05000423/LER-1997-010, :on 970129,electrical Calculation Discrepancies Identified in Min Voltage Analysis for Class 1E Electrical Sys.Caused by Lack of Configuration Mgt for Comprehensive Calculation Program.Program Being Revised

:on 970129,electrical Calculation Discrepancies Identified in Min Voltage Analysis for Class 1E Electrical Sys.Caused by Lack of Configuration Mgt for Comprehensive Calculation Program.Program Being Revised

ML20136A554
Person / Time
Site:	Millstone
Issue date:	02/28/1997
From:	Peschel J NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML20136A551	List: 05000423/LER-1997-010, :on 970129,electrical Calculation Discrepancies Identified in Min Voltage Analysis for Class 1E Electrical Sys.Caused by Lack of Configuration Mgt for Comprehensive Calculation Program.Program Being Revised
References
LER-97-010, LER-97-10, NUDOCS 9703070202
Download: ML20136A554 (4)

LER-1997-010, on 970129,electrical Calculation Discrepancies Identified in Min Voltage Analysis for Class 1E Electrical Sys.Caused by Lack of Configuration Mgt for Comprehensive Calculation Program.Program Being Revised

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(v), Loss of Safety Function
4231997010R00 - NRC Website

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i NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED 8Y oM8 NO. 3150-0104 14-95)

EXP1REs o4/30/98

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FACILITY NAME 11)

DOCKET NUMBER (2)

PAGE (3)

Millstone Nuclear Power Station Unit 3 05000423 1 of 4 TirLE 14)

Electrical Calculation Discrepancies in Minimum Voltage Analysis For Class 1E Electrical Systems EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY YEAR F AcluTY NAME DOCKET NUMBER NUMBER 01 29 97 97 010 00 02 28 97 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5: (Check one or more) (11)

ODE (m 5

20.2201(b) 20.2203(a)(2)tv) 50.73(a)(2)(i) 50.73(a)(2)(viii)

POWER 20.2203(a)(1) 20.2203(a)(3)(i) 50.73(a)(2)(ii) 50.73(a)(2)(x)

LEVEL (10) 000 20.2203(a)(210) 20.2203(a)(3)(ii) 50.73(a)(2)(iii) 73.71 20.2203(a)(2)(ii) 20.2203(a)(4) 50.73(a)(2)(iv)

OTHER or in NRC Form 366A 20.2203(a)(2)(iv) 50.36(c)(2) 50.73(a)(2)(vii)

LICENSEE CONTACT I OR THIS LER (12)

NAME TELEPHONE NUMBER linclude Area Codel J.M. Peschel, MP3 Nuclear Licensing Manager (8601437-5840 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT Os3)

CAUSE

SYSTEM COMPONENT MANUFACTURER REPoRTA8LE

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE To NPRDs To NPRos W

SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED MONTH DAY YEAR SUBMISSION g

YES NO (if yes, complete EXPECTED SUBMISSION DATE).

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16) j On January 13,1997, with the plant in Mode 5, a review of electrical calculations associated with Class 1E 480V and 120V systems identified discrepancies between related electrical calculations used to demonstrate design basis compliance. On January 29,1997, these concerns were sufficiently substantiated to question the validity of the Degraded Grid Voltage calculations. A prompt report was made, pursuant to 10CFR50.72(b)(2)(iii) as an event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to shutdown the reactor and maintain it in a safe shutdown condition.

The degraded grid voltage (OGV) relays are required to ensure that safety related equipment and devices either have adequate voltage to perform their safety functions or are not damaged due to a degraded voltage condition. These analytical limit worst-case minimum values were not utilized as the source voltage for separate voltage drop calculations performed for the 480V and 120V bus loads. If the 4160V bus voltage were to be at its analytical limit worst-case minimum value then inadequate voltage at individual devices supplied by the distribution system could result. Therefore, these systems may not be able to perform their design safety functions under degraded grid voltage conditions.

The cause was determined to be a lack of configuration management for the comprehensive calculation program which is required to establish and maintain the design basis of the unit. The calculation program is being reviewed and revised as part of the ongoing 50.54(f) effort. In addition, in order to address configuration management of the calculation program, formal work practices have been established for processing nuc(ear engineering calculations.

~ 9703070202 970228 PDR ADOCK 05000423 S

PDR

NRC Fo'RM 36:A U.s. NUCLEAR REGULATORY Commission 14 95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3) ~

YEAR SEQUENTIAL Revision Millstone Nuclear Power Station Unit 3 05000423 NUM8ER NUMBER 2 of 4 97 010 00 TEXT (11more space is required, use additional copies of NRC Form 366A) (11) 1.

