ML20114B902
| ML20114B902 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 08/21/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20114B898 | List: |
| References | |
| NUDOCS 9208310349 | |
| Download: ML20114B902 (6) | |
Text
f* "%g UNITED STATES T
E NUCLEAR REGULATORY COMMISSION WASHINGTON, D C. 20555 v...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0.73 TO FACILITY OPERATING LICENSE NO. NPF-30 UNION ELECTRIC COMPANY
_C_AMMAY PL ANT. UN I T 1 DOCKET No. 50-483 1.0 LtLTRODUCTION i
In a letter dated August 11, 1992, the Union Electric Company (the licensee) requested changes to the Technical Specifications (TS) to Facility Operating License No. NPF-30 for the Callaway Plant, Unit 1.
The proposed change would grant a one-time only extension to the surveillance interval specified for Technical Specification (TS) Surveillance 4.3.1.1, Table 4.3-1, Functional Unit 1 (Manual Trip) by adding a footnote to Note 16 which states that
" complete verification of OPERABILITY of the manual reactor trip switch circuitry shall be performed prior to startup f rom the first shutdown to Mode 3 occurring after August 7, 1992." This change was required due to the discovery that the existing surveillance procedure does not adequately verify the operability of the shunt trip contacts associated with the manual reactor trip function.
However, since the surveillance procedure entails increased risk of performing the surveillance in Mode 1 or 2, it was requested that the amendment allow continued operation of the unit until the next planned or unplanned shutdown.
2.0 EVALUATION The Reactor Trip Systen, (RTS) maintains reactor operation within a safe region by automatically tripping the reactor whenever the limits of the region are approached.
The RTS automatically initiates a reactor trip:
a.
whenever necessary to prevent 'nel damage for an anticipated operational transient; b.
to limit core damage for infrequent faults; and, so that energy generated in the core is compatible with the design c.
provisions to protect the reactor coolant pressure boundary for limiting fault conditions.
The reactor trip circuits automatically open the reactor trip breakers whenever a condition monitored by the RTS reaches a preset level.
To ensure a reliable system, high quality is factored into the design, components, manufacturing, quality control and testing.
In addition to redundant channels and trains, the design approach provides an RTS that monitors numerous system variables, thereby providing protection systems functional diversity.
The 9208310349 920821 PDR ADOCK 05000483 p
2 extent of this diversity has been evaluated for a wide variety of postulated accidents.
Callaway Final Safety Analysis Report (FSAR) Section 7.2 describes the RTS detail, including each of the automatic trip functions and the protection provided by each trip.
A manual trip function is provided as part of the RTS.
The manual trip function consists of two switches with two outputs on each switch. One output is used to actuate the Train A reactor trip breaker (R18) and the other output actuates the Train B RTB.
Operating a manual trip switch removes the voltage from the undervoltage trip attachment (UVTA) coil, de-energizing the shunt trip relay as well (as is the case for automatic reactor trips).
The manual t'. ip switch also directly energizes the shunt trip attachment (STA) coil.
The manual reactor trip function serves as a backup to the automatic trip functions.
Only automatic trip functions are assumed in the analysis of the FSAR Chapter 15 accidents.
Red and green position lights are included on the Main Control Board for breaker position.
These lights are powered from the same fused 125 VDC supply used for closing and shunt-tripping the circuit breakers.
Illumination of the green light indicater the breaker is open and power is available for closing and tripping the breaker.
The red light indicates that the breaker is closed.
Since the red light is connected in series with the shunt trip coil, the light indicates that power is available to the shunt trip device and that there is circuit continuity in the shunt coil.
This provides an indication that the shunt trip coil is ready to perform its function when required.
The shunt trip coils in the reactor trip breakers are powered from the 125 VDC Class 1E station batteries.
Normally, the shunt trip coils are in a de-energized condition.
When the trip breakers are closed, the red lamp current (approximately 50 mA) flows through the trip coil to monitor the circuit continuity.
