ML20082E677
| ML20082E677 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 07/23/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20082E672 | List: |
| References | |
| NUDOCS 9108010181 | |
| Download: ML20082E677 (4) | |
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UNITED STATES
- ' ! 1 7 i NUCLEAR REGULATORY COMMISSION
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.125 TO FACILITY OPERATING LICENSE NO. DPR-30 COMMONWEALTH EDIS0N COMPANY AND IOWA-ILLIN0IS GAS AND ELECTRIC COMPANY OLAD CITIES NUCLEAR POWER STATION, UNIT 2 DOCKET N0. 50-265
1.0 INTRODUCTION
By letter dated April 18, 1991, Commonwealth Edison Company (the licensee) r proposed changes to the Technical Specifications (TS) for Quad Cities Nuclear Power Station, Unit 2.
The proposed changes reflect a modification to the fast acting solenoid valves which initiate rapid closure of the turbine control valves. The new design uses a pressure switch, rather than a limit switch, to initiate a reactor scram.
A similar amendment was issued for Unit 1 on February 21, 1991.
2.0 DISCUSSION AND EVALUATION The staff evaluated the licensee's submittal in four distinct areas:
a.
Pressure switch vs. limit switch function - the new design must not change the original intent of the function.
b.
Setpoint calculation - the calculation has to be develcped using well developed standards.
c.
Surveillance interval - the calibration interval must be consistent with the design and the setpoint calculation, d.
TS cnanges - the proposed TSs must reflect the new design.
The objective of the turbine control fast acting solenoid valves is to protect the turbine from overspeed when the load is suddenly removed. The logic to determine the load reduction is the load control unit of the Electro-Hydraulic Control System.
The load unbalance signal activates relays which send a signal to the turbine fast acting solenoid va'ves.
Actuation of the fast acting solenoid valves inputs to the Reactor Protection System to provide a reactor scram. The objective of the scram l
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2 is to anticipate the rapid inctease in the pressure and neutron flux which may result f rom the fast closure of the turbine contrel valves and subsequent failure of the turbine steam bypass valves.
The existing design uses a limit switch off the fast acting solenoid valves to initiate a reactor scram. The limit switch is a simple on-off status indicator that chanes status depending on the position of the fast acting solenoid valves.
3 is no periodic calibration of the on-off devices and there is no setpoint calculations associated with the limit switch.
The existing fast acting solenoid valves have failed several times during surveillance testing.
Because of these failures, the licenseo has decided to replace the valves with new valves as recommended by the NSSb vendor, General Electric. The new fast acting solenoid valves are manufactured by Parker-Hannifan and have been used with gocd results since 1976. The function of the new solenoid valves re; rains the same.
However, the reactor scram is now initiated by a pressure switch instead of a limit switch, ihe new design does introduce a new failure mode due to the tubing which ctnnecte the pressure switch to the solenoid valve.
Rupture of the tubing would initiate a reactor scram. However, this is a conservative action.
The industry use of the pressure switch as input to the Reactor Protection System has proven more reliable than the existing limit switch. Therefore, the function of the pressure switch to replace the existing limit switch is uteptable.
& new fast acting solenoid valves require a determination of the pressure setroint. General Electric, in its generic instrument setpoint methodology
, WC-31336, Oct aber 1986), addressed the Turbine Control Valve Fast
' bsure. The licensee has followec the Ocneral Electric methodology. The staff is presently reviewing the General Electric generic setpoint metho-dolcq but has nct completed the res p.
Consequently, the Quad Citic.s setpoint calculation has been reviewed oc an individual basis, The ongoing General Electric methodolcg> eu luation his been found acceptable for this particular seg oint calculation. Accordingly, the Quad Cities calculation was reviewed for consistency with the General Electric generic setpoint calculation.
The pressure switches directly measure the trip oil pressure that causes the turtine ccntrol valves to close in a rapid manner. This oil pressure is normally about 1500 to 1600 psig, and the control valve does not start to close until the pressure drops to 400 psig.
It is considered possible in normal operations for the pressure to drop to 740 psig due to transients.
Therefore,-the analytical limit is 400 psig, and the operational limit is 740 psig.
The instrurnent accuracy of the pressure switch is two percent of full scale.
Accuracy is conservatively estimated to be one percent of full range.
Full scale is 3000 psig.
The instrument drift for a six-month
1 a
.~ interval is equal to the instrument accuracy.
Drift is assumed to be random and calculated to be 4104 psig for an 18-month refueling outage.
The licensee reported the drift that was actually experienced by the same pressure switches at other plants. The data indicate that the drift assumed by the licensee is conservative.
Using the above data and the methodology of NEDC-31336, General Electric performed the pressure setpoint calculatlon.
The setpoint calculation determined the allowable value or TS value of 460 psig and the nominal trip i
setpoint of 590 psig.
The staff concludes that the setpoint calculation is consistent with the General Electric setpoint methodology and, therefore, is acceptable, The proposed fast acting solenoid valves are designed for the pressure i
switch to be actuated within 30 milliseconds of the time the control valves begin to close.
This time is consistent with the design values used in the I
reload licensing calculations to analyze the load reject without bypass valve transient.
Verification of the 30 milliseconds actuation will be conducted during post-modification testing.
Therefore, this modification does not involve a reduction in the margin of safety as previously determined.
The proposed calibration frequency is every refueling outage.
This proposed frequency is consistent with the guidance in NUREG-0133, " General Electric Standard Technical Specifications," Revision 4 This interval is also consistent with TS for BWR plants licensed in the 1980s. General Electric used the 18-month interval in the pressure setpoint calculation.
This frequency is used by General Electric in its generic setpoint metho-dology (NEDC-31336). Therefore, the staff concludes that the surveillance interval for the turbine control valve fast closure is acceptable.
4 The proposed TS change revises Table 4.1-2 to require that the fast acting solenoid valves pressure switch be calibrated every refueling outage.
Page 3.1/4.1-10 of the TSs is revised to delete the description of the turbine control valve fast closure scram device as a simple on-off switch.
Table 3.1-3 and Section 2.1.F are revised to accurately define the trip level setting of the turbine control valve fast closure scram to greater than 460 psig Electro-Hydraulic Control oil pressure.
In addition, the appropriate sections to the Bases are provided to reflect the new design of the fast acting solenoid valves. Therefore, the staff concludes that the proposed TS changes reflect the new design of the turbine control fast acting solenoid valves.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendments.
The State official had no camments.
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4.0 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. 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 coment on such finding (56 FR 24206).
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 or environmental assessment need be prepared in connection with the issuance of the amendments.
5.0 CONCLUSION
The Comission 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 rcgulations, 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:
J. Ibarra, SICB Date:
July 23, 1991 l
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