ML17158B605
| ML17158B605 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 04/29/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17158B604 | List: |
| References | |
| NUDOCS 9605020292 | |
| Download: ML17158B605 (4) | |
Text
WASHINGTON, D.C. 20S5&0001
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UNITED STATES NUCLEAR REGULATORY COMMISSION Yg Cy SAF Y
VA UATION OF NON-CODE REPAIRS ON REACTOR WATER CLEANUP SYSTEM HEAT EXCHANGER SUS UEHANNA STEAM ELECTRIC ST TION UNIT 1
DOCKET NO. 50-387
- 1. 0 INTRODUCTION In a letter to NRC dated April 23, 1996, the licensee of the Susquehanna plant requested relief from performing ASHE Code Section XI repairs on the Unit 1
Reactor Water Cleanup System (RWCS) Regenerative Heat Exchanger in accordance with 10 CFR 50.55a(g)(6)(i).
The heat exchanger is an ASHE Class 3 component.
On April 16, 1996, during an unrelated surveillance in the room housing the exchanger, a steam leak (less than 1 gpm) was found at the'connection of the end bell flange and the flange of the heat exchanger header.
The licensee believes that the cause of the leak is cracking of the internal diaphragm weld.
Currently, the licensee is monitoring for possible changes in the leak rate via monitoring of room temperature and a video camera.
Article IWA-4000 of Section ll of the American Society of Mechanical Engineers (ASHE) Code requires that the identified flaw be removed and that a weld repair, post repair inspection, and a post repair pressure test be performed.
- 1. 1 Licensee Requested Relief In the letter, the licensee proposed a temporary non-Code repair using a
clamp/cap nut system with a compound to be injected into the voids in the end bell flange and hardened at elevated temperature.
The temporary repair will be in place until the upcoming refueling outage starting September
- 1996, at which time the ASHE Code repair will be completed.
1.2 Basis The licensee indicated that to perform a Code repair at this time is impractical.
Such a repair would require 72 to 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br />.
Currently Unit 1 is at 100X power.
Removing the RWCS from service is also not feasible since that would allow impurities to build up in the reactor coolant, and would result in exceeding the chemistry limits of both the Technical Specifications and EPRI guidelines within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
The other concern is that conductivity is estimated to reach the Technical Specification limit within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
In either case, the plant would have to be shut down.
2.0 STAFF EVALUATION The staff evaluation of the licensee's relief request consists of the following:
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1.
The imposition of Section IWA-4000 of the ASIDE Code would require that the licensee perform the set of actions described in Section 1 above.
These activities would take an extended period of time to complete, would result in water chemistry degradation and would require a plant shutdown.
A plant shutdown is undesirable and can be avoided by performing a temporary repair.
The staff considers that a Code repair on a temporary basis would be impractical because of its effects on the reactor water quality from the required out-of-service time for the reactor water cleanup function and because it would result in an unnecessary plant transient caused by the plant shutdown.
2.
The licensee's explanation of the cause of the leak is based on sound engineering
- judgment, although it is not verified.
Confirmation of the existence of cracking of a weld on an internal diaphragm requires removal of the RWCS from service, which is impractical at this state of plant operation.
In addition, the licensee did not observe any signs of degradation of the fasteners connecting the end bell flange and the flange of the heat exchanger header.
3.
The proposed repair using a clamp/cap nut system with compound injection should stop a small leak (less than 1 gpm).
The licensee indicated that they had performed a similar type of temporary repair several times in the past and the repairs were successful.
However, the RWCS heat exchanger is a high energy system with temperature exceeding 500' and pressure exceeding 1000 psig; the licensee should evaluate stress redistribution caused by the repair, such as effects of the additional weight of the
- clamps, and verify that there are no adverse effects on other parts of the heat exchanger.
The fasteners in the flange joint are currently subject to operating pressure and temperature because of the leaking fluid.
- However, no degradation of the flange joint has been observed.
Also, upon the completion of the temporary repair, the mechanical clamps would reduce the tensile stresses in the fasteners.
Consequently, structural integrity of the heat exchanger header should not be a concern.
4.
The NRC staff has assessed the effects of additional heat load from the leak on adjacent instrumentation and concluded that there is no safety impact.
The licensee also indicated in a conference call that the leak has not caused an unacceptable safety hazard to the adjacent environment.
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Pursuant to 10 CFR 50.55a(g)(6)(i),
the staff concludes that the requirements of the Code relative to a permanent repair are impractical as discussed above and imposes an alternative temporary non-Code repair on the leaking RWCS heat exchanger, provided that the licensee performs a permanent code repair of the defect during the next refueling outage scheduled to begin in September
- 1996, completes a structural integrity assessment, and confirms the root cause of the leak during the upcoming refueling outage.
NRC should be informed if the stress assessment results or the root cause finding deviate from the licensee's current assessment.
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~ The Commission is hereby granting a one-time relief from performing the repair as per the ASME Code.
The relief granted is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Principal Contributor:
S.
Hou Date; April 29, 1996
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