This current is not large enough to actuate the trip coil armature.
The reactor trip signal applies a nominal voltage of 125 VOC to each shunt trip coil in the redundant trains.
As the breaker trips, its auxiliary switch opens to de-energize the shunt trip coi_1~.
The Callaway Technical Specifications define the surveillance testing requirements for the RTS. All surveillances associated with the automatic reactor trip functions are current and the automatic trip function is OPERABLE.
Technical Specification Table 4.3-1 Functional. Unit 19 (Reactor Trip Breaker) and its associated Note 7 requires that each train be tested on a 62-day Staggered Test Basis and that TA00T independently verifies the OPERABILITY of the undervoltage and shunt trip attachments.
This surveillance requirement has been met for each RTB and demonstrates the operability of the diverse tripping mechanisms for the RTBs.
The current surveillance procedure used for_the manual trip function independently tests the shunt trip and undervoltage trip functions at the breakers, but does not test the wiring and control room switch contacts for each function, the STA and UVTA, independently.
The Callaway RTB design included both the undervoltage and shunt trip coils since the plant was licensed in 1984.
The preoperational test procedure 4
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3 verified that the undervoltage and shunt trip attachments were independently activated from the manual trip switches.
The undervoltage portion of the manual trip function was properly tested in accordance with Technical Specifications through Refuel 2 in the fall of 1987. The shunt trip tast specified by the current surveillance procedure has subsequently been cetermined to be inadequate.
Prior to Refuel 3, the requirements for testing the UV and shur trip portion of the handswitch circuitry were deleted for unknown reasons.
The manual trip function has been utilized to trip the reactor during refueling outages at least once every 18 months since initial startup.
This has verified that the manual reactor trip function provide a reactor trip through at least one path and most likely both the undervoltage and shunt trip attachments.
The proposed TS change would allow continued operation of Callaway Unit I until a revised surveillance procedure is performed during the next olanned or unplanned shutdown.
The revised procedure would individually verify the operability of the manual trip function trip contacts for both the trip and bypass breakers.
Generic Letter 85-09 describes the precautions which are applicable to testing of the manual shunt trip contacts and which will be incorport.ted into the licensee's revised procedure.
The Callaway reactor protection system is highly reliable and it is unlikely that a n.anual trip would be required to mitigate an anticipated or design basis event.
In addition, although the surveillance procedure has been incomplete, there is no reason to believe that any element of the manual trip function is inoperable.
The manual shunt trip circuitry tested satisfactorily during preoperational testing. Additional confidence is-provided by the fact that the manual trip functions have performed as expected when utilized on several occasions during operation. The redundancy of the reactor trip system also ensures that a failure of any single manual shunt trip contact would not prevent a successful manual trip resulting from the undervoltage relays or manual shunt trip.
Based on the testing history for the manual trip function, the design of the switch, and the periodic use_of manual trip switch for plant l
shutdowns and surveillance tests, there is a high degree of confidence that the manual trip circuitry is fully functional.
Based upon its review, the staff finds the proposed change to the surveillance requirements for testing of the manual shunt trip circuitry does not have a l
significcnt safety impact and is therefore acceptable.
3.0 EMERGENCY CIRCUMSTANCES In the letter dated August 11, 1992, the licensee requested that this proposed i
amendment be treated as an emergency since, unless approved, the Technical Specifications would require a shutdown of the unit. L A Temocrary Waiver of Complianc3 was granted to allow' for continued operation from the period of' discovery of this ciscrepancy on August-7, 1992, until this emergency Technical Specification amendment could be reviewed and issued.
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1 Regarding the timeliness of the licensee's submittal, the discrepancy between the Technical Specification surveillance requirements and the existing surveillance procedure was determined to render the manual trip function inoperable on August 7,1992. Upon determining that the surveillance procedure was inadequate to satisfy the Technical Specifications, the licensee requested and received a Temporary Waiver of Compliance on August 7,1992, and requested a Technical Specification change on an emergency basis by letter dated August 11, 1992.
