ML20137K827

Application for Amend to License NPF-62,consisting of TS Table 3.3.8.1-1, Loss of Power Instrumentation

ML20137K827
Person / Time
Site:	Clinton
Issue date:	04/01/1997
From:	Jackie Cook ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20137K836	List: ML20137K827 U-602714, Proposed Tech Specs Table 3.3.8.1-1 Re Loss of Power Instrumentation
References
U-602714, WC-159-97, NUDOCS 9704070109
Download: ML20137K827 (16)

Text

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Illinois Power Company \

Chnton Power Station ,

.* P.O. Box 678 ' i

. Clinton. IL 61727 l h .

Tel 217 935-8881 u e 27:4 1

PerWER SE.100a j WC-159-97 April 1, 1997 1 l

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' Docket No. 50-461 10CFR50.90 l Document Control Desk' Nuclear Regulatory Commission  !

Washington, D.C. 20555 {;

Subject:

~ Clinton Power Station Proposed Amendment of  ;

. Facility Ooeratino License No. NPF-62 (LS-97-001)  !

1

Dear Madam or Sir:

j As discussed in Clinton Power Station (CPS) Licensee Event Report (LER)94-005, the degraded voltage relays at CPS and their setpoints are not sufficient to t ensure proper operation of all Class IE equipment, contrary to the current licensing j basis for CPS. As interim corrective action, Illinois Power (IP) installed an  ;

undervoltage alarm for the Division 1,2, and 3 4.16-kV buses and established i contingent operator actions in order to minimize the potential that the Class IE loads -l will not receive adequate voltage for proper operation. Subsequent review of these  !

interim administrative controls has concluded that, although the use of compensatory  !

, administrative controls reduces the risk associated with a degraded voltage condition,  !

i reliance on the interim administrative controls can potentially result in a malfunction of l equipment important to safety of a different type than previously evaluated in the CPS j Updated Safety Analysis Report (USAR) rnd therefore constitutes an unreviewed safety  :

question. In addition, IP has concluded that the interim administrative controls can i

r. result in a small reduction in the margin of safety as defined in the CPS Technical Specifications (TS). I L -

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. Pursuant to 10CFR50.90, IP hereby applies for amendment of Facility Operating 0 4 0 0 72 "_ License No. NPF-62, Appendix A Technical Specifications, for CPS. This request

' consists of a proposed change to Technical Specification (TS) Table 3.3.8.1-1, " Loss of l Power Instrumentation." The proposed TS change requires the interim administrative ,  ;

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. controls to be maintair,ed to minimize the potential that the Class IE loads will not receive adequate voltage in the event of a degraded voltage condition. These controls g Ii are to be maintained until IP completes planned modifications for upgrading the degraded voltage protection instmmer.tation and distribution system for all three K> l 9704070to? 97o4ot 9

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l U-602714 Page 2 divisions of safety-related AC power. The new interim administrative controls primarily I consist of system planning controls on the voltage of the 345-kV offsite grid, notification  !

of plant operators under offsite grid conditions that may result in a degraded voltage i condition if CPS tripped off-line, and utilizing an installed degraded voltage alarm that will prompt operators to take action to transfer the 4.16-kV buses to their associated diesel generators in the event voltage is not adequate to ensure proper operation of the Class IE loads. It should be noted that IP is currently performing calculations to reconfirm that the associated 3940-VAC and 3890-VAC alarm and operator action points, respectively, are still adequate. IP will provide the results of these calculations when they become available.

IP has also performed an evaluation of the proposed degraded voltage relay configuration relative to the current licensing basis degraded voltage relay configuration using Probabilistic Risk Assessment (PRA) techniques. This conservative evaluation concluded that, assuming a degraded voltage condition and no operator actions are taken, the calculated Core Damage Frequency (CDF) increases 170 percent (from 5.5E-6 events per year to 1.5E-5 events per year). If operator actions are assumed to restore room cooling functions within four hours, the calculated change in CDF increase is reduced to 17 percent (from 5.5E-6 events per year to 6.4E-6 events per year). This is considered non-risk significant.

A description of the proposed changes and associated justification (including a Basis For No Significant Hazards Consideration) are provided in Attachment 2. A  ;

marked-up copy of the affected page from the current TS is provided in Attachment 3. A l marked-up copy of the affected pages from the current TS Bases is provided in Attachment 4. Further, an affidavit supporting the facts set forth in this letter and its attachments is provided in Attachment 1. Following NRC approval of this request, IP will revise the CPS TS Bases, in accordance with the TS Bases Control Program of TS 5.5.11, to incorporate the changes identified in Attachment 4.

