ML17228B263
| ML17228B263 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 09/01/1995 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17228B262 | List: |
| References | |
| NUDOCS 9509080331 | |
| Download: ML17228B263 (4) | |
Text
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G UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C.
20555-0001'O F CILITY OPERATING LICENSE NO.
6 FLORID POWER AND LIGH COMPANY LUGIE PLA UN O.
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~BAC GROUN In its letter of February 27, 1995, Florida Power 8 Light (licensee) proposed that the technical specification (TS) for the emergency bus undervoltage protection system at St. Lucie Unit 2 be revised.
The proposed TS amendment pertains to the loss of voltage (LOV) and degraded grid voltage (DGV) sections of the undervoltage protection
- system, which are shown under Item 6, "Loss of Power," in Tables 3.3-3 and 3.3-4, under "Engineered Safety Features Actuation System Instrumentation."
The licensee proposes to change (I) the total number of channels, required number of channels to trip, and the required actions for the LOV relays to accommodate an improved coincident trip logic and relay replacement in Table 3.3-3 and (2) the format used to state the time delay for the DGV relays in Table 3.3-4.
The licensee plans to make this change during refueling cycle 9, which is scheduled for September 1995.
- 2. 0 EVALUATION The undervoltage protection system monitors the voltages of the emergency buses and trips the incoming circuit breakers to the emergency buses if the undervoltage condition stays below the settings (i.e., trip voltage and time delay) of its LOV or DGV relays in order to prevent continuous operation of safety-related loads below the minimum voltages required for proper operation.
Should an undervoltage condition occur, the relays will initiate separation of the emergency buses from the offsite power source and sequence load onto respective emergency diesel generators.
The undervoltage protection system at St. Lucie Unit 2 provides LOV and DGV protection in two emergency buses (4. 16 kV and 480 V) in each train.
Any one of these (four) emergency buses in either train can initiate a transfer from the offsite power source to the onsite emergency diesel generator power source.
The undervoltage protection system is covered in the TS in Tables 3.3-3 and 3.3-4.
Table 3.3-3 specifies the total number of channels, required number of channels to trip, minimum required channels
- operable, applicable plant operational
- modes, and action requirements if one channel becomes inoperable for both LOV and DGV relays.
Table 3.3-4 specifies the minimum acceptable trip voltage value and the maximum acceptable time delays and the respective allowable values for both LOV and DGV relays.
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The staff has reviewed the proposed changes in Tables 3.3-3 and 3.3-4 of the TS.
Its evaluation of each of the proposed changes is as follows:
Tble3
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For the 4. 16-kV LOV relays in the above table, the licensee proposes that the total number of channels and required number of channels to trip be changed from "1/Bus" to "2/Bus" and the required action statement be changed from "12" to "17" when one of the operable channels becomes inoperable.
The current LOV function is provided by a single (CV-2), electromechanical, inverse time voltage relay on each 4.16-kV emergency bus and transfers to the onsite power sources when the bus falls below its characteristic curve setpoint.
Timing of the trip is inversely proportional to the voltage level.
Because the existing
- 4. 16-kV LOV relay (i.e., single channel) if tripped is vulnerable to a single relay failure or spurious voltage transient, the licensee plans to replace it, with two solid-state relays.
The licensee believes that the solid-state relays are more reliable than the electromechanical relays and easier to calibrate and maintain in the field.
With installation of new solid-state
- relays, a change to the coincident trip logic is also possible and can also' prevent spurious trips of the offsite power source.
Thus, the licensee ';
proposes to change the trip logic to coincident two-out-of-two-trip logic.i' In addition, if one channel is found to be inoperable during plant operating modes (1, 2, 3), the current action 12 statement in Table 3.3-3 requires a
plant shutdown if the inoperable channel cannot be restored to operable status within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.
The licensee states this action is appropriate for the existing design of a single relay per bus.
