ML16141A912
| ML16141A912 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 04/26/1995 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16141A913 | List: |
| References | |
| NUDOCS 9505020244 | |
| Download: ML16141A912 (5) | |
Text
- PS REGuZ UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION REQUEST FOR RELIEF FOR DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNITS 1. 2. AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
The Technical Specifications for Oconee Nuclear Station, Unit Nos. 1, 2, and 3, 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 first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) on the date 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The 1989 Edition, with no Addenda, of Section XI is the applicable edition of the ASME Code for the Oconee Unit 1, 2, and 3 Third 10-year Inservice Inspection (ISI) Interval.
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 and subject to Commission approval.
9505020244 950425 PDR ADOCK 05000269 PDR
-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 requirements. 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.
In a letter dated June 22, 1994, the licensee, Duke Power Company (DPC),
proposed an alternative examination to the requirements of the ASME Boiler and Pressure Code,Section XI.
Duke Power Company requested approval for the implementation of the alternative rules of ASME Section XI Code Case N-498-1, dated May 11, 1994, "Alternative Rules for 10-Year System Hydrostatic Testing for Class 1, 2, and 3 Systems" pursuant to 10 CFR 50.55a(a)(3) for 10-year hydrostatic testing on Class 3 systems. Duke Power Company indicated, in a letter dated May 27, 1992, that it had addressed this issue for Class 1 and 2 systems by reference to Code Case N-498 as was previously approved by the NRC in Regulatory Guide 1.147.
2.0 EVALUATION 2.1 Licensee's Request This submittal is requesting approval pursuant to 10 CFR 50.55a(a)(3) for use of Code Case N-498-1, "Alternative Rules for 10-Year System Hydrostatic Testing for Class 1, 2, and 3 Systems" for Class 3 systems.
2.1.1 Licensee's Component Identification Class 3 systems subject to hydrostatic testing.
2.1.2 ASME Code,Section XI. RequirementsSection XI, Table IWD-5223, Categories D-A, D-B, and D-C, Items 01.10, 02.10 and D3.10 (for Class 3) contains the requirements for system hydrostatic and leakage testing. The Code requires system hydrostatic testing once per 10 year interval at or near the end of the interval.
2.1.3 Licensee's Proposed Alternative Testing The licensee proposed to use the alternative contained in Code Case N-498-1, a system leakage test, in lieu of hydrostatic testing, for Class 3 systems.
-3 2.1.4 Licensee's Basis for Relief The licensee stated the following basis for relief:
Consistent with the philosophy of ASME Code Case N-498 Revision 1, this request is based on performing VT-2 examinations at nominal operating pressures in lieu of the interval hydrostatic pressure tests. A review of all the Class 3 interval hydrostatic pressure tests performed at Duke Power Company to date has shown that a leak has never occurred in the base metal or in an existing weld.
All leaks that have occurred have been in mechanical joints such as packing glands and body-to-bonnet connections. This review covers a time period of twenty years for Oconee, twelve years for McGuire and eight years for Catawba. Additionally, the ASME Boiler & Pressure Vessel Code,Section XI Task Group for Code Case N-498 Revision 1, surveyed 41 nuclear utilities and this survey revealed that a hydrostatic test only increases the leakage rate from that of a leakage test run at nominal operating pressure.
That is, no new leakage was identified in any instance by raising the test pressure from operating pressure to hydrostatic pressure.
Therefore, performing a VT-2 examination at nominal operating pressure provides reasonable assurance of system integrity.
ASME Code Case N-498 Revision 1 has been approved by the ASME Boiler & Pressure Vessel Code Committee and the Board on Nuclear Codes and Standards as an acceptable alternative to the rules of the ASME Boiler & Pressure Vessel Code,Section XI.
The burdens imposed by Class 3 hydrostatic.testing (IWD-5223) are as follows:
(1) The system isolation and coordination (required for hydrostatic testing at elevated pressures during a refueling outage) potentially increases critical path time and possible limiting conditions for operation ([LCOs]), as opposed to testing at operating pressure.
(2) System hydrostatic tests frequently require securing relief valves in a closed position or disassembly of check valves to maintain an open flow path which requires time and personnel exposure.
(3) The required time to complete system hydrostatic tests compared to system pressure tests results in a significant increase in the total amount of work force, radiological exposure and radwaste from hydrostatic equipment decontamination without a compensating increase in the level of quality or safety.