Description of Event

On January 13,1997, with the plant in Mode 5, a review of electrical calculations associated with Class 1E 480V and 120V systems identified discrepancies, non-conservative assumptions, and a lack of coordination between related electrical calculations used to demonstrate design basis compliance. These discrepancies included the use of assumed supply voltage levels which were greater than those which had previously been calculated to exist under digraded voltage conditions. These elevated voltages were used as input to calculations performed to evaluate the 480V and 120V systems. As a result the performance of 480V and 120V systems under degraded voltage conditions was questioned.

On January 29,1997, these concerns were sufficiently substantiated to question the validity of the Degraded Grid Voltage calculations. A prompt report was made, pursuant to 10CFR50.72(b)(2)(iii) as an event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to shutdown the reactor and maintain it in a safe shutdown condition.

The Final Safety Analysis Report (FSAR) in table 8.1-2 (Acceptance Criteria for Electrical Systems) specifies that the unit must meet the criteria contained within Branch Technical Position (BTP) PSB-1. BTP PSB-1 requires that safety related buses have a second level of undervoltage protection in addition to the loss of power (LOP) relays. These degraded grid voltage (DGV) relays are required to ensure that safety related equipment and devices either have ad:quate voltage to perform their safety functions or are not damaged due to a degraded voltage condition.

A DGV trip separates the safety related buses from non safety related buses and offsite power sources under digraded grid voltage conditions. The DGV trip setpoint was based upon calculations which showed that actuation at or above the setpoint selected would result in voltage being maintained above the minimum design voltage rrquirements for the motors supplied from the 4160 volt and 480V AC buses.

These analytical limit worst-case minimum values were not utilized as the source voltage for separate voltage drop calculations performed for the 480V and 120V bus loads. The calculations performed for the 480V and 120V buses assumed a higher input voltage than that resulting from DGV trip setpoints analysis. If the 4160V bus voltage were to be at its analytical limit worst-case minimum value then inadequate voltage at individual devices supplied by the distribution system could result. As a result, the 480V Inverters, Battery Chargers and non-regulated 120V distribution panel loads do not meet the design basis requirements imposed by the " Degraded Voltage Protection Scheme Relay Settings

• calculation and they may not be able to perform their design safety functions under degraded grid voltage conditions.

This condition is being reported pursuant to 10CFR50.73(a)(2)(v), as an event or condition that alone could have prsvented the fulfillment of the safety function of structures or systems that are needed to shutdown the reactor and maintain it in a safe shutdown condition, ll.

Cause of Event

The cause was determined to be a lack of configuration management for the calculation program which is required to establish and maintain the design basis of the unit.

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NRc FdRM 366A U.s NUCLEAR REGULATORY CoMMISsloN a

' (4 95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL REVISION Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 3 of 4 97 010 00 TEXT (If more space is required, use additional copies of NRC Form 366A) t17) 111. Analysis of Event No direct means exists to cetermine if bus voltage has existed in the range of concern. However, the plant has not 1

experienced a transient concurrent with a degraded grid voltage condition. Therefore, therc has been no safety consequences as the result of a degraded grid voltage condition.

The potential degraded performance of the 480V and 120V systems under degraded grid voltage conditions is safety

~

significant in that it could result in condition outside the design basis of the plant and the inability of multiple safety systems to meet their design function.

Based on plant loading in Mode 5 & 6 and existing sub-station operating procedures, there is no creditable situation which would cause the 480 volt system to operate at levels which would challenge the operability of the 480V inverters, Battery Chargers and non-regulated 120V distribution panel loads in Mode 5 or 6. Additionally, the FSAR do:s not explicitly state that degraded voltage protection is required in Modes 5 and 6. However, prudence requires i

that compensatory measures be implemented in mode 5 & 6.

IV. Corrective Action

Administrative controls have been established to require monitoring of Bus 34C and 34D voltages in modes 5,6 to assure adequate voltage is maintained at the Motor Control Center (MCC) level. These administrative controls will remain in place until such time as the condition being reported has been corrected.

The calculation program is being reviewed and revised as part of the ongoing 50.54(f) effort. in addition, in order to address configuration management of the calculation program, fomial work practices have been established for processing nuclear engineering calculations.

Additionally, the following corrective action will be taken:

1. A review of calculations, setpoints and components will be performed to ensure voltage for safety related equipment will be adequate and to restore configuration control for the degraded grid voltage calculations.

Setpoints and/or components will be revised or modified, if needed..

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NPC YdRM 366A U.S. NUCLEAR REGULATORY COMMISSION i

' (4-95)

UCENSEE EVENT REPORT (LER) i.

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL REVislON Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 4 of 4 97 010 00 TEXT (11more space is required, use additional copies of NRC Form 366A) (11)

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Additional Information

j None

Similar Events

None Manufacturer Data Ells System Code Medium Voltage Power System - Class 1E EB Low Voltage Power System - Class 1E ED Ells Component Code Relay Undervoltage:

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NRC FORM 368A (4-95)