ML20199F697
| ML20199F697 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 01/23/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20199F688 | List: |
| References | |
| NUDOCS 9802040081 | |
| Download: ML20199F697 (3) | |
Text
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g UNITED STATES g
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NUCLEAR REGULATORY COMMISSION t
WASHINGTON, D.C. J06er 9001 e
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.156 TO FACILITY OPERATING LICENSE NO. NPF-49 NORTHEAST NUCLEAR ENERGY COMPANY. ET AL.
81LLSTONE NUCLEAR POWER STATION. UNIT NO. 3 DOCKET NO. 50-423
1.0 INTRODUCTION
By letter dated November 14, 1997, the Northeast Nuclear Energy Company, et al. (the licensee), submitted a request for changes to the Millstone Nuclear Power Station, Unit No. 3 Technical Specifications (TS).
The requested changes to TS 4.5.2.d.1 would clarify the wording and increase the setpoint for the open pressure interlock (OPI).
2.0 BACKGR0bND l
One function of the residual heat removal (RHR) system is to provide cooling of the reactor coolant system (RCS) n
'emove decay heat from the core.
The RHR system is a low pressure system t
, most of the piping and components s
rated at 600 psia.
Since the RCS operates at 2235 psig, the RHR system requires isolation valves to prevent carpressurization.
The OPI is present on two of the three isolation valves (the third valve is normally closed with its power breaker locked out). The OPI prevents inadvertent opening of the suction / isolation valves when the RCS pressure is above the design pressure of the P'IR system considering RHR pump discharge pressure.
Licensee Event Report 97-031 described an event which concluded that the RHR system OPI did not comply with TS surveillance requirements. As a result of inappropriate calibration techniques, the OPI bistable was calibrated to a nominal 390 psia decreasing pressure and did not consider the effects of instrument uncertainties and reset tolerances. As a result, the bistables could prematurely trip on a decreasing pressure signal (above 390 psia) and then reset on an increasing pressure signal at an even higher pressure. TS Surveillance Requirement 4.5.2.d.1 currently requires verifying automatic action of the RHR system from the RCS by ensuring that with a simulated or actual RCS pressure signal greater than or equal to 390 psia the interlockr prevent the valves from being opened.
Therefore, the requirements of the la were not being met.
In its letter dated Nosamber 14, 1997, the licensee proposed (1) changing the pressure from 390 psia to 412.5 psia to take the bistable reset into account and, (2) to delete the words "or actual reactor coolant system pressure."
9802040081 900123 PDR ADOCK 05000423 P
' 3.0 EVALUATION 3.1 Setpoint Change In the November 14 letter, the licensee stated that a number of f actors are taken into account in the setting of the OPI:
Additional system pressure protection is provided by the RHR suction a.
relief valves; these valves have a setpoint of 44013% psig (426.8 a53.2 psig).
Therefore, the OPI setpoint must act exceed the minimum setpoint of the RHR suction relief valve of 426.8 psig (441.8 psia, assuming a 15 psi conversion from psig to psia).
b.
The RCS system presJure plus the RHR pump discharge pressure developed when the pumps are operating must not exceed the 600 psig piping and component limit. During recent RHR system testing, the licensee determined that the maximum develo differential pressure (dead head pressure). ped pump discharge pressure is 195 psid Therefore, based on this c
, the OPI setpoint should be no higher than 405 psig (600 psig - 195 psi = 405 psig or 420 psia).
t c.
The current operating procedures for the RHR system discuss initiating RHR/RCS cooldewn at less than 390 psia /350*F (Mode 4 is defined as Km less than 0.99, percent rated thermai power equals zero, and temperature less than 350*F and greater than 200*F).
Therefore, the OPI setpoint should be greater than 390 psia, in order to account for instrument inaccuracies, deadbands, resets, etc., the licensee stated that 412.5 psia was determined to be the upper limit at which the OPI bistables will reset after actuation and allow the RHR suction valves to be opened. The licensee stated that at any pressure above 412.5 psia the OPI bistables will prevent the valves from opening.
By accounting for bistable inaccuracles and reset deadbands, the bistables can continue to be calibrated so the valves can be opened at or below a nominal 390 psia.
The NRC staff has reviewed the proposed change to the OPI setpoint and finds the change acceptable in _that (1) there is sufficient margin between the setpoint and the minimum setpoint of the RHR suction relief valve of 426.8 psig (441.8 psia), (2) there is sufficient margin between the setpoint and the RHR system pressure minus the pump W.scharge pressure (600 psig -
195 psi = 405 psig or 420 psit), (3) the setpoint takes into account bistable inaccuracies and reset deadbar.ds, and (4) the isolation valves can contin,ue to be opened at less than 390 psia for RHR systemeperation.
3.2 Wording Change in the November 14 letter, the licensee stated that the bistable receives an eiectric current to actuate.
Therefore, the bistable is not reading the
" actual reacter coolant system pressure." The licensee stated that deleting the words " actual reactor coolant system pressure" clarifies that the OPl generates instrument signals derived from pressurc transmitters measuring RCS pressure. The NRC staff has reviewed the change in wording and finds the
-3 change acceptable in that it clarifies the wording to more accurately describe the verification test used for the OPI.
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4.0 STATE CONSULTATION
l In accordance with the Commission's regulatiens, the Connecticut State officia'i was notified of the proposed issuance of the amendment.
The State official had no comments.
5.0-ENVIR0ltiGTJL CCNSIDERATION The amendment changes the surveillance requirements.
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:si occupational radiation exposure.gnificant increase in individual or cumulative The Commission has previously issued a proposed finding that the amendment ir.velves no-significant hazards consideration, and there has been no public comment on such finding-(62 FR 66138 dated December 17,1997). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR' 51.22(c)(9).
Pursuant-to 10 CFR 51.22 environmental assessment need be prepar(b) no environmental impact statement or ed in connection with the issuance of
- the amendment.
6.0-CONCLUSION
'The Commission has concluded,-based on the considerations discussed:above, that:- (1) there is-reasonable assurance that the health and safet public will not be endangered by operation in the proposed manner,y off the activities will. be conducted in compliance with-the Commission's reg (ulations,
- 2) such and-(3) theLissuance of the amendment will not be inimical to the common defense and security or to-the-health and safety of the public.
' Principal Contributor: J.- Andersen Date:
Jamary 23, 1998 e
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