Part 21 Report - 1998-541
ACCESSION #: 9807280312
Illinois Power Company
Clinton Power Station
P. O. Box 678
Clinton, IL 61727
Tel 217 935-5623
Fax 217 935-4632
Walter G. MacFarland IV
Senior Vice President
ILLINOIS and Chief Nuclear Officer
POWER U-603033
4F.140
An Illinova Company
July 20, 1998
Docket No. 50-461
10CFR21.21
Document Control Desk
Nuclear Regulatory Commission
Washington, D. C. 20555
Subject: 10CFR21 Report 21-98-039: Medium and High Density Silicone Seals
Designed and Installed by BISCO using Dow Coming SYLGARD 170
Material Can Shrink due to Coefficient of Thermal Expansion
Dear Madam or Sir:
On February 20, 1998, while performing a walkdown to qualify
penetration seals in accordance with NUREG 1552, "Fire Barrier Penetration
Seals in Nuclear Power Plants," Illinois Power (IP) identified cracks in
penetration seal DG-762-01-5003 located in the Division 3 Diesel Generator
Room HVAC Fan Room intake plenum. The cracks extended completely through
the seal in the M-board separator material at the interface between the M-
board and the SF-60 sealant, and between the SF-60 sealant and a pipe
passing through the seal. The M-Board is a refractory fiber board made
predominately of alumina silica used within the penetration seal to divide
a penetration into sections for which a tested design configuration can be
applied. The penetration seal was designed and installed by BISCO. The
BISCO SF-60 sealant material was manufactured by Dow Coming as SYLGARD 170
material.
Inspections of other similar penetration seal configurations revealed
that the shrinkage issue is a generic concern for medium and high density
penetration seals.
Condition report 1-98-02-385 was initiated to track an investigation
and resolution of this issue. On June 4, 1998, IP determined this issue
was potentially reportable under the provisions of 10CFR21.
IP is providing the following information in accordance with
10CFR21.21(d)(4). Initial notification of this matter will be provided by
facsimile of this letter to the NRC Operations Center in accordance with
10CFR21.21(d)(3) within two days of the date the responsible officer signs
this letter.
U-603033
Page 2
(i) Walter G. MacFarland, IV, Senior Vice President and Chief
Nuclear Officer of IP, Clinton Power Station, Highway 54, 6 Miles
East, Clinton, Illinois, 61727, is informing the Nuclear
Regulatory Commission of a condition reportable under the
provisions of 10CFR, Part 21.
(ii) The basic components involved in this condition are penetration
seals containing Dow Coming SYLGARD 170 material (BISCO SF-60 and
BISCO SF-150NH sealant material) installed at Clinton Power
Station (CPS).
(iii) The penetration seals were installed by BISCO with sealant
material supplied by BISCO, a subsidiary of The BRAND Companies,
Park Ridge, Illinois. The BISCO organization no longer exists.
(iv) IP identified cracks in penetration seals. The cracks extend
completely through the seal in the M-board separator material at
the interface between the M-board and the SF-60 sealant, and
between the SF-60 sealant and a pipe passing through the seal.
The M-Board is a refractory fiber board made predominately of
alumina silica used within the penetration seal to divide a
penetration into sections for which a tested design configuration
can be applied.
IP attributes the cracks in the penetration seals to shrinkage of
the medium and high density sealant material due to the
coefficient of expansion of the sealant material. Dow Coming
manufacturer literature for SYLGARD 170 material states that the
material has a notable volume coefficient of thermal expansion
which results in the cured sealant material increasing or
decreasing in volume approximately 8 percent for each 100 degrees
Centigrade of temperature differential. The literature further
states that allowances should be made to accommodate volume
expansion and prevent pressure build-up at higher temperatures.
To minimize normal thermal expansion and contraction stresses,
the literature recommends that the SYLGARD 170 material be cured
at a temperature midway between the high and low extremes in the
operating temperature cycle required for the seal application.
