ML20006E856

Safety Evaluation Accepting Util Response to Generic Ltr 88-01

ML20006E856
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	02/15/1990
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20006E851	List: ML20006E850 ML20006E856
References
GL-88-01, GL-88-1, NUDOCS 9002260435
Download: ML20006E856 (2)

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NUCLEAR REGULATORY COMMISSION j

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WASHINGTON. D. C. 20666 ENCLOSURE SAFETY. EVALUATION.BY THE 0FFICE OF NUCLEAR. REACTOR REGULATION y

EVALUATION OF NRC. GENERIC. LETTER 88-01. RESPONSE VERMONT. YANKEE NUCLEAR. POWER.C0RPORATION-

-VERMONT. YANKEE. NUCLEAR. POWER. STATION 1

s DOCKET.NOS. 50-271

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1.0 INTRODUCTION

Vermont Yankee Nuclear Power Station, the licensee, subm,tted its-response to NRC' Generic Letter (GL) 88-01, "NRC Position on IGSCC ir. BWR Austenitic Stain-i less Steel Piping" for Vermont Yankee Nuclear Power Station by letter dated July 27,1988, and additional information requested by the staff was provided by letter dated July 25, 1989. GL-88-01 requested Licensees and construction' permit holders to resolve the IGSCC issue for BWR piping made of austenitic stainless steel that is 4 inches or larger in nominal diameter and contains reactor coolant at a temperature above 200 degrees Fahrenheit during power c

-operation regardless of Code classification. The licensee was requested'to address.the following:

1.

The current plans regarding pipe replacement and/or other measures taken to mitigate IGSCC and provide assurance of continued long term integrity.

and re116b111ty.

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The Inservice? Inspection (ISI) Progrom to be implemented at the next refueling outage for austenitic stainless steel piping covered under the scope of this letter that conforms to the staff-positions on inspection schedules, methods and personnel, and sample expansion included in -

GL-88-01.

3.

The Technical Specification change to include a statement in the section on ISI-that the ISI Program for piping covered by the scope of this letter will be in staff positions on schedule, methods and personnel, and

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sdmple expansion included in GL-88-01 (See model BWR Standard Technical SpecificationenclosedinGL-88-01).

It is recognized that the Inservice Inspection and: Testing sections may be removed from the Technical Specifications Improvement programs.

In this case, this requirement shall remain with the ISI section when it is included in an alternative document.

' 9002260435 900215 PDR-ADOCK 05000271 P

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.The conf 1rmation' of your plans; to ensure that the' Technical Specifica-j i

tions related to leakage detection will be in conformance with.the staff, positions on leak detection included in-GL-88-01.

5.

.The plans to notify, the NRC in.accordance with 10 CFR 50.55a(g)'of any flaws identified that do not meet IWB-3500 criteria of Section XI of the.

Code for continued operation without evaluation, or a change found in the q

4 condition of the welds previously known to be cracked and your evaluation.

of the flaws for continuea operation and/or your repair plans.

2.0 OISCUSSION

-The licensee's response to NRC GL-88-01 has been reviewed by the staff with i

the_ assistance of its contractor, Viking S The attached Technical Evaluation Report (TER)ystems International (VSI).

is VSI's evaluation of the' licensee's-response to NRC GL-88-01.

The staff has reviewed the TER and concurs with the

- evaluations, conclusions, and recomendations contained in the TER.

In the-review of the. licensee's.GL-88-01 submittal,' the statf has found the following i

position to be unacceptable: the licensee's position concerning leakage detec-tion as required in GL-88-01, (e.g., Requirements concerning the Conformance l-with Position:C of Regulation Guide 1.45; leakage detection requirement of plant shutdown initiated when in any period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> _ or less, an increase is D

indicated in the rate of unidentified leakage in excess of 2 pm; frequency of monitoring; and operability of: leakage monitoring instruments. For a detail discussion of this item see sections 2.0 ana 3.0 of TER attached to the SE.

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L The staff has re-evaluated the frequency of leakage monitoring. After discus-L sions with several BWR operators the staff concluded that monitoring every four j

hours creates an unnecessary aaministrative hardship to the plant operators.

i Thus, RCS' leakage measurements may be taken every eight hours instead of every l

four hours as required in GL-88-01.

3.0 C0_NCLUSION i

Based on.the review of the licensee's NRC GL-88-01 response the staff concludes that the response as evaluated is acceptable with the exception of the licensee's position as identified above. The licensee is requested to submit'a TS change that would require leakage detection as outlined in 1

GL-88-01.

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The staff also concludes that the proposed IGSCC inspection and mitigation l

l program will provide reasonable assurance of maintaining the long-term structural integrity of austenitic stainless steel piping in the Vermont Yankee Nuclear Power Station.

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TECHNICAL EVALUATION REPORT ON:

ai RESPONSE FROM'THE

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r VERMONT YANKEE NUCLEAR POWER CORPORATION TO GENERIC LETTER 88-01'

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-VERMONT YANKEE NUCLEAR POWER STATION a

Published September, 1989 q

f prepared by Robert C. Bates

.Armand Lakner 5

1 Viking Systems. International 2070 Wm. Pitt Way Pittsburgh, PA Prepared for:

Fit!q U.S. Nuclear Regulatory Commission Washington, D. C. 20555 under Contract No. NRC-03-87-028, Task Order 005

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ABSTRACT

.This report contains an eva uat on of the licensee (Vermont Yankee s

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Nuclear Power Corporation) submittal for the Vermont Yankee Nuclear

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Power Station which was submitted in response to the NRC Generic Letter

