ML20217M421
| ML20217M421 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 04/03/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20217M411 | List: |
| References | |
| NUDOCS 9804080101 | |
| Download: ML20217M421 (4) | |
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1 UNITt 3 STATES
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THE SECOND 10 YEAR INTERVA L INSERVICE INSPECTION PLAN REQUESTS FOR REl IEF NO. 97-04. NON-CODE REPAIR OF VALVES DUKE ENERG( CORPORATION CATAWBA NUCLEAR STATION. UNITS 1 AND 2
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DOCKET NOS.150 413 AND 53-414
1.0 INTRODUCTION
Title 10 of the Code of Federal Reaulations (10 CFR) Section 50.55a(g) requires nuclear power facility piping and components to meet the appicable requirements of Section XI of the American Society of Mechanical Engineers (AS ME) Boiler and Pressure Vessel Code (hereafter referred as the Code).Section XI of the Code specifies Code-acceptable repair methods for flaws that exceed Code acceptance limits in piping that is in service. A Code repair is required to restore the structural integrity of flawed Code piping, independent of the operational mode of the plant when the flaw is detected. Those repairs not in compliance with Section XI of the 1
Code are non-Code repairs. However, the implementation of required Code (weld) repairs to ASME Code Class 1,2, or 3 systems is often impractical for nuclear licensees since the repairs normally require an isolation of the system requ ring the repair, and often a shutdown of the nuclear power plant.
Altematives to Code requirements may be used by nuclear licensees when authorized by the Director of the Office of Nuclear Reactor Regulation if the pr,oposed altamatives to the requirements are such that they are shown to provide an acceptable level of quality and safety in lieu of the Code requirements [10 CFR 50.55a(a)(3)(i)], or if compliance with the Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety [10 CFR 50.55a(a)(3)(li)].
- A licensee may also submit requests for relief froin certain Code requirements when a licensee has determined that conformance with certain Code requirements is impractical for its facility
[10 CFR 50.55a(g)(5)(iii)]. Pursuant to 10 CFR 50.55a(g)(6)(l), the Commission will evaluate determinations of impracticality and may grant relief and may impose altemative requirements as it determines are authorized by law.
Generic Letter (GL) 90-05, entitled " Guidance for Performing Temporary Non-Code Repair of
' ASME Code Class 1, 2 and 3 Piping," dated June 95,1990, preddes guidance for the staff in evaluating relief requests submitted by licensees fo.r temporary non-Code repairs of Code Class 3 piping. Under GL 90-05, impracticality exists if the flew detected during plant operation is in a section of Class 3 piping that cannot be isolat ed for completing a code repair within the period permitted by the limiting condition for operation (LCO) of the affected system as c 9004000101 900403g ApocK osooo4 a gm o
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. specified in the plant Technical Specifications, and performance of Code repair necessitates a plant shutdown.
2.0 BACKGROUND
. In November of 1997, Duke Energy Corporation ( the licensee) identified a leak on the bodies of valves 1RN-291 'and 1RN-351 located in the Nuclear Service Water (RN) System at Unit 1 of the Catawba Nuclear Station. Valves 2RN-291 and 2RN-351 (which are located at Unit 2) have also been ultrasonically examined and the examination revealed thinned areas but no through-wall body leakage. The subject valves are the component cooling system heat exchanger -
cooling water outlet flow control valves. The valves control com~ onent cooling water - ' ' -
p temperature by throttling the flow of RN water through the component cooling water system heat exchangers. One valve per unit normally throttles RN flow in the temperature control mode on the operating component cooling train, while the valve on the opposite nonoperating i
train is fully open to serve as an RN pump miniflow protection, line. The train functions are switched approximately every 2 weeks. Valves 1/2RN-291 are 'A' train valves, while valves 1/2RN-351 are "B" Train valves. The valves are 12-inch Fisher Controls pneumatically-operated valves. The "V" is a notch designed into the ball to allow for fine throttling control at '
low flow conditions. These valves are tested quarterly per the Catawba inservice Testing (IST)
Program by stroking in the closed-to-open direction. No relief from any testing requirements is being proposed by the licensee. The valves are 300 pound ANSI Class Section ill Class 3 valves with carbon steel bodies.
The Unit i valves have thinned areas in the body adjacent to the "V" notch that has pitted areas where through-wall leakage has occurred. The cause of the leakage is that while operating in the temperature control mode at low cooling flow demand, the valve is almost closed and the "V" notch passes most of the flow that is requirod for temperature control. This ball position i
. allows the flow to impinge on the valve body in a narrow area, which has created a condition to set up a corrosion-assisted flow erosion. After the leak was discovered, the licensee installed a removable rubber patch over the leaky areas in order to stop leakage for house keeping purposes. Because of the short time interval between the tilhe of discovery of leak and t5e planned start of the Unit 1 EOC 10 refueling outage, no additionalinspections were performed after the leak was discovered in addition, the licensee performed an evaluation of the flaws using the "through-wall' approach of GL 90-05. The evaluation concluded that the valves in their current conditions were acceptable for service.
