ML20062M640
| ML20062M640 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 01/03/1994 |
| From: | Tosch K NEW JERSEY, STATE OF |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| RTR-NUREG-0619, RTR-NUREG-619 NUDOCS 9401110048 | |
| Download: ML20062M640 (4) | |
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l State of New Jersey l
Department of Environmental Protection and Energy Division of Environmental Safety, Health and Analytical Programs CN 415 Trenton, NJ 08625@15 Gerald P. Nicholls, Ph.D.
Jeanne M. Fox Dkector-Acting Commissioner
' January 3, 1994 i
U.S.
Nuclear Regulatory Commission ~
Document Control Room Washington, D.C.
20555 Ladies and Gentlemen:
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Subject:
Oyster Creek Nuclear Generating Station (OCNGS) i Docket No. 50-219 Revision to NUREG-0619 Routine Inspection Criteria for Feedwater (FW) and Control Rod Drive Return Line (CRDRL)'
Nozzles By letters dated July 12, 1990- and ' Juh 8,
1992,oGPU. Nuclear Corporation (GPU) submitted-to the.
U.J.,
Nuclear LRegulatory Commission - (NRC) a proposal requesting an! exemption from 'some -
inspection requirements for the aforementioned components.
Specifically, GPU. requested:
(1) to eliminate routine' internal liquid Dye Penetrant ~(PT) examinations (except if flaws. which would J compromise nozzle integrity are known to be pre-existing or have been-detected first via the proposed Phased-Array Ultrasonic test (UT) technique), and utilize'instead UTs-as the ~ primary method to detect, characterize, and-monitor. flaws on these components; the UTs to ' he performed per ASME Boiler and Pressure Code, Section 'XI;.
(2) to only perform UT inspections on those components.once.
each Inservice Inspection (ISI) intervalL(every 10 years) and not longer than ten years.between inspections,-11n conformance with the current requirements of the ASME Code; and (3) to. defer certain' routine PT inspections required $to bes performed during (past). oncoming outages.
The' staff - of ' the New ' Jersey Department ofI Environmental.
Protection & Energy's (NJ DEPE) Bureau.of Nuclear Engineering (BNE).
reviewed twelve pieces of communication that were. exchanged-between :
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the NRC and licensee (GPU)-from January 1990 to June 1993, as'well as several pertinent regulatory documents.
This subject is being studied by the licensee and being evaluated by the NRC for over a decade now.
The BNE review identified the following broad areas of' concern:
(A)
Whether the Automated Phased-Array UT' technique has the capability to reliably detect and.characterizr, thermal fatigue cracks per NUREG-0619 criteria, ior the complex configurations of said systems.
(B)
Whether the Automated Phased-Array UT. examination's are capable of detecting defects that -can grow to; an unacceptable, per ASME Code, size prior to the next routine inspection.
(C)
Whether it' is justifiable to reduce the frequency of oven UT surface examinations'(conducted from the exterior)-to once every ten years, even though the overall conditions that caused the thermal fatigue cracking in the first place (before the - repairs and modifications since 7R) potentially still exist; essentially setting aside some of the recommendations of NUREG-0619, such as'using the-number of startup/ shutdown cycles as-an indicator - to '.-
determine the inspection frequencies.
Based on the information contained'in these communications,.
and~ subsequent clarifications provided by the licensee,'the-BNE staff has evaluated these. issues and has;the following' comments:
Item (A):
The'BNE has no concerns with the conclusion'that-the Automated Phased-Array'UT technique (after incorporating. the '
1992 refinements) has the capability of detecting thermal fatigue cracks of 1 inch in depth.
For the FW nozzle, the NRC intended to limit crack growth to less than 1 inch during 40 years of operation (the licensed life of the plant).
Item (B):
GPU stated that
" reportable" indications (attributed to thermal fatigue) were not detected in any of'the 5 nozzles examined via the Automated Phased-Array UTs during the 14R outage.
