ML20136G089
| ML20136G089 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 10/04/1993 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20136C539 | List:
|
| References | |
| FOIA-96-485 TAC-M87217, NUDOCS 9703170197 | |
| Download: ML20136G089 (5) | |
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i a j-SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION j
REVIEW OF THE REQUEST FOR RELIEF FROM THE STRUCTURAL INTEGRITY REQUIREMENTS FOR THE ST. LUCIE UNIT 1 REFUELING WATER TANK MATERIALS AND CHEMICAL ENGINEERING Bpa#CH TAC NO. MB7217 FLORIDA POWER AND LIGHT COMPANY SAINT LUCIE UNIT 1 DOCKET NO.:
50-335
1.0 BACKGROUND
I According to the provisions of 10 CFR 50.55a(g)(4), activities relative to ASME Code Class 1, 2, and 3 structures, systems and components (including supports) are required to comply with the in-service testing and structural integrity requirements of the ASME Code (henceforth referred to as the
" Code"),Section XI, during the service life of the plant. However, relief of the requirements may be granted, in part, under the provisions of 10 CFR 50.55a(g)(6)(1) should the Commission determine that compliance with certain Code requirements is impractical, and if the Commssion determines that relief of the requirements is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the interest 1
of the public.
2.0 Licensee's Relief Reauest J
On July 30, 1993 the staff of the Florida Power and Light Company (FPL, the licensee), submitted a letter requesting relief / rom the code " Repair i
Requirements for a Class 2 Tank." The licensee determined a few weeks earlier
-1 that the St. Lucie Unit I refueling water tank (RWT) had been losing inventory. The RWT is an ASME Code Class 2 structure fabricated from welded Type 6061-T6 aluminum plates, and constructed in accordance with requirements 1
of ANSI Code 896.1-1967. The tank is required by the plant's Technical l
Specifications (TS) to contain a minimum 401,800 gallons of a 1720 ppe borated j
water solution. The licensee determined the loss of inventory to be caused by a pinhole leak in the tank's bottom plate.
Section XI of the ASME Code, requires that any repairs to ASME Class 2 components or structures be done accordance with the requirements of ASME Section XI, IWA/IWC'4000 or with criteria specified in the original design 1
code of record. Under these circumstances, FPL is required to make any needed 1
repairs of the RWT in accordance with the requirements of IWA/IWC 4000 since ANSI Code B96.1-1967, the design code of record, does not contain any criteria 9703170197 970301 PDR FOIA BINDER 96-485 PDR i
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for repairing defects contained in the walls of the tanks. The licensee seeks i
to.tpair the pinhole in the bottom plate of the tank to mitigate the amount of leakage out of the pinhole, and to preclude exceeding the 10 CFR Part 20 requirements for radioactive effluents to unrestricted areas. The licensee believes, however, that relief under the provisions of 10 CFR 50.55a(g)(6)(1) is warranted in this case, since a Code repair would require the licensee to shutdown the plant, resulting in additional, unnecessary cycling of the plant's safety systems.
2.0 EVALUATION OF THE RELIEF RE0 VEST Code Reauirement ASME Boiler and Pressure Vessel Code,Section XI, 1983 Edition through the Summer 1983 Addenda, Articles IWA/IWC-4000 and IWA/IWC-7000, respectively.
Code Relief Reauest Relief is requested from performing a Code repair for a leak detected during plant operation in the St. Lucie Unit I refueling water tank (RWT), an ASME Code Class 2 structure, e
Basis for Relief
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An immediate Code repair to the RWT would require emptying of the tank's borated water contents, an emergency shutdown source, and is impractical unless the facility is shut down.
Proposed Alternative Proaram t
The licensee proposes the following alternatives in lieu of an immediate Code repair:
1.
Perform a remote visual (VT-3) examination of the tank using a I
submersible device prior to performing a temporary leak mitigating repair.
2.
Perform a temporary repair of the bottom plate using an epoxy sealant and a aluminum backing plate.
3.
Continue monitoring the RWT level by members of Operations and Chemistry Departments.
4.
