ML20247M402
| ML20247M402 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 05/18/1989 |
| From: | Murphy W VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20247M408 | List: |
| References | |
| BVY-89-45, NUDOCS 8906050036 | |
| Download: ML20247M402 (7) | |
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- TVERMONT YANKEE-NUCLEAR POWER CORPORATION x
3 Ferry Road, Brattleboro, VT 05301-7002 BVY 89-45 yf ENGINEERING OFFICE y
68 "^'" 8" May 18' 1989 DOLToN. MA 01740
.]
(508)779 6711 United States Nuclear Regulatory Commission Washington, DC 20555 Attention:
Document Control Desk
References:
(a) License No. DPR-28 (Docket No. 50-271)
(b) Letter, VYNPC to USNRC, FVY 83-88, Proposed Change No. 105, dated August 5, 1983 (c) Letter, USNRC to VYNPC, NVY 84-143, dated June 27, 1984 (d). Letter, VYNPC to USNRC, FVY 85-26, dated March 4, 1985 (e) Letter, USNRC to VYNPC, NVY 89-52, dated March 24, 1989
Subject:
RPS Power Protection Panel Specifications - Proposed Change No. 105, Supporting Information and Clarifying Submittal
Dear Sir:
By letter dated August 5, 1983 [ Reference (b)] and supplemented March 4, 1985 [ Reference (d)], Vermont Yankee proposed changes to the Technical Specifications related to the Reactor Protection System (RPS) Power Protection Panel. Subsequently, the NRC staff requested, by letter dated March 24, 1989 [ Reference (e)], that Vermont Yankee provide supporting information to resolve.certain concerns associated with the staff's review of the subject license amendment request. Accordingly, Vermont Yankee herewith provides, an an enclosure to this letter, the requested supporting information.
The enclosure to this letter addresses each of the three NRC staff findings transmitted in Reference (e). Additionally, Vermont Yankee submits this clarification to the subject proposed Technical Spe.cification change and encloses the revised Technical Specification pages consistent with the enclosed responses to the NRC staff findings No. 1 att. No. 3.
We trust that the enclosed information is satisfactory; however, should there be any questions or should further information be required concerning this matter, please contact this office.
Very truly yours, g6000 8%h VERMON YANKEE NUCLEAR POWER CORPORATION P
PNU 4
Warren P. M rphy WPM /dhm/0303w Vice President and M a of Operations Enclosure cc: USNRC Region I USNRC Resident Inspector - VYNPS USNRC NRR Project Manager - VYNPS g
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,7-U ENCLOSURE Supporting Information Vermont Yankee Proposed Technical Specification Change No. 105 RPS Power Protection Panel Specification NRC Staff Finding No. 1 LCO 3.10.5 RPS Protection Systems Versus LCO 3.8.4.4 (Model Technical-
' Specification)
The NRC staff has stated that the proposed Limiting Condition for Operation (LCO) on Page 177 provides no separate LCO provision ' to restore one inoperable panel to an operable status within 30 minutes when both RPS power protection panels become inoperable and no justification has been provided for its-omission.
Vermont Yankee Response to Staff Finding No. 1 The proposed LCO states that after one or more protection panels is made or found to be inoperable, the panel shall be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
If the panel cannot be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, it shall be tripped. The NRC recommends the following words:
a.
With one RPS electric power monitoring channel for an in-service RPS MG set or alternate power supply inoperable, restore the inoperable channel to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or remove the associated RPS MG set or alternate power supply from service.
b.
With both R'PS electric power monitoring channels for an in-service RPS MG set or alternate power supply inoperable, restore at least one to operable status within 30 minutes or remove the associated RPS MG set or alternate power supply from service.
Vermont Yankee's concern with the NRC's recommended wording'is that it describes conditions which will not occur with Vermont Yankee's RPS protection panel configuration, and therefore, could cause confusion to the plant operators and lead to a violation of the Technical Specification requirements.
It is our understanding that for a protection panel to be declared inoperable, one of two events must take place: either the protection panel setpoints must be found to be incorrect during testing, or the protection panel must spuriously actuate (trip) during normal operation.
In either case, the r,orrce of power (MG set or alternate supply) that the subject protection panel serves, is taken out of service. We acknowledge that during normal o;*eration, it is possible that the'setpoints of a protection pane) might change or an internal compor.ent might fail such that the protection panel is inoperable, but the redundant protection panel would still be available to provide the required protection function. - _ _ - _
ENCLOSURE (Continued)
Supporting Information.
Vermont Yankee Proposed Technical Specification Change No. 105 RPS Power Protection Panel Specification l
l For example, as discussed in the reply to staff Finding No. 2, when a protection panel is being tested its circuit breaker must be tripped. The associated source of power (MG set or alternate source) cannot be connected to an RPS bus when the associated protection panels circuit breaker is open because the. protection panel cannot be bypassed..That source of power is then j
considered to be "out of service." The LCO statement would not apply in this
.i case since the source of-power is not "in-service."
