IR 05000293/1993011

Insp Rept 50-293/93-11 on 930606-11.No Violations Noted. Major Areas Inspected:Licensee Corrective Actions of Previously Identified Electrical Distribution Sys Functional Insp Findings & Observations

ML20062K250
Person / Time
Site:	Pilgrim
Issue date:	08/04/1993
From:	Bhatia R, Ruland W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
To:
Shared Package
ML20062K249	List: IR 05000293/1993011 ML20062K242
References
50-293-93-11, NUDOCS 9312210253
Download: ML20062K250 (11)

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U.S. NUCLEAR REGULATORY COMMISSION

REGION I

' REPORT N /93-11 DOCKET NO. - 50-293 l LICENSE N DPR-35 LICENSEE: - Boston Edison Company RFD N Rocky Hill Road -

Plymouth, Massachusetts 02360 -

FACILITY NAME: Pilgrim Nuclear Power Station, Unit 1 INSPECTION DATES: June 6 - 11,1993 -

INSPECTOR: l' 74F/4a Ram S. Bhatia, Reactor Engineer Date Electrical Section, EB, DRS

l APPROVED BY: . I% I Williain H. kuland, Chief Date'

Electrical Section, EB, DRS )

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9312210253 930919 PDR ADOCK 05000293 G PDR

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Area Insnected: This was an announced inspection to review the licensee's corrective actions

! of previously identified electrical distribution system functional inspection (EDSFI) findings .

l and observation '

t Results: No violations or deviations were identified. All six open items (one violation and .

l five unresolved items) previously identified in the EDSFI Inspection Report No. . 50-293/91-j 80 were closed. These items are discussed in Section 2.0 of this inspection _ repor _

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DETAILS PURPOSE The purpose of this inspection was to review and verify the licensee's corrective actions for previously identified NRC findings during the 1991 Electrical Distribution Systems Functional Inspection (EDSFI) for Pilgrim Nuclear Power Station. The review included the licensee's actions addressed in their written responses to the EDSFI report dated

? mst 9,1991; June 30,1992; and to the Notice of Violation, dated November 25,199 FOLLOWUP OF PREVIOUSLY IDENTIFIED FINDINGS (Closed) Unresolved Item No. 50-293/91-80-01 Regarding the Adequacy of Transformers During the previous inspection, the team was concerned that the non class 1E fans on the Class IE transformers (X21 and X22 4.16kV-480/277V), under a postulated failure of fans during turbine trip /LOCA scenario, may not have an adequate kVA rating to supply the required loads to mitigate the accident. The licensee had no exact calculation to dispute this concer During this inspection, the inspector noted that the licensee had performed a calculation and reevaluated the adequacy of the Class IE transformers (X21, X22) load rating. The licensee concluded that these. transformers can operate continuously at their base 1000 kVA rating under the worst-case loading scenario and postulated failures of the non class-IE fans. It was determined by the licensee that the 1000 kVA base-rated transformers could sustain 1240 kVA overload condition (worst-case loading) for approximately 30 days with only a slight degradation in transformer life. The calculation revealed that the life expectancy of this type of transformer under this condition will be reduced by only 0.2 days. The calculation was based on the ANSI /IEEE standards, assuming 20 years as a typical nominal transformer life for this type of transformer. The inspector's review of the transformer's loading calculation revealed that the worst-case 480V system load requirements during a LOCA and assuming no normal load-shed (conservative), on the X22 transformer to be approximately 1240 kVA. Based on this load requirement and utilizing the ANSI /IEEE Standard C57.98-1989 guidelines for a similar type of transformer would be reduced only by 0.2 days from 20 years life expectancy. In addition, the licensee determined in their above evaluation that these transformers, during the above overloading condition for 30 days, would not reach their insulation hot spot temperature of 194" The inspector reviewed the methodology and key parameter recommended in the IEEE/ ANSI Standard to the licensee's calculation and found no deficiencies. The inspector also verified that the transformer data used in the calculation and the other assumptions used were consistent with the industry standards for this type of transformer. The inspector had no other concerns except the inspector questioned the licensee's tracking mechanism of such l

