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 *** END OF DOCUMENT ***

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