' 88-01 in which Vermont Yankee was requested to (1) Furnish their current plans relating to piping replacement and other measures to mitigate IGSCC, inspection, ~ repair,. and leakage detection. (2)-Indicate

'whether they plan to follow the NRC Staff positions, or propose alternative measures. Vermont Yankee's plans are evaluated in Section i

-2'of this report in terms of compliance to NRC Staff positions. Vermont Yankee presented an alternative position to the NRC Staff position concerning leakage measurements which is evaluated in Section 3 of this report.-

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SUMMARY

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7i The Licensee,' Vermont Yankee Nuclear Power Corporation, submitted a f

response _to the NRC Generic Letter 88-01. Vermont Yankee's response-l pertaining to the austenitic stainless s. eel piping in the Vermont-t

, Yankee Nuclear Power Station (a BWR nuclear power' plant) was evaluated in terms of:'(1) Their previous and planned actions to mitigate IGSCC to provide assurance of continued long-term service. -(2) Their Inservice Inspection-(ISI) Program.

(3) Their Technical Specifications 3 pertaining to ISI and their plans to ensure that leakage detection will be in conformance with the NRC Staff position.

(4) Their plans f

to notify the NRC of significant flaws identified (or changes in the condition of the welds previously known-to be cracked) during inspection and evaluation of such flaws.

' Vermont-Yankee endorses 12 of the 13 NRC Staff. positions which are

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. outlined in Generic Letter 88-01, and they proposed an alternative to one (that concerning leakage detection).

~Almost all welds are IGSCC Category A as a result of extensive piping replacement program, and most of those welds were made using HSW or were treated after welding with IHSI. Only six areas (four welds and two crevice areas) are nonresistant, and these are classified as IGSCC T

category D.

No further mitigation treatments are planned.

L Inspection plans conform with the NRC Staff positions on schedules and on methods and personnel; however, Vermont Yankee incorrectly interpreted requirements for sample expansion, and they, therefore,

.do not comply with the NRC Staff position on this item. A change to the. Technical Specification on ISI was promised.

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'k CONTENTS a:-

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' ABSTRACT SUMMARIY ii 1

1. INTRCDUCTION' P

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2. EVALUATION OF RESPONSE TO GENERIC LEITER 88-01 2

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2 2.1 Documents Evaluated p'

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2.2-Review of Vermont Yankee's Responses to' Staff Positions and' Implementation of Those Peettions 3

d' 2.3 Review of Classification of Welds, Previous Mitigating Actions, and Previous Inspections 5

2.3.1 Welds Excluded from Scope of Generic Letter 88-01 5

5-2.3.2 Summary of Mitigating Actions 2.3.3 Summary of IGSCC Classifications 6

a 2.3.4 Summary of Materials and Processes in Piping......

6 2.3.5 Materials and Processes'in Nozzle Assemblies 10 2.3.6 Previous Inspection Program

............., 13 2.3.7 Evaluation of Previous Mitigating 14 i

Actions and Inspections 2.4 Current Plans for Mitigating Actions 15

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2.4.1 Vermont Yankee's Position 15 2.4.2 Evaluation of Conformance to Staff Positions and Recommendation 15 iii

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' 2.5 Plans for Future Inspections:

D-15 2.5.11 Inspection Schedules-r 1

15 2.5.2 Personnel and Methods J

f 17 2.5.3 Sample Expansion 18-A 2.5.'4 Inaccessible Welds................ -..

2.5.5 Evaluation and Recommendations.....:.. ;...... L181 2.6 Changes in the Technical Specification 19-Concerning ISI' 2;6.1. Summary of Vermont Yankee's Position lit j

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2.6.2 Evaluation and Recommendation q

b 1-(L 2.7 Confirmation of Leakage Detection L

20 in the Technical Specification -

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20-2.8 Plans for Notification of the NRC of Flaws 20-2.8.1 Vermont Yankee's Position 1"

21 2.8.2 Evaluation and Recommendation L

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3. ALTERNATIVE POSITION.........................

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..- 22 3.1. Requirements for Leakage Detection 1

y 23 3.2 Vermont Yankee's Position Concerning Leakage Detection 1

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3.3 Evaluation and Recommendation 24

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4. CONCLUSIONS AND RECOMMENDATIONS 27-

5. REFERENCES 1

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1. INTRODUCTION 3

. Inte'rgranular stress ' corrosion cracking (IGSOC) near weldsents in i

F Boiling Water' Reactor (BWR) piping has'been-occurring for almost 20 years. : Substantial efforts in research and development have been sponsored by th's BWR Owners Group for'IGSCC Research, and the.results 4

of this program, along with other related work by vendors, consulting.

' firms and confirmatory research sponsored by the NRC, have permitted

'i 4-the development of NRC Staff positions regarding the IGSCC problems.

The technical basis for NRC Staff positions is detailed in Reference-

-1, and further background is provided in Reference 2.

The results of these research and development programs prompted the NRC to issue Generic Letter 88-01 (see Reference 3) requesting all licensees of.1%CR's and holders of construction permits tos t

i (1) Furnish their current plans relating to piping replacement, inspection, repair, and leakage detection.

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(2) Indicate whether they:

(a) Plan to follow the' staff positions, or (b) Propose alternative measures.

i, Specifically, Generic Letter 88-01 stated that an acceptable licensee i-L

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' response would include the following items:

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(1) Current plans regarding pipe replacement and/or other measures l_

taken or to be taken to mitigate IGSCC and provide assurance of continued long-term piping integrity and reliability.

