ML15239A323
| ML15239A323 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 01/19/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML15239A322 | List: |
| References | |
| NUDOCS 9502080301 | |
| Download: ML15239A323 (5) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THE SECOND TEN-YEAR INTERVAL INSERVICE INSPECTION REQUEST FOR RELIEF 93-07, REVISION 1 FOR DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNIT 2 DOCKET NO. 50-270
1.0 INTRODUCTION
The Technical Specifications for Oconee Nuclear Station state that the inservice inspection and testing of the American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable Addenda as required by Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).
Section 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulties without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the second 10-year interval comply with the requirements in the latest e616'ion and addenda of Section XI of the ASME Code incorporated by reference i '10 CFR 50.55a(b) on the date 12 months prior to the start of the 120-month inspection interval, subject to the limitations and modifications listed therein. The applicable edition of Section XI of the ASME Code for the Oconee Nuclear Station, second 10-year inservice inspection (ISI) interval is the 1980 Edition through Winter 1980 Addenda. The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b) subject to the limitations and modifications listed therein.
502080301 950119 PDR ADOCK 05000270 P
-2 Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission in support of that determination and a request made for relief from the ASME Code requirement. After evaluation of the determination, pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose alternative requirements that are determined to be authorized by law, will not endanger life, property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed.
On February 15, 1994, the ASME approved Code Case N-416-1 entitled "Alternative Pressure Test Requirement for Welded Repairs or Installation of Replacement Items by Welding Class 1, 2, and 3,Section XI, Division 1."
By letter dated August 9, 1994, Duke Power Company requested approval to use Code Case N-416-1 pursuant to 10 CFR 50.55a(a)(3) for two socket welds on the Core Flood Tank (CFT) side of valves 2CF-20 and 2CF-22.
2.0 EVALUATION The staff has evaluated the information provided by the licensee in support of Request for Relief No. 93-07, Revision 1, as follows:
Code Requirement:
IWC-5210(a)(2) states that a system hydrostatic pressure test per IWA-5211(d) shall be performed for repaired and replaced components, or portions of systems that have been altered.
Licensee's Code Relief Request:
The licensee has requested approval to use Code Case N-416-1 in lieu of performing the Code-required system hydrostatic pressure test of Class 2, 2-inch socket welds on the Core Flood Tank (CFT) side of CFT drain line block Valves 2CF-20 and 2CF-22.
Licensee's Basis for Requesting Relief:
(as stated)
Performing a hydrostatic test to examine both of these 2" socket welds would result in an undue burden without a compensating increase in the level of quality or safety.
Code Case N-416-1 has been approved and issued for use by ASME. This Code Case allows the combination of NDE and a system leakage test as an acceptable alternative to a hydrostatic test following repairs and replacements by welding. The use of this Code Case will alleviate the burden while providing a technically approved alternative to assure an acceptable level of quality or safety is maintained.
Although the valve line-up for performing a hydrostatic pressure test would not violate the Technical Specification Low Temperature Over Pressurization (LTOP) requirements, LTOP would be challenged. The
-3 window of time to perform this test is limited to a small period due to the restrictions of operability, LTOP, containment integrity, personal safety, and production of the borated water for the test medium.
A hydrostatic test would dictate the generation of an additional 6,000 gallons of borated water to be added to the 16,600 gallons presently in the CFTs. During the time of the test most of the borated water would have been depleted from the Bleed Holdup tanks for defueling or refueling. Therefore, the majority of the 6,000 gallons would have to be produced from the Boric Acid Mixing Tank with a capacity of about 500 gallons. It takes about one day to produce the 500 gallon batch of borated water and approximately 10 to 12 days to produce the 6,000 gallons needed to perform the test. This would extend the refueling outage several days. Each day the refueling outage is extended costs Duke Power approximately $260,000 in power replacement costs. After the test, Oconee would have to process this 6,000 gallons of borated liquid waste. The boron would have to be extracted and processed for burial and the water processed to acceptable radiation levels for release.
Modification of the system has been used on Units 1 and 3 to provide an alternative means to test these welds. The cost to perform this system modification has been approximately $3200 for each weld. In addition to the cost, this modification creates 5 needless welds on each CFT drain line solely to test one weld on each valve.
