ML20137D508
| ML20137D508 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 04/27/1995 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20136C539 | List:
|
| References | |
| FOIA-96-485 NUDOCS 9703260188 | |
| Download: ML20137D508 (5) | |
Text
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'4 UNITED STATES g
g NUCLEAR REGULATORY COMMISSION Attac.
o WASHINGTON, D.C. 2006H001 A...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REA TECHNICAL SPECIFICATION CHANGE FOR EMERGENCY B ST. LUCIE. UNIT 2 DOCKET NO. 50-389 1
BACKGROUND In its letter of February 27, 1995, protection system at St. Lucie Unit 2 be revised.that the The proposed TS amendment pertains to the loss of voltage of the undervoltage protection sy(stem, which are shown under Ite Power," in Tables 3.3-3 and 3.3-4, under " Engineered Safety Features Actuat System Instrumentation."
The licensee proposes to change (1 the total number the LOV relays to accommodate an. improved coinci replacement in Table 3.3-3 and (2) the format used to state the time delay fo the DGV relays in Table 3.3-4.
scheduled for September 1995.The licensee plans to make this change d EVALUATION The undervoltage protection system monitors the voltages of the emergency buses and trips the incoming circuit breakers to the emergency buses if the delay) of its LOV or DGV relays in order to prevent contin 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 OGY protection one of these (. in two emergency buses (4.16 kV and 480 V) in each train.
four Any from the offsite po)wer source to the onsite emergency diesel emergency buses in either train can initiate a transfer The undervoltage protection system is covered in the TS in source.
Tables 3.3-3 and 3.3-4.
required number of channels to trip, minimum required channels o applicable plant operational modes, and action requirements if one channel becomes inoperable for both LOV and DGV relays.
Table 3.3-4 specifies the mir.imum acceptable trip voltage value and the maximum acceptable time delays and the respective allowable values for both LOV and DGV relays. 9703260188 970301 PDR FOIA
-BINDER 96-485 PDR
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The Electrical Engineering Branch has reviewed the proposed changes in Tables 3.3-3 and 3.3-4 of the TS.
Its evaluation of each of the proposed l
changes is as follows:
Table 3.3-3. 6.a.(1). 4.16-kV Emeraency Bus Undervoltaae (Loss of Voltaae) i 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 i
from "l/ Bus" to "2 to "17" when one o/ Bus" and the required action statement be changed from "12" f the operable channels becomes inoperable. The current l
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 i
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.
In addition, if one channel is found to be inoperable during plant operating i
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 j
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 i
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-l kV LOV protection scheme has already'been implemented at St. Lucie, Unit 1.
The staff has reviewed the proposed changes for the total number of channels and required number of channels to trip from "l/ Bus" to "2/ Bus" and the requimed 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 trapsi nt and make it easier to test and maintain the system as i
well as provide opranonal flexibility, The staff
'edes that the proposed change from "l/ Bus" to "2/ Bus" for tfi e
4.16-kV L 4ectiewskstem is acceptable. With the design upgrade to st id
-state rol
, the staff also concludes that the change in the required action statement from *12" to "17"'for one inoperable channel is acceptable.
Table 3.3-3. 6.a.(2). 480-V Emeraency Bus Undervoltaae (Loss of Voltaae)
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 becosas inoperable. The licensee contends that Table 3.3-3
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erroneously lists the total number of channels for the 480-V LOV function as "2/ Bus" instead of "7/ Bus." With this correction, Table 3.3-3 for the 480-V i
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 operational 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 j
function can preserve plant operation with one channel in the tripped i
condition. Therefore, the proposed change of the required action st2tement i
from "12" to "17," when one of the channels becomes inoperable, is acceptable.
Table 3.3-4. 6.b.(1). 4.16-kV Emeroency Bus Undervoltaae (Deoraded Voltaae)
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 2 3848 Y 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., 2 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 i 0.1 second and their surveillance are performed every 18 months. However, they will be controlled administratively through the updated FSAR and maintained in the field-controlled (engineering) drawings. The licensee further states that according taiGener#c ter (GL) 93-08 and as a part of line-item TS improvemen'iMs1$
tied to relocate the tables of the reactor trip system and the a Ddg.isa ty features actuatior, system instrument response time limits fr the updated FSAR.
It is also allowed to administra changes in accordance with the provision of 10 CFR 50.59 withou o process a licensing amendment request.
The staff reviewed the subject field drawing (attached) and finds that the time delays have to be set at 9 & 0.1 seconds. Because there is no change in the DGV allowed time delay assumed in the original accident analysis, GL 93-08 permits relocation of TS parameters to licensee-controlled documents, and a similar TS format has been 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.
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l SALP INPUT FACILITY NAME: St. Lucie, Unit 2 SUPMARY OF REVIEW:
In its letter of February 27, 1995, Florida Power & Light (licensee) proposes that the technical specification (TS) for the emergency bus undervoltage protection system at St. Lucie Unit 2 be revised. The proposed 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 TS Tables 3.3-3 and 3.3-4, under " Engineered Safety Features i.
Actuation System Instrumentation." The Electrical Engineering Branch has reviewed the proposed TS amendment request and applicable documents.
It
- j recommends that the proposed changes for St. Lucie Unit 2 be approved.
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HgtRATIVE DISCUSSION OF LICENSEE PERFORMANCE l
FUNCTIONAL AREA: ENGINEERING / TECHNICAL SUPPORT:
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Changing "With a 10-second time delay" to 9.0 1 0.1 seconds for the DGV time delays would have been sufficient for the proposed TS change in Table 3.3-4, i
rather than moving it to other parts of the licensee's controlled documents 4
(i.e., updated FSAR and field drawings). The staff realizes that it allows administrative control of TS changes in accordance with the provision of l
i 10 CFR 50.59 without the need to process a licensing amendment request. For this TS amendment change, the staff failed to convince the licensee to follow
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the staff's advice. The staff finds that the licensee's overall engineering j
and technical support was excellent and personnel were responsive to the
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staff's questions.
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Author:
P. Kang j
Date:
4/15/95 f
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