(2) An' inservice inspection (ISI) program to be implemented at the next refueling outage for austenitic stainless steel piping.

l; (3) A change to the Technical Specifications to include a statement i

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.in the'section on ISI that the inservice' inspection program forpipingvillbeinconformancewiththestaffpositions-

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on schedule, methods and personnel, and sample expansion.

(4) Confirmation of plans to ensure that the -Technical. Specification-l related to' leakage detection will-be'in conformance with the.

L Staff position on leak detection.

(5) Plans to notify the NRC, in accordance with 10CFR50.55a(o),-

I-of any flaws identified that do not meet IWB-3500 criteria of Section-XI of the ASME Code for continued operation without evaluation, or a change found in the condition of the welds j

previously known to be cracked, and an evaluation of the flaws J

T for continued used operation and/or repair plans.

l This report contains a technical evaluation of the response which'.

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~ Vermont Yankee Nuclear Power Corporation (called either Vermont Yankee-or VY in this report) submitted in response to the NRC Generic Letter 88-01 pertaining to the. Vermont Yankee Nuclear Power Station- (hereafter S

called Vermont Yankee).

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4 2.- EVALUATION OF RESPONSE TO GENERIC LET1'ER 88-01 r

This evaluation consisted of a review of the response to NRC Generic Letter 88-01 of January 25, 1988 by Vermont Yankee to determine if their performance and plans are in conformance with the NRC Staff s

positions or if proposed alternatives are acceptable. Prcposed inspection schedules and amendments to the Technical Specification were included in the review..

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2.1 Documents Evaluated Review was conducted on the information pertaining to Vermont Yankee l

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~t provided by the Licensee in the following documents.

(1) " Vermont Yankee Response to NRC Position on'IGSCC in BWR-Austenitic Stailess Steel Piping (Generic Letter.88-01),"

l L Vermont Yankee Nuclear Power Corpo. ration,l License No. DPR-28 7

.(Docket No. 50-271),~P.O.' Box 169, Ferry Road, Brattleboro,-

-VT 05301, July 27, 1988.

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(2) " Vermont Yankee's Response to NRC's Request for Additional-Information: USNRC Generic Letter 88-01," Vermont Yankee.

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, Nuclear Power Corporation, License No. DPR-28 (Docket No.

50-271), 7.0". Box 169, Ferry Road, Brattleboro, VT 05301, i

July 25, 1989.

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Hereafter in this report, these documents will be referred-to j

as Vermont Yankee-Submittals No. 1-and No. 2, respectively, and collectively as the Vermont Yankee Submittals.

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2.2 Review of' Vermont Yankee's Responses to Staff Positions and Implementation of Those Positions.

' Generic Letter 88-01 outlines 13 NRC Staff positions pertaining to (1) materials, (2) processes (3) water chemistry, (4) weld j

overlay, (5) partial replacement, (6) stress improvement of cracked g

weldments, (7) clamping devices, (8) crack evaluation and repair -

criteria, (9) inspection methods and personnel, (10) inspection schedules, (11) sample expansion, (12) leak detection, and (13) li reporting requirements. Generic Letter 88-01 states that the licensee should indicate in their submittal whether they endorse these NRC Staff positions or propose alternative positions. Table 1, which is reproduced from a similar table in Vermont Yankee Submittal No. 2, shows Vermont Yankee's positions on each of these items.

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Table 1-I Summary of Vermont Yankee's Responses to Staff Positions o

VY Has/Will f

VY Accepts NRC Applied Consider for-Staff Position Staff Position In Past Future Use i t l'J Materials

.yes

'yes yes_

j 2.-Processes yes yes

.yes

3. Water Chemistry.

yes.

yes yes

4. Weld' Overlay yes yes yes 4

5.' Partial Replacement yes yes yes 6.' Stress Improvement of Cracked Weldments yes no no

7. Clamping Devices yes no yes

.8. Crack Evaluation and Repair Criteria-yes yes yes

9. Inspection Method and Personnel yes yes.

yes i

.10. Inspection Schedule yes yes yes li

11. Sample Expansion yes yes yes no(a) _

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12. Leak-Detection

13. Reporting Requirements yes yes yes (a) Alternative position proposed. See text for discussion.

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-J Note that Vermont' Yankee indicated acceptance of twelve of'the-13 NRC Staff positions. Note..also that Vermont Yankee-indicated 4

7 that.they have applied most of these items-in the past, and they.

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~will consider application of most of these items in the. future.

Vermont Yankee does not endorse' the NRC Staff position on leakage

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detection, and they have proposed an alternative position on this item which is discussed in Section 3 of this report..

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a 2.3 Review of Classification of Welds. Previous Mitimatina Actions and Previous Inspections N

2.3.1 Welds Excluded from Scope of Generic Letter 88-01 I

e Vermont Yankee Submittal-No. 2 states:

i "As stated in... welds in the Core Spray System outboard.

of the first isolation valve were excluded from the scope of the submittal., The basis for this exclusion is the-f fact thati the Core Spray System is normally a nonflowing L

line. As such, the' temperatures beyond the valve will be less than 200*F."

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L 2.3.2 Summary of Mitigating Actions-1 1 -..

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Extensive piping replacement and mitigating treatments were l'

applied throughout the austenitic piping system in Vermont Yankee during the decade from 1977 to 1986. The result of these programs is that nearly all piping, nozzles, and welds

'in the'austenitic system are composed of resistant materials.

