ML19341A157

Fracture Toughness of Steam Generator & Reactor Coolant Pump Supports,Indian Point Unit 3, Technical Evaluation Rept

ML19341A157
Person / Time
Site:	Indian Point
Issue date:	09/30/1980
From:	Allten A, Noell P, Stilwell T FRANKLIN INSTITUTE
To:	Fair J Office of Nuclear Reactor Regulation
References
CON-NRC-03-79-118, CON-NRC-3-79-118 TER-C5257-170, NUDOCS 8101220243
Download: ML19341A157 (18)

Text

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TECHNICAL EVALUATION REPORT FRACTURE TOUGHNESS OF STEAM GENERATOR AND REACTOR COOLANT PUMP SUPPORTS POWER AUTHORITY OF THE STATE OF NEW YORK INDIAN POINT UNIT 3 NRC DOCKET NO. 50-286 NRC TAC NO. 08777 FRC PROJECT C5257 NRC CONTRACT NO. NRC-03-79-118 FRC TASK 170 Preparedby Franklin Research Center Authors: T.C.Stilwell, P.N.Noell, The Parkway at Twentieth Street A.G.Allten, K.E.Dorschu Philadelphia, PA 19103 FRC Group loader: T.c.stilwell Prepared for Nuclear Regulatory Commission Washington, D.C. 20555 Lead NRC Engineer: J. R. Fair sep tember, 1980 This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any a0ency thereof, or any of their employees, makes any warranty, expressed or Implied, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, apparatus, product or process disclosed in this report, or represents that its use by such third party would not infringe privately cwned rights.

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CONTENTS Section Title Page 1

SUMMARY

. . . . . . . . . . . . . 1 2 INTRODUCTION . . . . . . . . . . . . 2 3 BACKGROUND . . . . . . . . . . . . . 3 4 CRITERIA APPLIED IN THE EVALUATION . . . . . . . 5 4.1 Fracture-Toughness Grouping of Materials Used in Support Construction . . . . . . . 5 4.2 Plant Grouping for Fracture-Toughness Ranking of S/G and RCP Support Structures . . . 6 4.3 Criteria for Fracture-Toughness Adequacy of S/G and RCP Supports . . . . . . . . . 6 5 TECHNICAL EVALUATION . . . . . . . . . . 8 5.1 Use of Group I Materials . . . . . . . . 10 5.2 Use of Group II Materials in Thick Sections . . . 11 5.3 Use of other Metals of Problematic Fracture Toughness . . . . . . . . . . . 12 5.4 Lack of Information, Welding . . . . . . . 12 5.5 Comments on the Stress Summary . . . . . . 12 6 CONCLUSIONS . . . . . . . . . . . . 14 TABLE Section Title g 5.1 COMPONENT SUPPORT

SUMMARY

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FRACTURE TOUGHNESS OF STEAM GENERATOR AND REACTOR COOLANT PUMP SUPPORTS

1.

SUMMARY

I Information concerning aspects of the fracture-toughness design of the steam generator (S/G) and reactor coolant pump (RCP) supports for the Indian Point Unit 3 nuclear power station was submitted to the Director of Nuclear Reislation by the Power Authority of the State of New York (PASNY) letter  ;

dsted November 21, 1978. This information was reviewed at the Franklin i Research Center (FRC) and evaluated in accordance with the criteria of the  !

Nuclear Regulatory Commission (NRC) as set forth in NUREG 0577-Draft j (henceforth referred to simply as NUREG 0577).

FRC found that the design of the RCP and S/G supports incorporates structural members ordered to steel specifications classified by NUREG 0577 as Group I (governing products exhibiting relatively poor fracture toughness characteristics). These are:

1. Seamless pipe ordered to the American Society for Testing i and Materials Specification A-53 and used for major members of the RCP support frame and also in the S/G support structure.

2. Nuts ordered to ASTM Specification A-307 and listed by the licensee as one of the materials of construction for principal elements of these structures.