However, with the installation of new solid-state LOV relays that use the coincident trip logic, the licensee proposes an action 17 statement that allows plant operation to continue after the inoperable channel is placed in the tripped condition.
The licensee also states that a similar replacement of the relays and their logic for the 4.16-kV LOV protection scheme has already been implemented at St. Lucie, Unit l.
The staff has reviewed the proposed changes for the total number of channels and required number of channels to trip from "1/Bus" to "2/Bus" and the required action statement for the 4. 16-kV LOV protection system.
It finds that the proposed changes represent improvements to the LOV system, since they eliminate the present LOV trip vulnerability from a single relay failure or random voltage transient and make it easier to test and maintain the system as well as provide operational flexibility.
The staff concludes that the proposed change from "1/Bus" to "2/Bus" for the
- 4. 16-kV LOV protection system is acceptable.
With the design upgrade to solid-state relays, the staff also concludes that the change in the required action statement from "12" to "17" for one inoperable channel is acceptable.
The licensee proposes that the total number of channels be changed from
" "2/Bus" to "3/Bus" and the required action be changed from "12" to "17" when one channel becomes inoperable.
The licensee contends that Table 3.3-3 erroneously lists the total number of channels for the 480-V LOV function as "2/Bus" instead of "3/Bus."
With this correction, Table 3.3-3 for the 480-V LOV channels coincides with the 480-V LOV relay configurations currently existing at St.
Lucie Unit 2.
On this basis, the licensee also contends that it can afford to change the required action statement from "12" to "17" if one channel is found to be inoperable during plant oper ational modes.
With regard to the change in the total number of channels for 480-V LOV relays from "2/Bus" to "3/Bus," the staff reviewed the current minimum operable channels required for the coincident logic scheme (i.e.,
two out of three)>.
With three 480-V LOV relay channels, the staff finds that the LOV protection
'unction can preserve plant operation with one channel in the tripped condition.
Therefore, the proposed change of the required action statement from "12" to "17," when one of the channels becomes inoperable, is acceptable..
Table 3.3-4 6.b.
1
. 6-kV Emer enc Bus Undervolta e
De raded Volta e For a DGV condition coincident with a safety injection actuation signal, Table 3.3-4 lists the trip value for the 4. 16-kV DGV relays as
~ 3848 V with a 10-second time delay.
The licensee proposes that "with a 10-second time delay" be changed to "with < 10-second time delay."
The DGV relays are designed to initiate the disconnection of offsite power when the prescribed minimum acceptable trip voltage value and the maximum acceptable time delay limits (i.e.,
~ 3848 V and 10 seconds) are exceeded.
Although the time delay establishes the existence of a sustained degraded voltage condition, it does not allow exceeding the maximum time delay that is assumed in the final safety analysis report (FSAR) accident analysis.
The licensee asserts that the proposed TS changes only the format used for stating the time delay.
This is to ensure that the 10-second time limit would not be exceeded and to allow optimizing the field settings to account for component and calibration equipment tolerances.
Because setting the time delays exactly at 10 seconds for the DGV relays is difficult, the licensee states that the proposed TS wording will allow the DGV time delay settings to account for tolerances for the relays and testing equipment without exceeding the 10-second time limit.
In fact, these time delays are actually set at 9 seconds with allowed tolerances of 2 0. 1 second in the field-controlled (engineering) drawings and their surveillances are performed every 18 months.
Because there is no change in the DGV allowed time delay of maximum of 10 seconds as used in the original accident analysis, and a similar TS format has been previously approved for St.
Lucie Unit 1, the staff concludes that the proposed time delay format "with < 10-second time delay" for the 4. 16-kV DGV relays is acceptable.
3.0 S
Based upon the written notice of the proposed amendment, the Florida State official had no comments.
4.0 This 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 (60 FR 16187).
Accordingly, this amendment meets the eligibilitycriteria 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 this amendment.
5.0 CONC US 0 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:
P.
Kang Date:
September 1,
1995