ML20212A737
| ML20212A737 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 02/25/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20212A698 | List: |
| References | |
| NUDOCS 8703030405 | |
| Download: ML20212A737 (5) | |
Text
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.126 TO FACILITY OPERATING LICENSE NO. DPR-53 BALTIMORE GAS AND ELECTRIC COMPANY CALVERT CLIFFS NUCLEAR POWER PLANT UNIT NO. 1 DOCKET NO. 50-317 INTRODUCTION By the letter dated July 31, 1986, as supplemented on January 21, 1987, the Baltimore Gas and Electric Co., (BG&E, the licensee) has requested a change to Surveillance Requirement 4.7.1.5 of the Technical Specifications (TS) for demonstrating main steam isolation valve (MSIV) operability at Calvert Cliffs Unit 1.
The requested change is to delete the. current requirement for full MSIV closure "within 3.6 seconds" and substitute a requirement for full MSIV closure "in less than 5.2 seconds."
The original application requested an MSIV closure time of 6 seconds; however, during the course of NRC staff review, data from factory testing indicated that closure time under loaded conditions is slightly greater than under unloaded conditions.
To assure the MSIV closure time stays within the 6 seconds on which the safety analysis is based, a closure time for testing was specified as 5.2 seconds.
This does not affect the substance of the proposed change.
The licensee's request is an integral part of a major MSIV modification at Calvert Cliffs.
Rationale for the TS change, specific proposed modified TS and details of the MSIV modifications were included in the July 31, 1986 letter.
This staff evaluation concerns both the acceptability of the TS change and the technical adequacy of the MSIV modifications.
MSIV modifications for Unit I were completed during the fall 1986 refueling outage.
BACKGROUND The original MSIV design at Calvert Cliffs included a hydraulic valve closure actuator capable of developing adequate force to close the MSIV against a reverse steam flow.
This required a physically large actuator with commensurately large hydraulic system capacity.
The design of this hydraulic system is such that it tends to lose capacity unless the system is continually maintained.
On at least one occasion, the MSIV's were de-clared inoperable because the hydraulic system capacity was not adequate to fully close the MSIV's.
8703030405 870225 PDR ADOCK 05000317 p
. In order to preclude any repeat of MSIV inoperability due to lack of hy-draulic system capacity, the licensee will modify both the MSIV's and their associated actuators.
The valve internals will be changed to include a balanced disc design.
Utilizing a balanced disc will allow valve closure under all conditions, including reverse flow, but will require substantially less actuator force and a much smaller actuator.
A completely new actuator will be installed and the original actuator, hydraulic system, and associated piping and controls will be removed.. The new actuators will be much smaller and will be mounted directly on their respective MSIV's.
The MSIV modifications and new actuators, along with the TS change, are the subject of this staff evaluation.
EVALUATION In Chapter 14 of the Calvert Cliffs Nuclear Power Plant Units 1 and 2 Updated Final Safety Analysis Report (UFSAR), an MSIV closure time of 6 seconds is assumed for a steam line break event (SLB) inside and outside the containment, and a closure time of 12 seconds is assumed for a feedline break event (FLB) inside and outside the containment.
Since the limiting event is an SLB, closure of the MSIV's in less than 6 seconds would be within the bounds of the accident analysis.
With the balanced disc,.MSIV closure time is not as significantly affected by steam backpressure as it was with the original MSIV configuration.
However, steam flow across the valve seat can increase closure time of the modified MSIV by up to 0.6 seconds over the closure time for no steam flow conditions.
To ensure that the MSIV will close in less than 6.0 seconds for all possible steam flow conditions resulting from the SLB event,
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the licensee has requested that the MSIV must fully close in less than 5.2 seconds for no steam flow conditions.
Therefore, the staff concludes that the licensee's proposed change to TS 4.7.1.5 is acceptable since it is supported by the analysis of record.
In the analysis, a time delay of 0.9 seconds between reaching the low steam generator pressure trip setpoint and the actual commencement of MSIV closure is assumed for both the SLB and FLB events.
In discussions with the NRC staff, the licensee has confirmed that the MSIV modifications and the change of actuators will not adversely impact the signal delay time assumed in the UFSAR analysis.
This also is acceptable.
The above discussion considers the proposed TS change only with respect to the UFSAR Chapter 14 accident analysis.
Other factors will have an effect on maximum allowable MSIV closure time.
These factors are discussed later in this evaluation.
The existing MSIV bodies are Seismic Category 1, Safety Class 1.
As stated above, the actual MSIV's were not replaced; only new internals were installed.
Therefore, MSIV acceptability for their intended service is covered by the plant UFSAR and existing staff evaluations.
The MSIV actuators, however,
. are completely new.
Each actuator is designed in accordance with applicable portions of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME)Section VIII.
Material selection is in accordance with ASME Section VIII and Section II, and welding is in accordance with ASME Section VIII and Section IX.
Quality assurance and inspection are in accord-ance with ASME Section V and Section VIII.