If the protection panel l
were found to be " inoperable" during testing, it would not be returned to
)
l service until repairs were-completed. Additionally, the second part of the j
NRC's suggested wording (the 30-minute LCO) would not apply because regardless of the operability status of the redundant protection panel, the associated source of power has already been taken out of service because of the first protection panels' inoperable status.
Likewise, if during normal operating conditions the protection panel i
spuriously ~ actuated (circuit breaker trips), the' associated source of power j
would be disconnected from the RPS bus and therefore be automatically removed from service.
In summary, we believe that the NRC suggested wording does not directly apply to Vermont Yankee's configuration.
If a protection panel was found to be inoperable during testing, the LCO would not apply (or would already be met) j since the associated power source had already been taken out of service cs part of the testing procedure. Likewise, the only way for a protection panel to be found to be inoperable during normal plant operation is to have the panel circuit breaker trip. This action automatically disconnects the
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associated source of power from.the RPS Bus and takes that power source 1
out-of-service.
In either of the above cases, the operability status of the redundant protection panel is not a concern sints the power source is taken out of service as a result of the inoperable status (open circuit breaker) of the first panel. Therefore, the 30-minute LCO would not be applicable to Vermont Yankee given our proposed LCO.
We balieve that the LCO statement originally submitted was appropriate for Vermont Yankee. However, for clarification purposes, Vermont Yankee has revised the proposed LCO 3.10.B.5 (see Technical Specification P.177 attached) to read as follows:
"From and after the date that one of the two redundant RPS power protection panels on an in-service RPS MG set or alternate power supply is made or found to be inoperable, the associated RPS MG set or alternate supply will be taken out of service until the panel is restored to operable status." - _ _ _ _ _ ___ - __-_______-_ _ _ ___-_- -____
l l1.
ENCLOSURE (Continued)
)
Supporting Information
'I Vermont Yankee Proposed Technical Specification Change No. 105 RPS Power Protection Panel Specification l
NRC Staff Finding No. 2 SR 4.10.6 RPS Power Protection Versus SR 4.8.4.4 (Model Technical Specification)
I 1
The NRC staff has stated that the proposed Surveillance Requirement (SR) on Page 175a includes no provision which requires channel functional test once per six months. No justification has been provided for not performing the channel functional test.
Vermont Yankee Response to Staff Finding No. 2 Vermont Yankee has submitted a testing frequency of once-per-operating cycle rather than the six-month frequency suggested by the NRC for the following reasons:
a.
In order to test a protection panel, it must be taken out of service.
This requires momentarily de-energizing the RPS bus.
b.
Vermont Yankee's experience with the protection panels indicates that the setpoints do not experience significant drift during an operating cycle.
In accordance with its instruction manual, the protection panel must be taken out of service before testing. This is initiated by the keylock switch on the protection panel. The keylock switch must be turned from che " NORMAL" position to the " CAL / TEST" position to enable (i.e., energize) the panel test jacks. Additionally, the keylock switch trips the panel circuit breaker when the switch is moved from the " NORMAL" to the " CAL / TEST" position. As shown on the attached one-line diagram of Vermont Yankee, the protection panel cannot be bypassed, so opening the panel circuit breaker effectively removes the associated power source of power from service.
For this reason, in order to test the panels, the following cequence would occur:
1.
Transfer one RPS bus to the alternate supply and remove one operating MG set from service.
2.
Perform a test on first protection panel.
3.
Perform a test on the second protection panel.
4.
Return the RPS bus from alternate supply to MG set.
5.
Repeat 1 through 4 for the other MG set.
6.
Test the alternate supply. - _ _ _ _ - - _.
fo' ENCLOSURE (Continued)
Supporting Information.
Vermont Yankee Proposed Technical Specification Change No. 105 RPS Power Protection Panel Specification I
1 l
L As' stated in the Precautions Section for OP-2134,." Reactor Protection System,"
shifting an RPS bus from one source of power to another, because it momentarily de-energizes the RPS bus, causes the f ollowing:
a.
A half-scram and half-isolation will occur on the system being switched.
b.
The Reactor Building HVAC System will trip.
c.
The Standby Gas Treatment System will start.
d.
Power will be lost to the AEOG radiation monitor.
Although the RPS is designed to be tested while the plant is operating, typical RPS tests affect only one portion of the RPS at a time. That is, the typical RPS test does not cause all of the four effects above since it does not de-energize the bus. Testing of the RPS power protection panels at Vermont Yankee, however, de-energizes an entire RPS bus and causes the four actions described above.
The protection panels at Vermont Yankee have been installed and have been operating for more than three full operating cycles. During that time there has been no protection panel equipment failures. Further, the calibration tests performed each refueling outage indicates that there was very little drift in the protection panel setpoints between tests. The operating history does not indicate a need for increased testing frequency.
