Information Notice No. 86-76: Problems Noted in Control Room Emergency Ventilation Systems
SSINS No.: 6835
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
All nuclear power reactor facilities holding an operating license or a
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
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
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
John J. Hayes, NRR
1. Summary of Control Room Habitability Reviews
2. List of Recently Issued IE Information Notices.
Attachment 1 IN 86-76
August 28, 1986
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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.
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.
August 28, 1986
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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
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
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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