Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9711210231
LICENSEE EVENT REPORT (LER)
FACILITY NAME: Clinton Power Station PAGE: 1 OF 7
DOCKET NUMBER: 05000461
TITLE: Design of Diesel Generator Ventilation Subsystems Outside
Design Basis as a Result of Failure to Include Minimum
and Maximum Outside Air Temperature Extremes Due to
Design Error
EVENT DATE: 09/29/86 LER #: 97-022-01 REPORT DATE: 11/13/97
OTHER FACILITIES INVOLVED: DOCKET NO: 05000
OPERATING MODE: 4 POWER LEVEL: 000
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR
SECTION:
50.73(a)(2)(i), 50.73(a)(2)(ii), 50.73(a)(2)(v), 50.73(a)(2)(vii) & OTHER
LICENSEE CONTACT FOR THIS LER:
NAME: M. M. Gandhi, Engineering Projects TELEPHONE: (217) 935-8881,
Engineer Extension 4082
COMPONENT FAILURE DESCRIPTION:
CAUSE: SYSTEM: COMPONENT: MANUFACTURER:
REPORTABLE NPRDS:
SUPPLEMENTAL REPORT EXPECTED: NO
ABSTRACT:
The diesel generator (DG) room ventilation system was designed based on
an outside air temperature range of -2 degrees Fahrenheit (F), winter
minimum temperature, and 96 degrees F, summer maximum temperature. The
Updated Safety Analysis Report (USAR) identifies temperature extremes of
-22 degrees F and 112 degrees F based on surrounding area temperature
data. Analysis determined that the DG ventilation system is unable to
maintain DG room temperature within the design limit during the area
extreme high temperature identified in the USAR. The cause for this
condition was design engineers, oversight. During the investigation,
annunciator power supplies located in the DG rooms were identified as not
meeting Class 1E qualification due to improper implementation of a design
modification. Corrective actions include revising procedures, evaluating
components for increased room temperature, installing a temporary
modification to reduce temperature inside a control panel, design changes
to the DG Direct Current (DC) electrical distribution system, reviewing
other ventilation systems for the design deficiencies, correcting the
USAR, correcting the DG DC annunciator power supply Class 1E deficiency,
evaluating the effects of outside air temperature extremes and verifying
Class 1E deficiencies do not exist in other control panels. This
condition is reportable under 10CFR21.
END OF ABSTRACT
TEXT PAGE 2 OF 7
DESCRIPTION OF EVENT
On July 24, 1997, the plant was in Mode 4 (COLD SHUTDOWN) for the sixth
refueling outage (RF-6). Reactor (RCT) coolant temperature was being
maintained within a band of 100 to 12 degrees Fahrenheit (F) and pressure
was zero pounds per square inch. Engineers were investigating condition
report (CR) 1-97-06-302 which identified an issue involving increased
Emergency Diesel Generator (EK] Room Heating, Ventilating, and Air
Conditioning (HVAC) system [VJ] fan [PAN] horsepower consumption during
low outside ambient temperature conditions.
At about 0745 hours, during the investigation, questions were raised
about the design of the diesel generator room ventilation subsystems.
The diesel generator room ventilation subsystems were designed to limit
the temperature in the diesel generator room to 130 degrees F with the
diesel generator operating and between 65 degrees F and 104 degrees F
when the diesel generator is not operating. These design requirements
were based on an outside air temperature range of minus 2 degrees F,
winter minimum temperature, and 96 degrees F, Bummer maximum temperature,
or 1 percent and 99 percent of the temperature extremes for Central
Illinois. The diesel generator ventilation system was designed in
accordance with the American Society of Heating, Refrigerating and
Air-Conditioning Engineers (ASHRAE) Fundamentals Handbook chapter on
weather data and design conditions. However, the Clinton Power Station
(CPS) Updated Safety Analysis Report (USAR) identifies surrounding area
extremes of minus 22 degrees F (Springfield, IL) and 112 degrees F
(Springfield, IL). Actual Clinton Power Station extremes documented in
the USAR are minus 19.8 degrees F and 95.4 degrees F. Due to the
limitations of the original design requirements, it was determined the
diesel generator room ventilation subsystems may not b adequate to
support operability of the diesel generators during extreme outside
temperatures that exceed the recommended levels in the ASHRAE
Fundamentals Handbook.
The operations Shift Supervisor was notified about this issue at 0830
hours, and he directed that Engineering perform further evaluations.
