Part 21 Report - 1998-073

ACCESSION #: 9804130273 LICENSEE EVENT REPORT (LER) FACILITY NAME: Clinton Power Station PAGE: 1 OF 6 DOCKET NUMBER: 05000461 TITLE: Incorrect Cable Resistance and Brake Horsepower Data Used in the Design of Divisions 1 and 2 Emergency Diesel Generator Vent Fans Results in design of Fan Motors Being Outside the Design Basis of the Plant EVENT DATE: 09/29/86 LER #: 97-034-01 REPORT DATE: 04/03/98 OTHER FACILITIES INVOLVED: None DOCKET NO: 05000 OPERATING MODE: 5 POWER LEVEL: 000 THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR SECTION: 50.73(a)(2)(ii) OTHER LICENSEE CONTACT FOR THIS LER: NAME: A. B. Haumann, Nuclear Engineering Department TELEPHONE: (217) 935-8881, Extension 4078 COMPONENT FAILURE DESCRIPTION: CAUSE: SYSTEM: COMPONENT: MANUFACTURER: REPORTABLE NPRDS: SUPPLEMENTAL REPORT EXPECTED: NO ABSTRACT: Station engineers determined that during degraded voltage conditions, the Divisions 1 and 2 emergency diesel generator (EDG) room vent fans, 1VD01CA and 1VD01CB, could cause off-site power supply breakers to trip on undervoltage during transient electrical bus loading conditions associated with a block start Loss of Coolant Accident (LOCA). Improper cable resistance values and brake horsepower ratings were used in the original design of the 1VD01CA and 1VD01CB vent fans. This condition is outside the design basis of the plant. The cause of this event was determined to be insufficient detail provided in a S&L standard and design engineer's oversight when determining the brake horsepower ratings of 1VD01CA and 1VD01CB. Corrective actions include revising calculations, developing a new cable impedance standard, providing required reading for appropriate individuals on the new cable impedance standard, verifying other S&L standards, and performing a plant modification to correct this condition. The cable resistance issue is also reportable under 10CFR21. END OF ABSTRACT TEXT PAGE 2 OF 6 DESCRIPTION OF EVENT On October 23, 1997, the plant was in Mode 4 (COLD SHUTDOWN) for the sixth refueling outage (RF-6), and reactor [RCT] coolant temperature was being maintained within a band of 100 to 120 degrees Fahrenheit (F) and pressure was zero pounds per square inch (psi). Engineers were investigating degraded voltage margins and identified that at least five electrical voltage calculations for the Alternating Current (AC) [ED] and Direct Current (DC) [EJ] electrical distribution system design used improper cable [CBL] resistance data provided by Sargent & Lundy (S&L) in Table B of S&L Standard ESA-102, "Electrical Engineering Standard for Electrical and Physical Characteristics of Class B Electrical Cables.` The standard established the Clinton Power Station (CPS) design basis cable resistance used for determining cable tray [TY] loading and voltage drop calculations. Per S&L Power and Control Cable Specification STD-EA-253, "General Specification for Power and Control Cable Insulated with Ethylene-Propylene Rubber," CPS cables with voltage ratings at or below 1 Kilovolts (KV) have "tin-coated" copper conductors; however, Table B of Standard ESA-102 provides resistance data for "uncoated" copper conductor cables. Coated cables have higher resistance values than uncoated cables and yield slightly lower equipment terminal voltages than established in at least five electrical calculations. Condition report 1-97-10-414 was written to investigate and track this issue. The operations Shift Supervisor (SS) entered additional restraints against restoring operability for Technical Specification (TS) Limiting Condition for Operation (LCO) 3.8.2, "AC Sources-Shutdown," and 3.8.10, "Distribution Systems-Shutdown," as operability per these TS LCOs was already restrained for other reasons. On December 19, 1997, engineering determined that the Divisions 1 and 2 emergency diesel generator room vent fans (FAN], 1VD01CA and 1VD01CB, could cause the auxiliary power system to separate from the off-site power source and transfer to the emergency on-site power system during a Loss of Coolant Accident (LOCA) block start coincident with a degraded offsite voltage condition. This determination was based on increased cable resistance due to tin coated conductors and higher than originally calculated fan brake horsepower. The brake horsepower for these fan motors is based on a fan operating temperature of 96 degrees F. Analysis has identified that the fans are required to operate at temperatures below 96 degrees F. As air temperature decreases, more horsepower is required to drive the fans. The combination of increased brake horsepower and cable resistance could cause the Divisions 1 and 2 emergency diesel generator room vent fans to exceed a 13 second starting time under degraded