Additionally, other mitigating actions have been applied to most welds, so double mitigation has resulted in those L

welds. The material compositions, IGSCC classifications, 5

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- and mitigating treatments are ' described in greater ' detail-l below.

i jb 2.3.3 Summary'of IGSOC Classifications-r Summaries of the IGSCC' classifications and the materials-

-used in the piping, nozzle assemblies, and welds were provided-3 in Vermont Yankee Submittal No. I as shown in Tables 2 and 3.

Note that all welds in the' piping in the Recirculation-system, Residual Heat Removal system,-Core Spray system,.

and the Reactor Cleanup system are classified as IGSCC-Category A.

Most of the welds in the nozzle assemblies (i.e.,

. nozzle,to safe end welds, safe:end to piping welds. nozzle J

to seal assembly welds.,and nozzle to hydraulic return line welds) are also IGSCC Category A welds.. Exceptions are in NSA and N5B, Uhich contain a total of six IGSCC Category D. welds (actually four welds and two non-welded crevices which'are treated as IGSCC Category D welds).

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4 2.3.4 Summary of Materials and Processes in Piping a

'As stated.in Section 2.3.1 of this report, a portion of the s

3 piping in the Core Spray system operates at a temperature below 200'F, so that-portion of piping is outside of the

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i scope'of Generic Letter 88-01. According to Vermont Yankee Submittal No. 1, the remainder of the Core Spray piping (i.e.,

that between the reactor pressure vessel'and the first-x" isolation valve) as well as the piping in the Recirculation system, the Residual Heat Removal system, the Core Spray System is composed of Type 316L stainless steel.

Ab Vermont Yankee Submittal No. I further states that all shop welds in the Recirculation system and the Residual Heat Removal system were made with Type 316L filler wire, and 6

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^ Summary _ of Materials, Processing, and IGSCC Classifications

' of Welds in Piping Systems at Vermont Yankee i

_,yaterials and Processina IGSOC Categ..

System Piping-Welds-of-Welds

.j Recirc. - A 316L Shop welds - 316L (SHT)

A Field welds - 308L (IHSI)

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Recirc..- B.

316L

-Shop welds - 316L (SHT).

-A Field welds - 308L (HSW)

A RHR 316L iShop welds - 316L (SHT)

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' Field welds - 308L (IHSI)

A CS 316LL

'308L A

RWCU 316L 308L (HSW for most welds)

A Explanation of abbreviations:

Recire. - A Reactor Recirculation System except for four-inch A note in the Vermont Yankee Submittal' bypass line.

states that all cast pump and valve bodies were evaluated.

for~ carbon and ferrite content and' clad, if necessary.

Recire. - B Reactor Recirculation System four-inch bypass line.

RHR Residual Heat Removal System.

CS Core Spray System from the reactor pressure vessel to the first isolation valve. The remainder of the system operates at < 200*F and is outside of the scope of Generic-Letter 88-01.

RWCU Reactor Water Cleanup System.

i SHT Indicates that weld was solution heat treated.

IHSI Indicates that Induction Heating Stress Improvement was applied to weld.

HSW Indicates that the welding process was Heat Sink Welding.

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Summary ~of Materials, Processing, and IGSCC Classifications of Welds in Reactor Pressure Vessel Nozzles at Vermont Yankee r

- Nozzle to Safe-End'And Safe End to Pipina IGSCC.

Nozzle Safe End Weld Material Categ.

Nozzle

' Material-Material' Noz/ Safe End Safe End/ Pipe of Welds i

N1A thru N1B1 Clad-(308L) 316L 308L (IHSI) 308L A

N2A thru N2K Clad (308L) 316L 308L (IHSI)

A

- NSA and NSB not given In 600 Overlayed In 82 D

q A-N6A and N6B: Clad (308L)- 304L 308L A

N7 Clad.(308L) 304L 308L Nozzle to Instrument Seal Assemblies and Nozzle to Hydraulic Return Line IGSCC Nozzle Seal Assb. Hydr. Line Weld Categ.

g Nozzle-Material

' Material Material Material-of Welds L

N8A and:N8B Clad (308L) 304L 306L A.

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304L 308L A

. N9 Clad (308L) i Notes.

L Clad (308L) indicates that nozzle was clad with 308L.

-In 600 and.In 82 indicate Inconel 600 and Inconel 82, respectively.

l IHSI indicates that Induction-Heating Stress Improvement was applied to weld.

NSA and NSB each contain a non-welded mechanical crevice from the thermal sleeve. The two welds and the crevice region on each safe end are classified as IGSCC Category D.

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q those welds were solution heat treated after welding. Field-

- welds in these' systems were made with Type 308L filler wire.

The field l welds in the Recirculation system were stress

. improved after welding using the Induction-Heating Stress Improvement (IHSI) process, and the field welding in the

- Residual Heat Removal system was. performed using Heat Sink k

Welding (HSW).

r Vermont Yankee Submittal No. 1 also describes the weld

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material used:for welds in the piping system. Filler wire used for welds in the Cores Spray system and the Reactor.

l Water Cleanup (RWCU) systems was Type 308L. Most of the

-l welds in the RWCU were made using HSW.

.l Vermont Yankee Submittal No.- 2 elaborates with the following statements pertaining to the piping systems:

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" Reactor Recirculation - All piping in the Recirculation 4

System is low carbon Type 316 stainless steel. All shop l t

welds were solution annealed and all field welds were IHSI treated (with the exception of the four-inch bypass line piping, where the welds were performed using water-b'acked welding). All-shop welds were made using low carbon Type 316 stainless steel weld wire, and:the-field j

welds were made using low carbon Type 308 stainless steel weld wire. Cast pump valve bodies were evaluated for l,

carbon and ferrite content and clad, if necessary, to ensure an IGSCC resistant weld region."

