Information Notice No. 88-60: Inadequate Design and Installation of Watertight Penetration Seals

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

                                 August 11, 1988

                                   WATERTIGHT PENETRATION SEALS 


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees to potential 
problems resulting from inadequate design and installation of penetration 
seals whereby the seals may not provide watertight barriers between redundant 
safe shutdown trains.  It is expected that recipients will review this 
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 June 3, 1988, with Vogtle Unit 1 at 100 percent power, an inadvertent 
pressurization of the fire protection system caused 1/4 to 1/2 inch of water 
to accumulate around cable penetrations on the B train cable spreading room 
floor.  The water then seeped through the floor into the control room below.  
The water entered various process panel cabinets causing a spurious 
pressurizer high level signal and alarm.  The spurious signal also resulted in

a pressurizer level deviation signal that caused the pressurizer backup 
heaters to cycle on and off.  In addition, the water caused a pressurizer 
power-operated relief valve to open.  


During the review of this event, the licensee identified an unanalyzed con-
dition in which a postulated fire in the B train cable spreading room, with 
either actuation of the sprinkler system and/or manual fire suppression 
activities, could result in a loss of functions required for safe shutdown as 
follows: loss of control room train B and auxiliary shutdown panel via 


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                                                           August 11, 1988 
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the fire, and loss of control room train A via water leaking into control room
panels.  A second auxiliary shutdown panel (not required by the NRC) would 
still be available; however, no indication would be available since the 
indication circuits on that panel are not isolated from the control room.

Testing showed that the water seeped between the concrete floor and the 
penetration embedded steel angle (see Figure 1, attached).  The licensee 
applied a silicone sealant around the perimeter of all the floor penetrations 
where the concrete and the angle iron meet.  Testing showed that the sealant 
was watertight. 

The licensee found through additional testing that there was a second leak 
path within the cable bundles penetrating the foam sealant material.  If a 
large number of cables are so tightly massed that foam does not completely 
surround the individual cables, leakage can occur along the cables.  The 
licensee applied sealant around and between individual cables and at the 
interface of the foam and the steel angle where foam shrinkage can cause a 

Through testing, the licensee showed that a penetration seal with limited 
conductors penetrating the silicone seal material is watertight.  As an 
additional precaution, an elastomer cap was placed over the seal to protect 
the foam and sealant from damage by water impingement in the event of fire 
suppression activity (see Figure 2, attached).  

The licensee began a review to determine whether there were other seals that, 
because of leakage, could cause an unanalyzed event.  The review located all 
instances in which a room containing one train of safe shutdown equipment was 
located above another room containing the redundant train of safe shutdown 
equipment.  The licensee broadened the scope of review to include other con-
ditions in which leakage could affect safety-related equipment.  

General Design Criterion 3 in Appendix A to 10 CFR 50 states, in part:  "Fire 
detection and fighting systems of appropriate capacity and capability shall be
provided and designed to minimize the adverse effects of fires on structures, 
systems, and components important to safety.  Firefighting systems shall be 
designed to assure that their rupture or inadvertent operation does not sig-
nificantly impair the safety capability of these structures, systems, and 
components."  The NRC has identified numerous occurrences of system inter-
action between fire suppression systems and systems important to safety.  
"Actuation of Fire Suppression System Causing Inoperability of Safety-Related 
Equipment" was the subject of Information Notice 83-41.   The scenario at 
Vogtle Unit 1 is of particular significance in that it could involve the 
potential loss of redundant and auxiliary safe shutdown trains. 


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

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

Technical Contact:  D. Oudinot, NRR 
                    (301) 492-1174 

Attachments:  1.  Figure 1, Penetration Seal Leakage Path
              2.  Figure 2, Proposed Typical Seal Repair
                    (Upper Cable Spreading Room)
              3.  List of Recently Issued NRC Information Notices

Page Last Reviewed/Updated Friday, May 22, 2015