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condition of the transformer usage in the future. In response, the licensee put these transformers on the plant tracking system, by which the licensee is committed to evaluate remaining transformer life based on service usage yearly from the year 2000 onward Based on the results of the above licensee's evaluation and the tracking mechanism in place to assess transformer condition and the load requirement verification, the inspector concluded that the transformer can operate as required to mitigate the accident conditions without any significant loss of transformer life. Therefore, this item is close .2 (Closed) Unresolved Item No. 50-293/91-80-02 Regarding the Adequacy of Degraded Voltage Relay Setpoint During the EDSFI inspection, the team noted that the licensee was in the process of completing the review of the load flow and voltage drop studies. Based on the outcome of these studies, the licensee was committed to evaluate the adequacy of the existing degraded voltage relay setpoints to ensure that emergency buses and associated equipment will operate and would not be damaged during a sustained undervoltage conditio Subsequent to the inspection, BECo notified the .NRC by letter on August 9,1991, that under certain station operating conditions a sufficient voltage may not be available to some loads at the 480V and 120V levels with the existing degraded voltage relay setpoints. In addition, when the swing bus B6 (480 Vac) was being supplied from its alternative source B2 (480 Vac) and the 345 kV grid voltage is between 340 kV and 349 kV, the potential exists that the voltage at 480V motor control centers (MCCs) B14, B18, and B20 and 120 Vac distribution panels Y4 and Y41 would be below the manufacturer's minimum voltage requirement to ensure proper operation of some safety-related loads. Based on this letter and compensatory measures taken and the commitment to modify the plant by the next planned refueling outage (9R), the team determined that the above actions were adequate for continued operatio During this inspection, the inspector noted that the licensee had informed the NRC of their corrective actions in their letters dated November 25,1991, and June 30,1992. By selected document review and walkdown of installed plant equipment, the inspector verified the completion and the adequacy of the licensee's corrective actions. The documents reviewed included:

• Voltage drop and load flow study completed by the Stone and Webster Cor (Calculation PS-65).  :

• The compensatory measures established to control the grid voltage were still in place and being reviewed by engineering for further action * Degraded voltage study under worst-case scenario (LOCA without load shed concurrent with the turbine generator trip condition-Calculation PS65A)

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L e Abnormal electrical system alignments study (considsring failure of a trip signal to disconnect the largest load on an MCC during a LOCA and the .

addition of the largest nonoperating load during the MCC worst-case scenario ,

calculation PS-65 e Plant Design Change (PDC) No.91-59A; X55 and X56 transforme replacemen ,

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e PDC No.91-59B; X57 and X58 transformer replacemen '

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! * PDC No. 92-39; Replace _ control power transformers-480V MCCs (65 control

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circuits in various MCCs).

• PDC N'o. 93-05;-Replace standby gas treatment' system feeder cables (f6r the' , ,

exhaust fans VEX 210A and B, and heaters VGTF201A and B,Lwith largerc ,

feeder cables).

The inspector's review ~of the above-documents, including the design modifications and their 10 CFR 50.59 safety evaluations, test results and selected l portions of the changes . verified by; physical walkdown revealed no concerns. LThe inspector concluded that thefexisting degraded <

voltage relay setpoints were adequate for all safety loads under' the worst-case scenario.1This -[

item is close r (Closed) Unresolved Item No..50-293/91-80-_03 Regarding the" Adequacy of  :

Circuit Breaker and Transformer Ratings ,

l This item pertains to a lack of adequate ac fault analysis to evaluate the$dequahy;of the - J interrupting rating of the class 1E circuit breakers and the insulation coordination study ~ to ' ',

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support the breaker insulation level (BIL) associated with the _4.16 kV_ buses, transformers -

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and switchgear. At the conclusion of previous inspection, the licensee was in the process of - j l completing the review of the analysis for the short circuit. calculations'to resolve these  ;

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concern During this inspection, the inspector noted that the licensee-had completed a short 'circuiti study (PS-95, Revision 2) to evaluate the_ interrupting rating of the clas's 1E and. non class ;

