ML20070E043
| ML20070E043 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 02/21/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20070E042 | List: |
| References | |
| NUDOCS 9103040170 | |
| Download: ML20070E043 (4) | |
Text
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%.....y SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMEN 0 MENT NO.129 TO FACILI1Y OPERATING LICENSE NO. OPR-29 P
COMMONWEALTH EDISON COMPANY AND 10WA-ILLIN01S GAS AND ELECTRIC COMPANY QUAD CITIES, NUCLEAR POWER STATION, UNIT 1 DOCKET NO. 50-254
1.0 INTRODUCTION
By letter dated December 18, 1990, CommonwealthEdisonCompany(thelicensee) proposed changes to the Technical Specifications (TS) for Quad Cities Nuclear Power Station, Unit 1.
Additional clarifying information that did not change the initial proposed no significant hazards consideration deter-mination was submitted by letters dated February 4 and 13,1991.
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.
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 developed using well develcped standards, c.
Surveillance interval - the calibration interval must be consistent with_the design and the setpoint calculation.
d..
Technical Specification changes - the proposed Technical
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Specifications 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 valves.
Actuation of the fast acting solenoid valves inputs to the Reactor Protection System to provide a 9103040170 910221 ADOCK0500g4 DR
-2 reactor scram.
The objective of the scram is to anticipate the rapid increase in the pressure and neutron flux which may result from the fast closure of the turbine control 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 changes ctatus depending on the position of the fast acting solenoic valves.
There 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 testin[.
Because of these failures, the licensee has decided to replace the valves with new valves as recommended by the NSSS vendor, General Electric.
The new fast acting solenoid valves are manufactured by Parker-Hannifan and have been used with good results since 1976.
The function of the new solenoid valves remains the same.
However, the reactor scram is now initiated by a pressure switch instead of a limit switch.
The new design does introduce a new failure mode due to the tubing which connects 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 acceptable.
The new fast acting solenoid valves require a determination of the pressure setpoint.
General Electric, in its generic instrument setpoint methodology (NEOC-31336, October 1986), addressed the Turbine Control Valve Fast Closure.
The licensee has followed the General Electric methodology, The staff is presently reviewing the General Electric generic setpoint methodology but has not corr.pleted the review.
Consequently, the Quad Cities setpoint calculation has been reviewed on a individual basis.
The on going General Electric methodology evaluation has been found acceptable fer this particular setpoint 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 turbine control 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 instrument 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 interval is equal I
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0 1 to the instrument accuracy.
Drif t is assumed to be random and calculated to be 2104 psig for an 18-1 nth refueling outage.
By letter dated February 4, 1991, the licensee reportec the drift that was actually experienced by the same prescure 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 calculation. The setpoint calculation determined the allowable value or Technical Specification value of 460 psig and the nominal trip 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 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 reioad. 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 modificttion 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-0123, " General Electric Standard Technical Specifications," Revision 4.
This intervel is also consistent with Technical Specifications 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 L
generic setpoint methodology (NEDC-31336). Therefore, the staff concludes that the surveillance interval for the turbine control valve fast closure is acceptable.
The proposed Technical Specification change revisch Table 4.1-2 to require that-the f ast acting solenoid valves pressure switch be calibrated every refueling outage.
Page 3.1/4.1-10 of the Technicel Specifications is revised to delete the description of the_ turbine ontrol valve fast closure scram device as a simple or.-off switch. Table 3. -3 and Section 2.1.F are revised to accurately define the trip level setti 9 of the turbine control
- valve-fast closure scram to greater than 460 psit Electro-Hydraulic Control oil pressure.
In addition, the appropriate sect ons to the Bases are provided to reflect the new design of the fast icting solenoid valves.
Therefore, the staff concludes-that the proposed Technical Specification changes reflect the new design of the turbine control fast acting solenoid valves.
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3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendment. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
This amendment changes a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR P.irt 20.
The NRC staff has determined that the amendment involves no significent increase in the amounts, ard 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.
Accordingly, the amendment meets the eligibility ~'iteria 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 amendment.
5.0 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 will not be endar.gered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) th( issuance of this amendment will not be inimical to the common defense and tocurity or to the health and safety of the public.
Principal Cont ibutor:
J. Ibarra, SICB Date: February 21, 1991 I
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