However, the possible existence of any other non-thermal.
fatigue-induced indications (via UT inspection during~14R) was not discussed..
The BNE reviewed GPU's conceptual methodology for sizing crack depth propagation and' finds it acceptable.
Briefly, their approach assumes initial fatigue crack depths (0.172 inch' for the FW nozzles and 0.132 inch for the CRDRL nozzle),
with 'these: values representing the minimum detectable notch depth in the' respective mockup systems.
Then, GPU-stated that they have applied linear elastic fracture mechanics methods, per ASME Code,.to assess crack
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growth, and concluded that the cracks of those assumed depths will 1
not grow to a depth greater than those acceptable per ASME Code over a 10-year interval; any cracks of smaller depth than those are inherently represented by the^ assumed crack sizes.
In addition, the thermal fatigue cracks implanted and detected via UT in the GPU mockup were reported to be hairline cracks, compared to the larger actual thermal fatigue cracks originally detected in the FW before the 7R modifications.
Although the BNE has no concerns with the conceptual methodology, our staff has not reviewed all the details of the calculations and assumptions used by GPU in implementing this methodology, and is not in a position to provide meaningful comments on the final crack propagation depths over a 10-year interval, as calculated by GPU.
However, BNE discussed with GPU and clarified the following:
(a)
The UT data allows the ana'/sts to distinguish between thermal fatigue cracus vs "all other indications".
(b)
GPU surface flaws data do not suggest that thermal fatigue cracks are more likely to be initiated at locations where these "other indications" are present.
(c)
If any of these "other indications" has any " depth'.
initially or developed subsequently, such surface flaws are monitored as cracks.
Item (C):
Accepting that the crack depth propagations predicted by GPU's fracture mechanics analysis, based on ASME Code, Appendix XI, are representative of potential actual
- cracks, (a)
The BNE suggests that there should be a well-defined monitoring and maintenance program to ensure that the auxiliary components (which helped mitigate the earlier thermal cycling conditions in the FW nozzles) will maintain their effectiveness over a 10-year interval.
(b)
The BNE raised the question relating to the presence and frequency of occurrences of '" challenges" (not necessarily associated with startup/ shutdown. cycles) potentially contributing to crack initiation / propagation, and on how will these " challenges" impact on the need for more frequent UTs or other associated inspections.
Such
" challenges" may include, but not limited to, vibrations from various sources, or water hammers.
GPU's response was that conditions to ind6ce water hammers are not likely, and any vibrations are expected to be very minor contributors to the propagation of any potential cracks.
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-(c)
Also, the BNE raised..the questiion.i of whether thet "once in 10 years" inspection schedule will remain-fixed or will the frequency of the proposed.; UT. inspections ;
still be dictated. by a predetermined number-of future
' transients events (per NUREG-0619l or.f other ' inspection f}
requirements), and in this:latter-case what will'be this target number.
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GPU's response expressed confidence that the operation of q
the plant is not; expected to result ~ in the number' of-4' startup/ shutdown cycles (90 such cycles /within a 10-year-period or even during the; remaining life 'of the plant) ttoi necessitate PT inspections according.to.the NUREG-0619 schedule.
GPU re-iterated.- that the FW nozzle thermal'~
cracking issue'has been' resolved.
The BNE staff is available to participate 1and wishes to' be-included-in discussions relating to.this issue.
If you have any questions, please contact ~ Suren Singh' at (609) 987-2039, or Ariadni Kapsalopoulou at (609)2987-2052.
Sincerely,.
b/
Kent Tosch,. Manager Bureau-'of Nuclear Engineering.
c:
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Lipoti, Assistant Director RPP -- NJ DEPE' M. Miller, State Liaison, Region I -- US NRC' A. Dromerick, Senior Project Manager 6-- US NRC L. Briggs,-Senior Resident' Inspector,0CNGS - 'US NRC' M. Laggart, Licensing Manager -- GPU' l
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