ML17157C233
| ML17157C233 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 03/02/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17157C232 | List: |
| References | |
| NUDOCS 9303100337 | |
| Download: ML17157C233 (6) | |
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'NITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555 II SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.
TO FACILITY OPERATING LICENSE NO.
NPF-22 PENNSYLVANIA POWER 8E LIGHT COMPANY ALLEGHENY ELECTRIC COOPERATIVE INC.
SUS UEHANNA STEAM ELECTRIC STATION UNIT 2 DOCKET NO. 50-388
- 1. 0 INTRODUCTION By letter dated November 30,
- 1992, the Pennsylvania Power and Light Company (PPSL) and Allegheny Electric Cooperative, Inc. (the licensees) submitted a
request for changes to the Susquehanna Steam Electric Station (SSES),
Unit 2, Technical Specifications (TS).
The requested changes would revise the
- SSES, Unit 2, TS to authorize operation of the Reactor Water Cleanup (RWCU) System in the current fuel cycle with the non-regenerative heat exchanger discharge high temperature channel substituting for the inoperable
'B'WCU high flow isolation trip channel.
During a routine surveillance channel check on November 15, 1992, operators for PP8L noted a significant decrease in the 'B'WCU Flow-High isolation channel.
The licensee determined that the associated instrument met the channel check acceptance criteria and continued to investigate the cause of the decrease in indicated flow.
The licensee subsequently confirmed that the channel was inoperable.
Attempts to restore the inoperable channel were unsuccessful.
Since further repair activities would involve primary containment entry and, potentially, complete defueling of the reactor vessel, PPE L requested an extension to the temporary waiver of compliance from Technical Sp'ecification (TS) Action Requirement 23 of Table 3.3.2-1" which is referenced in TS 3.3.2, Action b, footnote (*), previously granted by the staff on November 17, 1992.
The purpose of the extension was to allow continued operation of the RWCU system while the staff evaluated the licensee's application for the subject TS change.
The Temporary Waiver of Compliance was verbally granted on November 23,
- 1992, and confirmed by letter dated November 25, 1992.
The Temporary Waiver will terminate upon issuance of the subject amendment.
By letter dated November 30,
- 1992, the licensee proposed a one-time change to the
- SSES, Unit 2, TSs.
The proposed change would allow continued operation of the RWCU system for the duration of the sixth operating cycle for Unit 2 with one operable RWCU Flow-High isolation channel.
To ensure the necessary diversity of isolation system actuation is maintained for all RWCU piping, PP&L proposed that the Non-Regenerative Heat Exchanger (NRHX) Discharge Temperature-High channel be substituted for the inoperable B
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isolation channel.
The proposed TS change reduces the required number of operable RWCU Flow-High channels in Table 3.3.2-1 to one; adds the requirement for one operable NRHX Discharge Temperature-High channel to Table 3.3.2-1; adds setpoint requirements to Table 3.3.2-2 for the NRHX Discharge Temperature-High channel; adds the NRHX Discharge Temperature-High channel to Table 3.3.2-3; and adds surveillance requirements for the instrument associated with the NRHX Discharge Temperature-High channel to Table 4.3.2.1-1.
2.0 BACKGROUND
The RWCU system penetrates the primary containment and is provided with inboard and outboard containment isolation valves.
In order to maintain the integrity of the reactor coolant pressure boundary and to minimize the radiological consequences in the event of a break in the RWCU system piping, the RWCU system is equipped with diverse and redundant leak detection devices which provide isolation signals to the RWCU system containment isolation valves.
In addition to the protection provided by the RWCU Flow-High isolation, RWCU Area Temperature-High, RWCU Area Ventilation Differential Temperature-High, and RWCU Differential Flow-High instruments detect leakage in certain sections of the RWCU system and initiate isolation.
Reactor Vessel Level
- Low, Low (Level 2) provides automatic isolation of the RWCU system for large break flows which exceed feedwater system makeup capability and result in a decreasing reactor vessel water level.
Although not capable of initiating automatic RWCU isolation, area radiation and main steam tunnel temperature monitoring is available to provide operators warning of a leak or break in the RWCU piping.
The licensee has p'erformed a detailed evaluation of the adequacy of leak detection for the entire length of RWCU piping outside primary containment.
Based on this evaluation, PP&L determined that the RWCU Flow-High isolation function is necessary to provide diversity to detect and isolate leaks in the section of piping from the downstream RWCU differential flow element to the point where the RWCU piping ties into the feedwater system piping.
