United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-44, Supplement 1: Potential Damage to Redundant Safety Equipment as a Result of Backflow Through the Equipment and Floor Drain System

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

                               August 30, 1990


Information Notice No. 83-44, SUPPLEMENT 1:   POTENTIAL DAMAGE TO 
                                                  REDUNDANT SAFETY EQUIPMENT
                                                  AS A RESULT OF BACKFLOW 
                                                  THROUGH THE EQUIPMENT AND 
                                                  FLOOR DRAIN SYSTEM 

Addressees: 

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

Purpose: 

This notice supplements information contained in NRC Information Notice 
83-44 concerning potential damage to redundant safety equipment as a result 
of backflow through the equipment and floor drain system and addresses the 
effect of internal flooding of nuclear power plants on safety-related 
equipment.  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 regulatory requirements; therefore, no specific 
action or written response is required. 

Background: 

The NRC issued Information Notice No. 83-44 to amplify the information 
provided in IE Circular 78-06, "Potential Common Mode Flooding of ECCS 
Equipment Rooms of BWR Facilities," in response to an event at a PWR 
facility.  IE Circular 78-06 applied specifically to Emergency Core Cooling 
System (ECCS) equipment rooms and flooding of areas at lower elevations.  
Information Notice No. 83-44 expanded this concern to other safety-related 
compartments and to damage as a result of backflow through equipment and 
floor drainage systems. Since the issuance of Information Notice No. 83-44, 
the NRC has received an unexpectedly high number of reports from the nuclear 
industry pertaining to actual and possible occurrences of internal flooding.  

Description of Circumstances: 

On July 7, 1990, the Quad Cities licensee, Commonwealth Edison, was 
investigating a backed-up sump pump in the basement of the Unit 2 reactor 
building.  While attempting to clear the lines, the licensee discovered that 
the check valves were inoperable in the floor drain lines from the ECCS 
equipment rooms.  Each drain line has both a flap-type and a ball-type check 
valve in series between the ECCS equipment room and its respective sump.  
Upon inspection, the licensee found that the flap-type check valves were 
stuck open as a result 


9008240057 
.

                                                  IN 83-44, Supplement 1 
                                                  August 30, 1990 
                                                  Page 2 of 3 


of debris and corrosion buildup and that three of the four balls in the 
ball-type check valves had corroded and eroded away completely.  In 
addition, these eight check valves had been omitted from the licensee's 
maintenance programs.  

These inoperable check valves could have enabled flood water from the 
following sources to render ECCS equipment inoperable: service water piping, 
ECCS suction piping, the reactor building drain tank, and possibly the fuel 
pool and suppression pool.  As a corrective action, the licensee has 
replaced and tested all the check valves in the ECCS room floor drains and 
has included these valves in its maintenance programs.  It should be noted 
that this situation is not adequately covered in the Quad Cities Final 
Safety Analysis Report (FSAR) or properly addressed in available 
probabilistic risk assessment (PRA) analyses for similar plants. 

Recently, the Office for Analysis and Evaluation of Operational Data (AEOD) 
completed an Engineering Evaluation Report, AEOD/E90-07, "Effect of Internal 
Flooding of Nuclear Power Plants on Safety-Related Equipment."  This report 
documents a review of operational events from 1980 to 1989 that resulted in 
internal flooding in the secondary containment, auxiliary building, and 
turbine building of nuclear power plants.  The study also presents reported 
conditions since 1984 that could have led to the flooding of safety-related 
equipment compartments.  Some of these events caused a loss of a significant 
amount of safety-related equipment needed for decay heat removal, plant 
shutdown, and plant cooldown, and have resulted in precursors that could 
have resulted in severe core damage accidents.  One plant probabilistic risk 
assessment has identified internal flooding to be a significant contributor 
to the risk of core damage. 

Discussion: 

Evaluation of the operational events identified errors by maintenance 
personnel, procedural deficiencies, and inadequate design as the key 
elements leading to internal flooding.  Based upon the findings, the 
following were identified as potentially generic inadequacies: 

o    Existing Flood Protection 
     
     The areas of particular concern include the adequacy of flood barriers 
     to prevent unisolable flooding and common-mode flooding, adequacy of 
     the floor drain system to prevent flooding of one area of the plant 
     from propagating to other areas, and adequacy of flood warning 
     instrumentation to provide the operators with an early signal of 
     flooding in the plant.

o    Maintenance Procedures and Personnel Training 
     
     Some licensees have not always conducted adequate reviews of 
     maintenance procedures and personnel training to minimize the risk of 
     unanalyzed internal flooding events caused by single component failures 
     or personnel errors. In addition, the AEOD report indicated that 
     several significant flooding events occurred during cold shutdown or 
     refueling outages.  This indicates weaknesses in maintenance planning 
     and administrative controls intended to minimize the risk of flooding 
     during such outages.
.

                                                  IN 83-44, Supplement 1 
                                                  August 30, 1990 
                                                  Page 3 of 3 


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:  N. Su, AEOD
                     (301) 492-4434

                     J. Raleigh, NRR
                     (301) 492-1172

Attachment:    List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Tuesday, November 12, 2013