ML20138K035
| ML20138K035 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 05/06/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20138K032 | List: |
| References | |
| NUDOCS 9705120027 | |
| Download: ML20138K035 (4) | |
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NUCLEAR REGULATORY COMMISSION i
2 WASHINGTON. D.C. 300SH001 f
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j SAFETY' EVALUATION $YTHEOFFICEOFNUCLEARREACTORREGULATION
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RELATED TO AMENDMENT NO. 89 TO FACILITY OPERATING LICENSE NO. NPF-37,-
AMENDMENT NO. 89 TO FACILITY OPERATING LICENSE NO. NPF-66, AMENDMENT NO. 81 TO FACILITY OPERATING LICENSE NO. NFF-72, L
i AND AMENDMENT NO. 81 TO FACILITY OPERATING LICENSE NO. NPF-77 i
l COMMONWEALTH EDISON COMPANY l
BYRON STATION. UNIT NOS. 1 AND 2 BRAIDWOOD STATION. UNIT NOS. 1 AND 2 i
DOCKET NOS. STN 50-454. STN 50-455. STN 50-456 AND STN 50-457 J
1.0 INTRODUCTION
By letter. dated November 4, 1996, as supplemented on December 4; 1996, and March 20, 1997, Commonwealth Edison Company (Comed, the licensee), proposed to i
amend the Technical Specifications (TS) for Byron Nuclear Power Station, Unit 1 (Byron 1); and Braidwood Nuclear Power Station, Unit 1 (Braidwood 1).
The licensee proposed to revise TS 3.6.1.6, " Containment Vessel Structural Integrity" to allow a one-time exception to requirement 4.6.1.6.1.e.1) of the TS surveillance requirements-(TSSR). in support of Unit I steam generator replacement (SGR)_ at each station.
The TSSR requires that the voids in sheathing filler grease, which inhibits the corrosion of prestressing tendon, shall not exceed 5 percent.
To facilitate detensioning and removal of the selected prestressing tendons from the tendon sheathing prior to cutting an opening in the containment, during cool weather, the licensee plans to remove the grease during a warmer season. Thus, the Amendment requests a waiver from the TSSR requirement until after the replacement of the respective steam generators. The March 20, 1997, submittal provided additional clarifying-information that did not change the initial proposed no significant hazards consideration determination.
2.0 EVALUATION The containment structures for Byron and Braidwood stations consist of cylinders with shallow-dome roofs supported by flat circular foundation slabs.
-The cylinder and dome'of each containment structure are prestressed with hoop, vertical and dome tendons.
Each tendon consists of 170 stress relieved, cold drawn' wires, and is' installed in 6-inch diameter sheet metal tendon sheathing.
The sheathings are filled with corrosion inhibiting grease to protect the tendons. To accommodate the replacement of the steam generators at Byron 1 and Braidwood 1, a temporary access opening through the containment 9705120027 970506 PDR ADOCK 05000454 P
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cylindrical wall will be required. This opening will be approximately 20 feet wide and 22 feet high, located 62 feet above grade.
Twenty-one hoop tendons and 10 vertical tendons will be intercepted by the opening. These tendons will have to be removed prior to cutting the opening. The proposed Amendment requests the potential removal of grease from 35 tendons.
The schedule for cutting the opening in Byron 1 containment indicates that the plant will be shut down in November 1997 for SGR activities.
Expected cold weather during this month will make it difficult to remove thickened grease from the tendon sheathings. Therefore, the licensee plans to remove the grease from the selected tendons in June 1997. Thus, the selected tendons will remain without grease for 5 months during operation of the plant and reactor.
Braidwood 1 requested approval to operate without grease in some tendons from May 1, 1998 until its fall 1998 refueling outage. That outage is currently scheduled to begin on September 5, 1998.
Without the amendment to the TSSR, this condition would violate the requirement that the voids in the sheathing filler grease not exceed 5 percent of the net volume of the sheathing.
The licensee's technical evaluation consists of ensuring that the containment integrity will not be compromised due to the lack of corrosion inhibiting grease in 35 tendons during the 6 month period.
The licensee provides the following reasons in support of the proposed TS Amendment:
1.
A source of dry air will be used to pressurize the tendon sheathing to remove the grease. Use of dry air will ensure that no moisture is introduced in the sheathing.
2.
During tendon fabrication all tendon wires were completely immersed in rust protective coating.
3.
The coiled tendons and the interior surface of the tendon sheathing were coated after fabrication to provide additional corrosion protection during storage and handling.
4.
Initial installation of the grease involved pumping heated grease into the sheathing to completely fill the sheathing.
5.
The results of the prior three surveillances met the TSSR requirements for prestressing forces, grease qualifications, and anchorages of tendons.
6.
Experience data for other similar plants (Fort Calhoun, Wolf Creek) indicated that with voids of up to 36 percent existing for several years, the tendon wires showed no signs of corrosion.
7.
Industry experience:
several tendons were removed from a containment structure (non-operating plant), wrapped in plastic and stored outside from April to December subject to weather elements (rain, sun, snow, and freezing temperatures).
In December, the plastic wraps were opened and
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l five to ten gallons of water were found. The inspection of individual wires showed no signs of corrosion. The licensee notes this as a demonstration of the effectiveness of the_ corrosion protection methods i
(items 2, 3, and 4 above) used for tendons in containments.
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. The licensee states that the end anchorages of hoop and vertical tendons i
are protected from exposure to weather because of the existing enclosures over buttresses and done walkways at all Units of Byron and
- l Braidwood.
The licensee stated that following the steam generator replacement outage, the tendons will be retensioned to their required level of prestressing force and the sheathing will be refilled with grease.
In addition, the licensee stated 1
that it will include in the next tendon surveillance, one of the tendons from each group (horizontal and vertical).
The staff recognizes the validity of the above reasons as support fer the proposed TS amendment, and agrees with the licensee's contention r ^ ding the effectiveness of the original rust-preventive coatings.
The dry I ocedure j'
for removing the grease will ensure that the moisture is not int,. uced during the grease removal process. Abo, the enclosures over the ends of the exposed i
anchorages of the 35 tendons will protect them against direct intrusion of l
moisture in the uncovered tendons. Considering the short period (6 months or less) involved in implementation of the amended TS, the staff concludes that 1
the containment integrity will not be comp'mmised during this period.
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3.0
SUMMARY
Based on the review of the licensee's amendment request and its additional
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information, the staff concludes that the containment structural integrity 1
will not be compromised under operating and shutdown modes prior to defueling 4
of the respective reactors during the period when the grease is removed from the selected prestressing tendons. Based on the schedule of SGR activities, j
the period will not exceed 6 months.
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4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendments. The State official had no comment:
5.0 DIVIRORTiIALCONSIDERATION The amendments change a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve no i
significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the
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_4 amendments involve no significant hazards consideration, and there has been no public comment on such finding (62 FR 2186). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, i
and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: H. Ashar Date:
May 6, 1997
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