United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-76: Problems Noted in Control Room Emergency Ventilation Systems

                                                            SSINS No.: 6835 
                                                                   IN 86-76 

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                               August 28, 1986

Information Notice No. 86-76:   PROBLEMS NOTED IN CONTROL ROOM EMERGENCY 
                                   VENTILATION SYSTEMS 

Addressees: 

All nuclear power reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

This notice is provide to alert recipients to problems noted in the 
operation of control room emergency ventilation systems during recent plant 
visits by an NRC review team. It is expected that recipients will review 
this information for applicability to their facilities and consider actions, 
if appropriate, to preclude a similar problem occurring at their facilities.
However, suggestions contained in this notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.

Description of Circumstances: 

During a recent visit to the Trojan Nuclear Plant, the NRC review team 
observed the licensee perform a monthly surveillance test of the cooling 
capability of the control room emergency ventilation system. The NRC review 
team terminated its involvement shortly after the surveillance test began 
because the licensee's procedure was deemed inadequate and the test would 
not produce any meaningful results. Specifically, the team noted that the 
emergency ventilation system was initiated with the supply dampers left 
shut; these dampers were designed to provide 150 standard cubic feet per 
minute (cfm) of outside makeup air in the radiological emergency mode. The 
toilet and laboratory exhaust fans (4050 and 3740 cfm capacity, 
respectively) were left running. This condition resulted in a slight vacuum 
in the control room, although the system is designed to maintain 1/8-inch 
H2O positive pressure in the emergency mode. In addition, the humidity 
control had been adjusted to 100 percent (thus the heaters would remain off 
for any humidity less than 100 percent) even though the Technical 
Specifications require the system to be tested with the heaters on. 

When the makeup air dampers were opened, it was determined that 460 cfm of 
filtered outside air was being supplied instead of the designed 150 cfm. In 
addition, it was discovered that a 2-inch drain pipe on the cooling units 
down stream of the filter housing was drawing 41 cfm of unfiltered outside 
air into the system. The drain pipe was connected by a drain line header to 
both trains 



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                                                          IN 86-76       
                                                          August 28, 1986 
                                                          Page 2 of 2    

of the emergency ventilation systems. This drain arrangement constituted a 
common-mode failure and a lack of train separation of an engineered safety 
feature. On the basis of these findings, Region V inspectors asked Trojan to
recalculate the operator doses expected during an accident. The licensee 
calculated 1.7 rem whole body, 195 rem to the thyroid, and 30.6 rem to the 
skin: The general design criteria (GDC 19) in Appendix A of 10 CFR Part 50 
specifies that the control room be designed to allow occupancy through the 
course of an accident without exceeding 5 rem whole body or its equivalent 
to any part of the body. Because 30 rem to any organ (skin or thyroid) is 
equivalent to a 5 rem whole-body dose, a violation resulted. The violation 
was categorized as a Severity Level II violation because both trains of the 
system were inoperable for a long period of time and a civil penalty 
resulted. 

The NRC has made several plant visits to review control room ventilation 
systems as part of the resolution of the generic issue on control room 
habitability (Item III D.3.4 of NUREG-0737). Although Trojan has been the 
only plant visit to date with problems severe enough to result in an 
enforcement action, several similar problems have been noted at other 
facilities visited. Attachment 1 provides a discussion of these common 
problems noted. Currently the NRC is scheduled to visit six more facilities 
in response to the generic issue. 

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office. 


                                   Edward L. Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  Roger L. Pedersen, IE
                    (301) 492-9061

                    John J. Hayes, NRR
                    (301) 492-7471

Attachments:
1.   Summary of Control Room Habitability Reviews
2.   List of Recently Issued IE Information Notices. 
.

Attachment 1                                               IN 86-76       
                                                           August 28, 1986 
                                                           Page 1 of 2 

                SUMMARY OF CONTROL ROOM HABITABILITY REVIEWS

The following is a summary of the common problems noted in control room 
emergency ventilation systems during recent NRC plant visits to gather 
information on Control Room Habitability (Generic Issue 83). Items discussed
were noted at two or more facilities visited. 

System Understanding 

The NRC review team noted that there appeared to be no individual or group 
designated as responsible for the ventilation systems at the plant visited. 
This appears to lead to a lack of understanding of the systems and their 
operation. Most of the systems reviewed to date do not accurately reflect 
the system descriptions provided by the licensees in their submittals 
required by item III D.3.4 of TMI Action Plan (NUREG-0737). In addition, the 
following concerns were noted in the way surveillance testing is being 
performed on these systems. 

1.   Most plants measured control room temperature in the center of the 
     room.  However, the basis of the requirement is to ensure operability 
     of solid-state electrical equipment, not operator comfort. Therefore, 
     measuring the air temperature at the instrument panels is more 
     appropriate (see IE IN 85-89 for additional information on the effects 
     of control room cooling on solid-state instrumentation). 

2.   The purpose of maintaining a positive pressure in the control room 
     during emergency operation is to ensure any leakage is out of (rather 
     than into) the control room. Several licensees show compliance with 
     their technical specifications by comparing control room pressure to 
     the outside atmospheric pressure. Because areas adjacent to the control 
     room envelope (CRE) can be at higher-than-atmospheric pressure, a 
     relative negative control room pressure may exist across the CRE 
     boundary, providing a motive force for inleakage. This is also a 
     concern where the control room ventilation system is routed through 
     adjacent areas.  Clearly it is appropriate to measure the differential 
     pressure relative to the highest pressure adjacent to the CRE boundary 
     or ventilation system. 

3.   Laboratory testing of charcoal efficiency is being performed at 
     temperatures much higher than any temperature expected during the 
     course of an accident. This can result in an erroneously high 
     efficiency measurements. Retention efficiencies as low as 70% were 
     noted when samples of charcoal that had just passed its surveillance 
     tests (greater than 90% efficient) were retested at 30C. 
.

                                                            Attachment 1   
                                                            IN 86-76       
                                                            August 28, 1986 
                                                            Page 2 of 2    

Excessive Unfiltered Inleakage 

The general condition of some of the ventilation systems reviewed was poor. 
Many of the following conditions were discovered that resulted in leakage of
unfiltered air into the systems reviewed. 

1.   Holes and openings: Many holes left from construction and unplugged 
     openings were found in the system duct work and in the air handling 
     units themselves. 

2.   Drains: Uncapped drains (or drains improperly left open to the 
     atmosphere) were found that allow the air handling units to draw air 
     into the system. In addition, water loop seals in some drains were 
     found dry. 

3.   CRE penetrations: Some control rooms were found with "numerous" 
     unsealed penetrations across the CRE. 

Many of these problems were not discovered until the NRC review team 
performed flow balance and differential pressure measurements on the control
room ventilation systems. 
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