" Residual Heat Removal System - Same as Reactor Recirculation System."

" Core Spray System - The Core Spray Sy. stem is normally a non-flowing system. The portion from the reactor 9

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. pressure vessel to the first isolation valve is low carbon:

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. Type-316' stainless steel. The welds are low' carbon Type

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-308 stainless steel.:'Since the' system is non-flowing, J

J the temperature will beibelow 200*F.before the fir'st valve; thus, the remaining portion of the system'does not fall under the requirements of Generic Letter 88-Ol'."

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" Reactor Water Clean-Up System - The Reactor Water Clean-Up. System. piping is low carbon Type 304 or low carbon 7

L Type 316 stainless steel. The welds are low carbon Type-F 308 stainless steel. Most welds were performed using waterbacked welding."

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2.3.5 Materials and Processes in Nozzle Assemblies

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Ac' cording to. Vermont Yankee Submittal No. 1, the nozzle assemblies identified as NSA and NSB contain nonresistant materials. Although the nozzle to safe end welds were overlaye'd and the' safe end to piping welds were made with O

Inconel 82,-the nozzle material was not identified, and'the safe end material is Inconel 600. These four welds-along with.a non-welded crevice from the thermal sleeve on each e

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' safe end'(for a total of six areas) are Classified as IGSCC Category D welds.

Vermont Yankee Submittal No. 1 states that several of the welds in nozzle assemblies are outside of the scope of Generic

't Letter 88-01 because they are constructed of-carbon steel or they are less than 4-inches in diameter. Concerning the remaining nozzles assemblies: Corrosion resistant cladding (CRC) has been applied to the nozzles, safe ends are made j

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of Type 308L stainless steel, and welds were made with either Type 304L or Type 308L stainless steel. In addition the 10 y

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welds in NIA through N1B and N2A through N2K were stress improsed using IHSI.

The following statements concerning nozzle assembly welds

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are contained in Vermont Yankee Submittal No. 2:

"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 velded to the recirculation system. The nozzles are clad with low carbon Type 308-stainless steel weld metal in the non-furnace-sensitized condition. The safe end is low carbon Type 316 stainless steel; the weld metal is low carbon Type 308 stainless 1:

steel. The safe end to nozzle weld was stress mitigated using Induction Heating Stress Improvement (IHSI)."

"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 stainless steels the weld inetal is low carbon

'l Type 308 stainless steel. The nozzle to safe end weld

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was IHSI treated."

i "N3A throuah N2D - These four nozzles are the main steam outlet n9zzles. They are manufactured from low-alloy steel and do not fall under the requirements of Generic Letter 88-01."

"N4A through N4D - These four nozzles are the main feedwater inlet nozzles. They are manufactured from low-alloy steel and do not fall under the requirements of Generic Letter 88-01."

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"N5A and NSB - These two nozzles are the core spray f

r>zzles. The nozzle.to safe end welds are weld overlaid.

1 The core spray safe ends are manufactured from-non-furnace-sensitized Inconel Alloy 600. They contain j

b a non-welded mechanical crevice from the thermal sleeve.

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... The weld between the safe end and piping system is Inconel 82. The two welds and the creviced region on each safe end are Category D weldsents."

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f "N6A and N6B - These two nozzles on the reactor pressure l

vessel top head are clad with non-furnace-sensitized l

low carbon Type 308 stainless steel. The safe ends are low carbon Type 304 stainless steel. The weld metal f

is low carbon Type 308 stainless steel."

"!J,- This is the reactor vessel top head vent nozzle.

The nozzle is clad with non-fernace-sensitized low carbon I

Type 308 stainless steel. The safe end is low carbon Type 304 stainless steel. The weld metal is low carbon Type 308 stainless steel."

i I

"K8A and N8B - These two nozzles are the jet pump

.f.nstru m n nozzles. The nozzles are clad with non-furnace-sensitized low carbon Type 308 stainless

]

steel. The instrument seal assemblies are low carbon It Type 304 stainless steel. The veld metal is low carbon Type 308 stainless steel."

3 "N9 - This is the control line hydraulic return line t

nozzle. The nozzle is clad with non-furnace-sensitized low carbon Type 308 stainless steel. The hydraulic return line has been rerouted and the nozzle is capped with Type 316 stainless steel pipe cap clad with low carbon 1

12 l

l

Fr i'

I y

Li, Type 308 stainless steel weld metal."

"NIO - This nozzle is the core delta P nozzle tap and l

standby liquid control system injection point. It is a two-inch nozzle and does not fall under the requirements of Generic Letter 88-01."

"N11A and N11B - Tnese nozzles are the reactor vessel ir level instrumentation tape. They are two-inch nozzles and do not fall under the requirementa of Generic Letter 88-01."

"N12A and N12B - These are the same as N11A and N11B."

"N13 and N14 - These nozzles are one-inch leskage tape for the reactor pressure vessel head 0-ring seals. They do not fall under the requirements of Generic Letter 88-01."

"N15 - This nozzle is the two-inch reactor vessel bottom head draiu.