1 Accordingly, pursuant to 10 CFR 50.91(a)(5), the Commission has determined that there are emergency circumstances warranting prompt approval of the proposed change.
4.0 FINAL NO SIGNIFICANT HAZARDS DETERMINATION The Commission's regulations in 10 CFR 50.92 state that the Commission may make a final determinatica tbst a license amendrent involves no significant hazards considerations if operation of that facility in accordance with the amendment would not:
1.
Involve a significant increase in the probability or consequences of an accident previously evaluated; or 2.
Create the possibility of a new or different kind of accident from any accident previously evaluated; or 3.
Involve a significant reduction in a margin of safety.
This amendment has been evaluated against the standards in 10 CFR 50.92.
It does not involve a significant hazards consideration because:
i 1.
The change would not involve a significant increase in the probability or consequences of an accident previously evaluated.
The manual reactor trip function Trip Actuating Device Operational Test (TADOT) was correctly performed during preoperational testing.
Since that time, due to procedural inadequacy, the manual trip surveillance did not verify the operation of control room switch contacts or the wiring from the control board -to the reactor trip switchgear.
This portion of the circuitry was exercised during shutdowns; however, this routine use was not part of a surveillance test nor did it confirm independent-operation of the undervoltage trip attachment-(UVTA) and shunt trip attachment (STA).
Although the surveillance testing did not adequately test this portion of th" manual reactor trip function, there is no reason to believe that -ay element of the manual trip function is not functional.
If, for some reason, manual actuation of the shunt and UV trip-failed to operata, the diversity and redundancy of the Reactor Protection System would still enable it r
i i
to perform its design-function.
The accidents evaluated in l
Chapter 15 of the Callaway Final Safety Analysis Report (FSAR)
.. ~. -.
5 rely on the automatic trip functions of the Reactor Protection System.
No credit is assumed for the manual trip function.
Further, all surveillances performed on the automatic trip functions, with the independent verification of UVTA coil de-energization and STA energization via the closing of the shunt trip relay contact, have been performed correctly.
Therefore, since the response of the plant to an accident is unchanged, there is no significant increase in the probability or consequences of an accident previously evaluated as a result of _ this proposed change.
2.
The change would not create the possibility of a new or different kind of accident from any accident previously evaluated.
The proposed change does not involve any design changes or hardware modifications nor will there be any changes to the.
intended manner of plant operation or in the method by which any safety-related plant system performs its safety function.
No new accident initiators, transient precursors, failure mechanisms, or limiting single failures are introduced as a result of this change.
3.
The change would not involve a significant reduction in a margin of safety.
The proposed change does not alter the manner in which safety limits or limiting safety system settings are determined.
The proposed change will have no effect on those plant systems necessary to assure the accomplishment of protection functions and meet the accident analysis acceptance criteria in FSAR Chapter 15.
There will be no impact on DNBR limits, F,, F-delta-H, Loss of Coolant Accident - Peak Clad Temperature, or any other defined i
safety margin.
The Bases of Technical Specification 3/4.3.1 are not changed..since the ability of the Reactor Protection System, with its attendant diversity to ensure the subcriticality fui.ction, is.not compromised.
While some minor uncertainty could be postulated to apply to the manual reactor trip switch contacts-and control room wiring to the reactor trip switchgear, this is insignificant when one considers the impact of this portion of the circuitry on the overall reactor protection system reliability.
5.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Missouri State official was notified of the proposed issuance of the amendment.
The State official had no comments.
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6.0 ENVIRONMENTAL CONSIDERATION
This amendment involves-a change to 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 or a change to a surveillance requirement. The 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 made a final no significant Sazards consideration finding with respect to this amendment.
Sccordingly, this 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 t.th the issuance of this amendment, 7.0 CONCLUS!Off 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 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 this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
C. E. Carpenter, Jr.
Date: August 21, 1992 i