ML20127J659
| ML20127J659 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 01/15/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20127J639 | List: |
| References | |
| NUDOCS 9301250221 | |
| Download: ML20127J659 (7) | |
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g*...*f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 89 TO FACILITY OPERATING LICENSE NO. NPF-ll AND AMENDMENT NO. 74 TO FACILITY OPERATING LICENSE NO. NPF-18 COMMONWEALTH EDISON COMPANY LASALLE COUNTY STATION. UNITS 1 AND 2 DOCKET NOS. 50-373 AND 50-374
1.0 INTRODUCTION
By letters dated April 24, 1991, on June 2, 1992, and December 1, 1992, Commonwealth Edison Company (CECO) requested amendments to facility Operating License Nos. NPF-11 and NPF-18 for the LaSalle County Station, Units 1 and 2.
The requests involve three changes to the Technical Specifications:
(1) add Action Statements 3.1.3.1.d and 3.1.3.1.e to Technical Specification (TS) 3.1.3.1 in the event that the scram discharge volume (SDV) vent and drain valves become inoperable; (2) delete current Surveillance Requirement J
4.1.3.1.4 b for the SDV level detector instrumentation since it is currently addressed in TS 4.3.1.1 and TS 4.3.6 for the Reactor Protection System (RPS) and Control Rod Block instrumentation, respectively; and (3) delete the requirement for the SDV vent and drain valve surveillance to be performed from a normal control rod configuration of less than or equal to 50% rod density (Surveillance Requirement 4.1.3.1.4.a).
The December 1, 1992, submittal supplemented the earlier requests and did not change the proposed no significant hazards consideration determinations.
2.0 DISCUSSION The purpose of the SDV is to serve as a collection volume for water displaced by the control rod drive pistons during a scram. During normal operation, the SDV vent and drain valves remain open to allow operational leakage from the control rod drives to drain from the SDV to the reactor building equipment drain tank, ensuring that a sufficient air volume is available in the SDV at all times to allow a complete scram. The SDV vent lines are open to the reactor building atmosphere, and assure proper drainage of the SDV.
The SDV consists of header piping that connects to the scram outlet valve of each hydraulic control unit and drains into an instrument volume.
1here are two headers and two instrument volumes, each receiving approximately one half of the control rod drive (CRD) discharges. The SDV vent and drain lines each have two redundant isolation valves in series.
These valves automatically close upon the receipt of a scram signal to isolate the SDV and prevent the discharge of reactor coolant into the reactor building following a scram.
The valves also close automatically upon a loss of air or electrical power.
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l 1 The two redundant automatic isolation valves located on each SDV vent and drain line provide assurance that the SDV will be isolated during a scram, thereby limiting the amount of reactor coolant discharged to the reactor building equipment drain tank, or to the reactor building atmosphere.
Leakage from the SDV could potentially impact both offsite doses and the ability to maintain adequate core cooling following a scram.
The staff has previously reviewed the consequences of a structural failure of the SDV following a scram in NUREG-0803,
In this evaluation, the staff concluded that, for a bounding leakage case corresponding to a ru?ture of the SDV, the offsite doses would be well within the limits of 10 CFR ) art 100, and that adequate core cooling would be maintained.
The failure to isolate one or more SDV vent or drain lines is bounded by this evaluation.
In order to permit control rods to insert completely during a scram, an adequate free volume must exist in the SDV to accommodate the water displaced by CRD pistons as the control rods are inserted into the reactor. As a precautionary measure, the reactor will automatically scram if the water level in the SDV exceeds the high level setpoint.
This assures that the reactor is shut down while an adequate volume remains in the SDV to fully insert the control rods.
The SDV high level scram can be manually blocked only when the reactor mode switch is in the shutdown or refuel positions, permitting control room operators to reset a scram signal and reopen the SDV vent and drain valves to drain the SDV. Water level in the SDV is detected by both float-type level switches and differential pressure (dP) type level transmitters.
