ML20151K722
| ML20151K722 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 07/27/1988 |
| From: | Murphy W VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| FVY-88-62, GL-88-01, GL-88-1, NUDOCS 8808030262 | |
| Download: ML20151K722 (12) | |
Text
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yERMONT YANKEE NUCLEAR POWER CORPORATION FVY 88-62 RD 5. Box 169, Ferry Road, Brattleboro, VT 05301
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v 1671 WORCESTER ROAD F RAMING H AM, M ASSACHUSETTS 01701 TEL E PHOSE 617-672-4100 e
g y gg U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Attn Document Control Desk References a)
License No. DPR-28 (Docket No. 50-271) b)
U5tRC Gener ic Letter 88-01, "tRC Pos i t ion on IGSCC in BLR Austenitic Stainless Steel Pipings" dated 1/25/88 c)
Letter, VYbPC to USBRC, FVY 88-19 "Long-Term Operation With Core Spray Safe End Nozzle Weld Overlayss" dated 3/1/88 d)
Letter > UStRC to VYBPC > NVY 88-80> dated 5/9/88 Dear Siri
Subject:
Vermont Yankee Response to BRC Position on IGSCC in BLR Austenitic Stainless Steel Piping (Generic Letter 88-01)
In accordance with the requirements of the U.S. Nuclear Regulatory Commission, Generic Letter 88-01 [ Reference b)], Vermont Yankee herewith submits information relative to intergranular stress corrosion cracking (IGSCC) mitiga-tion at the Vermont Yankee Nuclear Power Station and our plans relating to piping replacement, inspection, repairs and leakage detection. Vermont Yankee's response to each of the five specific Generic Letter items is provided below.
ITEM 1 Generic Letter 88-01 requested our current plans regarding pipe replacement and/or other measures taken or to be taken to mitigate IGSCC and provide assurance of continued long-term piping integrity and reliability. Vermont Yankee has had an ongoing program of IGSCC mitigation, beginning with replacement of the recirculation bypass line in 1977 and culminating with replacement of the recirculation and residual heat removal systems in 1986.
The attached report: "Evaluation of Vermont Yankee Nuclear Power Station for Comp l i a nce w i th U9RC Pos i t i on on IGSCC i n BLR Aus ten i t i c Sta i n l es s Steel Piping," describes the measures taken to mitigate IGSCC and provide assurance of continued long-term piping integrity and reliability.
ITEM 2 The Generic Letter requests that an 151 Program be implemented at the next refueling outage for austenitic stainless steel piping covered under the l
scope of the letter confirming with the staff positions on inspection sche-dules, methods and personnel > and sample expansion included in this letter.
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VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatorv Commission July 27, 1988 Page 2 All piping systems at Vermont Yankee falling under the requirements of Generic Letter 88-01 are Category A and do not require augmented inspec-tion. With the exception of six specific items, all reactor vessel pressure components and appurtenances at Vermont Yankee meet or exceed LGNRC recuirements for IGSCC mi t igation and qua l i f y for Category A status.
In fact, most welds have "double mitigation" consisting of a resistant material coupled with a stress mitigating measure.
The six items that do not meet Category A status are the two Inconel Alloy 600 core seray safe ends (which contain a non-welded crevice), the two core spray safe end-to nozzle welds (which are weld overlay repaired),
and the two core spray low carbon safe end-to piping systems welds (inconel Alloy 600 welded to Type 316 low carbon stainless steel).
These components are Category D and will be inspected at the next refueling outage using inspection methods and personnel meeting the requirements of the subject Generic Letter.
The requirements for sample expansion are not applicable since the inspection will include 100 percent of the Non-Category A com-ponents.
Ultrasonic examination to detect possible flaws will be conducted using Level 11 and Level III examiners qualified at the EPRI NDE Center to exa-mine weld overlay repairs. Examination techniques are based upon the EPRI weld overlay inspection methodology with modifications and additions empirically demonstrated on the Vermont Yankee weld overlay mockup.
The EPRI overlay In-Service inspection (ISI) methodology relies on detection of crack faces utilizing multiple refracted longitudinal wave probes incident at, or nearly perpendicular to, an oriented, propagating crack face.
Transducer size selection is a function of long range overlay roughness.
Transducer focal length is based on empirical calibration demonstration.
The program implemented at Vermont Yankee is significantly more in depth than the EPRI methodologvi even though Vermont Yankee has determined the inspection of Iconel weld overlays to be somewhat less difficult than stainless steel overlays. Enhanced surface preparation requirements at installation allows Vermont Yankee more latitude in transducer selection.