voltage conditions. CPS degraded voltage analysis calculation 19-AQ-02, assumes that the 1VD01CA and 1VD01CB fans accelerate to operating speed in less than 13 seconds. Failure of the fans to start within 13 seconds could cause the off-site power supply breakers [BKR) to trip on undervoltage due to initial transient loading during a LOCA block start, resulting in the transfer to the emergency on-site power source. Considering the increased cable resistance due to tin-coated copper conductors and increased brake horsepower due to colder air temperatures, the assumptions of calculation 19-AQ-02 may not be valid. Therefore, the design of the Divisions 1 and 2 emergency diesel generator room vent fans, 1VD01CA and 1VD01CB, is not in accordance with the design basis of the plant. The operability of Division 3 emergency diesel generator room vent fan is not affected by this condition. TEXT PAGE 3 OF 6 The tin coated copper conductors and increased brake horsepower conditions for the Divisions 1 and 2 emergency diesel generator room vent fans have existed since initial plant licensing on September 29, 1986. At that time the plant was in Mode 5 (REFUELING) for initial fuel loading, and reactor coolant temperature was ambient and pressure was atmospheric. No automatic or manually initiated safety system responses were necessary to place the plant in a safe and stable condition. This event was not affected by other inoperable equipment or components. CAUSE OF EVENT The cause of this event was determined to be insufficient detail provided in S&L standard ESA-102, Table B. ESA-102, Table B did not identify and quantify cable construction and installation elements which affect resistance and reactance values. Additionally, the 1VD01CA and 1VD01CB brake horsepower ratings were based on a less conservative temperature of 96 degrees F rather than the minimum design temperature due to the design engineer's oversight. CORRECTIVE ACTIONS CPS has developed a cable impedance standard, EE 02.00, "Cable Resistance and Reactance Data," that contains the correct cable impedance values for CPS. S&L standard ESA 102 has been clearly marked to indicate that it is not applicable for use in determining cable impedance at CPS and that Standard EE-02.00 should be used. A briefing was held with the individuals who are qualified to prepare electrical calculations to make them aware that a new cable impedance standard has been issued that reflects the correct impedance values for CPS. Electrical calculations will be revised to reflect the correct cable impedance for tin coated copper conductors. Appropriate power loading and voltage calculations will be revised to account for safety related Heating Ventilation and Air Conditioning (HVAC) fan motor horsepower ratings at their minimum design operating temperature. The Updated Safety Analysis Report (USAR) will be revised to reflect the horsepower ratings of safety related HVAC equipment at their minimum design operating temperature. A sample of S&L standards will be reviewed to verify accuracy, degree of precision, and proper application of the standard at CPS. Any anomalies found during the review will be evaluated for impact on the plant, and corrected if required. Based on the results of this review, the need for additional action will be evaluated. TEXT PAGE 4 OF 6 CPS has installed a temporary modification to delay the start of the 1VD01CB supply fan during a LOCA block start accident. Delaying the start of the supply fan will allow the auxiliary power system voltage to recover from the initial power demand caused by the simultaneous starting of safety related equipment. This temporary modification will prevent an undesired separation of the off-site power source from the auxiliary power system. A similar temporary modification is being prepared for the 1VD01CA supply fan. The final determination as to whether a permanent design change is necessary will be determined after the completion of a modification that affects degraded voltage values. ANALYSIS OF EVENT This event is reportable under the provision of 10CFR50.73 (a) (2) (ii) (B) due to the design of the 1VD01CA and 1VD01CB fan motors being Outside the design basis of the plant. An assessment of the safety consequences and implications of this event has determined that this event has potential safety significance. During a LOCA block start accident concurrent with low outside ambient air temperatures and degraded off-site grid voltage, the auxiliary power system may separate from the off-site source because of low bus voltage. In this case the safety loads would be picked up by the corresponding divisional DG and the safety loads would restart on the emergency on-Bite power system, however; this condition