IP has reviewed the proposed changes against the criteria of 10CFR51.2T ' -

categorical exclusion from environmentalimpact considerations. The proposed enanges do not involve a significant hazards consideration, or significantly increase the amounts or change the types of efliuents that may be released offsite, nor do they significantly increase individual or cumulative occupational radiation exposures. Based on the foregoing, IP concludes that the proposed changes meet the criteria given in 10CFR51.22(c)(9) for a categorical exclusion from the requirement for an Environmental Impact Statement.

It should be noted that CPS is currently in a shutdown condition (Mode 4) for its sixth refueling outage (RF-6). IP has recently determined that the degraded voltage relays must currently be considered inoperable (even during Mode 4) for all three divisions since, with the current setpoints, they are not capable of automatically ensuring adequate voltage to all Class IE equipment. This in turn required IP to declare all three emergency standby l

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diesel generators inoperable at CPS. This condition places limitations on system

' configurations and outage activities. Therefore, IP respectfully requests prompt NRC review of this request at the highest possible priority. ,

Sincerely yours, ,

.G. Cook

Senior Vice President  ;

DAS/krk -

I I Attachments  ;

cc: NRC Clinton Licensing Project Manager NRC Resident Office, V-690 i Regional Administrator, Region III, USNRC ,

Illinois Department ofNuclear Safety  ;

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1 John G. Cook, being first duly sworn, deposes and says: That he is Senior Vice President ofIllinois Power; that this application for amendment ofFacility Operating License NPF- [

62 has been prepared under his supervision and direction; that he knows the contents ,

thereof; and that to the best of his knowledge and belief said letter and the facts contained therein are true and correct. ,

Date: This f ' day of April 1997.  !

Signed: iM John G. Cook I

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STATE OF ILLINOIS l SS. 'O m CW. SEAL" Thomas 8.Ehead

) NelaryI%Ic, State of Rhels De WTT COUNTY J ,

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Subscribed and sworn to before me this 1st day of April 1997.

I (Notary Public) 1 i

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• Page 1 of 12 c

P j Background As discussed in Clinton Power Station (CPS) Updated Safety Analysis Report (USAR) i Section 8.3.1, a first level of undervoltage protection (i.e., loss of power) and a second

. level of undervoltage protection (i.e., degraded voltage) were provided in the CPS design to ensure that adequate voltage is provided to all Class IE equipment down to the 120-VAC level. The degraded voltage protection instrumentation was installed utilizing the

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guidance of NRC Branch Technical Position (BTP) PSB-1, " Adequacy of Station Electric  !

Distribution Voltages." If voltages are not adequate, it was intended that the degraded voltage protection instrumentation automatically separate the Class IE equipment from ,

the degraded voltage source and transfer it to the associated diesel generator.

The need to revise the degraded voltage relay setpoints for continued compliance with the

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] above design requirements was identified in CPS Licensee Event Report (LER)94-005 j (Illinois Power letter U-602296 dated June 3,1994). As discussed in the LER, Illinois

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j Power (IP) personnel recognized, from a review of calculations prepared in response to  !

!- Electrical Distribution System Functional Inspection (EDSFI) findings at other plants, that  ;

the degraded voltage relays at CPS and their setpoints are not sufficient to ensure proper operation of all Class IE equipment, and that more accurate relays are required for proper j

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i degraded voltage protection. ' As interim corrective action, IP installed an alarm for the Division 1,2, and 3 4.16-kV buses and established contingent operator actione in order to l minimize the potential that the Class IE loads will not receive adequate voltage for proper operation. Longer-term actions were initiated to develop design change options for restoring the plant to within its licensing basis for automatic degraded voltage protection. 4 l By IP letter U-602554 dated February 22,1996, IP proposed an amendment to the CPS

. Technical Specifications (TS), in part, to revise the setpoints for the degraded voltage (second-level undervoltage) protection instrumentation. That amendment request was  ;

L provided in support of the longer-term corrective actions. As identified in that request and subsequent responses to NRC Requests for Additional Information (IP letters U-602613

j. dated July 24,1996, U-602635 dated October 4,1996, U-602657 dated November 19, 1996, and U-602669 dated November 25,1996), the longer-term corrective actions involve installation of more accurate undervoltage relays on the 4.16-kV buses and  ;

, installation of voltage regulating transformers to provide adequate voltage for several 120-VAC distribution panels. Calculations provided to the NRC staffin support ofIP's amendment request were based on the final configuration, i.e., with the new undervoltage  ;

relays and regulating transformers installed. IP's request also noted that the modifications were scheduled to be installed one division at a time during separate refueling outages, beginning in the sixth refueling outage (RF-6). IP's amendment request was subsequently 6 approved via Amendment No. I10 dated December 4,1996 which supported IP's original .

installation schedule.

