United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 93-34 - IN 93-34, Supplement 1: Potential for Loss of Emergency Cooling Function due to a Combination of Operational and Post-LOCA Debris in Containment

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555

                                  May 6, 1993

                                             COOLING FUNCTION DUE TO A
                                             COMBINATION OF OPERATIONAL AND
                                             POST-LOCA DEBRIS IN CONTAINMENT 


All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) issued Information Notice 
(IN) 93-34 because of the possible problems that could occur with operational
and post-accident debris blocking emergency core cooling pump strainers in a
boiling-water reactor (BWR) or containment sump screens in a pressurized-water
reactor (PWR).  The IN was based, in part, on an event that occurred at the
Perry Nuclear Plant.  The NRC is issuing this supplement to IN 93-34 to alert
addressees to additional information relating to that event.  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 are not NRC
requirements; therefore, no specific action or written response is required.

Description of Circumstances 

IN 93-34 described clogging of emergency core cooling (ECC) pump suction
strainers at the Perry Nuclear Plant, a BWR-6.  The latest strainer clogging
event occurred in March 1993, 2 months after the licensee had replaced the
strainers and thoroughly cleaned the suppression pool.  After the IN was
issued, the licensee chemically analyzed the debris on the strainer.  The
debris consisted of fibers from air filter material that had been
inadvertently introduced into the suppression pool and corrosion products that
had been filtered from the pool by the fibers adhering to the surface of the
strainer.  A small amount of the fibrous filter material also was found in the
suppression pool near the weir wall.

The licensee uses the fibrous material in the drywell in three air filters
that each have a surface area of about 5.57 square meters [60 square feet]. 
In addition, there are six similar air filters in containment.  The purpose of
the filters is to provide filtered air in containment and the drywell during
reactor outages.  It has been the licensee's practice to replace the filter
material at the end of each outage and to leave the material in the drywell
and containment during operation of the plant at power.  As a result of the 


                                                      IN 93-34, Supplement 1
                                                      Page 2 of 2
                                                      May 6, 1993

March 1993 event, the licensee intends to remove the filter material from the
drywell before startup to eliminate this source of fibrous material from the


NUREG-0897, Rev. 1, "Containment Emergency Sump Performance," which was
written in conjunction with resolution of Unresolved Safety Issue (USI) A-43,
addresses transport of fibrous thermal insulation from the containment to the
strainers during a loss-of-coolant accident (LOCA).  Resolution of USI A-43,
in part, was based on strainer head loss tests with fibrous thermal insulation
obstructing flow.  USI A-43 did not address the consequences on head loss of
the filtering action of the fibrous material on the strainer.  The Perry event
showed that filtering corrosion products, dust, and other debris from the
drywell during a LOCA may cause an unexpectedly rapid loss of net positive
suction head for the ECC pumps when they are needed to perform their intended

Related Generic Communications

o     NRC Information Notice 92-71:  "Partial Plugging of Suppression Pool
      Strainers at a Foreign BWR" 

o     NRC INFORMATION NOTICE 88-28:  "Potential for Loss of Post LOCA 
      Recirculation Capability Due to Insulation Debris Blockage"

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.

                                      ORIGINAL SIGNED BY

                                   Brian K. Grimes, Director
                                   Division of Operating Reactor Support
                                   Office of Nuclear Reactor Regulation

Technical contact:  Roger W. Woodruff, NRR
                    (301) 504-2917
List of Recently Issued NRC Information Notices

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