The operating temperature for the penetration seal does not
appear to have been a consideration in the selection of the seal
design or in the seal installation procedure for seal DG-762-01-
5003. The lack of consideration for the thermal expansion
limitations of the sealant material resulted in the sealant
material expanding and contracting during normal plant operating
conditions, crushing the M-Board as the sealant material expanded
and pulling the M-Board apart as the sealant material contracted.
The cycle of expansion and contraction resulted in cracks
extending completely through the penetration seal. The expansion
and contraction of the sealant material also resulted in gaps
completely through the seal at interfaces between the sealant and
the M-board, and at interfaces between the sealant and a pipe
penetrating the seal. The gaps developed as the bonds between
the sealant material and the M-board and pipe failed.
U-603033
Page 3
A condition which contributes to penetration seal shrinkage is
installation of the sealant material at an ambient temperature
much higher than the penetration seal operating temperature. The
governing factor appears to be the sealant temperature during
initial cure of the material. During original installation
(during plant construction), the sealant material temperature was
dictated by ambient temperatures and could have reached
temperatures in excess of 100 degrees Fahrenheit prior to
batching. As referenced in the Dow Coming SYLGARD 170 technical
data sheet, if the operating temperature of the penetration seal
is different from the installation temperature, the sealant will
expand or contract 8 percent for every 100 degrees Centigrade
increase/decrease in temperature.
The larger the penetration seal, the more susceptible it is to
damage caused by the expansion and contraction. The inspections
at CPS to date indicate that penetrations sealed using SF-60 or
SF-150NH material and having configurations with dimensions
greater than 12 inches appear to be susceptible to this shrinkage
issue.
IP has concluded that this issue should be reported under the
provisions of 10CFR21. The basis for this conclusion is that
this issue could result in a reduction in the fire barrier
capabilities of installed penetration seals intended for the
protection of safety-related redundant equipment and electrical
power and control circuits.
(v) The penetration seal shrinkage condition was identified on
February 20, 1998. On June 4, 1998, IP determined this issue was
potentially reportable under the provisions of 10CFR21.
(vi) CPS has approximately 800 penetration seals that may be
susceptible to the shrinkage issue. Other facilities using BISCO
SF-60, BISCO SF-150NH, or Dow Coming SYLGARD 170 material could
be affected by this deficiency.
(vii) As of July 10, 1998, IP has inspected 157 of the suspected
penetration seals and has found unacceptable cracks/gaps in 32
penetrations.
IP will inspect and rework/repair the suspected penetration seals
as necessary. Potentially affected fire rated seals which
constitute divisional barriers are being inspected first. A
repair crew has been mobilized to fix deficient fire rated seals
in this category. Rework/repairs are in progress to minimize the
cumulative impact of the deficient fire rated seals prior to
plant restart. Resolution of this issue for the remaining
deficient seals is currently scheduled to be completed by May
1999.
IP revised the procedure for repairing penetration seals to
provide instructions for repairing seal damage in medium and high
density seals.
U-603033
Page 4
IP will review the adequacy of existing penetration details and
installation procedures and revise them as necessary to limit
gaps and cracks resulting from thermal expansion and contraction
of the sealant material in new penetration seals. This action
will be completed by May 1999.
(viii) IP recommends that other facilities perform inspections for
unacceptable shrinkage if they use BISCO SF-60, BISCO SF-150NH or
Dow Corning SYLGARD 170 material in penetration seals.
Additional information about this issue may be obtained by
contacting R. P. Bhat, Fire Protection Engineering, at (217) 93 5-888 1,
extension 3963.
Sincerely yours,
Walt G. MacFarland, IV
Senior Vice President and
Chief Nuclear Officer
RSF/mlh
cc: NRC Clinton Licensing Project Manager
NRC Resident Office, V-690
Regional Administrator, Region III, USNRC
Illinois Department of Nuclear Safety
INPO Records Center
BRAND Fire Protection Services, Incorporated
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