Transducer size and focal length are selected based upon the parameters determined necessary for proper examination. Each transducer is then demonstrated capable of detecting diffracted signals within its focal range.
Particular attention is paid to the weld overlay - base metal interface.
Examinations of the creviced areas and the safe end-to pipe welds will be similarly addressed.
EPRI cualified examiners will be utilized as appli-cable, with examination techniques developed for inconel mater ials and cre-viced configurations.
Vermont Yankee is in the process of evaluating existing techniques and equipment and uill establish examination methodo-logy as dictated by this evaluation.
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VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatory Commission July 29, 1988 Page 3 IT89 3 The Generic Letter requests licensees to modify their Technical Specifications to include a statement in the section on 151 that the ISI Program for piping covered by the scope of this Generic Letter will be in conformance with the staff's position on schedules methods and personnel, and sample expansion specified in the letter. Vermont Yankee's Technical Specifications related to 151 and IST Program requirements are currently under review by the NRC staff (Proposed Change No. 77).
This license amendment request includes the incorporation of numerous ISI and IST Technical Specification Surveillance Requirements within VY's ISI and IST Programs. Accordingly, Vermont Yankee will address this Generic Letter item as part of the NRC's current review of VY's ISI Program associated with the pending license amendment request.
Therefora, Vermont Yankee herein commits to address this Generic Letter item in a supplemental sub-mittal associated with the existing NRC staff review of Vermont Yankee's ISI Program requirements.
ITEM 4 Generic Letter 88-01 requests confirmation of our plans to ensure that the Technical Specification related to leakase detection will be in conformance with the staff position on leak detection included in the subject letter.
Vermont Yankee believes that our existing Technical Specifications related to leak detection are sufficient and, therefore, do not consider it necessary to alter current Technical Specification leak rate monitoring requirements.
The basis for this determination is that Vermont Yankee's 1GSCC Mitisation Program has ensured that all piping systems at Vermont Yankee under the requirements of the subject Generic Letter are Category A.
At the completion of the Pipe Replacement Program, enhanced leakage detec-tion requirements were removed as they were determined to be no longer necessary. Currently, the only applicable (Category D) components at Vermont Yankee are the two core spray nozzle-to-safe end weld overlays, the two non-welded safe end thermal sleeve crevices and the two Inconel 600 to low carbon stainless steel safe end-to reducer welds.
This is a very small population. Further, there has never been a reported instance of a weld overlay developing a leak, and there has never been a reported instance of un crecived Inconel 600 developins a leak.
Testing reported by the Electric Power Research CEPRI NP-2617, September 1982) demonstrates that un creviced Inconel 600 is immune to IGSCC. Furthers the term "crevice" is not precisely defined.
The design of the core spray safe end thermal sleeve is significantly different than the inlet riser safe end thermal sleeve.
At other facilities which have experienced r evice area IGSCC, that design had 1/8 inch annulus over two feet lors.
The threaded region
VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Resulatory Commission July 27, 1988 Pas] 4 of the safe ends and the safe end-to reducer welds it Vermont Yankee were fully inspected in 1986 (the same inspection that detected the Inconel 182 cracking at the safe end-to nozzle weld) with no evidence of cracking.
In summary, Vermont Yankee considers 100 percent inspection every two cycles of a small population of welds with a low probability of crackins as pro-viding adequate assurance of system integrity without incurring the opera-tional burden of increased leakage monitoring.
ITEM S The Generic Letter requests that we provides in accordance with 1DCFR50.55a(D), our plans to not i f y the NRC of any flaws identified that do not meet IUB-3500 criteria of Section XI of the Code for continued opera-tion without evaluations or a change found in the condition of the welds previously known to be cracked, and our evaluation of the flaws for con-tinued operation and/or our repair plans. As reauired by the Generic Letter, the NRC will be notified if Vermont Yankee detects any flaws that do not meet the criteria of IUB-3500 of ASME,Section XI, for continued operation without evaluation.
This notification will include our eva-luation of the flaws for continued operation or our repair plans, as appropriate.
In addition, Vermont Yankee will notify the NRC of any changes in the condition of welds known to be flawed associated with our Core Spray Safe End-to-Nozzle Weld Overlay Program described in our letter of March in 1988 CReference c)].
NRC approved continued operation with core spray safe end weld overlays on this basis of the program by letter dated May 9, 1988 [ Reference d)].
We trust that this information meets the requirements of the subject Generic Letter. Should you require additional informations please do not hesi-tate to contact us.