In addition, FRC found that these supports have major structural members l

with thick cross sections ordered to ASTM A-36 and ASTM A-108 Grade 1018. l l

NUREG 0577 assigns a Group II (intermediate fracture toughness ranking) to 1 ASTM A-36 and also to steels comparable to ASTM A-108 Grade 1018. Although ASTM A-108 Grade 1018 is not explicitly ranked by NUREG 0577, it is FRC's judgment that it clearly merits a Group II ranking.

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TER - C5257 - 170 (Interim) l NUREG 0577 provides nil ductility temperature (NDT) screening criteria by I which the fracture toughness suitability of materiala for use in S/G and RCP support structures can be quickly appraised. According to these criteria, use i of the Group II materials in thin structural members is acceptable, but gener-al use in thick members is not sanctioned. Specifically, the questioned appli-cations are: i

1. Thick flanged I-beama of ASTM A-36 steel which are  !

used for the main vertical and cross support members l of the S/G support.

2. Tie rods of 4 3/4-in diameter, made from ASTM A-108 Grade 1018 steel, which provide horizontal restraint to the RCPs.

Finally, some information needed to substantiate fracture-toughness ade- j quacy was not found in the submittal. Additional information relating to

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welding design, procedures, and inspections is required before a definitive judgment of their fracture-toughness adequacy can be rendered.

It may be possible to demonstrate the fracture-toughness adequacy of some or all of the questioned components by other methods. Acceptable alternative methods for such evaluations are discussed in NUREG 0577.

Pending such demonstrations, FRC recommends that a tentative Group I plant classification for fracture toughness of S/G and RCP supports be assigned to Indian Point Unit 3.

2. INTRODUCTION This report provides a technical evaluation of information supplied by PASNY with its letter of November 21, 1978 to the Director of Nuclear Reactor Regulation. The information concerns the fracture-toughness design of support for the S/Gs and RCPs for Indian Point Unit 3. The objective of the evalu-ation is to rank the design for fracture-toughness integrity on a relative scale in accordance with the grouping scheme and criteria established in NUREG 0577.

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The ranking is considered tentative because:

1. It is based solely on review of the information submitted.

2. KUREG 0577 and the criteria it contains had not been developed at the time that the information was requested from the licen-see. Additional, more specific information relevant to the plant grouping may be on hand and might have been submitted had NUREG 0577 been available to provide guidance at the time that the information was solicited. 1

3. BACKGROUND During the course of the NRC licensing review for two pressurized water reactors (PWR), North Anna Units 1 and 2, questions were raised regarding the fracture-toughness adequacy of certain members of the S/G and RCP supports.

The potential for lamellar tearing in,some support members was also questioned.

The staff's concern in the North Anna licensing process was that not enough attention might have been paid to the selection of materials for, and fabrication of, the S/G and RCP supports.

Fracture toughness af a material is a measure of its capability to absorb energy without failure or damage. Generally, a material is considered " tough" when, under stated conditions of stress and temperature, the material can withstand loading to its design limit in the presence of flaws. Toughness also implies that under specified conditions the material has the capability to arrest the growth of a flaw. A lack of adequate toughness (accompanied by the combination of lov operating temperature, presence of flaws, and non-redundancy of critical support members) could result in failure of the support structure under postulated accident conditions, specifically, loss-of-coolant accident (LOCA) and safe shutdown earthquake (SSE).

To address fracture toughness concerns at the North Anna facility, the licensee undertook tests not originally specified and not included in the relevant ASTM specifications. These tests indicated that material used in certain support members has relatively poor fracture toughness at 80 F metal temperature.

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In this case the licens4a agreed to raise (by ancillary electrical heat) the temperature of the S/G support beams in question to a minimum of 225 F every time, throughout the life of the plant, the reactor coolant system (RCS) is pressurized above 1000 psig. The NRC staff found this to be an acceptable resolution.