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Upon installation of the modification for Division 2 (modification AP-028) during the current refueling outage (RF-6), problems were experienced with the new regulating j

- transformers. The new transformers were found to be susceptible to radio frequency and  !

electro-magnetic interference (RFI/EMI) and as a result, the internal protective circuitry .  !

was causing spurious trips of one of the transformers. After an extended and unsuccessful l attempt to resolve the tripping problems, it was decided to reinstall the original non- j regulating transformers for the 120-VAC distribution panels. However, it was recognized

- that utilization of the new, more accurate relays calibrated to the setpoints approved in Amendment No. I10 would be the most appropriate configuration, from a safety point of

' view for providing automatic protection for the Class IE loads This automatic protection is sufficient to ensure adequate voltage for the Class lE loads with the exception of the 120-VAC distribution panels requiring the noted regulating transformers.  ;

Thus, major loads such as the ECCS pumps and 480-VAC valve operators will not be l adversely impacted. Circuits fed from the potentially affected 120-VAC distribution 'i panels primarily provide control power for various safety-related ventilation systems and  ;

plant indications. Because, with the new relays and settings, the range over which the  ;

degraded voltage protection is inadequate is on the order of 1% below the rated minimum for 120-VAC equipment (see Figure 1), it is reasonable to assume that the affected  ;

equipment would have a high probability of functioning and any damaging effects would be slight and occur over a relatively long period of time.

I Also during RF-6, CPS established a new operability determination program. That l program, which is based on guidance contained in NRC Generic Letter 91-18, l "Information to Licensees Regarding Two NRC Inspection Manual Sections on ,

Resolution ofDegraded and Non-Conforming Conditions and on Operability," requires  !

completion of a safety evaluation when manual actions are being credited to support  ;

operability of structures, systems,' or components with automatically initiated actions. j Review of the previously established interim corrective actions'(i.e., the undervoltage l alarm and contingent operator actions) concluded that use of these administrative controls I constitutes an unreviewed safety question. This conclusion was reached on the basis that the CPS USAR describes automatic actions that will take place within 15 seconds after the  !

4.16-kV bus voltage decreases below the degraded voltage protection relay setpoint. The r 15-second timer ensures that the Class IE equipment will not be damaged by a degraded voltage condition. IP has concluded that, given the new relay settings and the manual  !

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operator response time, there is an increased potential for 120-VAC Class IE equipment l to be damaged by a degraded voltage condition. This failure mode was not previously F evaluated in the CPS USAR due to the automatic degraded voltage protection. Thus, the -  ;

- condition constitutes a' malfunction of equipment important to safety of a different type than previously evaluated in the CPS USAR, as well as a reduction in the margin of safety as defined in the CPS TS. Further, IP has concluded that the automatic degraded voltage  ;

relays do not meet their requirements for operability based on their current setpoints.  !

Thus, the degraded voltage relays in all three divisions are currently considered inoperable.

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, Because the proposed configuration (i.e., use of the new relays at their new setpoints, with the original (non-regulating) transformers in place) is different than what was reviewed by 1

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LS-97 001  :

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' Page 3 of 12 l the NRC in support of Amendment No. I10, the NRC staff requested that IP include in . l the TS a commitment to maintain the previously established administrative controls in l effect until the degraded voltage protection instrumentation and' distribution system have  ;

been upgraded for all three divisions of safety-related AC power. These actions will ~ j minimize the potential that, in the event of a degraded voltage condition, the Class IE  !

loads associated with the 120-VAC distribution panels will not receive adequate voltage l

' during this interim time period. Therefore, by this amendment request, and as further  ;

described below, IP proposes to incorporate an additional limitation on footnote (b) to TS l Table 3.3.8.1-1, " Loss ofPower Instrumentation," to require the interim administrative  !

controls be maintained until installation of the permanent modification (s) on all three

' divisions of safety-related AC power. Because there are no qualified replacement regulating transformers readily available, these modifications are currently planned to be completed prior to restart from the seventh refueling outage (RF-7).

Description of Proposed Channes ,

' In accordance with 10CFR50.90, IP proposes to revise footnote (b) associated with TS  :

Table 3.3.8.1-1, " Loss of Power Instrumentation," which was incorporated by (

Amendment No. I10 to require use of the revised setpoints for the new relays in a j particular division based on release for operations (RFO) of the plant modification that installs the new undervoltage relays for that division. Specifically, IP proposes to add to the note a new sentence that reads, " Administrative controls as described in the

" Administrative Controls" section of Attachment 2 to Illinois Power Company letter U-  !

i 602714 dated April 1,1997 shall be maintained until RFO of the corresponding plant modifications for Divisions 1,2, and 3."