It does not fall under the requirements of Generic Letter 88-01."

l 2.3.6 Previous Inspection Programs j

o j -

Vermant Yankee Submittal No. I did not disclose their previous I

inspection schedules (including inspection of the stress l-l; improved welds) except for stating that the threaded region of the safe ends and the safe end-to-reducer welds were fully l

inspected in 1986 with no evidence of cracking. However, j

l' 4

Vermont Yankee Submittal No. 2, responding to a request j

to list all inspections that were conducted per NUREG l

0313. Revision 2, stated that all six IGSCC Category D welds i

l is I

l

f,..

f were inspected in 1987 and 1989.

b 2.3.7 Evalttation of Previous Mitimatinn Actions and Insoections and Recommendation Extensive summaries of previous mitigating actions were provided which show that piping replacement using resistant materials (per guidelines provided in NUREG 0313. Revision j

2 and Generic Letter 88-01) has been applied at Vermont Yankee so that all welds in'the piping. systems are classified as f

IGSCC Category A welds. In addition all of those welds were either welded using HSV or stress improvement was applied f

after welding. Thus, in Vermont Yankee's IGSCC mitigation

+

program most piping welds within the scope of Generic Letter 8801 have received double mitigation treatments (replacement resistant material plus an additional mitigation process).

In the noszie assemblies, only six welds are IGSCC Category D welds, and the remainder are IGSCC Category A welds.

The six welds that are classified as IGSCC Category D, although composed of corrosion-susceptible materials, have been inspected using methods and personnel that comply with current NRC Staff requirements.

Acceptance of the IGSCC classifications assigned to the welds at Vermont Yankee that are within the scope of Generic Letter 88-01 is recommended.

t 14

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2.4 Current Plans for Mitiaatina Actions 2.4.1 Vermont Yankee's Position No plan for additional mitigation treatments was provided by Vermont Yankee.

2.4.2 Evaluation of Conformance to Staff Positions and Recommendation All welds that are within the scope of Generic Letter 88-01

-have already received some mitigating treatment, and most welds have received double sitigation treatments (i.e.,

replaced with resistant material plus application of either HSW or IHSI) with the result that all welds except those in nozzle assemblies NSA and NSB (in which a total of four welds and two crevices are classified as IGSCC Category D) are IGSCC Category A welds. The welds in NSA and NSB were also mitigated by the application of overlays, and Vermont Yankee noted that their Overlay Program was described to the NRC in a letter dated March 1, 1988 and was approved by the NRC for continued operation in a letter dated May 9, 1988. Thus, acceptance of the Vermont Yankee position is recommended.

2.5 Plans for Future Inspections l

2.5.1 Inspection Schedules Vermont Yankee Submittal No. I contains the following statements:

"All piping systems at Vermont Yankee falling under the i

15 i

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requirements of Generic Letter 88-01 are Category A and.

1 do not require augmented inspection. With the exception of six specific items, all reactor vessel pressure l

components and appurtenances at Vermont Yankes meet or j

[

exceed USNRC requirements for IGSCC niitigation and qualify l

for Category A status. In fact, most welds have ' double r

mitigation' consisting of a resistant material coupled i

with a stress mitigating measure."

l

{'

"The six items that do not meet Category A status are

... Category D and will be inspected at the next refueling I

outage..."

Vermont Yankee Submittal No. 2 states that the six IGSCC i

Category D welds will be inspected every two refueling outages j

with the next inspection scheduled for 1990.

2.5.2 Personnel and Methods

\\

Vermont Yankoe Submittal No. I contains the following statements:

" Ultrasonic examination to detect possible flaws will j

be conducted using Level II and' Level III examiners qualified at the EPRI NDE Center to examine weld overlay

. repairs. Examination techniques are based upon the EPRI weld overlay inspection methodology with modifications and additions empirically demonstrated on the Vermont l

Yankee veld overlay mockup. The EPRI overlay In-Service l

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 16

--.n

E 1

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j i

i selection is a function of long-range overlay roughness.

Transducer focal length is based on empirical calibration demonstration."

j "The program implemented at Vermont Yankee is significantly more in depth than the EPRI methodology, even though Vermont Yankee has-determined the inspection q

of Inconel weld overlays to be somewhat less difficult l

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 f

interface."

" Examinations of creviced areas and the safe end-to-pipe walds will be similarly addressed. EPRI qualified examiners will be utilized as applicable, with examination techniques developed for Inconel materials and creviced configurations. Vermont Yankee is in the process bf evaluating existing techniques and equipment and will establish examination methodology as dictated by this evaluation."

2.5.3 Sample Expansion P

The only statement in Vermont Yankee Submittal pertaining to sample expansion is the following:

"The requirements for sample expansion are not applicable since the inspection vill include 100 percent of the 17 1

'W j,

=1 Non4ategory A components."

2.5.4.Inace.pssible Welds In a reply to a question concerning inacessible welds, Vermont Yankee Submittal No. 2 states:

i "No welds are excluded from the scope of Generic Letter 01~because of accessibility issues."

i In this report, that statement is taken to mean that Vermont Yankee does not have any inaccessible welds that are within I

the scope of Generic Letter 88-01.

2.5.5 Evaluation and Recoa.mendations In this report, the statement quoted in Section 2.5.1 (that IGSCC Category A welds do not require an augmented inspection program is taken to mean that these welds will be inspected according to a schedule similar to that called for in Section XI of the ASME code). This schedule complies with the l

requirements outlined in NUREG 0313, Revision 2.

Vermont Yankee's plans concerning inspection schedules for inspection of IGSCC Category D welds (i.e., 100% inspection every two refueling outages) complies with the NRC Staff position.

I Thus, acceptance of Vermont Yankee's position on inspection schedules is recommended.

Vermont Yankee's position concerning inspection methods and personnel also satisfies the requiremtns of Generic Letter 88-01. Thus, acceptance of this position is recommended.

However, Vermont Yankee has misinterpreted the requirements for sample expansion. Specifically, they have no plan for 18

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t E

l'..

