United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-77, Supplement 1: Debris in Containment Emergency Sumps and Incorrect Screen

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

                               December 3, 1993


NRC INFORMATION NOTICE 89-77, SUPPLEMENT 1:  DEBRIS IN CONTAINMENT EMERGENCY   
                                             SUMPS AND INCORRECT SCREEN                                                    CONFIGURATIONS


Addressees

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

Purpose

On November 21, 1989, the U.S. Nuclear Regulatory Commission (NRC) issued
Information Notice (IN) 89-77 to alert addressees to problems that could occur
with post-accident debris blocking emergency core cooling systems.  The IN was
based, in part, on an event that occurred at the Trojan Nuclear Plant where
debris were found in the containment sump and portions of the sump screen were
found to be missing.  The NRC is issuing this supplement to IN 89-77 to alert
addressees to additional potential problems that may not have been previously
considered.  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

On October 1, 1993, personnel at Arkansas Nuclear One (ANO), found several
breaches in the integrity of the Unit 1 reactor building sump.  These breaches
consisted of (1) 22 semicircular holes (scuppers) at the base of the sump
curb, each approximately 15.2 cm [6 in.] in diameter; (2) 4 conduit
penetrations in the sump screen, totaling approximately 930 cm2 [1 ft2]; (3) a
small conduit penetration in the sump curb, approximately 2.5 cm [1 in.] in
diameter; (4) two defects in the screen mesh covering the sump, one L-shaped
cut approximately 30.5 cm by 35.6 cm [12 in. by 14 in.], one straight cut
approximately 30.5 cm [12 in.] long; and (5) reactor building drain headers,
ranging in size from approximately 5.1 cm to 25.4 cm [2 in. to 10 in.] that
lacked protective screen material.  On October 22, 1993, seven 7.3 cm 
[3 in.] long by 2.5 cm [1 in.] high holes were identified in the grout at the
base of the Unit 2 containment sump curb.

Although these two containment sumps had been inspected for debris on several
occasions, the breaches in the integrity of the sump screens and the lack of 


9311190457.

                                                      IN 89-77, Supplement 1
                                                      December 3, 1993
                                                      Page 2 of 3


reactor building drain header screens had gone unnoticed.  The licensee had
focused its inspections on debris and did not question the existence of
penetrations through the screen and curb.  In Unit 1, the scuppers were part
of the original design and while shown on plant drawings, the drawings were
unclear with respect to screen installation; whereas, the holes in the grout
at the base of the Unit 2 containment sump curb were not identified in the
design nor on drawings.  These holes in Unit 2 were only visible after close
examination because of the construction of the sump curb.  The penetrations
and cuts in the screen were not recognized as a problem until an electrician
questioned the existence of the penetrations while working in the Unit 1
containment.

Discussion

The ability of the pressurized-water reactor containment emergency
recirculation sump or the boiling-water reactor (BWR) suppression pool to
provide an adequately filtered source of water for the ECCS is essential
during the long-term cooling phase of a loss-of-coolant accident (LOCA). 
Failure to adequately filter the ECCS water source could result in degradation
and eventual loss of ECCS function as a result of damaged pumps or clogged
flow paths.  This latest event and other events discussed in earlier related
generic communications listed below have demonstrated various problems in
ensuring an adequate source of recirculating water.  In particular, the
consideration of flow paths that bypass the sump screens (such as the reactor
building drain headers in the ANO case) is a potential concern which has not
been previously noted.  Failure to ensure that the physical condition and as-
built configuration of the screening material, and the screening of other
penetrations that communicate with the sump, preclude bypass of the filtering
function could lead to loss of the ECCS function. 

Related Generic Communications

* Generic Letter 85-22: "Potential for Loss of Post LOCA Recirculation         
  Capability Due to Insulation Debris Blockage."

* NRC Information Notice 88-28:     "Potential for Loss of Post LOCA           
  Recirculation Capability Due to Insulation Debris Blockage."

* NRC Information Notice 89-77:     "Debris in Containment Emergency Sumps and
  Incorrect Screen Configurations."

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

* NRC Information Notice 93-34:     "Potential for Loss of Emergency Cooling   
  Function Due to a Combination of Operational and Post-LOCA Debris in         
  Containment."
.

                                                      IN 89-77, Supplement 1
                                                      December 3, 1993
                                                      Page 3 of 3


* NRC Information Notice 93-34, Supplement 1: "Potential for Loss of Emergency
  Cooling Function Due to a Combination of Operational and Post-LOCA Debris in
  Containment."

* NRC Bulletin 93-02: "Debris Plugging of Emergency Core Cooling Suction       
  Strainers."

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 Office of
Nuclear Reactor Regulation (NRR) project manager.

                                    /s/'d by BKGrimes

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

Technical contacts:  Chuck Paulk, RIV
                     (817) 860-8236

                     Ramon Azua, RIV
                     (402) 426-9611

                     Linda Smith, RIV
                     (501) 968-3290

                     John Hickman, NRR
                     (301) 504-3017

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