Other industry codes / standards invoked by ASME and/or followed in the design and manufacture of the actuators include ASTM, AISI, and AWS standards.
Design of the new actuators to the above codes and standards is in conformance with NRC criteria as stated in NUREG-0800.
Finally, an actuator of the same generic design has successfully passed a qualification test program which included testing for radiation, seismic, thermal aging, operational aging, and LOCA simulation. The new actuators are designed to Seismic Category 1, Safety Class 1 requirements, which conform to Ger.eral Design Criteria (GDC) 1 and 2.
(Other applicable GDC are bounded by the plant UFSAR and staff evaluations pertaining to existing MSIV's).
Based on the above, the staff concludes that the design of the new MSIV actuators is acceptable for their intended service.
The design of the new actuators includes two hydraulic circuits for each actuator.
These hydraulic circuits control MSIV closure on demand to allow rapid valve closure without exerting excessive force on the MSIV seat and disc.
Each circuit, individually, has the capability to initiate and control valve closure within the proposed TS time limit.
The design of the actuators and associated hydraulic control circuits is such that failure of the hydraulic pressure boundary in any way will cause MSIV closure. 'The staff finds the new MSIV actuators acceptable with regard to hydraulic control circuitry independence, redundancy, and pressure boundary fail safe design.
Control of hydraulic fluid flow within the MSIV actuator hydraulic circuits is accomplished through the use of solenoid and pilot operated valves, and flow control devices.
Each hydraulic circuit has a solenoid valve which controls a pressure operated dump valve.
When open, the dump valve allows hydraulic fluid to be exhausted from under the actuator piston to a sump tank via a pressure compensated flow control.
The two solenoid control valves for each MSIV are powered from separate, independent Class IE 125 VDC station batteries.
The solenoid control valves are also Class IE, as are the feeder circuits from the station batteries to the valves.
A second solenoid valve in each actuator hydraulic circuit is used in conjunction with the solenoid control valve to facilitate slow closure of the MSIV for test purposes.
This second solenoid valve is also Class IE and is powered from the same circuit as its associated control valve.
Each MSIV actuator hydraulic system also has a single solenoid valve to control compressed air flow to an integral pneumatically operated hydraulic pump which is used to open the MSIV's.
This pneumatic solenoid valve is Class IE and is powered from the same circuit as one of the solenoid control valves.
The above design requires energizing the solenoids to effect MSIV closure.
Based on a review of the design, the staff i
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. concludes that no single failure of an active or passive component would disable the actuators to the extent they could not effect MSIV closure in time to meet the UFSAR accident analyses requirements.
Therefore, the staff concludes that the MSIV actuator. controls are acceptable with respect to independence and redundancy.
In addition to automatic operation, MSIV closure can be initiated manually in the control room.
The latter capability includes fast closure as may be required for an emergency response, or slow stroking for test purposes.
There is no local (at the MSIV) control of any kind, either manual or electrical.
Provisions have been made for monitoring MSIV position and actuator condition in the control room.
Indicator lights are provided for MSIV open, 10% closed, and. full clored.
A common trouble alarm is provided to annunciate actuator low hydraul!c pressure, low nitrogen pressure, and/or low hydraulic fluid level.
Indication is also provided to show when the solenoid valves required for MSIV testing are energized.
Local indications of pressure and fluid levels are also provided.
The staff concludes that the controls and instrumentation provided are acequate for MSIV control and monitoring and, as such, are acceptable.
The staff review of the licensee's proposed TS change and attendant MSIV modifications, as detailed in the above evaluations, concentrated on determining that the proposed changes and modifications would provide a level of protection at least equal to the original configuration.
A detailed comparison of the significant features of the original and new designs is given below.
APPENDIX A DETAILED MSIV COMPARISON Original New 1 hydraulic circuit 2 hydraulic circuits 2 solenoid control valves 2 solenoid control valves energize solenoids to energize solenoids to close MSIV's close MSIV's Loss of hydraulic fluid Loss of hydraulic fluid MSIV inoperable MSIV inoperable Manual override if No manual override if solenoids fail solenoids fail Complex, large, many Compact, less complex, components, external fewer components, no piping external piping l
. Orignial New MSIV closure time Partial fail safe design l
adversely affected by steam backpressure MSIV closure time only slightly affected by steam backpressure Based upon its review, the staff concludes that the modified MSIV's with the new actuators are at least the equivalent of the original MSIV's and their associated actuators.
Accordingly, the staff also concludes that the modified MSIV's with their new actuators and the associated change in the MSIV full closure time specified in TS 4.7.1.5 are acceptable.
ENVIRONMENTAL CONSIDERATION This amendment involves a change in the installation or use of a facility component located within the rectr:cted area as defined in 10 CFR Part 20 or a change in surveillance requirements.
The staff has determined that this 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 Commission has previously published 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 S51.22(c)(9).
Pursuant to 10 CFR S51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
CONCLUSION We have 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, and (2) such activities will be conducted in compliance with 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.
Date: February 25, 1987 Principal Contributor:
Ed Tomlinson I
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