H sample expansion in the event that cracks are found in IGSCC F

Category A welds. This is in contrast to the requirements

]

of Generic Letter which specifically requires sample expansion in the event that cracks are found in IGSCC Category A, B, or C welds. Thus, rejection of Vermont Yankee's position

)

on sample expansion is recommended. It is further recommended

[1 that Vermont Yankee should revise its position on sample j

expansion to include IGSCC Category A welds.

L 2.6 Changes in the Technical Specification Concerning ISI

-1 2.6.1 Summary of Vermont Yankee's Position Vermont Yankee Submittal No. I states the followingt r

" Vermont Yankee's Technical Specifications related to ISI and IST Program requirements are currently under 7

review by the NRC staff (Proposed Change No. 77). This license amendment request includes the incorporation of numerous ISI and IST Technical Specification i

Surveillance Requirements within VY's ISI and IST P m rams. Accordingly, Vermont Yankee will address this Gensric Letter item as part of the NRC's current review l

i of VY's Program associated with the pending license L

l>

amendment request. Therefore, Vermont Yankee herein commits to address this Generic Letter ites in a supplemental submittal associated with the existing NRC l.

b staff review of Vermont Yankee's ISI Program l

requirements."

t l=

2.6.2 Evaluation and Recommendation r

Since Vermont Yankee committed to addressing the changes i.

in Technical Specification concerning ISI in a supplemental L

19

EC

,, ~,,.

-submittal associated with the existing NRC Staff review of l

Vermont Yankee's ISI Program requirements, tentative acce;4ance of the Vermont Yankee position (pending actual fulfillment of that commitment) is recommended.

0 2.7 Confirmation of Leakane Detection in the t

Technical Specification s

Recall from Table 1 that Vermont Yankee proposed an alternative position to the NRC Staff position concerning leakage detection.

f Table 4, constructed from information contained in a sfailar table in Vermont Yankee No. 2, also indicates that alternative positions are proposed for several portions of the NRC Staff position on leakage detectica. Note that Vermont Yankee indicated that their L

Technical Specification complies with the requirement for limiting the total unidentified leakage to 5 gpa and the description (or t

definition) of unidentified leakage. Vermont Yankee proposed an alternative position on the remaining aspects of leakage detection which is discussed in Section 3 of this report.

[

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2.8 Plans for Notification of the NRC of Flaws i

2.8.1 Vermont Yankee's Position Vermont Yankee r]ans to adopt the NRC Staff position on notification. Specifically, the Vermont Yankee Submittal states:

"As required by the Generic Letter, the NRC will be notified if Vermont Yankee detects any flaws that do not meet the criteria of IWB-3500 of ASME,Section II, for continued operation without evaluation. This 20

I s

.e 2

l i

Table 4 Licensee Positions on Leakage Detection {*)

Already TS will be Alternate l

Contained Changed Position i

Position in TS _

to include Proposed

1. Conforms with Position C of no no yes Regulatory Guide 1.45 t

2. Plant shutdown should be initiated when (a) within any period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> no no yes or less, an increase is indicated in the rate of f

unidentified leakage in

. excess of 2 gpe, or F

(b) the total unidentified leakage yes attains s rate of 5 gpa.

3. Leakage monitored at four hour no no yes intervals or less.

L

4. Unidentified leakage includes all yes I

except:

l' (a) leakage into closed systems, l'

or (b) leakage into the containment atmosphere from sources that are located, do not interfere l'

with monitoring systems, or l1 not from throughwall crack.

5. Provisions for shutdown within 24 no no.

yes-hours due to inoperable meesurement' instruments in plants with Category D, E, F, or G welds.

x (a) See text for discussions concerning alternate proposals and other cotaments.

21

Qff f

<e'

. 4._

s notification will include our evaluation of the flaws x

.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..."

2.8.2 Evaluation and Recommendations Since Vermont Yankee plans to comply with the NRC Staff a;

position, acceptance _of their plans for reporting of flaws and evaluation of fisws is recommended. Furthermore, as indicated in Table'1, Vermont Yankee endorses the NRC position concerning crack evaluation and-repair criteria. They further indicated that they will apply this item in the future.

Thus acceptance of Vermont Yankee's position on this item is also recommended.

3. ALTERNATIVE POSITION 3.1, Requirements for Leakane Detection l

l Generic Letter 88-01 requires confirmation that the Techr.ical Specification related to leakage will be in conformance with the NRC Staff position including: (1) Conformance with Position C of Regulatory Guide 1.45. (2) Requirements concerning frequency of sump level monitoring. (3) Requirements concerning excessive unidentified leakage or an excessive increase in unidentified leakage where unidentified leakage is defined in a specific manner.

(4) Requirements for operability of leakage monitoring instruments.

As discussed in Section 2.7, Vermont Yankee's Technical 22 G

y, N

}

,i'c l

t Specification conforms with part of Item (3) including the definition of unidentified leakage. An alternative pocition on the other asp,*ct of leakage detection is presented triow.

3.2 Vermont Yankee's Position Concerninn Leakane Detection

?

The Vermont Yankee Submittal contains the following statement.

" 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 IGSCC Mitigation Program has ensured that all piping systems at Termont Yankee under the requirements of the subject Generic Letter are Category A.

At the completion of the Pipe Replacement Program, enhanced leakage detection 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 I L

-and the two Inconel 600 to low carbon stainless steel safe end-to-reducer velds. This is a very maall population.

Further, there has never been a reported instance of a weld overlay developing a leak, and there has never been a reported E

instance of un-creviced Inconel 600 developing a leak. Testing reported by the Electric Power Research (EPRI NP-2617, September j-1982) demonstrates that un-creviced Inconel 600 is immune to

'~

IGSCC. Further, the term " crevice" is not precisely defined.