CR 1-97-07-250 was initiated to investigate and track the extreme
temperature issue. On July 25, 1997, at approximately 0051 hours, an
operability determination completed by the Operations Shift Supervisor
concluded that the outside ambient temperature band required for proper
operation of the Diesel Generator Room HVAC system was 5 degrees F to
102.7 degrees F for the Divisions 1 and 2 diesel generator rooms, and 5
degrees F to 104 degrees F for the Division 3 diesel generator room.
This was based on an engineering evaluation which determined that when
outside temperatures are below 5 degrees F or above 102.7 degrees F for
the Divisions 1 and 2 diesel generator rooms, and below 5 degrees F or
above 104 degrees F for the Division 3 diesel generator room, the DG HVAC
system may not maintain the temperature in these rooms within design
limits.
TEXT PAGE 3 OF 7
The Operations Shift Supervisor implemented interim actions to ensure
continued operability of the emergency diesel generators. On July 25,
1997, surveillance procedures CPS 9000.01 D001, "Control Room
Surveillance Log - Mode 1, 2, 3," and CPS 9000.01 D002, "Control Room
Operator Surveillance Log - Mode 4, 5 Data Sheet," were revised to
require monitoring of outside air temperature. If outside ambient
temperature was not within the required temperature range for the
respective diesel generator (5 to 102.7 degrees F for Divisions 1 and 2,
or 5 to 104 degrees F for Division 3), appropriate actions in accordance
with CPS Technical Specifications for the inoperable diesel generators)
were to be taken. on August 4, 1997, CPS surveillance procedures 9000.01
D001 and 9000.01 D002 were revised again to require actions in accordance
with CPS administrative procedure 1014.06, "Operability Determination,"
and the CPS Technical Specifications for the inoperable diesel
generators). Further analysis showed that temperatures higher than
102.7 degrees F were acceptable for Division I and II diesel generator
rooms; however, to ensure conservative operation, CPS procedures were
not revised to reflect the higher temperature.
As a long-term solution to the Diesel Generator area extreme high
temperature issue, an evaluation was performed to determine the maximum
temperature that the diesel generator rooms could reach during the area
extreme high outside air temperature of 112 degrees F. The evaluation
determined that the diesel generator room temperature could be maintained
at or below 140 degrees F during this condition. Engineering then
commenced an evaluation to ensure that all diesel generator supporting
components were operable for temperatures up to 140 degrees F.
On August 21, 1997, at about 1730 hours, during the evaluation, engineers
determined that temperatures within the Division 3 diesel generator
control panel (located within the Division 3 DG room) could reach 23
degrees F higher than room temperature. An annunciator power supply [JX]
within the Division 3 diesel generator control panel was not qualified
for temperatures above 140 degrees F. overheating of the annunciator
power supply could result in a low impedance fault which could cause the
control power [JC] circuit breaker [BKR] in the DG Direct Current (DC)
Distribution Panel to open, shutting down the diesel generator. It was
determined that outside air temperatures greater than 91 degrees F could
cause temperatures in the annunciator control panel to exceed 140 degrees
F (140 degrees F, minus 26 degrees F room temperature rise, minus 23
degrees F panel temperature rise, equals 91 degrees F outside air
temperature), thereby exceeding the maximum design temperature of the DC
annunciator power supply. CR 1-97-08-204 was initiated to investigate
and track this issue. The original operability determination was revised
as a result of this finding and a temporary modification was initiated to
remove the control panel doors to equalize room temperature and control
panel temperature. This temporary modification restored the Division 3
diesel generator to an operable status.
Investigation of the DC annunciator power supplies associated with the
Division 1 and Division 2 diesel generators on August 29, 1997, found
that they too were only qualified to 140 degrees F. These power supplies
are located in control panels similar to Division 3 where temperatures
inside the panel could be 23 degrees higher than room temperature. A low
impedance fault on the DC power supplies for these diesels could also
result in DG shutdown.
TEXT PAGE 4 OF 7
Also on August 29, 1997, engineers discovered the annunciator power
supplies for the Division 1 and Division 2 diesel generators were not
Class 1E qualified. These power supplies do not perform a Safety-related
function; however, they are connected to the Class 1E DC diesel generator
electrical distribution system [EJ]. Section 8.3.1.4.1.4 of the USAR
requires Non-Class 1E, non-division associated components, be
electrically isolated from Class 1E systems by an acceptable Class 1E
isolation device or have an adequate justification and analysis for
Non-Class 1E isolation. Engineers determined that Division 1 and
Division 2 diesel generator annunciator power supplies did not have Class
1E isolation and there was no justification provided. At this time both
Division 1 and Division 2 diesel generators were inoperable for other
reasons. A Limiting Condition for Operation Action Statement (Technical
Specification [TS) 3.8.2), was entered to ensure that the Non-Class 1E
power supply issue and the high temperature issue for Division 1 and 2
diesel generators were corrected prior to declaring the Division 1 and
Division 2 diesel generators operable. CR 1-97-09-201 was written to
investigate and track this issue.
