ML17332A835
| ML17332A835 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 07/05/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17332A834 | List: |
| References | |
| NUDOCS 9507120122 | |
| Download: ML17332A835 (5) | |
Text
~PR REGS Cy
"+*<<+
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055&4001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION RE UESTS FOR RELIEF FOR INDIANA MICHIGAN POWER COMPANY D.C.
COOK UNITS 1
AND 2 DOCKET NOS. 50-315 AND 50-316
- 1. 0 INTRODUCTION The Technical Specifications for D.
C. Cook, Unit Nos.
1 and 2, state that the inservice inspection (ISI) 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 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).
10 CFR 50.55a(a)(3) states that alternatives to the requireruents 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 ComponenIts,'"'o 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 modificaitions listed therein.
The 1983 Edition, Summer 1983 Addenda, of Section XI is the applicable edition of the ASME Code for the D.
C. Cook, Units 1 and 2, second 10-year 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 te the limitations and modifications listed therein and subject to Commissien approval.
In a letterer dated February 27, 1995, the licensee, Indiana Michigan Power Company (IIPMCo), proposed an alternative examination to the requirements of the ASME Boiler and Pressure
- Code,Section XI.
IMPCo requested approval for 9507120i22 950705 PDR ADQCK 050003i5 P
PDR i
the implementation of the alternative rules of ASME Section XI Code Case N-498-1, dated May ll, 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 1,
2, and 3 systems.
- 2. 0 EVALUATION 2.1 Licensee's Request The licensee's February 27, 1995, letter stated the following request:
Pursuant to the requirements of 10 CFR 50.55a(a)(3)(i),
we request approval to use ASME Section XI Code Case N-498-1, "Alternative Rules for 10-Year System Hydrostatic Testing for Class 1, 2, and 3 Systems" for both Unit 1 and Unit 2.
2.1.1 Licensee's Component Identification Components identified for this relief include Class 1, 2, and 3 systems subject to hydrostatic testing.
- 2. 1.2 ASME Code,Section XI, RequirementsSection XI, Table IWB-2500-1, Category B-P (for Class 1), Table IWC-2500-1, Category C-H (for Class 2),
and Table IWD-2500-1, Categories D-A, D-B, and D-C (for Class
- 3) contain 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 1, 2, and 3
systems.
- 2. 1.4 Licensee's Basis for Relief The licensee's February 27, 1995, letter provided the following basis for use of Code Case N-498-1:
Code Case N-498-1 provides for an alternative to hydrostatic testing which will retain an acceptable level of quality and safety for Class 1, 2, and 3 systems.
Specifically, it allows the use of a system leakage test in lieu of a hydrostatic test.
This code case was approved by the ASME Boiler and Pressure Vessel Code Committee on May ll, 1994, but is not included in the most recent listing of NRC approved code cases in Revision ll of Regulatory Guide 1. 147, "Inservice Inspection Code Case Acceptability ASME Section XI Division 1."
The system hydrostatic test is not a test of the structural integrity of the system.
Rather, it is an enhanced leakage detection test.
Leakage from Class 3 systems is normally the result of erosion/corrosion or joint seal/sealant age deterioration and is readily apparent to inspectors during a
system pressure test.
Industry experience indicates that, in most cases, leaks are found when the system is at normal operating pressure.
- Thus, we consider that the alternate requirements proposed in Code Case N-498-1 constitute a
reasonable, safe alternative to the existing hydrostatic testing requirements.
- 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 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.
IMPCo requested approval for the implementation of the alternative rules of ASME Section XI Code Case N-498-1, dated May ll, 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 1, 2, and 3 systems.
The licensee may 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, Rev.
11.
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 paragraph IWA-5000.
Currently, licensees incur considerable time and radiation dose carrying out hydrostatic test requirements.
A significant amount of effort may be
gV
~
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 are 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.
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 system leaks occur more frequently and the failure mode typically differs.
Based on a 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 (HIC), and general corrosion.
Licensees generally have programs in place for prevention, detection, and evaluation of EC and HIC.
Leakage from general corrosion is readily apparent to inspectors when performing a VT-2 examination during system pressure tests.
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.
Industry experience 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 ASHE 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 1, 2, and 3 systems, is authorized for D.C. Cook, Unit Nos.
1 and 2, pursuant to 10 CFR 50.55a(a)(3)(ii).
IHPCo'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 IHPCo in support of its request for relief and information on system testing and failures which the staff already had.
Based on the staff's analysis, the alternative for hydrostatic testing contained in the licensee's proposal is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for Class 1, 2, and 3 systems 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 Contributor:
C. K. Battige Date:
July 5, 1995
f t