By letter dated November 26,1997, the licensee requested a relief from the ASME Code,Section XI requirements to repair the valves (1RN-291,1RN-351,2RN-291, and 2RN-351)
? under the provisions of 10 CFR 50.55a(g)(5)(iii). The licensee based its request for relief on the basis that removable rubber patches have been installed over the leaky area for the Unit 1 valves (1RN-291 and 1RN-351) and that four separate calculations for all vahws using the.
~ "through-wall flaw" approach of GL 90-05 have been completed, which indicated that the valves
- are degraded but operable.- The licensee proposed to perform a permanent ASME Code repair for the Unit i valves during the EOC 10 scheduled to take place in late December 1997 (i.e.,
. the Code repair has aiready been completed). The Unit 2 valves will undergo a Code repair during the EOC 9 refueling outage scheduled to begin in September of 1998, a.
3-a 3.0 LICENSEE'S RELIEF REQWEST AND NRC STAFF EVALUATION i
The Code (1980 Edition of the ASME Code,Section XI, inclusive of the 1981 Winter Addenda) requires that repairs or replacements of ASME Code Class components be performed in accordance with rules found in Articles IWA 4000 or IWA-7000, respectively. The intent of these rules serve to provide an acceptable means of restoring the structural integrity of a j
degraded Code Class system back to the original design requirements.
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- Relief was sought from performing a repair or replacement of valves 1RN-291,1RN-351,
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2RN-291, and 2RN-351 in accordance with the. requirements of Article IWA-4000 or IWA-7000 R
respectively, to' expire at' the next Catawba Unit 1 scheduled outage (Refueling Outage 10) and i
the next Catawba Unit 2 scheduled outage (Refueling Outage 9).
j The licensee stated that the leakage noted on the Unit i valves had been eliminated by the installation of a removable rubber patch, a temporary non-Code repair. Code repair or j
replacement for the Unit 1 valves was scheduled to be completed during Refueling Outage 10,
' which took place at the end of November 1997, and at that time the repair was completed for valves 1RN-291 and 1RN-351. Code repair for the Unit 2 valves is planned for Refueling l
Outage 9, which is scheduled to take place in September 1998. Further, the licensee has determined that a Code repair is not practical at this time, in order to perform the Code repair, l
each component of the cooling water train as well as every system that relies on component exoling would have to be removed from service. These include residual heat removal, low-head injection, intermediate-head safety injection, containment spray, auxiliary feedwater, and the auxiliary shutdown panels. Thus, the Code repair would result in a loss of safety system i
j availability, in addition, the repair work would most likely exceed the Technical Specification allowed outage time and necessitate a plant shutdown.
l The licensee stated that Unit 2 valves 2RN-291 and 2RN-351 have been examined using j
ultrasonic testing (UT). The examination revealed that the valve bodies had localized wall
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thinning. The thinning was evaluated using the 'through-flav ( approach of GL 90-05. The evaluation determined that the stresses in the valve bodies are acceptable for the flawed I
conditions present in the valve bodies. Another UT examination was performed in February I
1998. The information from this inspection is being evaluated in order to determine if further i
inspection will be required before the next Unit 2 refueling outage. Further, the valves will continue to be tested quarterly in accordance with the plant's IST program and all normal inservice mspections will continue to be performed 4.0 STAFF CONCLUSION The staff has determined that the licensee's flaw evaluation was consistent with the guidelines and acceptance criteria of GL 90-05. The staff therefore finds the licensee's structuralintegrity and operability assessments to be acceptable. The licensee performed a non-Code repair of h.
the leaking Unit i valves and this temporary non Code repair remained in place for a short x
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period of time until a Code repair was completed during the EOC 10 Refueling Outage. For the i
Unit 2 valves, the licenses has performed an evaluation using the "through-wall" approach of GL 90 05. The evaluation determined that the valves are acceptable for continued operation 4
until they are permanently Code-repaired or replaced in the next refueling outage scheduled to take place in Septemtwr 1998.
l Permanent Code repair of the valves during unit operation would most likely necessitate l
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- exceeding the Technical Specification-allowed outage time, thus resulting in a unit shutdown.
l Therefore, the Code requirement is impractical as defined in GL 90-05. Given the small magnitude of the flaw and the licensee's altemative non-Code repair, reasonable assurance of structuralintegrity has been provided. The staff finds that performance ~of an immediate Code repair would impose an undue burden on the licentse. Therefore, relief is granted pursuant to
, 10 CFR 50.55s(g)(6)(i). The relief is granted retroactively to Unit 1, and expired at the end of the cycle 10 refueling outage (December 19g7). The relief for Unit 2 will expire at the end of the
< cycle 9 outage, or the next scheduled outage exceeding 30 days, whichever comes first.
Principal Contributor: George Georgiev Date: April 3,1998 i
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