L The design of the core spray safe end thermal sleeve is D

significantly different than the inlet riser saf.c end theraci At other facilities which have experienced crevice sleeve.

area IGSCC, that design has 1/8 inch annulus over two feet long. The threaded region of the safe ends and the safe end-23 4

T ' c..s 4

t P

to-reducer velds at Vermont Yankee'were fully inspected'in L

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 e.

every two cycles of a small population of welds with a low l

probability of cracking as providing adequate assurance of system integrity without incurring the operational burden of increased leakage monitoring."

3.3 Evaluation and Recommendation In the development of the requirements in Generic Letter 88-01, the NRC Staff considered the possibility that nearly all of the welds in some plants would be IGSCC Category A welds. Such plants were not exempted from the leakage requirements. Rather the leakage r

requirements were developed for all BWR nuclear power plants.

Thus, rejection of the Vermont Yankee position concerning leakage detection-is recommended.

It is further recommended that the Vermont Yankee Technical Specification should be amended to conform c

with leakage detection requirements as presented in Generic Letter 88-01.

4. CONCLUSIONS AND RECOMHENDATIONS L

t The Vermont Yankee Submittal endorses all except one of the 13 NRC Staff pcsitions. They did not endorse the NRC position on leakage detection. They did indicate that most of the 13 items have been applied in the past and that most items would be considered for

g application in the future.

Nearly all welds at Vrfmont Yankee are correctly classified as IGSCC x:

~-

Category A welds. These classifications result from an extensive program of piping replacement conducted during the decade from 1977 24 N

r

,...o' 1

Y to 1986. All piping material and welds in piping that are within the j

scope of Generic Letter 88-01 contain resistant material (i.e.. Type I

316L stainless steel for piping and Type 316L or Type 308L stainless steel for welds). In addition most welds were either made using heat sink welding or were treated after welding with IHSI.

L Most nozzles that are within the scope of Generic Letter 88-01 have corrosion resistant cladding, most safe ends contain either Type 304L t

or Type $16L, and nozzle-to-safe end welds and safe end-to-piping welds contain Type 308L stainless steel. A total of six creas in two core spray nozzles have been classified as IGSCC Category D.

These include four welds (which contain Inconel 600 base metal and Inconel 82 weld metal) and two non-welded crevice areas. The four welds were overlaid in accordance with a plan presented to and approved by the NRC.

Since such an extensive mitigation program has been completed, no j

mitigation efforts are required at Vermont Yankee, and no plans for such additional treatments was presented. However, inspection plans' have been developed that comply with the NRC Staff positions on schedules and on methods and personnel.

Vermont Yankee har no plans for sample expansion. They stated that none is needed since all six IGSCC Category D welds will be inspected during every second refueling outage and that all other welds are IGSCC Category A.

Evidently, Vermont Yankee has overlooked the requirement for sample expansion of IGSCC Category A welds that is delineated in Generic Letter 88-01.

Vermont Yankee stated that proposed changes to the Technical Specification concerning ISI and IST are currently being reviewed by the NRC. They further stated that the changes in the Technical Specification on ISI required by Generic Letter 88-01 vill be addressed as part of that review. and they committed to addressing that item in a supplemental submittal associated with the existing NRC staff 25 r

V

.9 4'

s

.a t

,- a review of Vermont Yankee's ISI 1 gram requirements.

!1 Vermont Yankee declined to change the Technical Specification concerning leakage..In fact, upon completion of the extensive mitigation program at Vermont Yankee, leakage requirements were deleted from the Technical Specification. Their position is that leakage requirements such as that advocated by the NRC Staff are unnecessary because only all except six IGSCC Category D areas (four welds and two crevices) are IGSCC

. Category A.

This position is not acceptable because the NRC Staff specifically included the leakage requirements in Generic Letter 88-01-(applicable to all BWR nuclear power plants) even though it was likely that nearly all'of the welds in some of those plants would be IGSCC Category A welds.

As a result of this' technical evaluation, the following recommendations are made.

(1) Acceptance of Vermont Yankee's position on plans for mitigating i

actions and their assignments of IGSCC classifications of the welds that are within the scope of Generic Letter 88-01.

(2) Acceptance of Vermont' Yankee's position concerning inspection schedules and concerning inspection methods and personnel.

However, Vermont Yankee's position concerning sample expansion is unacceptable, so revision of that position to comply with f

the NRC Staff position is recommended.

(3) Tentative acceptance of Vermont Yankee's position on changing j

the Technical Specification concerning ISI, pending receipt L

and evaluation of the promised supplemental submittal.

(4) Rejection of Vermont Yankee's position on leakage detection.

Vermont Yankee should amend its Technical Specification on leakage detection to conform with the NRC Staff position as 26

q c.

8 I

it is detailed. in Generic Letter 88-01.

(5) Acceptance of the remaining portions of the Vermont Yankee Submittai.

i i

5. REFERENCES 1

1.

" Technical report on Material Selection and Processing Guidelines i

for BWR Coolant Pressure Boundary Piping," NUREG 0313 Revision 2

U.S. Nuclear Reguistory Commission, Office of Nuclear Reactor Reguistion, January, 1988.

j

~

2.

" Investigation and Evaluation of Stress-Corrosion Cracking in Piping of Light Water Reactor Plants," NUREG 0531, U. S. Nuclear Regulatory I

Commission, February, 1979.

3.

"NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping,"

Generic Letter 88-01, U.S. Nuclear Regulatory Comairsion, January 25, 1988.

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