The design of the diesel generator room ventilation subsystems was
determined not to be in accordance with the licensing basis of the plant.
The design deficiency in the diesel generator ventilation subsystems had
existed since initial plant operation on September 29, 1986, when the
plant was in Mode 5 (REFUELING) for initial fuel loading. At that time,
reactor coolant temperature was ambient and pressure was atmospheric.
The Non-Class 1E DC annunciator power supplies for Division 1 and 2 DGs
were also not in accordance with the licensing basis of the plant. This
condition had existed since February 20, 1991, for the Division 1 DG and
January 29, 1992, for the Division 2 DG.
No automatic or manually initiated safety system responses were necessary
to place the plant in a safe and stable condition. No other equipment or
components were inoperable at the start of this event to the extent that
their inoperable condition contributed to this event.
CAUSE OF EVENT
The cause for the diesel generator ventilation system being inadequate
during extreme ambient high temperatures was due to design engineers,
oversight. The cause for the DC annunciator power supplies for Division
1 and 2 diesel generators not meeting Class 1E qualification requirements
was determined to be improper implementation of a plant modification. A
review during the modification process identified that provisions should
be made for Class 1E use; however, this requirement was never implemented
prior to final approval.
CORRECTIVE ACTION
An engineering evaluation for outside area extreme low temperatures has
determined that the diesel generator rooms can be maintained within the
design limits for the diesel generator.
An engineering evaluation was performed to verify diesel generator
support equipment operability during outside area extreme high
temperature. It was determined that all diesel generator components
remain operable up to the corresponding room and cabinet temperature
associated with the area extreme high temperature, with the exception of
the DC annunciator power supplies.
TEXT PAGE 5 OF 7
Electrically coordinated class 1E fuse protection will be provided for
the DC annunciator power supplies in Division 1, 2 and 3 diesel generator
control panels. This protection will prevent a low impedance fault of
the DC annunciator power supplies from tripping the diesel generator
control power. This design change also satisfies proper class 1E
isolation requirements for the Division 1 and 2 DGs in accordance with
USAR Section 8.3.1.4.1.4 for connections between non-Class 1E components
and Class 1E systems. The coordinated fuse protection has been installed
in Division 1 Diesel Generator and will be installed in Division 2 and 3
Diesel Generators prior to plant start up.
Surveillance procedures CPS 9000.01 D001 and CPS 9000.01 D002 have been
revised to monitor outside air temperature. If outside temperature is
not within the required temperature range for the respective diesel
generator, appropriate actions will be taken in accordance with CPS
administrative procedure 1014.06, "Operability Determination," and the
CPS Technical Specifications for the inoperable diesel generator(s).
These temperature monitoring requirements and limitations will be
discontinued once class 1E fuse protection is installed.
A Temporary Modification was installed on the Division 3 DG control panel
to remove the panel doors allowing the temperature inside the panel to
equalize with DG room temperature. This temporary modification will be
withdrawn after the Class 1E electrically coordinated fuse protection is
installed for the DC annunciator power supply.
Other safety-related HVAC systems with very high outside air flow rates
and/or low thermal inertia with short air changes were reviewed to
identify if similar issues to those discussed in this event exist. No
other deficiencies were found.
The CPS USAR will be revised to accurately identify the diesel generator
room temperature limitations.
Other class 1E panels with the same DC annunciator power supply as those
in the Division 1 and 2 DG control panels were evaluated for compliance
with USAR section 8.3.1.4.1.4. No deficiencies where identified.
ANALYSIS OF EVENT
This event is reportable under several criteria or provisions of
10CFR50.73. The event is reportable under the provisions of
10CFR50.73(a)(2)(ii)(B) because the design of the diesel generator room
ventilation subsystems, and the design of the Division 1 and 2 DC
annunciator power supplies, are not in accordance with the design
requirements of the plant. The diesel generators are required to
mitigate the consequences of an accident in the event of a concurrent
loss of offsite power. Failure of the DC annunciator power supplies
could have prevented the diesel generators from fulfilling their safety
function, therefore this event is reportable under 10CFR50.73(a)(2)(v).