Very truly yours VERMONT YAWEE NJCLEAR POWER CORPCRATION
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gm rren P.
y Vice Presi ent and Manager of Opera i
/dm ect UEPRC Res l ona l Adm i n i s trat or, Region I 1R RC Resident inspector, VWPS
VERMONT YANKEE NUCLEAR POWER CORPORATION L
U.S. Nuclear Regulatory Commission July 27, 1988 Page 5 STATE OF VERMONT)
)ss UDOHAN CCW TY )
Then persona l l y appeared bef ore me, Warren P. Murphy, who, being duly sworn, did state that he is Vice Presidat and Manager of Operations of Vermont Yankee Nuclear Pouer Corporation, that he is duly autherized to execute and file the foregoing document in the name and on the behal f cf Vermont Yankee Nuclear Power Corporation and that the statements therein are true to the best of his knowledge and belief.
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Notary Public My Commission Exp[ ires February 10, 1991 1
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EVALUATION OF (ERMONT YAbME f4JCLEAR POLER STATICN FOR CCePLIANCE WITH IRRC POSITION ON IGSCC IN ELR ALSTENITIC STAltLESS STEEL PIPitG (GDERIC Lti itd< ee-01) i i
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93tMY This report documents the status of the Vermont Yankee Nuclear Power Station with respect to compliance with the guidelines contained in USNRC Report, "Technical Report on Material Selection and Processing Guidelines for BWR~
Coolant Pressure Boundary Pipins - Final Reporte" commonly called "NUREG-0313, Revision 2."
This' report was prepared in compliance with USNRC directives contained in Generic Letter 88-01, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Pipings" dated January 25, 1988.
The generic letter applies to all BWR pipins made of austenitic stainless steel that is four inches or larger in nominal diameter and contains reactor coolant at a temperature above 200*F durins power operation, resardless of code classification.
It also applies to reactor vessel attachments and appurtenances such as jet pump instrument penetration assemblies and head spray and vent com-ponents.
With the exception of six items, all of the subject piping and components
-at Vermont Yankee meet or exceed USNRC requirements for IGSCC mitisation and qualify for Catesory A status.
In seneral, all welds have "double mitisation" consistins of a resistant material coupled with a stress mitisating measure.
The six items that do not meet Catescry A status are the two core spray safe ends, which have a non-welded Inconel 600 crevices the two core spray safe end-to nozzle welds: which are weld overtald and the two core spray safe end-to-pipe reducer welds which are inconel 600 base metal welds.
In the followins sections of the report, each reactor vessel nozzle and attached system is evaluated for compliance with blREG-0313, Revision 2.
The reactor pressure vessel is shown in Figure 1.
There are 15 categories of nozzles on the vessel for a total of 36 nozzles.
The nozzles are identified as N1 through N15. Each nozzle is described below and discussed in detall if it falls under the requirements of Generic Letter 88-01.
o N1A and N1B - These two nozzles are the reactor recirculation system outlet nozzles.
They are 28 inch nominal pipe size and are welded to stainless steel safe ends. The safe ends are welded to the recirculation system.
The nozzles are clad with low carbon Type 308 stainless steel weld metal in
k Page 2 i
the non-f urnace-sensi tized condi tion.
The safe end is low carbon Type 316 stainless steelt the wold metal is low carbon Type 3G8 stainless steel.
The cafe end to nozzle weld was stress mitisated using Induction Heating Stress improvement (IHSI). These are Category A weldments.
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o N2A through N2K - These 10 nozzles are the reactor recirculation system inlet nozzles.
The nozzles are clad with non-furnace-sensitized low carbon Type 308 stainless steel weld metal. The safe ends are low carbon Type 316 I
stainless steel; the weld metal is low carbon Type 308 stainicss steel.
The nozzle to safe end weld was IHS1 treated. These are Cate9ery A weld-ments.
o N3A through N3D - These fcur nozzles are the main steam outlet nozzles.
They are manufactured f rom low-alley steel and do not fall under the requirements of Generic Letter 88-01.
o N4A through N40 - These four nozzles are the main feedwater inlet nozzles.
They are manufactured f rom low alloy steel and do not fall under the requirements of Generic Letter 89-01.
o N5A and NSB - These two nozzles are the core spray nozzles. The nozzle to safe end welds are weld overlaid.
The core spray saf e ends are manufac-tured f rom non-furnace-sensitized Inconel Alloy 600. They contain a non-welded mechanical crevice f rom the thermal sleeve (see Figure 2).
The weld between the safe end and pipins system is Inconel 82.