-4 2.1.5 Evaluation Information prepared in conjunction with ASME Code Case N-498-1 notes that the system hydrostatic test is not a test of the structural integrity of the system but rather an enhanced leakage test. That this was the original intent is indicated in a paper by S.H. Bush and R.R. Maccary, "Development of In Service Inspection Safety Philosophy for U.S.A. Nuclear Power Plants," ASME, 1971.
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 since piping dead weight, thermal expansion, and seismic loads, which may present a far greater challenge to the structural integrity of a system than fluid pressure, are not part of the loading imposed during a hydrostatic test. Accordingly, hydrostatic pressure testing is primarily regarded as a means to enhance leakage detection during the examination of components under pressure, rather than as a measure to determine the structural integrity of the components.
Duke Power Company requested approval for the implementation of the alternative rules of ASME Section XI Code Case N-498-1, dated May 11, 1994, "Alternative Rules for 10-Year System Hydrostatic Testing for Class 1, 2, and 3 Systems" in lieu of 10-year hydrostatic testing of Class 3 systems. The licensee indicated, in a letter dated May 27, 1992, that they already use N-498, "Alternative Rules for 10-Year System Hydrostatic Testing for Class 1 and 2 Systems" since use of Code Case N-498 for Class 1 and 2 systems was previously approved by the NRC in Regulatory Guide 1.147. The rules for Code Class 1 and 2 in N-498-1 are unchanged from N-498. The staff found N-498 acceptable because the alternative provided adequate assurance and because compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Revision N-498-1 encompasses Class 3 components and specifies requirements for Class 3 that are identical to those for Class 2 components.
In lieu of 10-year hydrostatic pressure testing at or near the end of the 10-year interval, Code Case N-498-1 requires a visual examination (VT-2) be performed in conjunction with a system leakage test in accordance with IWA-5000.
Currently, licensees incur considerable time, radiation dose, and dollar resources carrying out hydrostatic test requirements. A significant amount of effort may be necessary (depending on system, plant configuration, Code class, etc.) to temporarily remove or disable Code safety and/or relief valves to meet test pressure requirements. The safety assurance provided by the enhanced leakage gained from a slight increase in system pressure during a hydrostatic test is offset or negated by the following factors: having to gag or remove Code safety and/or relief valves, placing the system in an off normal state, erecting temporary supports in steam lines, possible extension of refueling outages, and resource requirements to set up testing with special equipment and gages.
-5 Class 3 systems do not normally receive the amount and/or type of Non Destructive Examinations that Class 1 and 2 systems receive. While Class 1 and 2 system failures are relatively uncommon, Class 3 leaks occur more frequently and the failure mode typically differs. Based on the staff's review of Class 3 system failures requiring repair for the last 5 years in Licensee Event Reports and the Nuclear Plant Reliability Data System databases, the most common causes of failures are erosion-corrosion (EC),
microbiologically induced corrosion (MIC), and general corrosion. Licensees generally have programs in place for prevention, detection, and evaluation of EC and MIC. Leakage from general corrosion is readily apparent to inspectors when performing a VT-2 examination during system pressure tests. The industry, including DPC as stated in its letter of June 22, 1994, indicates that experience has demonstrated that leaks are not being discovered as a result of hydrostatic test pressures propagating a preexisting flaw through wall.
Duke Power indicates that leaks in most cases are being found when the system is at normal operating pressure.
Giving consideration to the minimal amount of increased assurance provided by the increased pressure associated with a hydrostatic test versus the pressure for the system leakage test and the hardship associated with performing the ASME Code-required hydrostatic test, the staff finds that compliance with the Section XI hydrostatic testing requirements results in hardship and/or unusual difficulty for the licensee without a compensating increase in the level of quality and safety. Accordingly, the licensee's proposed alternative, use of Code Case N-498-1 for Code Class 3, is authorized for the Oconee Nuclear Station, Unit Nos. 1, 2, and 3, pursuant to 10 CFR 50.55a(a)(3)(ii).
Duke Power Company's alternative is authorized until such time as the Code Case is published in a future revision of Regulatory Guide 1.147. At that time, if the licensee intends to continue to implement this Code Case, the licensee is to follow all provisions in Code Case N-498-1, with limitations issued in Regulatory Guide 1.147, if any.
3.0 CONCLUSION
S The staff evaluated the information provided by the DPC in support of its request for relief. Based on the information submitted, the alternative for hydrostatic testing contained in the licensee's proposal is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) as compliance with the specified hydrostatic testing requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Principal Contributors: K. Battige R. Martin Date:
April 26, 1995