Because similar materials and designs were used in other plants and be-cause similar problems were therefore possible, this matter was incorporated into the NRC Program for Resolution of Generic Issues as " Generic Technical Activity A-12--Potential for Low Fracture Toughness and Lamellar Tearing on PWR Steam Generator and Reactor Coolant Pump Supports."

Since the original licensing action (North Anna Units 1 and 2) involved only the S/G and RCP supports of PWRs, the staff's initial efforts were di-rected toward examination of the corresponding supports at other PWR facili-ties. However, the staff has kept in mind the possibility of expanding its review to include other support structures in PWR plants and support structures in boiling water reactor (BWR) plants.

The integrity of support embedments was not questioned during the North Anna licensing action, and emphasis was consequently placed on resolving the most immediate generic issue--whether or not problems similar to those un-covered at North Anna exist at other facilities. It was the staff's judgment that inclusion of an evaluation of support embedments in the initial review would require detailed, plant-specific investigations that were beyond the scope of the preliminary, overall generic review. Such considerations were deemed more suited to a subsequent phase when more detailed investigations of individual plants might be undertaken.

Requests for information were sent to licensees in late 1977. Responses to these requests were received during 1978. I l

Sandia Laboratories of Albuquerque, New Mexico, was retained to assist the j staff in the review and analysis of the information received from licensees and applicants. Based on an analysis of the information, the technical scudies made by Sandia Laboratories, and review of the issue by the NRC staff, the NRC developed an NRC staff technical position on these issues. This is y ranklin Research Center A Dusen of The Frankhn kaatute

l TER - CS257 - 170 (Intsrim) presented in NUREG 0577, " Potential for' Low Fracture Toughness and Lamellar Tearing on PWR Steam Generator and Reactor Coolant Pump Supports."

In addition, NUREG 0577 establishes criteria for evaluation of the fracture-toughness adequacy of S/G and RCP supports. NUREG 0577 also applies certain of these criteria to the support structures of a number of PWR plants to achieve plant groupings according to the relative fracture-toughness integrity of these supports. The plant ratings ares e Group I (lowest) e Group II (intermediate) e Group III (highest)

NUREG 0577 also emphasizes the tentative character of these rankings, acknowledging that a number of plants were classified as Group I because licensees had not submitted all the information needed for definitive classification. Therefore, they had not demonstrated that their plant merited a higher ranking. In this regard NUREG 0577 states:

Receipt of such (i.e., currently unsubmitted) information could result in the plants being moved to a lower susceptibility (to brittle failure) g oup after very little additional analysis.

The reply to the NRC Request from Indian Point was received too late for detailed review prior to issuance of NUREG 0577. However, based on infor-mation then available to NRC, a preliminary assessment was made leading to assignment of a plant group ranking in NUREG 0577.

The present evaluation applies the criteria of NUREG 0577 to the infor-mation received concerning the fracture-toughness design of the S/G and RCP supports to provide an independent assessment based upon the evidence sub-mitted.

4. CRITERIA APPLIED IN THE EVALUATION 4.1 FRACTURE-TOUGHNESS GROUPING OF MATERIALS USED IN SUPPORT CONSTRUCTION 4.1.1 Criterion Table 4.6--Material Groups--of Appendix C to NUREG 0577 groups materials according to their relative fracture-toughness as:

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l e Group I (poorest) e Group II (intermediate) e Group III (best) 4.1.2 Interpretation If no supplementary requirements were called out in the material specifi-cation aimed at procuring a product with fracture-toughness properties superi-or to those routinely supplied under the ASTM (or other standard) specification, then the material was grouped in accordance with Table 4.6.

If additional requirements aimed at procuring product fracture-toughness properties' were specified, consideration was given to crediting this specific material order with an improved material-group rating.

4.2 PLANT GROUPING FOR FRACTURE-TOUGHNESS RANKING OF S/C AND RCP SUPPORT STRUCTURES 4.2.1 Criterion Plants are classified on the basis of the construction materials used in the supports after giving consideration to the importance of their location and function within the structure and their consequent importance to support structure integrity. (Refer to pages 5 and 6 of NUREG 0577, Part I.)