This event is also reportable under the provisions of
10CFRR50.73(a)(2)(vii) because a single condition caused the three
subsystems of the emergency diesel generator HVAC system to become
inoperable. Finally, due to the previously unrecognized potential for
the diesel generators to be rendered inoperable from the effects of high
temperature on required equipment in the diesel generator rooms (when
outside air temperatures exceed levels that are not improbably
TEXT PAGE 6 OF 7
high), this event is also reportable under the provisions of
10CFR50.73(a)(2)(i)(B) as a condition or operation prohibited by the
Plant Technical Specifications. This is based on the fact that, to date,
there have been many occasions or periods of time when outside air
temperatures exceeded 91 degrees F. During those times, all three diesel
generators were inoperable (but were not declared inoperable since the
condition was unknown). Having three diesel generators inoperable at the
same time requires entry into Technical Specification (TS) 3.0.3. A
condition or operation requiring entry into TS 3.0.3 constitutes a
condition or operation prohibited by the plant Technical Specifications.
An assessment of the safety consequences and implications of this event
identified that this event has potential nuclear safety significance.
The failure of the diesel generator room ventilation subsystems to
perform their design functions during outside high air temperature
extremes could cause common mode failure of the divisional emergency
diesel generators to perform their functions of supplying sufficient
power to safety-related equipment. Specifically, extremely high outside
air temperatures could increase the diesel generator room temperature to
above the design limits and cause a power supply failure and subsequent
trip of the DC main feed circuit breaker to the diesel generator control
panel. A loss of power to the control panel could prevent the diesel
generator from performing its design function.
ADDITIONAL INFORMATION
No equipment or components failed as a result of this event.
Clinton Power Station has not reported similar events regarding
inadequate HVAC design and failure to provide proper Class 1E electrical
isolation in recent history.
For further information regarding this event, contact M. M. Gandhi,
Engineering Projects Engineer, at (217) 935-8881, extension 4082.
10CFR21 Report 21-97-036
On July 24, 1997, during investigation of condition report (CR)
1-97-06-302 which identified an issue involving increased Diesel
Generator Room Heating, Ventilating, and Air Conditioning System fan
horsepower consumption at low temperature and the effect on diesel
generator loading and electrical load distribution System, questions were
raised about the design of the HVAC system. These questions resulted in
an evaluation of the DG ventilation system for adequacy during extreme
high and low outside ambient air temperatures. Due to design limitations
on the diesel generator room ventilation subsystems, it was determined
adequate cooling capacity may not be available to support operability of
the diesel generators if outside temperatures exceed levels that are not
improbably high for the summer season. This issue was determined to be
potentially reportable under 10CFR21. IP has completed an evaluation of
this issue and concludes that it is reportable under the provisions of
10CFR, Part 21.
IP is providing the following information in accordance with
10CFR21.21(c)(4). Initial notification of this matter will be provided
by facsimile of this letter to the NRC Operations Center in accordance
with 10CFR21.21(c)(3) within 2 days of the date the responsible officer
approves this report.
TEXT PAGE 7 OF 7
(i) Wayne D. Romberg, Assistant Vice President 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 design of
the diesel generator room ventilation subsystems.
(iii) The design for the diesel generator room cooling subsystems was
supplied by Sargent & Lundy.
(iv) As discussed in the DESCRIPTION OF EVENT portion of this
report, the nature of the defect is the diesel generator room
ventilation subsystems are not designed to address the
temperature extremes of the area surrounding CPS and may not
perform their design functions during those extremes.
As discussed in the ANALYSIS OF EVENT portion of this report,
failure of the ventilation subsystems to perform their design
functions during temperature extremes could cause failure of
the diesel generators to perform their functions of supplying
sufficient power to Safety-related equipment.
(v) On July 24, 1997, IP identified that the diesel generator room
ventilation subsystems may not be designed to include the
temperature extremes of the area surrounding CPS and IP
determined that this issue was potentially reportable under
10CFR21.
(vi) This issue affects the design of the diesel generator room
ventilation subsystems for the Divisions 1, 2, and 3 emergency
diesel generators. IP is not aware of other facilities that
would be affected by this issue.
(vii) The corrective action that IP is taking for this event is
discussed in the CORRECTIVE ACTION section of this report.
(viii) IP has no additional information to offer.
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