The proposed changes are reflected in the marked up copies of pages from the current TS contained in Attachment 3. In addition, changes to the CPS TS Bases, consistent with the j l

proposed TS changes, are provided in Attachment 4.

Administrative Controls

.' To minimize the potential that the Class IE loads associated with the 120-VAC [

distribution panels will not receive adequate voltage, CPS will augment the previously  ;

established administrative controls until installation of the permanent modification (s) on all  !

three divisions of safety-related AC power. These controls act to minimize the potential '

for being in a degraded voltage condition and minimize the potential for equipment

damage in the event of a degraded voltage condition. l f

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To reduce the probability of being in a degraded voltage condition at CPS, IP will improve  :

controls on the 345.-kV grid voltage to maintain adequate voltage at CPS. If unplanned l conditions arise (such as storm damage or unplanned unit outages) such that a degraded voltage condition may exist if CPS trips off-line, IP System Dispatch will notify the CPS . '!

main control room. This will provide the plant operators with a heightened awareness of 3 the potential for a degraded voltage condition in the event of a plant trip. These controls '

will be in place prior to plant startup from the current refueling outage.  ;

To minimize the potential for equipment damage in the event of a degraded voltage i condition, IP has installed an undervoltage alarm as described in LER 94-005. _The  :

undervoltage alarm is designed to actuate in the main control room when the voltage of {

any of the Division 1, 2, or 3 4.16-kV buses decreases to 3940 VAC, thereby alerting 'i operators to the existence of a potential degraded voltage condition. In conjunction with j the undervoltage alarm, annunciator procedure CPS No. 5008.05, " Alarm Panel 5008 j Annunciators - Row 5," advises plant operators that, if the alarm activates, Class IE buses i i

could be experiencing a degraded voltage condition due to low grid voltage at the reserve

- auxiliary transformer (RAT) or the emergency reserve auxiliary transformer (ERAT). The procedure identifies actions that the operators are required to take in response to the alarm for voltages between 3940 VAC and 3890 VAC, including monitoring the bus voltages  ;

and attempting to increase the grid and/or bus voltages (via raising generator output voltage, having the Electric Supply Dispatcher attempt to raise grid voltage, reducing .

balance of plant auxiliary loads on the RAT, or transferring the bus to the alternate offsite source (RAT or ERAT), if available). If the 4.16-kV bus voltage is below 3890 VAC, the procedure requires the operator to start the emergency diesel generators and transfer the buses to the emergency diesel generator supply. IP is currently performing calculations to reconfirm that the 3940-VAC and 3890-VAC alarm and operator action points, respectively, are still adequate. IP will provide the results of these calculations when they become available.

Plant operators have been briefed on the second-level undervoltage logic scheme and the symptoms they could expect to see during a degraded voltage condition. The plant operators will receive additional training on the undervoltage alarm, possible causes for alarm actuation, and automatic actions and operator actions required in response to the alarm prior to plant restart from RF-6.

The above administrative controls will remain in effect until all three safety-related AC power distribution divisions have been modified to restore the required automatic undervoltage protection. As previously stated, these modifications are currently planned to be completed prior to plant restart from the seventh refueling outage (RF-7).

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• Attachment 2

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. Page 5 of 12 Justification for Proposed Changes As noted in IP's response to the NRC's June 3,1996 Request for Additional Information I (IP letter U-602613 dated July 24,1996), in accordance with the General Design Criteria i (GDC) of 10CFR50,' Appendix A, accidents are postulated to occur "with or without j offsite power available." In order to fulfill the requirements with offsite power available,  ;

proper equipment operation must be demonstrated with offsite power available at the i minimum expected offsite voltage. IP will perform adjustments to the CPS distribution  !

system prior to restart from the current refueling outage to ensure this requirement is met.

l Th'ecapability to mitigate accidents with offsite power voltages below the minimum ,

j expected value is outside the requirements of the GDC. However, embodied in the GDC concepts is that the safety buses will be transferred from the offsite sources to the onsite j

sources if bus voltage is inadequate.  ;

As discussed in CPS USAR Section 8.3.1, a first level of undervoltage protection (i.e., ,

loss of power) and a second level of undervoltage protection (i.e., degraded voltage) was j provided in the CPS design to ensure that adequate voltage is provided to all Class IE l equipment down to the 120-VAC level. This degraded voltage protection instrumentation  ;

t was installed utilizing the guidance of NRC Branch Technical Position (BTP) PSB-1,

> " Adequacy of Station Electric Distribution System Voltages." If voltages are not adequate, it was intended that the degraded voltage protection instrumentation would  :

automatically separate the Class IE equipment from the degraded voltage source and allow it to be transferred to the associated diesel generator. In order to bound all possible ,

bus loading conditions when evaluating the adequacy of the degraded voltage protection design, IP utilized the bus loading conditions expected post-LOCA. [

