Information Notice No. 88-28:Potential for Loss of Post-LOCA Recirculation Capability due to Insulation Debris Blockage

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

                                  May 19, 1988

Information Notice No. 88-28:  POTENTIAL FOR LOSS OF POST-LOCA 
                                   RECIRCULATION CAPABILITY DUE TO 
                                   INSULATION DEBRIS BLOCKAGE 


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees to potential 
problems regarding debris that could block containment emergency sump screens 
in a pressurized water reactor (PWR) or debris that could block emergency core 
spray pump or residual heat removal pump strainers in a boiling water reactor 
(BWR). 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 March 14, 1988, Pennsylvania Power & Light (the licensee for Susquehanna) 
notified the U.S. Nuclear Regulatory Commission of a 10 CFR Part 21 reportable 
item concerning deterioration of drywell insulation and the potential for the 
aluminum foil coating of the insulation to block emergency core cooling system 
(ECCS) strainers during a loss-of-coolant accident (LOCA).  

While the unit was in a refueling outage, the licensee inspected the 
Susquehanna Unit 2 drywell.  The licensee observed extensive delamination of 
the aluminum foil coating on the surface of the fiberglass insulation used on 
valve bodies and pipe hangers and in other areas that are awkward or difficult 
to insulate.  

The aluminum foil covering is 1-mil thick and is bonded to the outer covering 
of Alpha Maritex fiberglass cloth (style #2025/9480 HT) that is used as a 
covering for Temp-Mat insulation.  An upper-bound estimate is that 5000 square 
feet of this insulation is used in more than 300 different locations within 
the drywell.  The licensee estimates that 50 percent of the insulation has 
undergone some degradation.  This is the first time the licensee has observed 
degradation to this extent, although some degradation had been noticed 
earlier.  A different insulation material is used at Susquehanna Unit 1, and 
no insulation delamination has been observed at that unit.  Alpha Associates, 
Inc. supplied the insulation 

.                                                            IN 88-28 
                                                            May 19, 1988 
                                                            Page 2 of 3 

to the licensee through Bechtel. However, representatives of Alpha Associates, 
Inc., have indicated that other companies supply the same or similar 
insulation and that its use may be widespread. 

After the event at Susquehanna Unit 2, the licensee for Millstone Unit 1 
reported, that in a worst-case scenario, the net positive suction head margin 
for ECCS pumps could be compromised because of suction strainer blockage 
resulting from LOCA-generated insulation debris.  At Millstone Unit 1, 
Temp-Mat insulation is used without a foil facing.  In this case, the concern 
was that the fiberglass cloth covering would be freed during a LOCA and 
migrate to the ECCS pump suction strainers.  The licensee is evaluating the 
feasibility of replacing the existing strainers with strainers that have a 
larger area as a possible solution of the problem of transported insulation. 


In PWRs the containment emergency sumps provide for the collection of reactor 
coolant and chemically reactive spray solutions following a LOCA, thus serving 
as water sources to effect long-term recirculation for residual heat removal 
and containment atmosphere cleanup.  In a BWR, the suppression pool serves as 
the water source for effecting long-term recirculation cooling. 

Debris, transported as a result of an event, can block sump debris 
interceptors and sump outlets, resulting in degradation or loss of 
recirculation flow margin.  At Susquehanna, the ECCS core spray pump suction 
screen has a cross-sectional area of 18.3 square feet, while each residual 
heat removal pump suction screen has a cross-sectional area of 43.8 square-ft.  
In comparison, the insulation covering that could block recirculation flow 
covers an area of several thousand square feet.  However, the potential effect 
of insulation on sump performance is plant specific.  Thus, plant insulation 
surveys, methods for estimating debris generation and transport, debris 
transport experiments, and other information have shown that the effects of 
debris-blockage depend on the types and quantities of insulation used, the 
primary system layout within the containment, and post-LOCA recirculation flow 
rates.  The staff addressed similar concerns in resolving Unresolved Safety 
Issue A-43, "Containment Emergency Sump Performance."  In particular, the 
staff's technical findings concluded that a single generic solution is not 
possible, but rather that the effects of debris blockage are governed by 
plant-specific design features and post-LOCA recirculation flow requirements. 

The NRC staff has investigated the buoyancy, transport, and headloss 
characteristics of reflective metallic insulation and construction materials 
and the results are summarized in NUREG/CR-3616, "Transport and Screen 
Blockage Characteristics of Reflective Metallic Insulation Materials."  
Briefly, the tests showed that thin metallic foils could be transported at low 
flow velocities and that flow blockage could occur at the lower portion of the 

.                                                            IN 88-28 
                                                            May 19, 1988 
                                                            Page 3 of 3 

Although the exact cause of the degradation of the foil covering on the insu-
lation at Susquehanna is not known, the causes may include temperature, 
humidity, and the effects of radiation on the neoprene-type adhesive used in 
the bonding process. 

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical con-
tact listed below or the Regional Administrator of the appropriate regional 

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

Technical Contact:  L. Zerr, NRR
                    (301) 492-1177

Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment
                                                            IN 88-28 
                                                            May 19, 1988 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                            NRC INFORMATION NOTICES 
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-27          Deficient Electrical          5/18/88        All holders of OLs
               Terminations Identified                      or CPs for nuclear
               in Safety-Related                            power reactors. 

85-35,         Failure of Air Check          5/17/88        All holders of OLs
Supplement 1   Valves to Seat                               or CPs for nuclear
                                                            power reactors. 

88-26          Falsified Pre-Employment      5/16/88        All holders of OLs
               Screening Records                            or CPs for nuclear
                                                            power reactors and
                                                            all major fuel 

88-25          Minimum Edge Distance for     5/16/88        All holders of OLs
               Expansion Anchor Bolts                       or CPs for nuclear
                                                            power reactors. 

88-24          Failures of Air-Operated      5/13/88        All holders of OLs
               Valves Affecting Safety-                     or CPs for nuclear
               Related Systems                              power reactors. 

88-23          Potential for Gas Binding     5/12/88        All holders of OLs
               of High-Pressure Safety                      or CPs for PWRs. 
               Injection Pumps During a 
               Loss-of-Coolant Accident 

88-22          Disposal of Sludge from       5/12/88        All holders of OLs
               Onsite Sewage Treatment                      or CPs for nuclear
               Facilities at Nuclear                        power reactors. 
               Power Stations 

88-21          Inadvertent Criticality       5/9/88         All holders of OLs
               Events at Oskarshamn                         or CPs for nuclear
               and at U.S. Nuclear                          power reactors. 
               Power Plants 
OL = Operating License
CP = Construction Permit 

Page Last Reviewed/Updated Wednesday, March 24, 2021