reduces the plant's overall defense in depth. ADDITIONAL INFORMATION No equipment or components failed as a result of this event. IP has reported other events where off-site degraded voltage conditions reduced the safety margin of the plant in Licensee Event Reports 94-005 and 97-008. As a generic corrective action, IP is pursuing alternate methods in maintaining the off-site voltage being supplied to the Auxiliary Power System during degraded voltage grid conditions. For further information regarding this event, contact A. B. Haumann, Engineering Projects, at (217) 935-8881, extension 4078. TEXT PAGE 5 OF 6 10CFR21 REPORT 21-97-051 On October 23, 1997, Engineers were investigating degraded voltage margins and identified that at least five electrical voltage calculations for the Alternating Current (AC), and Direct Current (DC) electrical distribution system design used improper cable resistance data provided by Sargent & Lundy (S&L) in Table B of S&L Standard ESA-102, "Electrical Engineering Standard for Electrical and Physical Characteristics Of Class B Electrical Cables." The standard established the Clinton Power Station design basis cable resistance used for determining cable tray loading and voltage drop calculations. Per S&L Power and Control Cable Specification STD-EA-253, "General Specification for Power and Control Cable Insulated with Ethylene-Propylene Rubber," CPS cables with voltage ratings at or below I Kilovolts (KV) have "tin-coated" copper conductors; however, Table B of Standard ESA-102 provides resistance data for "uncoated" copper conductor cables. Coated cables have higher resistance values than uncoated cables and yield slightly lower equipment terminal voltages than established in at least five electrical calculations. Condition report (CR) 1-97-10414 was written to investigate and track this issue. IP determined that this condition was potentially reportable under 10CFR, Part 21 on October 25, 1997. IP completed its evaluation of this issue on January 16, 1998 and concluded that it was reportable under the provisions of 10CFR, Part 21. IP is providing the following information in accordance with 10CFR21.21(d)(4). Initial notification of this matter was made by facsimile of IP letter U-602908 to the NRC Operations Center in accordance with 10CFR21.21(d)(3) on January 16, 1998. (i) Walter G. MacFarland IV, Chief Nuclear officer of Illinois Power Company, Clinton Power Station, Highway 54, 6 Miles East, Clinton, Illinois, 61727, is informing the NRC of a condition reportable under the provisions of 10CFR21 by means of this report. (ii) The basic component involved in this report is the use of an incorrect design standard, S&L standard ESA-102, in the design of the cables installed at Clinton Power Station. (iii) The cable design using S&L standard ESA-102 was supplied to CPS by Sargent & Lundy. (iv) As discussed in the DESCRIPTION OF EVENT portion of this report, the nature of the defect is inaccurate cable resistance values supplied in S&L standard ESA-102 report for design of cables rated below 5 KV. This information was used in electrical voltage drop calculations for the AC and DC electrical distribution systems. As discussed in the DESCRIPTION OF EVENT portion of this report, under degraded voltage conditions, the impact of increased cable resistance in conjunction with air temperatures below 96 degrees F on the Divisions 1 and 2 emergency diesel generator room vent fans could cause off-site power supply breakers to trip on low voltage during a LOCA block start. A loss of off-site power reduces Clinton Power Station's defense in depth during a LOCA. TEXT PAGE 6 OF 6 (v) On October 23, 1997, Illinois Power identified that improper cable resistance values from data provided by Sargent & Lundy in Table B of S&L Standard ESA-102 were used in at least five electrical voltage calculations for the AC and DC electrical distribution systems. IP determined that this issue was potentially reportable under 10CFR, Part 21 on October 25, 1997. (vi) The improper cable resistance values were used to determine cable tray loading and voltage drop of cables rated for less than 5 KV at CPS. These applications have been evaluated and IP has concluded that this issue adversely affects the Divisions 1 and 2 emergency diesel generator room vent fans, 1VD01CA and 1VD01CB. IP is not aware of other facilities that may be affected by this issue. The supplier of the improper cable resistance values (Sargent & Lundy) is aware of this issue. (vii) The Corrective Actions that IP is taking for this condition are contained in the CORRECTIVE ACTION section of the LER. (viii) IP has no additional information to offer. *** END OF DOCUMENT ***

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