United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-56: Potential Problems with Silicone Foam Fire Barrier Penetration Seals

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

                                 August 4, 1988


Information Notice No. 88-56:  POTENTIAL PROBLEMS WITH SILICONE FOAM
                                   FIRE BARRIER PENETRATION SEALS


Addressees: 

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

Purpose: 

This information notice is being provided to alert addressees to potential 
problems in their installed fire barrier penetration seals that could result 
in the reduction of fire-resistive capabilities for protection of 
safety-related redundant equipment and electrical power and control circuits. 

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: 

In May 1987, B&B Promatec submitted a 10 CFR Part 21 notification advising NRC

that some silicone foam fire barrier penetration seals at Wolf Creek Nuclear 
Generating Station (WCNGS) did not meet minimum requirements.  The noncon-
forming conditions reported by B&B Promatec were described as voids, 
shrinkage, and lack of fill.  The conditions were not obviously visible 
because they were masked by fire-resistant boards that were typically 
installed on both sides of a wall penetration and the bottom side of a floor 
penetration.  WCNGS licensee personnel found the problems during replacement 
of damaged fire-resistant boards.  Thereafter, WCNGS adopted an inspection 
methodology in which the fire boards were removed, the silicone foam barriers 
were inspected and reworked as necessary, and the boards replaced.  

Initial results from sample inspections indicated that over 25 percent of the 
inspected seals were nonconforming.  Additional inspections performed before 
October 1987 revealed that 107 of 430 inspected seals required repair or 
rework and that 65 of the 107 contained voids.  The licensee for WCNGS 
subsequently determined that the void problem was caused, at least in part, by
underfill at the time of installation.  As a result of the WCNGS report, NRC 
has been evaluating whether the silicone foam nonconforming conditions found 
at WCNGS have generic applicability for plants other than those notified by 
B&B Promatec.  Part of this evaluation included a review of abstracts of 
licensee event reports. 



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Information obtained from this review indicates that a number of licensees 
have reported various fire barrier penetration seal nonconforming conditions. 
Some of the previously reported nonconforming conditions appear to be similar 
to those reported for WCNGS but are not limited to any particular vendor or 
installer.  Silicone foam was the only fire barrier penetration seal material 
that was specifically mentioned in the information reviewed, although some 
reports did not specifically identify the particular sealing material for the 
affected seals.  On the basis of this information, NRC believes that if 
generic problems exist, they may be limited to only silicone foam fire barrier
penetration seals but not to any particular vendor or installer.  

Discussion: 

This notice alerts addressees of the possibility that some installed fire 
barrier penetration seals may contain nonconforming conditions such as splits,
gaps, voids, and lack of fill in the sealing material.  These conditions may 
not be detected during routine inspection because the surface of the seal 
material is typically covered by a fire-resistant dam material.  Information 
that is available suggests that the extent of the possible problem may be 
limited to fire barrier penetrations filled with silicone foam material. 

Silicone foam has been used extensively as a fire barrier penetration sealing 
material in many nuclear power plants since the early 1970's.  For silicone 
foam seals installed since the mid 1970's, the silicone sealing material has 
been formulated of a two-component RTV 3-6548 base product manufactured by Dow
Corning.  The silicone foam seals are produced by mixing the two components, 
which then chemically react ("snap") a short time after they are mixed.  The 
resulting snap causes gas formation and material expansion, which produces a 
silicone foam cell structure.  Experience with silicone foam indicates that 
any one of many factors could affect the adequacy of the final seal instal-
lation.  These factors include the method of installation (e.g., damming 
technique), technical and quality control of material, material mixing 
process, pouring and curing process, method of final inspection, training and 
experience of installing personnel, and environmental factors, such as 
temperature and humidity.  Loss of control for any one of these factors could 
result in seals that do not meet minimum requirements.  

In many silicone foam fire barrier penetration seals, a permanent dam 
constructed from a fire-resistant material is used.  These dams must be 
present if they were part of the qualified seal design.  Normally, a permanent
dam is located on the bottom of floor and ceiling penetrations and on both 
sides (although sometimes only on one side) of wall penetrations.  One common 
installation method used in the past called for installing the permanent 
damming material first so that it would contain the liquid seal material 
during pouring and curing.  Since the permanent dam was part of final 
installation and because removal and reinstallation of the dam could be 
difficult and time consuming, final inspection of many silicone foam seals was
performed with the permanent dam in place.  When this approach was used, 
final determination of whether a proper seal had been attained 
was made without direct visual inspection of the seal surface, which appears 
to be a questionable practice.  Instead, indirect methods of checking, 
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such as tapping on the dam or inserting probe wires through the dam, were 
used.  In addition to precluding direct visual inspection of a new seal, 
installed dams also hinder subsequent detection of nonconforming conditions 
that may have been present since initial installation or that may have 
developed after initial installation.  

As mentioned earlier, licensees have reported various fire barrier penetration
seal nonconforming conditions in the past.  The reported conditions that 
suggest a generic problem are discussed below: 

Voids - One nonconforming condition for silicone foam seals is the presence of
voids.  Voids can be created in a number of ways.  First, proper preparation 
of the volume to be sealed is required before liquid fill.  Proper preparation
includes ensuring that the penetrating items (pipes and cables) have 
sufficient separation to permit the liquid to fill all the space in the 
volume.  Second, the mixed sealing material requires a sufficiently long 
"snap" time to ensure that the expansion process does not prevent free flow of
sealing liquid to all spaces in the volume.  Third, the gas formed during the 
expansion process needs to diffuse from the material without creating large 
gas bubbles or pockets.  Finally, a sufficient quantity of sealing material 
must be injected to ensure that all spaces within the volume will be filled. 

Gaps - Another nonconforming condition is the presence of gaps or the pulling 
away of silicone foam material from the surface of penetrating items or inside
surfaces of the fire barrier.  In some cases, these gaps extend only a short 
distance into the seal thickness.  In a few cases, gaps have been observed to 
extend completely through the entire thickness of the seal.  Causes of the 
gaps have been variously given as failure to inject sufficient sealing 
material during filling, bulging of damming material, shrinkage of silicone 
foam, and contraction of silicone foam caused by a temperature change.  The 
physical characteristics of the silicone foam are such that a 1 percent 
reduction in volume can be expected for a decrease of 20xF in temperature. 

Splits - A third nonconforming condition is splitting (cracking of solidified 
material) of the silicone foam material.  This condition was not reported at 
WCNGS but was reported by other licensees.  In conversations with NRC, B&B 
Promatec stated that the reasons for silicone foam splitting are not 
completely understood and that splitting is a topic of discussion in the power
sealer and insulation industry.  

Some of the actions taken by licensees as a result of finding nonconforming 
silicone foam fire barrier penetration seals include (1) programs for inspec-
tion and periodic reinspection of installed seals, (2) repair of nonconforming
seals, (3) evaluation of alternative materials for repairing old seals and in-
stalling new seals, and (4) development of alternative methods for installing 
and inspecting new silicone foam seals.  


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




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


Technical Contacts:  Joseph J. Petrosino, NRR
                     (301) 492-0979

                     C. Vernon Hodge, NRR
                     (301) 492-1169

Attachment:  List of Recently Issued NRC Information Notices

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Page Last Reviewed/Updated Tuesday, November 12, 2013