United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-61: Control Room Habitability - Recent Reviews of Operating Experience

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                 August 11, 1988


Information Notice No. 88-61:  CONTROL ROOM HABITABILITY - RECENT REVIEWS
                                   OF OPERATING EXPERIENCE


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose:

This information notice is being provided to alert addressees to potential 
problems resulting from design or analysis deficiencies identified in control 
room ventilation systems.  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:

The NRC has received several construction deficiency and licensee event 
reports pertaining to safety systems that are used to ensure control room 
habitability.  These reports identified potential safety concerns resulting 
from design deficiencies, which were attributed to inadequate analysis and an 
inability to justify those conditions that were assumed in previous evalu-
ations of plant design and operation.  These reports are summarized below.

Comanche Peak 1 and 2:  

On January 15, 1988, the permit holder determined that radiation doses to 
control room operators for some postulated radiological accidents could exceed
the limits of General Design Criterion 19 of Appendix A to 10 CFR 50.  This 
determination was attributed to an inadequate analysis of control room 
habitability systems for postulated radiological accidents.  Particular ac-
cident scenarios that were incompletely analyzed included a fuel handling 
accident and a rupture of a radioactive gaseous waste tank.  To correct this 
situation, the licensee is developing new calculations, upgrading the existing
control room intake radiation monitors and associated cables to safety-related
Class 1E requirements, and installing two additional safety-related Class 1E 
radiation monitors, one in each control room intake.





8808050248
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Quad Cities:  

On November 25, 1987, the licensee's engineering department discovered that 
design basis assumptions used in the control room habitability study were 
inconsistent with technical specification requirements.  The study was con-
ducted to satisfy a requirement of the NRC's TMI Action Plan.  The adsorption 
efficiencies of the standby gas treatment system and control room HVAC system 
were assumed at 99 percent for organic iodide removal.  The relevant technical
specifications, however, require only an organic iodide removal efficiency 
more than or equal to 90 percent.  All the filters meet the technical 
specification requirements.  Since December 31, 1984, tests of filter 
efficiencies indicate that the relevant assumptions of the study were met with
two exceptions.  The licensee attributes the cause for this condition to be an
inadequate review of design and analysis during the development of the study. 


Vogtle 1 and 2:

On July 2, 1987, plant engineering personnel identified an inadequacy in the 
dose analysis for control room operators.  On receipt of a safety injection 
signal or a control room outside air intake high radiation signal, the control
room heating, ventilating, and air conditioning (HVAC) system is automatically
transferred from the normal system units to the essential control room (ECR) 
fan-filter units in the emergency mode of operation.  The ECR system consists 
of two redundant and physically separated 100 percent capacity fan-filter 
units for each side of the control room, associated with the corresponding 
reactor unit (four for the combined Unit 1 and Unit 2 control room (Figure 
1)).  Each of the ECR units belongs to a different safety train, but portions 
of the outside air intake ductwork and control room supply and return ductwork
are common to each of the units.  On initiation of the ECR system, the 
associated motor-operated dampers for the essential units are automatically 
opened and those for the normal units are automatically closed.  

When both of the ECR fan-filter units are operating, loss of power to one of 
these units can reduce the amount of outside air available to pressurize the 
control room.  This can happen because the dampers losing power fail in the 
"as-is" position.  At the time of the identification of the problem, no back-
draft dampers were installed.  This degrades the ECR HVAC system by 
establishing flowpaths through the common ductwork and the ductwork of the 
failed unit back to the suction of the operating unit, which could potentially
reduce the outside air flow to the control room and reduce the control room 
pressure below the design value.  Maintenance of the design control room 
pressure is required to minimize unfiltered inleakage.  

The licensee concluded that the actual effect on control room pressure could 
not be calculated in the absence of test data and decided to modify the system
by installing backdraft dampers, as noted on Figure 1, for the ECR HVAC 
systems of both Units 1 and 2.
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                                                            IN 88-61
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On July 4, 1987, an additional condition was discovered that could have caused
an insufficient control room pressure.  All ECR systems share common outside 
air supply ductwork.  The common air supply ductwork has intakes from the out-
side atmosphere associated with both Units 1 and 2.  Redundant isolation 
dampers in series are provided for both Unit 1 and Unit 2 duct openings from 
the outside atmosphere.  During construction, the Unit 2 duct opening had been
isolated by locking the dampers closed.  If one of the outside air isolation 
dampers for Unit 1 had closed as the assumed single failure of an active 
component, no source of outside air would be available to the control room 
(shared by both Units) and the required pressure would not be maintained.  
Because the licensee had removed chlorine gas sources from the site, the 
capability to isolate toxic gases was no longer needed.  Thus, the licensee 
deactivated and tagged open the outside air isolation dampers.  

For all these problems, the licensee concluded that the defective conditions 
would have been discovered earlier with an adequate failure modes and effects 
analysis.