Prior to reaching the level which would cause a scram, separate level switches would cause a high level alarm to sound in the control room, giving operators time to take action before the automatic scram.
During normal operation, the only source of leakage into the SDV is from leakage past the scram outlet valves.
This leakage is typically maintained at very small values, because exces:ive leakage past the scram outlet valves would cause control rods to drift, and require that the affected control rods be fully inserted and isolated.
in the event that the SDV drain lines were isolated SDV level would increase such that ample time would be present for actions to be taken af ter receipt of e level alarm in the control room and before an automatic scram on high SDV level.
The licensee has proposed to incorporate operability requirements and allowed outage times for the SDV vent and drain valves, as well as associated compensatory actions for inoperable valves, into the plant Technical Specifications, The proposed TS operability requirements and allowed outage times are consistent with those included in Revision 0 of the BWR/6 Imaroved Standard Technical Specifications (STS). Additionally, the proposed c1anges to SDV vent and drain valve surveillance requirements are also consistent with the STS.
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3 3.0 EVALUATION t
the licensee has proposed to incor> orate new TS Action Statements 3.1.3.1.d and 3.1.3.1.e, which would prescriao actions to be taken if one or more SDV vent or drain valves were to become inoperable. Action 3.1.3.1.d applies if one of the two redundant valves in a SDV vent or drain line becomes inoperable.
In this case, the licensee would have 7 days to repair the inoperable valve or isolate the affected line.
If the affected line is not isolated within the required time period, the licensee would then be required to proceed to hot shutdown within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The staff concludes that this proposed Action Statement is acceptable because, in the event of a scram, the redundant valve on the line can still be expected to perform its function of isolating the SDV.
Alternately, if the inoperable valve was initially closed, ample time and warning would be present for the draining of the SDV before an automatic scram due to SDV high level would occur.
The licensee has further proposed to treat each vent and drain line separately by permitting entry into separate Action Statements for each vent and drain line. This is consistent with the STS, and the staff considers it to be acceptable as well.
1 Proposed Action Statement 3.1.3.1.e would permit the licensee to take up to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to repair two inoperable valves on the same vent or drain line, or to manually isolate the affected line.
If this requirement is not met, the licensee would proceed to hot shutdown within the following 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
The staff considers this proposed _ Action Statement to be acceptable because (1) the probability of a scram during the allowed outage time of the valves is c
acceptably low, and (2) in the event of a scram, the release of reactor coolant to the reactor building through the affected vent or drain line can be-terminated by resetting the scram, which would close the scram outlet valves, or by manually closing the isolation valves located on each SDV vent and drain line. Also, as discussed above, in-the event that a vent or drain line were isolated due to inoperable valves, ample time would exist to drain the SDV before an automatic scram due to high SDV level.
The licensee has also proposed to permit entry into separate Action Statements for each vent and drain line, as described in the STS. 1he staff considers this to be acceptable, following the isolation of one or more SDV vent or drain lines, the licensee has proposed to permit the administrative unisolation of the affected lines to
.i permit draining and venting of the SDV.
This-period allows any accumulated water in the line (from leakage-past the CRDs) to be drained, to preclude a reactor scram on SDV high level.
The staff has' reviewed this change and finds it to be acceptable, since the valves are operated from the control room and can be closed quickly if a scram occurs with the valve open, and operating with the valves unisolated is expected to be infrequent.
Additionally, the licensee proposed deletion of Surveillance Requirement 4.1.3.1.4.b for the SDV level detector instrumentation for both Units 1 and 2 j
because the requirement _ to perform a channel functional test of SDV instru-mentation at least once per 31 days is-currently addressed in the. Technical Specifications for the Reactor Protection System (RPS) instrumentation (TS 1
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3/4.3.1) and Control Rod Block instrumentation (TS 3/4.3.6). These speciff-cations provide appropriate action requirements and allowed outage times should one or more of the instruments become inoperable.