4.16 kV circuit breakers. The review of theLresults of this calculation ^ indicated that the act short-circuit ratings (momentary and interrupting) for all th 4'16 kV switahgear were within '

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the acceptable minimum values. - The worst-case ac short circuit momentary and interrupting - '

rating at the 4295V prefault voltage were determined to be 54,095 and.28,610 amperes,  :

within the 55,434 and 29,318 ampere ratings of the switchgear. ; Based on the inspector's i l review of the licensee's calculation and verification of the vendor and:

ANSI standard rating ~ of these breaker's, the inspector concluded that the'switchgear - 3 associated with the 4.16 kV buses was within the manufacturer's interrupting ratirig a

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To evaluate the adequacy of the BIL rating associated with the 4.16 kV switchgear and load center transformers, the licensee had performed a coordination study documented as calculation PS-111, Revision 0. In this study, an analysis was performed by using the EPRI's Electromagnetic Transient Program (EMTP). The licensee developed the complete station model including the representation of the 345 kV grid system, the startup transformer, the switchyard surge arresters, coupling capacitors, bushings, and the 4 kV cables. The study assumed a conservative lightning stroke of 1100 kV impulse applied at the startup transformer of the station. The inspector's review of this study results indicated that the worst-case resultant pulse would be 9 kV at a 4.16 kV switchgear location. Since 4.16 kV switchgear and load center transformers are rated at 60 kV BIL, the inspector concluded that the existing BIL rating was adequat Based on the above corrective actions performed by the licensee to demonstrate that the ac short-circuit rating and BIL rating of the 4.16 kV switchgear and load center transformers

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was adequate and found to be within the manufacturer's acceptable ratings, the inspector had no further questions. This item is close .4 (Closed) Unresolved Item No. 50-293/91-80-04 Regarding Electrical Penetration Protection This item pertains to inadequate documentation to demonstrate that the heat generated by the containment electrical penetration assemblies is within the manufacturer's recommended values and that the penetrations are protected by suitable electrical protective device During the EDSFI inspection, the team reviewed five penetration documents generated by the licensee and concluded that the penetrations had adequate primary protection but no backup protection. Subsequent to this inspection, the licensee (PCAQ Report 91-165) performed an engineering assessment and operability assessment and concluded that the penetrations were operabl In response to the above concern, the licensee, in their letter of November 25,1991, was committed to perform studies: 1) for the time-current curves (coordination protection) for each circuit and 2) evaluate the adequacy of penetration integrity within manufacturer s recommended ratings under the worst-case loading condition During this inspection, the inspector noted that the licensee had completed two calculations, PS-119, " Containment Electrical Penetrations," on June 3,1993, and PS-124, " Adequacy of Electrical Penetrations Under LOCA Conditions," on January 1,1993, respectively. From the review of these calculations, the inspector determined that the licensee had identified all the power and control circuits for the penetrations. In addition, for each penetration, protection coordination curves were developed. The inspector review of the above calculations revealed that all penetrations were capable of operating at full load under the

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I worst-case LOCA conditions. The inspector also noted that some of the nonessential (non-IE) circuit conductor imparities were below the protection setting of the circuit breaker or the fuse installed. Further evaluation of these circuits completed by the licensee concluded that these circuits had the adequate short circuit protection, in some cases (non IE) the overload protection setting could be enhanced further by lowering the overload setting. The licensee is in the process of evaluating additional modifications to further enhance these circuits overall protection. The licensee concluded that in all cases, the penetration circuits would be protected either by overload or by short circuit protectio The inspector's review determined that the above calculations and analysis had demonstrated

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that the electrical penetration were adequately protected and the penetration's ampacities were

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within the manufacturer's continuous rating. In addition, a selected review of circuits 4 revealed no concerns. Therefore, the inspector concluded that the licensee had established adequate documentation for the penetration assemblies. This item is close .5 (Closed) Unresolved Item No. 50-293/91-80-05 Regarding Large Motor Starting Effect on 120 Vac System During the previous EDSF1 inspection, the team noted that during steady-state loading conditions on the 120 Vac safety-related panels (Y-3, Y-31, Y-4, and Y-41), voltages