Re-evaluate the RWT for makeup capability and continued operability should the leak rate increase significantly above the current value (i.e., a 1.0 gpa increase above the current leak rate of 2.0 gpa).
5.
Perform an ASME Code repair of the plate wall during the next outage exceeding 30 days, but no later than the Fall 1994 refueling outage.
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1' 3.0 Staff Ey:1uation and Conclusions I
i The staff have detemined that the licensee's proposal for the use of an epoxy plug as a temporary leak mitigating measure is acceptable for the following j
reasons:
1.
The RWT is designed to withstand all nomal operating loads, as well as j
the dynamic loads which could be imparted to the tank during potential i l
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10 CFR 100 seismic events. The majority of the dynamic and static loads j
imparted on the tank are supported by the cylindrical reinforced concrete support foundation.
The only stress acting on the bottom plate is created by the static head of the tank's inventory. This load 3
is supported by a 985 dense fill of oiled sand directly below the bottom plate.
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2.
The licensee has determined that no carbon steel components are located i
in the vicinity of the leak, so boric acid corrosion of ferritic safety related components is not a concern. Furthermore, the licensee has indicated that the epoxy sealant is compatible with the tank's l
structural materials in borated environments. Chloride (Cl) is the only detectable impurity in the epoxy sealant. However, the C1 concentration in the sealant is normally < 50 ppa, so the potential for leaching of C1 into the RWT inventory will be infinitesimal in comparison to the inventory volume.
3.
The makeup capability to the RWT from the Boric Acid Makeup Tanks is more than sufficient to maintain the inventory in RWT should the epoxy seal prove to be ineffective, and the RWT's inventory continue to leak at its present rate.
In this case, with the RWT in its current degraded condition, the emergency core cooling systems would be fully capable of 1
of fulfilling their needed safety functions during design basis accident conditions. The licensee intends to perform further evaluations should the RWT continue to leak, ano should the leak rate increase signifi-I cantly above it current value (i.e., an increase of I gpa above the current rate of 2 gpa).
As a Code repair to the RWT would require the licensee to shut down the unit, and prematurely empty the RWT's borated water contents, the staff concludes that the Code repair requirements in this case are impractical as defined under the provisions of 10 CFR 50.55a(g)(6)(1). Furthemore, the staff concludes that FPL has provided a reasonable alternative leak mitigating program, whose scope includes sufficient monitoring for identifying any significant increase in leakage from the RWT bottom plate. FPL has therefore provided adequate assurance that the tank will not fall catastrophically during the remainder of the St. Lucie Unit 1 operating cycle.
Accordingly, the staff concludes that the grant of relief where Code requirements are impractical and the imposition of alternative requirements are authorized by law and will not endanger life or property or the cosumn defense and security and are othemise in the public interest, given due consideration the burden upon the licensee and facility that could result if the Code requirements were imposed upon the facility. Pursuant to
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i 10 CFR 50.55a(g)(6)(1), relief is granted until the next scheduled refueling outage for the St. Lucie Unit 1 facility. At that time the borated water contents must be drained from the RWT, and the leak to the RWT bottom plate must be repaired or replaced in accordance with the provisions of the Code.
Technical
Contact:
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i James Medoff, Chem. Eng.
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Materials and Chem. Eng. Branch Division of Engineering, NRR 4
j (301) 504-2715 i
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SALP INPUT FACILITY NAME:
ST. LUCIE UNIT 1
SUMMARY
OF REVIEW ACTIVITIES:
This review evaluates Florida Power and Light Company staff's (the licensee) proposed alternative plan, in lieu of the requirements ASME Code Section XI, to temporarily mitigate the amount of leakage discharging from a pinhole leak in the bottom plate of the St. Lucie Unit I refueling water tank (RWT). The licensee proposes to use an epoxy plug to seal the leak until a planned shutdown of sufficient duration can be reached, at which the licensee will e
perform a Code repair of the tank.
ENGINEERING AND TECHNICAL SUPPORT:
The licensee's submittal was well organized and well thought out. The submittal addressed all major safety concerns, and indicated that the proposed i
epoxy seal should prove to be a effective method of mitigating the amount of leakage discharging from the tank. Very little additional information was needed for evaluation of the licensee's submittal.
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