As previously discussed herein and as described in CPS LER 94-005, IP personnel  ;

recognized that the existing degraded voltage relays and their setpoints are not sufficient l to ensure proper operation of all Class IE equipment as required by the CPS USAR. IP  ;

determined that more accurate relays are required for the degraded voltage protection  ;

function. As interim corrective action, IP installed an alarm for the Division 1, 2, and 3 l 4.16-kV buses of electrical Divisions 1, 2, and 3 and established compensatory operator actions as a contingent measure to minimize the potential for degraded voltage resulting in inadequate voltage for proper operation of Class IE equipment. Longer-term corrective  ;

actions involve implementation of plant modifications that will automatically ensure  !

adequate voltage to all Class IE equipment. The TS requirements applicable after installation of these modifications were reviewed and approved by the NRC staff via  !

. Amendment No. I10 dateo December 4,1996. This amendment request proposes the j addition of a requirement to ensure that the new interim administrative controls are maintained until all three divisions of the degraded voltage instrumentation and distribution systems have been upgraded for restoring the plant to within its original [

licensing basis.  :

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As discussed in the NRC staffs safety evaluation accompanying Amendment No.110, .i there are two scenarios considered for determining the required degraded voltage ~  !

instrumentation setpoints. First, the relay Itast setpoint must be established above the i voltage necessary to ensure proper starting of equipment needed to mitigate a postulated. j LOCA (i.e., LOCA block start conditions), but below the minimum offsite voltage l expected following a LOCA while the safety buses are loaded with the LOCA loads. (The j

- latter ensures that a transfer to the diesel generator (s) occurs only when required.)

i Secondly, the relay itig setpoint must be established below the relay reset point, but above the voltage necessary to ensure safety-related equipment will continue to operate post- ,

LOCA. ' (As previously noted, LOCA bus loadings were utilized in order to bound possible bus loading configurations.) The adequacy of the new interim administrative i controls to fulfill each of the above-noted functions of the degraded voltage protection  :

instrumentation is addressed below.

During a design basis LOCA event at CPS with offsite power available, the accident loads will, with the exception of the Residual Heat Removal system pumps, be simultaneously j loaded (i.e., there are no intentional time delays, except five seconds for two of the j Residual Heat Removal system pumps) onto the offsite power source available at that  !

time. As a result, there will be a large initial voltage sag due to the simultaneous starting l inrush currents of the accident loads (motors). This voltage sag will cause the degraded  ;

voltage relays to drop out, regardless of whether the old or new undervoltage relays i and/or setpoints are utilized. Thus, the characteristics of the voltage sag during starting of l large AC motors following a postulated LOCA is such that the trip setpoint of the relay is  ;

t not critical for ensuring that the timer for the degraded voltage trip is initiated. When the '

relay drop out occurs, a timer is activated, and if voltage is still below the relay reset point after the timer times out, the degraded offsite power source is isolated and the loads are t automatically transferred to the associated diesel generator. Following the initial inrush  !

current transient, however, the voltage should recover to a value that will allow the safety .

loads to start and mn and will reset the degraded voltage relay before the degraded  !

voltage relay timer times out and separates the loads from offsite power. This is true ,

because the minimurn expected offsite voltage will be above the minimum 120-VAC Class i lE equipment requirements and the degraded voltage relay reset setpoint. However, due  !

to the lack of voltage regulating distribution transformers, it can be postulated that the [

4.16-kV bus voltage could recover to a value sufficient to reset the degraded voltage [

relays, but not high enough to ensure sufficient voltage to the 120-VAC Class lE <

equipment fed from the distribution transformers. It could also be postulated that the ,

4.16-kV bus voltage could decrease from a previously acceptable value to a value that is

ebove the degraded voltage relay drop out setpoint, but not high enough to ensure j sufficient voltage to the 120-VAC Class IE equipment. The potential for these two j scenarios to occur is small since the maximum relay setpoint tolerances are within 0.4%

~ and 1.1%, respectively, of the minimum ratings for the 120-VAC Class IE equipment (see Figure 1). It is reasonable to assume that the affected equipment would have a high  ;

. probability of functioning at such a slightly reduced voltage and any damage would be  :

slight and occur over a relatively long period of time. The 4.16-kV bus voltage at which  ;

annunciator procedure CPS No. 5008.05 instructs plant operators to transfer the 4.16-kV j

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• Page 7 of12  ;

buses to the diesel generators (i.e.,3890 VAC) ensures that adequate voltage will be  !

provided to all Division 1,2, and 3 Class IE loads. i In addition, IP has performed an evaluation of the proposed degraded voltage relay  !

configuration relative to the current licensing basis degraded voltage relay configuration  !