4.2.2 Interpretation Plants were assigned a plant-group ranking identical to the material-group ranking of the least fracture-tough material used in the construction, provided this usage is important to support integrity.

4.3 CRITERIA FOR FRACTURE-TOUGHNESS ADEQUACY OF S/G AND RCP SUPPORTS It is the clear intent of NUREG 0577 that licensees demonstrate the fracture-toughness adequacy of the S/G and RCP supports or that they take appropriate corrective measures to assure their fracture-toughness integrity.

NUREG 0577 provides guidance for such demonstrations.

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l TER - C5257 - 170 (Interim) 4.3.1 NDT Criteria for Screening

, 30 4 NDT + 1.30 + or <T 8uPports (4) 60 9 l

where: l l

e NDT is the mean nil ductility transition temperature appropriate j to the material as given by Table 4.4 of Appendix C to NUREG 0577.

e $ is the standard deviation for the data used to determine NDT as listed in Table 4.4.

e Tsupports is the lowest metal temperature that the support member will ever experience throughout the plant life when the plant is in an operational state. In the absence of measured, plant-specific data, Tsupports is taken as 750F.

e The temperature term, 300F or 604, is an allowance for section size (300F for thin sections and 600F for thick sections).

4.3.2 Interpretation If evidence is furnished by the licensee proving that other values of NDT, 8, ort s puts are actually valid for S/G or RCP supports and materials in the licensee's plant, such data may be used. In the absence of acceptable, contrary evidence, values, as stipulated above, are used.

4.3.3 Alternative Criteria NUREG 0577 also recognizes that fracture-tcughness integrity is a complex matter involving a number of interrelated factors, most of which are plant-specific. Consequently, demonstration of compliance with the screening criteria is but one means of providing satisfactory assurance of fracture-toughness adequacy.

NUREG 0577 not only recognizes that other means of showing compliance with the intent of NUREG 0577 are possible, but also offers extensive guidance relating to'several approaches by which such a demonstration may be achieved.

Because of the plant-specific character that such demonstrations must take, NUREG 0577 does not restrict the licensees to any single approach but, p Ubb Franklin Research Center A D6amon of The Frerndm ensatute

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TER - C5257 - 170 (Interim) instead, encourages each licensee to review the fracture-toughness adequacy of his S/G and RCP supports and submit evidence of his findings.

5. TECHNICAL EVALUATION A review has been made of information contained in the response dated November 21, 1978, from PASNY's Mr. Paul J. Early to a request for in-formation, dated October 4, 1977, from Mr. A. Schwencer of the NRC. The request sough.: information concerning the fracture toughness of, and the potential for lamellar tearing in, the S/G and RCP supports. A copy of this request (in generic form) may be found in NUREG 0577, Appendix B. Key items from PASNY's response concerning Indian Point Unit 3 were condensed to tabular form and are presented as Table 5.1.

FRC's review addressed only the fracture-toughness issues. Items found to be of concern are briefly susssarized below. A more expanded discussion of each concern follows this suusary.

Use of Group I Naterials. ASTM A-53 seamless pipe classified by NUREG 0577 as Group I (relatively poor fracture toughness) material is used for major members of the RCP support frame. The stresses reported in some of these members during SSE and LOCA are substantial.

Nuts procured to ASTM A-307 are shown on the materials list provided in response to Item 1 of the NRC's generic letter. No other indication of the function, location, and stresses for these nuts was found. ASTM A-307 exerts little control over the fracture toughness of the products which may be furnished to the specification and is consequently assigned a Group I fracture-toughness ranking by NUREG 0577.

Use of Gwup II Naterials. 1-beams with thick flanges formed from A-36 steel are used as major members of the S/G supports. ASTM A-36 steel is classified by NUREG 0577 as a Group II material. The NDT screening criteria provided by NUREG 0577 show thin section applications of A-36 steels to be acceptable for use in S/G and RCP supports but do not sanction use of A-36 in thick sections.