- available to most of the devices were adequate; however, some voltages were marginal. In addition, the licensee's calculation did not consider and evaluate the effect of large motor starting on these circuits. The team was concerned that during large motor starting, insufficient voltage may be experienced by some of these devices which could affect the

operation of these devices such as solenoids and motor starting coils in the MCC During this inspection, the inspector noted that the licensee had completed the 120 Vac circuit voltage evaluation. The minimum voltage levels at each 480V MCC under worst-case loading scenarios was determined (just before the MCC load transferred to the EDG on degraded voltage with LOCA and turbine trip, Calculation PS-67). Then considering the minimum MCC voltage (in their calculation PS-70, Revision 2), available voltage for each device in the circuit was determined. The licensee concluded that all devices supplied from the above 120 Vac power distribution panels would have sufficient voltage for operatio The inspector's review of the above documentation revealed that the licensee had adequately identified and considered the loading conditions of the equipment fed from each panel breaker and its associated devices, the worst-case cable lengths and minimum voltages at the MCC level. In addition, the inspector noted that the licensee's calculation assumed four installed regulating transformers, X55 through X58 capable of regulating the 120 Vac secondary voltage in the range of 120 Vac 4% for varying input voltages of 480 Vac, i 20%. The review of the licensee's calculation indicated that adequate margin exists

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between the supplied voltages and the manufacturer's minimum required voltage at the 120 Vac safety-related components. The inspector also verified by walkdown the plant installation of four regulating transformers considered in this calculation. The inspector's review of the above licensee's documentation and verification of selected sample revealed no concern Based on the above corrective action to demonstrate that all safety-related ac components at 120 Vac level can function under the worst-case voltage condition with adequate voltage j margin, this item is close .6 (Closed) Violation Item No. 50-293/91-80-07 Regarding Inadequate Corrective Actions on IIPCI/RCIC Inverter Failures The team review of the Licensee Event Reports (LERs) in the previous EDSFI inspection determined that the licensee did not perform an adequate root cause analysis for the RCIC/HPCI inverter failures. The licensee's root cause analysis and corrective action for the RCIC/HPCI inverter trip, as documented in PNPS Failure and Malfunction Report j (F&MR) No.91-103 and License Event Report (LER)91-106, "High Pressure Coolant Injection and Reactor Core Isolation Cooling System Became Inoperable Due to Tripped Inverters," did not assure that the cause of the condition was determined and adequate corrective action taken to preclude recurrence. In addition, the licensee had not evaluated the RCIC/HPCI inverter failure mode for a loss of coolant accident / loss of offsite power (LOCA/ LOOP) scenario and no evaluation was done of the battery charger respons Subsequent to the previor; mspection and the restart of the plant, a management meeting was held at the NRC Regional office on October 2,1991, to discuss the resolution of the above concern. In this meeting, the licensee discussed a broad range of alternatives and tests to be performed during the next available plant outage to determine the root cause and appropriate corrective action On October 15, 1991, the licensee requested relief (Limiting Condition Operation from 7 to 97 days) from the Technical Specification for RCIC system because the test data of the battery charger in question was not adequate to demonstrate sufficient margin from the trip setpoint. The licensee declared the RCIC system inoperable on October 9,1991. This waiver requested by the licensee was accepted by the NRC to allow design and installation changes to the RCIC inverter to prevent inverter trips until the next refueling outage as documented in the NRC letter, dated October 18, 199 During this inspection, the inspector noted that the beensee had completed a root cause analysis on November 11, 1991, documented in PM91-165 report. This multi-disciplinary analysis team (MDAT) formed to complete the above analysis was supplemented with special management participation. The inspector's review of the analysis revealed that the team had

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considered all appropriate information in evaluating this concern and the evaluation was thorough and comprehensive. This evaluation had considered all available test data from the ,

i previous trips, including the special test performed on the battery chargers under worst-case )

conditions, including a large motor starting and the past maintenance history, and the equipment system configuration design interfaces. The licensee's analysis concluded that the