A protection panel must be taken off-line in order to be tested, since Vermont Yankee's design does not include a bypass capability. Thus, use of a test module would not facilitate on-line testing at Vermont Yankee because removal of a protection panel for testing places the plant in a half-scram condition.
We believe that because of the impact on other plant equipment caused by protection panel testing and past operating experience, the submitted test frequency of once-per-operating cycle is justified.
NRC Staff Finding No. 3 SR Relay Setpoints The NRC staff has stated that the proposed SR on Page 177b provides no basis for selecting the setpoints and time delays on overvoltage, undervoltage, and underfrequency. I
f 1
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ENCLOSURE (Continued)
Supporting Information Vermont Yankee Proposed Technical Specification Change No. 105 RPS Power Protection Panel Specification VERMONT YANKEE RESPONSE TO NRC STAFF FINDING NO. 3 The undervoltage, overvoltage, and underfrequency setpoints are based on the following:
1.
Equipment input voltage and frequency ratings, as provided in equipment specifications, instruction manuals, drawings, and/or discussions with the equipment manufacturer. When only nominal values were available, a 1 0% range was assumed for voltages and iS% was assumed for frequency.
1 2.
Worst case voltage drop calculations, based on cable length given in the cable and conduit lists and equipment power (VA) requirements. These calculations were used to determine the minimum supply voltage requirements only.
3.
Because the RPS at Vermont Yankee uses equipment rated for 110 V ac, 115 V ac, and 120 V ac, the composite voltage range is narrower than the typical !10% of nominal. The composite input voltage rating is 118 V 16%.
Based on the above, the composite input voltage requirement of the RPS equipment is 118V 16% as measured at the protection panels. Minimum frequency requirement is 57Hz (60Hz -5%).
The time delays were included in the design of the protection panels to eliminate spurious trips due to transients and noise. The time delays must be short enough to allow protection panels to trip before the equipment operating limits are reached, therefore, maximum ~ delay settings are limited by RPS equipment ratings.
We are recommending that the time delay settings for the protection panels connected to the MG sets remain at the minimum values (less than 0.35 seconds) for the following reasons:
1.
Without detailed analysis of the design and transient response of the MG sets, it is difficult to predict exactly what would happen to the MG set output voltage during and following a voltage regulator failure. Review of MG set preoperational test data indicates that it is conceivable the output voltage might change to an unacceptable value almost instantaneously due to a regulator failure. A time delay setting of 0.35 seconds which is the minimum time stated in the manufacturers instruction manual for this equipment (0.3 seconds +0.05 seconds allowed as a calibration tolerance), provides adequate compensation for these uncertainties. -
3.' *l ENCLOSURE s
-(Continued)
Supporting Information Vermont Yankee Proposed Technical Specification Change No. 105-RPS Power Protection Panel Specification p
2.
.According.to plant records, there has never been a trip of the protection panals connected to the MG sets. This, we conclude, is due to the MG set output voltage regulation and isolation that the MG set provides from the.
transients which cause the alternate supply panels'to trip.
7 The time delay setpoints for the protection panels connected to the RPS alternate power supply, are presently 0.35 seconds or less, for underfrequency.
trip and four seconds or lesaLfor undervoltage and overvoltage trip. The time delay.setpoint for the undervoltage and overvoltage trip was chosen to eliminate spurious trips due to the normal fluctuations of voltage on the alternate. supply.. The, alternate supply.for the RPS is connected'to the plant Auxiliary Electric System and ultimately to the utility distribution grid, and therefore, subject to normal system voltage transients. As noted in the Vermont Yankee Voltage Study (YAEC-1205) the normal (continuous) operating voltage of the plant Auxiliary Electric System is 1 0% of nominal. That range' 1
exceeds the ' calculated composite range for.the RPS equipment. Therefore, the long time delay was necessary to minimize spurious tripping caused by normal system voltage variations.
Since_the 1985 [ Reference (d)] submittal, a voltage regulator was installed on the RPS alternate supply. That regulator maintains output voltage within'the required range of the RPS equipment (similar to the output'of the RPS MG sets)-
regardless of the voltage on the plant Auxiliary Electric System. Therefore, the time delay setpoint for'undervoltage and overvoltage trips for the protection panels connected to the RPS alternate supply will be revised to 0.35 seconds or less, the same as the RPS MG set protection panels.
Accordingly,-Vermont Yankee has revised the proposed Table 4.10.1 (see
. Technical Specification P.177b attached) to incorporate overvoltage and undervoltage time delay setpoints of <0.35 seconds for Panels C1 and C2.
Because the setpoint values for all listed parameters of Panels C1 and C2 are now the same as those of Panels A1, A2, B1, and B2, the two columns on Technical Specification P.177b have been merged into one column. _ _ _ _ _ _ _ _ _____ _ ___ _ __-___ _ _ _ _ _ _ _ _ - _ - _ _ - _