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.
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