulations and the issuance of this amendment will not be inimical to the common defense
- and security.or to-the health and safety of the public.
3 Principal Contributor:
T. Colburn Dated:.
July 18, 1990 i
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