ML17228A331
| ML17228A331 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 10/21/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17228A330 | List: |
| References | |
| NUDOCS 9310270030 | |
| Download: ML17228A331 (5) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAI T LUC UNIT 1.0 MQUGLEHD 0
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0 According to the provisions of 10 CFR 50.55a(g)(4), activities relative to ASHE 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 ASHE 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)(i) 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 of the public.
2.0 On July 30, 1993, the staff of the Florida Power and Light Company (FPL, the licensee),
submitted a letter requesting relief from the Code "Repair Requirements for a Class 2 Tank."
The licensee determined a few weeks earlier that the St. Lucie Unit 1 refueling water tank (RMT) had been losing inventory.
The RWT is an ASHE Code Class 2 structure fabricated from welded Type 6061-T6 aluminum plates, and constructed in accordance with requirements of ANSI Code B96. 1-1967.
The tank is required by the plant's Technical Specifications (TS) to contain a minimum 401,800 gallons of a 1720 ppm borated 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 ASHE Code requires that any repairs to ASHE Class 2
components or structures be done in accordance with the requirements of ASHE Section XI, IMA/IMC 4000 or with criteria specified in the original design Code of record.
Under these circumstances, FPL is required to make any needed repairs of the RWT in accordance with the requirements of IMA/IMC 4000 since ANSI Code B96.1-1967, the design Code of record, does not contain any criteria for repairing defects contained in the walls of the tanks.
The licensee seeks to repair 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)(i) 9310270030 93102i PDR ADOCK 05000335 I
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is warranted in this case, since a Code repair would require the licensee to shut down the plant, resulting in additional, unnecessary cycling of the plant's safety systems.
3.0 C de ire e
ASHE Boiler and Pressure Vessel
- Code, Se'ction XI, 1983 Edition through the Summer 1983 Addenda, Articles IWA/IMC-,4000 and IMA/IMC-7000, respectively.
Relief is requested from performing a Code repair for a leak detected during plant operation in the St. Lucie Unit 1 refueling water, tank (RMT), an ASHE Code Class 2 structure.
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.
P o osed lte t ve ro r 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
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 alumi'num backing plate.
- 3. Continue monitoring the RMT level by members of Operations and Chemistry Departments.
- 4. Re-evaluate the RMT for makeup capability and continued operability should the leak rate increase significantly above the current value (i.e.,
a 1.0 gpm increase above the current leak rate of 2.0 gpm).
- 5. Perform an ASIDE Code repair of the plate wall during the next outage exceeding 30 days, but no later than the Fall 1994 refueling outage.
4.0 U
The staff has determined that the licensee's proposal for the use of an epoxy plug as a temporary leak mitigating measure is acceptable for the following reasons:
- 1. The RMT is designed to withstand all normal operating loads, as well as the dynamic loads which could be imparted to the tank during potential 10 CFR 100 seismic events.
The majority of the dynamic and static loads 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 is supported by a 98X dense fill of oiled sand directly below the bottom plate.
- 2. The licensee has determined that no carbon steel components are located 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 structural materials in borated environments.
Chloride (Cl) is the only detectable impurity in the epoxy sealant.
However, the Cl concentration in the sealant is normally < 50 ppm, so the potential for leaching of Cl into the RWT inventory will be infinitesimal in comparison to the inventory volume.
3.
The makeup capability to the RMT from the Boric Acid Makeup Tanks is more than sufficient to maintain the inventory in RMT should the epoxy seal prove to be ineffective, and the RMT's inventory continues 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 fulfillingtheir needed safety functions during design basis accident conditions.
The licensee intends to perform further evaluations should the RWT continue to leak, and should the leak rate increase signifi-cantly above its current value (i.e.,
an increase of 1 gpm above the current rate of 2 gpm).
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)(i).
Furthermore, 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 fail catastrophically during the remainder of the St. Lucie Unit 1 operating cycle.
Accordingly, the staff concludes that granting of relief where Code requirements are impractical is authorized by law and the imposition of alternative requirements will not endanger life or property or the common defense and security and is otherwise in the public interest, given due consideration of the burden upon the licensee and facility that could result if the Code requirements were imposed upon the facility.
Pursuant to 10 CFR 50.55a(g)(6)(i), 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 RMT, and the leak to the RMT bottom plate must be repaired or the RMT bottom plate must be replaced in accordance with the provisions of the Code.
- James
- Nedoff, ENCB Date: October 21, 1993
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