1 using Probabilistic Risk Assessment (PRA) techniques. A conservative approach to the 3

PRA analysis was taken in that it assumes that the potentially affected 120-VAC loads fail l

in response to a degraded voltage condition. The only PRA-significant loads that may not j be supported with their design voltage without operator action are room cooling loads. '

This conservative PRA evaluation has concluded that, for all accident sequences that lead to core damage (other than loss of offsite power and station blackout), the calculated Core Damage Frequency (CDF) increases 170 percent (from 5.5E-6 events per year to 1.5E-5  :

events per year) assuming a degraded voltage condition exists and no operator actions are i taken. If operator actions are assumed to restore room cooling within four hours, the calculated CDF increase is reduced to 17 percent (from 5.5E-6 events per year to 6.4E-6 l events per year). This is considered non-risk significant. .

Further, the new interim administrative controls established by IP (as described previously) f minimize the potential for being in a degraded voltage condition and minimize the potential for equipment damage in the event of a degraded voltage condition. l l Basis for No Sinnificant Hazards Considerations As noted previously, Illinois Power (IP) proposes to revise footnote (b) associated with Clinton Power Station (CPS) Technical Specification (TS) Table 3.3.8.1-1, " Loss of l Fower Instmmentation," to require interim administrative controls be maintained to  !

minimize the potential that the Class IE loads will not receive adequate voltage until l perman"t modifications are installed. In accordance with 10CFR50.92, a proposed >

change w the operating license (or TS) involves no significant huards consideration if -

operation of the facility in accordance with the proposed change would not

(1) involve a significant increase in the probability or consequences of any accident previously  ;

evaluated, (2) create the possibility of a new or different kind of accident from any 3

accident previously evaluated, or (3) involve a significant reduction in a margin of safety. ,

j This request is evaluated against each of these criteria below.

(1) The changes addressed by this amendment request involve addition of a requirement to maintain in effect administrative controls to minimize the potential i that, in the event of a degraded voltage condition, the Class IE loads associated j with the Division 1,2, and 3 safety-related 4.16-kV buses will not receive adequate voltage, until all three divisions of the degraded voltage instrumentation i and distribution systems have been upgraded for restoring the required automatic  !

degraded voltage protection. Because there are no qualified replacement j regulating transformers readily available, these modifications are currently planned j to be completed prior to plant restart from the seventh refueling outage (RF-7). l The new interim administrative controls include establishing additional controls on j

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Attachment 2

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• Page 8 of12 j

- the 345-kV grid voltage and requiring notification of the main control room in the event unplanned conditions arise (such as storm dunage or unplanned unit  :

outages) such that a degraded voltage condition may exist if CPS trips off-line. l l These will minimize the occurrence of a degraded voltage condition and provide ,

. greater awareness'when there is an increased potential for degraded voltage.  :

. These controls will be in place prior to plant restart from the current refueling j outage.-  ;

l The General Design Criteria (GDC) of 10CFR50, Appendix A, require accidents to be postulated to occur "with or without offsite power available." In order to

, fulfill these requirements with offsite power available, proper equipment operation  ;

must be demonstrated with offsite power available at the minimum expected offsite i voltage. IP will perform adjustments to the CPS distribution system prior to  ;

restart from the current refueling outage to ensure this requirement is met. The i I

degraded voltage instrumentation and the new interim administrative controls  ;

described above together will provide equipment protection against voltages that  !

are below the minimum expected offsite voltage.

Consistent with the GDC, the accidents evaluated in the USAR are postulated to  !

occur with or without offsite power. The USAR does not evaluate the consequences of accidents concurrent with a degraded voltage condition. The new  !

interim administrative controls do not direct any operator actions to transfer the Class 1E loads to their associated diesel generator until the 4.16-kV bus voltage is below the minimum expected offsite voltage. Therefore, IP has concluded that 1 reliance on these controls will not result in a significant increase in the probability or the consequences of any accident previously evaluated in the Updated Safety

Analysis Report (USAR).