Beaver Valley 2:

On March 27, 1987, the permit holder determined that timers initiated by con-
tainment isolation phase B signals were not served with uninterruptible power 
as required.  These timers are designed to actuate banks of compressed air to 
supply the control room emergency pressurization system one hour after receipt
of the isolation signal.  They were powered from the respective fan control 
circuit energized by an emergency ac distribution panel fed from an emergency 
motor control center.  Loss of offsite power would interrupt power to the 
motor control center.  If a loss of power occurred after timer initiation, the
timers would reset to the beginning of the timing cycle and would not begin 
the cycle until power was restored to the emergency motor control center.  The
compressed air would thus not be supplied after one hour.  To enhance the 
reliability of the safety systems, the licensee revised the circuitry to power
the timers from the Class 1E 125-V dc battery system. 

McGuire 1:

On November 5, 1987, the licensee discovered during an 18-month surveillance 
test of the control area ventilation and chilled water system that control 
room pressure was below the technical specification requirement.  The licensee
determined that the cause was leaking seals on seven control room doors.  The 
doors were designed to seal by seating against sealing strips in the door 
frames.  Although not visibly deteriorated, the sealing material apparently 
had been deformed and compressed over time from normal use of the doors.  The 
licensee adjusted manual volume dampers to increase total train air flow and 
the proportion of outside air flow to the maximum 60 percent allowed in the 

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test procedure.  This action was effective in increasing control room pressure
to meet the technical specification requirement.  The licensee installed 
sealing tape around the seven doors and established a preventive maintenance 
program to inspect the seals on all control room doors every 6 months for a 
1-year period.  The licensee plans to determine an appropriate frequency for 
preventive maintenance of the door seals.  The surveillance test of the 
control area ventilation and chilled water system will also be repeated every 
6 months until sufficient information is obtained for determining an 
appropriate frequency.  

Farley 1:

On June 5, 1987, the licensee discovered that none of four fire dampers in the
control room ventilation system would fully close and latch with or without 
air flow because they had not been exercised and/or lubricated or, in one 
case, because a latch was damaged.  In addition, investigation revealed that 
the dampers would not have received an actuation signal from a Firestat set to
sense 160xF in the control room ceiling because of installation errors.  The 
licensee attributed the problems to three causes:  a design deficiency 
pertaining to the full closure and latching of the dampers, inadequate testing
of the actuation circuitry, and inadequate preventive maintenance of the 
dampers.  

Discussion:

In addition to the above, the NRC has recently completed an engineering evalu-
ation, "Design and Operating Deficiencies in Control Room Emergency 
Ventilation Systems," AEOD/E802, April 1988 based on recent events that 
highlight single failure vulnerabilities in control room emergency ventilation
systems.*  The NRC also has recently conducted a survey of control room 
habitability systems at 12 operating plants.  Numerous discrepancies were 
found between the analyzed and actual performance of these systems.  For 
example, differences exist between design, construction, operation, and/or 
testing of these systems and the descriptions and analyses provided in 
licensing documents, as for example in the assumptions used in the toxic gas 
and radiation dose calculations.  In addition, analyses assumptions have not 
always been consistent with technical specification requirements.  The NRC has
issued several information notices related to this subject (see Attachment 2).
Resolution of Generic Issue 83:  Control Room Habitability is also ongoing.





                           
*A copy of the report is available in the NRC Public Document Room, 1717 H 
 Street, N.W., Washington, D.C.  20555, for inspection and copying.
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No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni-
cal contacts listed below or the Regional Administrator of the appropriate 
regional office.




                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation


Technical Contacts:  Vern Hodge, NRR
                     (301) 492-1169

                     Charles R. Nichols, NRR
                     (301) 492-0854


Attachments:  
1.  Figure 1.  Schematic Air Flow Path Diagram of Essential Control Room
      Heating, Ventilating, and Air Conditioning System (ECR HVAC) at Vogtle.
      Assumed Containment Isolation Signal for Unit 1 with Train B Failed.
2.  List of Information Notices Related to Control Room Habitability Systems
3.  List of Recently Issued NRC Information Notices

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                                                            Attachment 2
                                                            IN 88-61
                                                            August 11, 1988
                                                            Page 1 of 1


                           LIST OF INFORMATION NOTICES
                  RELATED TO CONTROL ROOM HABITABILITY SYSTEMS


NO.                 TITLE                                   DATE

86-76          Problems Noted in Control Room          August 28, 1986
               Emergency Ventilation Systems

85-89          Potential Loss of Solid-State           November 19, 1985
               Instrumentation Following Failure
               of Control Room Cooling

83-62          Failure of Redundant and Toxic Gas      September 26, 1983
               Detectors Positioned at Control Room
               Ventilation Air Intakes
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Page Last Reviewed/Updated Tuesday, November 12, 2013