Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
November 1, 1990
Information Notice No. 89-30, SUPPLEMENT 1: HIGH TEMPERATURE
ENVIRONMENTS AT NUCLEAR
POWER PLANTS
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice supplement is being provided to present additional
information regarding the effects of elevated room temperature on the
operability of safety related equipment as discussed in NRC Information
Notice 89-30, issued March 15, 1989. It is expected that recipients will
review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. However, suggestions
contained in this information notice do not constitute NRC requirements;
therefore, no specific action or written response is required.
Description of Circumstances:
Information Notice No. 89-30 described events where elevated temperatures and
high humidity within the drywell or containment adversely impacted the
operability of safety related equipment. This supplement describes events
where high ambient temperatures in areas other than the containment or the
drywell caused the failure or degradation of safety related equipment.
On June 25, 1990, the Omaha Public Power District (the licensee) conducted a
full load test on the No. 1 emergency diesel generator (EDG) at Fort Calhoun
Unit 1. This test was conducted to establish a temperature profile for the
EDG room. The test was terminated when the output from the generator became
erratic as a result of the failure of a transistor in the static exciter
circuitry.
The licensee's investigation revealed that the transistor had failed because
of the effects of elevated temperatures in the static exciter/voltage
regulator cabinet which was located in the EDG room. Temperatures in the
cabinet had reached 140 degrees Fahrenheit (F) during the test. The
transistor was replaced and the EDG was returned to operable status. The
licensee also discovered elevated temperatures in the static exciter/voltage
regulator cabinet for the No. 2 EDG. In a recently completed engineering
analysis, the licensee verified that because of inadequate cabinet
ventilation, a potential common mode failure of both EDGs exists. The
analysis also concluded that this condition has likely existed since plant
startup.
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IN 89-30, Supplement 1
November 1, 1990
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To reduce the potential for heat buildup in the cabinets, the cabinet doors
were temporarily removed until a long term solution to the problem can be
formulated. The licensee's investigation of this event also revealed that
elevated room temperatures significantly impact the operating efficiency of
the EDGs and could lead to accelerated degradation.
Discussion:
The Fort Calhoun Station has two General Motors EMD 20-645E4 diesel generator
sets. The cooling system for each EDG consists of an engine radiator, an
engine-driven fan, and a pump that circulates cooling water through the
engine and radiator. Outside air is drawn into the EDG room by the fan, is
blown across the radiator, and exits through the roof of the building through
air ducts. Inlet air for the diesel turbocharger is drawn directly from the
EDG room.
In June 1988 the licensee modified the hangers on the diesel exhaust headers.
These modifications required that the insulating material on the headers be
removed. After removing the insulating material, the licensee was aware that
ambient temperature would increase. Therefore, the licensee performed an
analysis to support a design change that would allow the exhaust headers to
remain uninsulated. The analysis concluded that bulk temperature in the EDG
rooms would rise by only 9 degrees F and that this increase would not have an
adverse effect on the operability of the EDGs. The analysis did not
specifically address the effect of elevated room temperature on other
equipment located in the room.
When test runs were made during the summer months of 1989, the licensee found
that bulk room temperatures actually increased approximately 20 degrees F, or
more than twice the increase predicted by the licensee's analysis. This
elevated room temperature likely accelerated the degradation of the exciter
component that failed. However, the potential for the temperature buildup in
the unvented cabinet probably existed since the cabinets were installed.
The licensee also has determined that the 20 degree rise in ambient
temperature resulted in an increase in jacket water temperature and
turbocharger inlet air temperature. These temperature increases adversely
affect engine operating efficiency. Depending on the amount of increase,
elevated jacket water temperature and/or turbocharger inlet air temperature,
combined with heavy loading, may lead to accelerated degradation of the
engine. This degradation could result in engine failure or prevent the
engine from meeting its designed run time as assumed in the Final Safety
Analysis Report. To reduce the potential for engine degradation while
operating during periods of high ambient temperatures, unit loading would
have to be limited. Derating the EDG could result in the unit's dependable
output capability being less than required for design basis accident loads.
Because of variations in the configurations of intake air systems,
turbocharger inlet air may be preheated significantly. The temperature of
the air entering the turbocharger may be much higher than air temperature
elsewhere. Also, water-to-air heat exchangers are more sensitive to changes
in ambient temperature
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IN 89-30, Supplement 1
November 1, 1990
Page 3 of 3
than are water-to-water heat exchangers. However, an increase in service
water temperature in water-to-water heat exchangers may also result in the
derating of an EDG. The NRC is aware of other instances in which elevated
ambient temperatures resulted in the failure or degradation of safety related
components.
To avoid excessive cabinet temperatures and subsequent component failures,
the licensee for the Washington Nuclear Project, Unit 2, has instituted
administrative procedures to remove the doors from the static exciter voltage
regulator cabinet when the EDG room temperature exceeds 90 degrees F. The
licensee performed an analysis which concluded that internal temperatures in
the cabinets would exceed the long-term (greater than 24 hours) thermal
rating of the cabinet components if the EDG room temperature were to exceed
90 degrees F. Extended operation at or above this temperature would
significantly increase the probability of a component failure.
On December 16, 1985, the failure of a fan in an engineered safety features
(ESF) cabinet at Palo Verde Unit 1 resulted in the spurious actuation of
several ESF signals. These signals initiated the automatic start of the
Train A EDG, caused loads to be shed from the Train A vital bus, and
initiated the operation of the ESF load sequencer. The load shed signal did
not clear, prohibiting the automatic or manual sequencing of ESF electrical
loads. The licensee installed a control room alarm that annunciates on
cabinet exit air high temperature.
On June 4, 1984, at the McGuire Station, a total loss of control area
ventilation resulted in temperature build-up in instrumentation cabinets.
The elevated temperatures initiated several spurious solid state protection
system alarms and resulted in the operators having to reduce output from both
generating units. This event is described in detail in Information Notice No.
No. 85-89, "Potential Loss of Solid State Instrumentation Following Failure
of Control Room Cooling."
On September 21, 1982, a similar event occurred at Davis-Besse Unit 1, and
involved the failure of a 48-volt power supply in the Steam and Feedwater
Rupture Control System (SFRCS). The failure of the power supply was
attributed to heat buildup in the SFRCS cabinets. The licensee installed
fans in the cabinets to ensure more effective cooling.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate NRR project
manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: C. Paulk, Region IV
(817) 860-8236
N. Fields, NRR
(301) 492-1173
Attachment: List of Recently Issued NRC Information Notices
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