(2) This change only involves including administrative controls to minimize the ,

potential for degraded voltage resulting in inadequate voltage for proper operation i of all Class IE equipment. The only active administrative controle involve i

! manually transferring the 4.16-kV buses from the offsite power source to its l associated diesel generator in the event offsite voltage is not sufficient. The j method of performance of these actions are described in Section 8.3.1.1.2 of the  :

CPS US AR, The current degraded voltage protection instrumentation is provided in the plant design to respond to a previously analyzed event (i.e., a degraded ,

voltage condition). Thus, operation of the degraded voltage protection j instrumentation or performance of the administrative controls can not initiate an accident not previously analyzed. ,

(3) As'previously discussed, in accordance with the GDC of 10CFR50, Appendix A, accidents are required to be postulated to occur "with or without offsite power available " In order to fulfill these requirements with offsite power available, '

proper equipment operation must be demonstrated with offsite power available at the minimum expected offsite voltage. IP will perform adjustments to the CPS

~

Attachment 2

- to U-602714 LS-97-001

- Page 9 of12 distribution system prior to restart from the current refueling outage to ensure this requirement is met. The degraded voltage instrumentation and the new interim administrative controls together will provide adequate equipment protection against voltages that are below the minimum expected offsite voltage, and hence, maintains the margin of safety.

} The new interim administrative controls include establishing additional controls on the 345-kV grid voltage and requiring notificaion of the main control room in the i event unplanned conditions arise (such as storm damage or unplanned unit outages) such that a degraded voltage condition may exist if CPS trips off-line.

4 These will minimize the occurrence of a degraded voltage condition and provide greater awareness when there is 'an increased potential for degraded voltage.

These controls will be in place prior to plant restart from the current refueling outage.

) As discussed in the NRC staffs safety evaluation accompanying Amendment No.

110, there are two scenarios considered for determining the required degraded voltage instrumentation setpoints. First, the relay Tsg! setpoint must be 4 established above the voltage necessary to ensure proper starting of equipment needed to mitigate a postulated LOCA (i.e., LOCA block start conditions), but below the minimum offsite voltage expected following a LOCA while the safety buses are loaded with the LOCA loads. (The latter ensures that a transfer to the diesel generator (s) occurs only when required.) Secondly, the relay trip setpoint ]

must be established below the relay reset point, but above the voltage necessary to l ensure safety-related equipment will continue to operate post-LOCA. (As j previously noted, LOCA bus loadings were utilized in order to bound possible bus i loading configurations.) The adequacy of the new interim administrative controls to fulfill each of the above-noted functions of the degraded voltage protection instrumentation is addressed below.

During a design basis LOCA event at CPS with offsite power available, the accident loads will, with the exception of the Residual Heat Removal system pumps, be simultaneously loaded (i.e., there are no intentional time delays, except five seconds for two of the Residual Heat Removal system pumps) onto the offsite power source available at that time. As a result, there will be a large initial voltage

, sag due to the simultaneous starting imush currents of the accident loads (motors).

This voltage sag will cause the degraded voltage relays to drop out, regardless of

whether the old or new undervoltage relays and/or setpoints are utilized. Thus, the characteristics of the voltage sag during starting oflarge AC motors following a postulated LOCA is such that the trip setpoint of the relay is not critical for ensuring that the timer for the degraded voltage trip is initiated. When the relay drop out occurs, a timer is activated, and if voltage is'still below the relay reset point after the timer times out, the degraded offsite power source is isolated and the loads are automatically transferred to the associated diesel generator.

Following the initial inrush current transient, however, the voltage should recover

- , , - , n, + - . , , . - , . . . - . , . . - - ~. . .- ~_ - - _ _ - - - - _ - _ - - _ _ - _ - _ - _ . _ _ _E

Attachment 2 .

to U-602714 I LS-97-001 Page 10 of 12 -

to a value that will allow the safety loads to start and run and will reset the. ]

degraded voltage relay before the degraded voltage relay timer times out and separates the loads from offsite power. This is true because the minimum expected

offsite voltage will be above the minimum 120-VAC Class IE equipment requirements and the degraded voltage relay reset setpoint. However, due to the  ;

lack of voltage regulating distribution transformers, it can be postulated that the

. 4.16-kV bus voltage could recover to a value sufficient to reset the degraded '

! voltage relays, but not high enough to ensure sufficient voltage to the 120-VAC )

Class IE equipment fed from the distribution transformers It could also be postulated that the 4.16-kV bus voltage could decrease from a previously ,

acceptable value to a value that is above the degraded voltage relay drop out j setpoint, but not high enough to ensure sufficient voltage to the 120-VAC Class IE equipment. The potential for these two scenarios to occur is small since the maximum relay setpoint tolerances are within 0.4% and 1.1%, respectively, of the minimum ratings for the 120-VAC Class IE equipment. It is reasonable to assume that the affected equipment would have a high probability of functioning at such a slightly reduced voltage and any damage would be slight and occur over a relativelylong period of time.

In addition, CPS has an undervoltage alarm designed to actuate in the main control

room when the voltage of any of the Division 1,2, or 3 4.16-kV bus voltage has

decreased to 3940 VAC, which will alert operators to the existence of a potential degraded voltage condition. This value will provide plant operators with an early  !

