United States Nuclear Regulatory Commission - Protecting People and the Environment


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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