United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-30, Supplement 1: High Temperature Environments at Nuclear Power Plants

                                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.  


9010260154 
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                                                  IN 89-30, Supplement  1 
                                                  November 1, 1990 
                                                  Page 2 of 3 


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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