The burden incurred to perform the test with the system in the current configuration or to modify the system configuration in order to perform the test is unnecessary in light of the availability of a technically approved Code alternative.
Licensee's Proposed Alternative Examination:
The subject 2-inch socket welds received a surface, nondestructive examination (PT) and a VT-2 pressure test inspection at normal operating pressure.
Evaluation:
In lieu of hydrostatic pressure testing for welded repairs or installation of replacement items by welding, Code Case N-416-1 requires a visual examination (VT-2) be performed in conjunction with system leakage testing using the 1992 Edition of Section XI, in accordance with paragraph IWA-5000, at nominal operating pressure and temperature. This Code case also specifies that NDE of the welds be performed in accordance with the applicable Subsection of the 1992 Edition-of Section III.
The 1989 Edition of Sections XI and III are the latest editions referenced in 10 CFR 50.55a. The staff has compared the system pressure test requirements of the 1992 Edition of Section XI to the requirements of IWA-5000 of the 1989 Edition of Section XI. In summary, the 1992 Edition imposes a more uniform set of system pressure test requirements for Code Class 1, 2, and 3 systems.
The terminology associated with the system pressure test requirements for all three Code classes has been clarified and streamlined. The test frequency and test pressure conditions associated with these tests has not been changed.
The hold times for these tests has either remained unchanged or increased.
-4 The corrective actions with respect to removal of bolts from leaking bolted connections has been relaxed in the 1992 Edition, but use of this change has been accepted by the staff in previous safety evaluations. The post-welded repair NDE requirements of the 1992 Edition of Section III remain the same as the requirements of the 1989 Edition of Section III. Therefore, the staff finds this aspect of Code Case N-416-1 to be acceptable.
Hardships are generally encountered with the performance of hydrostatic testing performed in accordance with the Code. For example, since hydrostatic test pressure would be higher than nominal operating pressure, hydrostatic pressure testing frequently requires significant effort to set up and perform.
The need to use special equipment, such as temporary attachment of test pumps and gages, and the need for individual valve lineups can cause the testing to be on critical path. Testing the subject welds would dictate the generation of an additional 6,000 gallons of borated water, which would have to be reprocessed after the test. System modifications would be required to allow testing of these welds without the generation of the additional borated water.
Piping components are designed for a number of loadings that would be postulated to occur under the various modes of plant operation. Hydrostatic testing only subjects the piping components to a small increase in pressure over the design pressure and, therefore, does not present a significant challenge to pressure boundary integrity. Accordingly, hydrostatic pressure testing is primarily regarded as a means to enhance leakage detection duringl the examination of components under pressure, rather than solely as a measure to determine the structural integrity of the components.
The industry indicates that experience has demonstrated that leaks are not being discovered as a result of hydrostatic test pressures propagating a preexisting flaw through wall. They indicate that, when leaks are found, in most cases they are found when the system is at normal operating pressure.
This is largely due to the fact that hydrostatic pressure testing is required only upon installation and then once every 10-year inspection interval, while system leakage tests at nominal operating pressures are conducted a minimum of once each 40-month inspection period for Class 2 systems. In addition, leaks may be identified by plant operators during system walkdowns which may be conducted as often as once a shift.
Following the performance of welding, the Code requires volumetric examination of repairs or replacements in Code Class 2. Considering the NDE performed on Code Class 2 systems and considering that the hydrostatic pressure tests rarely result in pressure boundary leaks that would not occur during system leakage tests, the staff believes that increased assurance of the integrity of Class 2 welds is not commensurate with the hardship of performing hydrostatic testing.
-5
3.0 CONCLUSION
The staff concludes that compliance with the Code hydrostatic testing requirements for welded repairs or replacements of Code Class 2 components would result in hardships without a compensating increase in the level of quality and safety. Accordingly, the licensee's proposed alternative to use Code Case N-416-1 is authorized for Oconee Unit 2, pursuant to 10 CFR 50.55a(a)(3)(ii).
Principal Contributor: L. Wiens Date: January 19, 1995