The deletion of those TSs will not affect the current surveillance requirements as they are addressed in the above mentioned TSs. The staff concludes that deletion of Surveillance Requirement 4.1.3.1.4.b from both Unit I and Unit 2 TSs is acceptable because the testing of SDV vent and drain valve operability is adequately addressed in TS 4.3.1.1 and TS 4.3.6.
In their June 2,1992, submittal, the licensee proposed changing Surveillance Requirement 4.1.3.1.4 to verify SDV vent and drain operability since this requirement causes an unnecessary plant transient every 18 months, and challenges plant safety systems.
The licensee proposed amending TS Surveillance Requirement 4.1.3.1.4 to read as follows:
"The scram discharge volume shall be determined OPERABLE by demonstrating the scram discharge volume drain and vent valves OPERABLE at least once per 18 months by verifying that the drain and vent valves:
r a.
Close within 30 seconds after receipt of a signal for control rods to scram, and b.
Open after the scram signal is reset,"
This proposed change would eliminate the need for Note
- at the bottom of page 3/4 1-5, which gives exception from Specification 4.0.4, since there would be no requirement to change modes to perform the surveillance.
The current TS requires that the SDV vent and drain valves be verified operable when control rods are scram tested from a normal control rod configuration of less than or equal to 50% rod density.
This rod configuration requires the reactor to be in Operational Condition 1 (power operation), or Operational Condition 2 (startup), when the surveillance is performed.
Performance of the 4.1.3.1.4.a surveillance during shutdown conditions will still ensure that these safety functions will be met, even though the test conditions of nearly ambient temperature and pressure, and reduced CRD discharge flow due to the rods being fully inserted prior to the scram signal do not-match operating conditions.
The maximum SDV pressure during shutdown conditions will be equal to the static pressure head of the RPV water, as opposed to rated pressure during the test at 50% rod density. However, backpressure due to a scram from. rated pressure will not significantly affect the ability to meet the 30 second closure criterion because the SDV is vented initially. The peak pressure prior to SDV isolation is, tnerefore, negligible.
The initial test condition of reactor coolant temperature will also not be significant to the outcome of the surveillance.
The cooler reactor coolant temperature during shutdown conditions will have negligible effect (if any) on the valve stroke times measured in the surveillance..The quantity of CRD discharge flow will not affect the ability to meet the 30 4
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second valve closure requirement, since the 50V will not become pressurized until some time after the valves have closed.
Single control rod scram time testing is sufficient to detect any obstructions in the piping leading to the SDV.
Backpressure equal to full reactor pressure could affect the ability of the SDV vent and drain valves to open.
However, the ability for these valves to open against reactor pressure is demonstrated after each reactor scram during operation.
Since the initial conditions of pressure, temperature, and CRD discharge flow rate will have no appreciable effect on vent and drain valve perforn'ance, performance of the 4.1.3.1.4.a surveillance during shutdown conditions will not affect the validity of the surveillance results.
Thus, this proposed Technical Specification change will still ensure the safety functions of the SDV vent and drain valves and, therefore, is not a reduction of safety.
The staff has reviewed the amendments submitted by Ceco for the LaSalle County Station, Units 1 and 2, proposing TS changes.
Based on this review, the proposed changes are acceptable.
4.0 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 comments.
5.0 ENVIRONMENTAL r0NS10 ERAT 10N 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 and change surveillance requirements.
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 published proposed findings on June 12,1991, and July 6,1992, that the amendments involve no significant hazards consideration (56 FR 27039 and 57 FR 30242), and there has been no public comment on such findings. Accordingly, the amendments meet the eligibility criteria for categorical-exclusion set forth in 10 CFR-Sl.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.
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6.0 CONCLUSION
i The Commission 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 regulations, and (3) the issuance of the amendments will not be inimical to the common defenr3 and security or to the health and safety of the public.
Principal Contributor:
B. Whitacre Date:
January 15, 1993 t'
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r-NRC form 8-0 (4-79)
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