Only the RWCU Flow-High isolation and the Reactor Vessel Level
- Low, Low (Level 2) provide isolation capability for leaks or breaks in this section of piping.
The licensee determined that a break in the section of piping of concern coupled with a failure to isolate due to failure of the A RWCU Flow-High channel or the associated containment isolation valve would be a low probability event.
PP&L prepared a probabilistic evaluation of this case and determined the probability of this event to be 1. lxlO for a 15-month operating cycle.
The evaluation conservatively assumed minimum pipe wall thickness in determining the probability of a pipe break.
The piping in the subject section is 4" ASME Section III Class 2 SA-106 Grade B seamless carbon steel piping which is not subject to intergranular stress corrosion cracking.
In order to verify its operability, an additional calibration of the A RWCU Flow-High channel was performed.
The licensee has also committed to provide additional guidance to operators to ensure heightened awareness of the degraded condition of the RWCU high flow leak isolation function.
These compensatory measures are intended to reduce the probability of an unisolated leak or break in the RWCU piping.
In addition to the operable A RWCU Flow-High channel isolation, PPKL has determined that a high RWCU system flow, equal to the setpoint of the high flow instrument, will cause the temperature measured at the discharge of the NRHX to exceed the temperature instrument's RWCU isolation setpoint of 140'F.
Once the instrument senses a
RWCU water temperature above the NRHX Discharge Temperature-High
- setpoint, isolation of the outboard RWCU containment isolation valve is initiated.
PP8L has confirmed that the operable A RWCU Flow-High channel initiates isolation of the redundant inboard RWCU containment isolation valve.
Although the NRHX discharge temperature instrument is not safety grade, PP8L has verified that the instrument's power supply and the equipment associated with initiating RWCU isolation is safety grade.
Also, the licensee has determined that the power supply and containment isolation circuitry for the A
RWCU Flow-High and the'NRHX Discharge Temperature-High channels are physically and electrically separate, and operate in different divisions.
The NRHX discharge temperature instrument is designed to initiate RWCU isolation following failure of its thermistor probe due to an open or short circuit, or failure of its power supply.
A previous failure of the temperature instrument caused RWCU isolation.
The licensee's TS change request includes provisions for surveillance testing of the NRHX Discharge Temperature-High instrument which is consistent with that of other temperature instruments.
3.0 EVALUATION For sections of the RWCU system provided with leak detection and isolation capability by the RWCU Area Temperature-High, the RWCU Area Ventilation Differential Temperature-High, or the RWCU Differential Flow-High instruments, the staff concludes that sufficiently diverse and redundant means of leak detection and isolation are provided regardless of the RWCU high flow isolation functional capability.
Therefore, the capability to detect and isolate leaks in portions of the RWCU system where only the operable A RWCU Flow-High channel and the Reactor Vessel Level
- Low, Low (Level 2) device provide isolation capability for leaks or breaks is of primary concern in this evaluation.
The staff has determined that, under normal operating conditions, the NRHX Discharge Temperature-High and RWCU Flow-High channels have comparable RWCU isolation capability for a break in the piping section of concern.
This was confirmed by calculations indicating that less than a 50 gpm increase in RWCU flow will result in steady state NRHX discharge temperature above the isolation setpoint.
For comparison, the RWCU Flow-High setpoint is greater than 100 gpm above normal RWCU system flow.
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Although the NRHX discharge temperature instrument is not safety grade the staff concludes that the instrument reliability is adequate for one cycle of operation.
This conclusion is based on the low probability of a break in the section of piping of concern coincident with a failure of the operable RWCU Flow-High channel to isolate RWCU flow, the fail-safe characteristics of the NRHX temperature instrument, and the proposed TS surveillance testing of the NRHX temperature instrument.
The staff found that the temporary substitution of the NRHX Discharge Temperature-High channel for the inoperable B
RWCU Flow-High isolation channel under TS 3.3.2 is acceptable for the duration of the sixth operating cycle for Unit 2.
This action is consistent with the requirements of General Design Criterion 54 of Appendix A to 10 CFR Part 50 with regard to provision of leak detection and isolation capabilities for piping systems which penetrate containment having redundancy, reliability, and performance capabilities which reflect the importance to safety of isolating these systems.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Pennsylvania State official was notified of the proposed issuance of the amendment.
The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to 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 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 issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (57 FR 59363).
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(b) no environmental impact statement or environmental assessment need be prepared 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 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 amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
S.
Jones Date:
March 2, 1993