The two welds and the creviced region on each safe end are Category D weldments.
o PEA and N6B - These two nozzles on the reactor pressure vessel top head are clad with non-furnace-sensitized low carbon Type 308 stainless steel. The safe ends are low carbon Type 304 stainless steel. The safe ends are low carbon Type 304 stainless steel. The weld metal is low carbon Type 308 stainless steel. These are Category A weldments.
o N2 - This is the reactor vessel top head vent nozzle.
The nozzle is clad with non-furnace-sensitized low carbon Type 308 stainless steel.
The safe end is low carbon Type 304 stainless steel. The weld meta.' is low carbon Type 308 stainless steel. This is a Category A weldment.
o NSA and NSB - These two nozzles are the Jet pu-- instrument nozzles. The nozzles are clad with non-furnace-sensitized ;ca carbon Type 308 stainless steel. The instrument seal assenblies are low carbon Type 304 stainless steel. The weld metal is low carbon Type 308 stainless steel.
These are Cateserv A weldments.
o N2 - This is the control rod hydraulic return line nozzle.
The nozzle is clad with non-furnace-sensitized low carbon Type 308 weld metal. The hydraulic return line has been rerouted and the nozzle is capped with a Type 316 stainless steel pipe cap clad with low carbon Type 308 stainless steel weld metal.
This is a Cateecrv A weldment.
Enclosure i Page 3 o
N19 - This nozzle is the core delta P nozzle tap and standby liquid control systen injection point.
It is a two-inch nozzle and does not fall under the requirements of Generic Letter 88-01.
I o
N11A and N11B - These two nozzles are the reactor vessel level Instrumen-l tation taps. They are two-inch nozzlet and do not fall under the require-ments of Generic Letter 88-01, o
N12A and N128 - These are the same as N11A and N118.
o N13 and N14 - These two nozzles are one-inch leakage taps for the reactor pressure vessel head 0 rins seals. They do not fall under the requirements of Generic Letter 88-01.
o N15 - This nozzle is the two-inch reactor vessel bottom head drain.
It does not fall under the requirements of Generic Letter 88-01.
Thus, with the exception of the two core spray safe ends and associated welds, the reactor pressure vessel meets the requirements of Generic Letter 88-01 for Category A weldments.
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PIPING SYSTEMS The Reactor Recirculation System and the Core Spray System are the only two piping systems connected to the reactor vessel that fall under the requirements of Generic Letter 88-01.
The Residual Heat Removal System and the Reactor Water Clean"Up System are connected to the Recirculation Systemi portions of these systems also fall under the equirements of Generic Latter 88-01.
o Reactor Recirculation Svstem - All pipins in the Recirculation System is low carbon Type 316 stainless steel. All shop welds were solution annealed and all field welds were IHS1 treated (with the exception of the four-inch bypass line pipins, where the welds were performed using water-backed welding). All shop welds were made using low carbon Type 316 stainless steel weld wire, and the f! eld welds were made usins low carbon Type 308 stainless steel weld wire.
Cast pump and valve bodies were evaluated for carbon and ferrite content and clade if necessary, to ensure an IGSCC resistant weld region.
The entire Reactor Recirculation System is Cate90cv A.
o Epsidual Fkat Pemoval System Same as the Reactor Recirculation System. All stair less steel portions of the Residual Heat Removal System are Cate9ery A.
Enciesure 1 Page 4 o
Core Spray System - The Core Spray System is normally a non-flowing system.
The portion from the reactor pressure vessel to the first isolation valve is low carbon Type 316 stainless steel. The welds are low carbon Type 308 stainless steel. This portion of the Core Spray System is Category A.
Sinc? the system is non-flowins, the temperature will be below 200*F before the first valvei thus, the remaining portion of the system Coes not fall under the requirements of Generic Letter 38-01, o
Reecter Water Clean-Up System - The Reactor Water Clean-Up System piping is low carbon Type i or low carbon Type 316 stainless steel. The welds are low carbon stainlesc steel. Most welds were performed usins water-backet
..e. The Reactor Water Clean-Up System is Catenary A.
Thus, all pipins systems falling under the requirements of Generic Letter 88-01 are Category A.
Slit %RY All piping systems at Vermont Yankee that fall under the scope of Generic Letter 88-01 are Category A and do not requi-e augmented inspection.
All reactur vessel pressure components and appurtenances that fal! under the scope cf Generic Letter 88-01 are Category As ard do not require augmented inspections excret for the two core spray safe ends ar.d associated welds. These components are Category D and will require augmented inspection.
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