. warning that offsite voltage is approaching the minimum required value and will  ;

provide time to restore bus voltage, thus minimizing the potential for a plant event l with a degraded voltage condition. To support the undervoltage alarm, annunciator procedure CPS No. 5008.05, " Alarm Panel 5008 Annunciators - Row 5," advises plant operators that, if the alarm activates, Class IE buses could be i experiencing a degraded voltage condition due to low grid voltage at the reserve auxiliary transformer (RAT) or the emergency reserve auxiliary transformer (ERAT). The procedure identifies actions that the operators are required to take in response to the alarm for voltages below 3940 VAC but above the minimum voltage requirements for the Class IE loads, including monitoring the bus voltages and attempting to increase the grid and/or bus voltages (via raising generator output voltage, having the Electric Supply Dispatcher attempt to raise grid voltage, reducing balance of plant auxiliary loads on the RAT, or transferring the bus to the alternate offsite source (RAT or ERAT, if available). If 4.16-kV bus voltage is below the minimum required for proper operation of Class IE loads, the

procedure requires the operator to start the emergency diesel generators and

, transfer the buses to the emergency diesel generator supply. The vslue at which the annunciator procedure requires the operator to transfer the 4.16-kV buses to their associated diesel generators is based on extensive voltage calculations to be above the minimum required voltage at the 4.16-kV bus with LOCA loading.

Each emergency diesel generator is capable of providing sufficient voltage for

g ,' O '

Attachment 2 to U-602714 LS-97-001 '

Page 11 of12

- proper Class 1E equipment operation. ~ Thus upon transfer to the emergency diesel generators, adequate voltage is assured for ti.: Class IE loads.

Plant operators were briefed on the second-level undervoltage logic scheme and the symptoms they could expect to see during a degraded voltage condition. In addition, the plant operators will receive additional training on the undervoltage alarm, possible causes for alarm actuation, and automatic actions and operator actions required in response to the alarm prior to plant restart from the current refueling outage.

Notwithstanding, IP has performed an evaluation of the proposed degraded voltage relay configuration relative to the current licensing basis degraded voltage relay configuration using Probabilistic Risk Assessment (PRA) techniques. A conservative approach to the PRA analysis was taken in that it assumes that the potentially affected 120-VAC loads fail in response to a degraded voltage condition. The only PRA-significant loads that may not be supported with their design voltage without operator action are room cooling loads. This conservative PRA evaluation has concluded that, for all accident sequences that lead to core damage (other than loss ofoffsite power and station blackout), the calculated Core Damage Frequency (CDF) increases 170 percent (from 5.5E-6 events per year to 1.5E-5 events per year) assuming a degraded voltage condition exists and no

- operator actions are taken. If operator actions are assumed to restore room cooling within four hours, the calculated CDF increase is reduced to 17 percent (from 5.5E-6 events per year to 6.4E-6 events per year). This is considered non- l risk significant.

Based on the actions taken to reduce the probability of being in a degraded voltage j condition, the small magnitude of potentially unmitigated degraded voltage, the l high likelihood of affected equipment continuing to function at such a slightly l

- reduced voltage, the small increase in CDF, the annunciator and preplanned  ;

operator actions to mitigate the effects of a degraded voltage condition in the  ;

unlikely occurrence, IP has concluded that reliance on the administrative controls i for operability isjustified and does not involve a significant reduction in a margin  :

ofsafety. l Based on the fore 8oing, IP concludes that this request does not involve a significant  ;

hazards consideration.  !

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4 OPERATOR ACTION-REQUIRED TO PROVIDE Atta an2nt 2 PROTECTION TO 120 VOLT EQUIPMENT 3.j;g2;14

_' Page 12 of 12 70-  !

60-ALARM AT 3940 40-30- U 20-00 10-9 CC 3900- TRANSFER i LOADS TO D.G. 3901 3890 C"> 90-890 3888 5 REQUIRED FOR EQUIPMENT SETPOINT 12.5 h gAgoR h j T 80- R 120 VOLT 6

U (E0lflRE 0.4%) ,

Z 70- DISTRIBUTION -'3 76s PROTECTED OPERATOR O TRANSFORER SYSTEM DROP N 62' RESET Rf0U 0 60- OUT SETPOINT - (1.1 %)

g REQUIREMENTS (TRIP) 'I l C 3850- N3_848s y l4 40-PROTECTED

%EAYT l O 30-20-10- l 3800-90-80-70-3760 EQUIPENT- OPERATOR DIV. 1, 2. & 3 DPERATOR ACTION REQUIREENT ACTION (NEW RELAYS)

REQUIRED TO SECOND LEVEL (DEGRADED)

PROTECT EQUIPMENT VOLTAGE RELAYS Figure 1