HPCI and RCIC inverters tripped because the existing battery chargers were not designed to 4 regulate the de output when subjected to an ac input voltage transient. The existing battery

chargers slow response time during ac transient conditions (such as large motor starting)

tends to increase the de output voltage of the chargers up to a peak value of approximately

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159.5 V under worst-case condition. To resolve the above concerns, the licensee has replaced the existing HPCI/RCIC inverters with new inverters of higher trip setpoint and 500 VA rating. The new inverters were designed with a wider input voltage (105-160 Vde)

j tolerance and an automatic reset capability (as documented on PDC No. 91-63). In addition, the licensee has also replaced the existing battery chargers (Dil, D12 and D14) with new

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battery chargers with a higher rated capacity and larger tolerance. The licensee also completed the evaluation to determine the effect of the voltage perturbations on the 125 Vdc devices (91XE-4-ER-O-EO) supplied from the 125 Vdc buses to assure that expected voltage

. transients would not prevent these devices from performing their safety function. The

) inspector's review of the study results and walkdown to verify the installation revealed no concern !

The inspector noted that the licensee had upgraded the root cause analysis corrective j measures evaluation procedure (1.3.102, Revision 1, effective date June 29,1992) based on i

their overall review of their existing root cause evaluation process and their response to the inverter concerns. The inspector's review of the revised procedure revealed that the

procedure reflects adequate detati to ensure a root cause analysis with a uniform approach, ,

i requirements for the documentation and review process. In addition, the licensee has issued l

. a new procedure utilizing industry experience to strengthen the Pilgrim Station root cause

analysis process. By discussion with the staff members (engineering and management), the inspector determined that the licensee had given the root cause/ corrective action and lesson learn critique training to all applicable staff. A sample of the training record reviewed by the inspector revealed no concern l

Based on the above licensee's corrective actions to replace the existing battery chargers,

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inverters, and procedure changes, training completed and verification of voltage and other j actions completed as per BECo letters of August 9 and November 25,1991, the inspector concluded that adequate steps have been taken by the licensee to resolve the above concern This item is closed.

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4 10 i .7 Observations Inspector review of the licensee's corrective actions pertaining to several observations -)

identified in the EDSFI inspection report revealed that the licensee had completed several- 'l

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actions to enhance their electrical system distribution system functional performance. The, I

inspector noted that the licensee' had evaluated the plant nonessential load on the EDGs and -

i implemented modification No. 92-31 to reduce the loads on the EDGs. In addition, the ..

l licensee had added load details in their applicable documents which could be used to shed the ,

j nonessential loads at the discretion' of. operators. ' Several other observations pertaining to the : "

EDGs, such as overcurrent, loss of field and field ground protection were being' evaluated 1 l and further corrective actions were being reviewed for implementatio '

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S UNRESOLVED ITEMS i

I Unresolved items are matters about which additional information is necessary to determine f n j 1 whether they are acceptable or they constitute a violation. .Several unresolved items are -  ;

] ' discussed in de' ail under Section 2.0.

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' EXIT MEETING The inspectors met with licensee personnel denoted in ' Attachment 1 of this report at the .. .

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conclusion of the inspection on June 11, 1993. At that time, the scope of the inspection and'.

j inspection results were summarized. . The licensee acknowledged the inspection m fi dings as:

i detailed in this report and had no additional comments regarding the inspection results.

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Attachment: Persons Contacted and Exit Meeting Attendees -

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- ATTACIIMENT 1 i PERSONS CONTACTED AND EXIT MEETING ATTENDEES j

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Boston Edison Company

J. Calfa Senior Compliance Engineer J

P. Hamilton Division Manager Licensing F. Mogolesko PM-Nuclear Engineering Department

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G. Mchugh, J Nuclear Engineering Department Manager -

j B. Chenard Division Manager Power System i W. Rothert General Manager Technical .

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R. Sheridan Quality Assurance Department Audit Division f

S. Das Senior Electrical Engineer, Nuclear Engineering Department!

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