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Use of Naterials of Problematic Fracture Toughness. The tie rods providing horizontal restraint for the RCPs are 4 3/4-in in diameter and are formed from l ASTM A-108 Grade 1018 steel. FRC recommends a Group II fracture-toughness ranking for this steel. ASTM A-108 Grade 1018 meets the NUREG 0577 screening criteria when used in thin members but fails it when used in thick members.

The tie rods are unquestionably both thick and important to structural in-tegrity.

Insufficient Intornation on Weldim Practices. The information provided with respect to welding design, welding procedures, and inspection methods was deemed insufficient to document their fracture-toughness adequacy or even to permit meaningful independent assessment.

5.1 USE OF GROUP I MATERIALS 5.1.1 Use of ASTM A-53 Seamless pipe ordered to ASTM specification A-53 Grade B is used in tha hot finished condition for major members of the RCP frame structure and also in the S/G supports. This specification provides little control over the fracture-toughness characteristics of the product, and consequently, the material is classified as a Group I (relatively poor fracture toughness) steel by NUREG 0577. ASTM A-53 Grade B also fails to meet the NUREG 0577 NDT screening criteria for use in RCP and S/G support structures.

The licensee also submitted a stress summary showing that the most se-verely stressed member in the A-53 RCP pipe columns will experience stresses of the order of one-half yield strength under upset conditions ar.5 could ex-perience stresses approximately equal to yield strength under postulated faulted loading conditions. Therefore, in this design it appears that a ma-terial of relatively low fracture toughness is used in an application s$ere computed design stresses are substantial. The need for a comprehensive fracture-toughness evaluation is evident.

5.1.2 Use of A-307 Fasteners Ites 1 of the NRC's generic request for information asked the licensee to e

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TER - C5257 - 170 (Interim) provide engineering drawings of all principal elements of the S/G and RCP supports, and to also furnish a listing of materials of construction.

Table 2.1.2 of the licensee's response provides this list of materials.

The table shows ASTM A-307 as a specification to which nuts were procured.

Materials ordered to A-307 are assigned Group I (relatively poor fracture toughness) ranking by NUREG 0577.

No further reference to these nuts was found in the text of the submitted documents, nor could their use be identified from the supplied drawings of the S/G and RCP supports.

Therefore, no judgment can be made concerning how important such nuts may be to the overall structural integrity of the supports. However, inclusion of the nuts on the list of materials accompanying drawings of the principal ele-ments of the S/G and RCP support structures suggests that this usage be re-tained as an open issue to be resolved with the licensee.

5.2 USE OF GROUP II MATERIALS IN THICK SECTIONS Structural shapes of ASTM A-36 steel are used extensively throughout the S/G and RCP support structures.

ASTM A-36 is classified by NUREG 0577 as a Group II material (i.e., one of intermediate fracture toughness). According to the NUREG 0577 NDT screening criteria, use of A-36 in thin sections is acceptable; but its use in support members with thick sections may not be acceptable.

Thick sections are found in the flanges of a number of I-beams used as principal members of both the S/G and RCP supports. Examples of these structural members are I-beams of the following sizes:

e 36 WF 160 e 36 WF 230 e 14 WF 158 Since support members which are thick flanged I-beams formed from A-36 steel do not meet the requirements of the screening criteria given in NUREG gg MU Franklin Research Center A Onasen of The Frankhn insature

TER - C5257 - 170 (Interim) t 0577, the fracture toughness adequacy of such members must be established by l other means. NUREG 0577 provides guidance with respect to acceptable methods for making such evaluations. Documentation of the fracture-toughness adequacy of the thick A-36 members by any one of these methods is necessary before this usage can be dismissed from concern.

5.3 USE OF OTHER METALS OF PROBLEMATIC FRACTURE TOUGHNESS Horizontal restraint of the reactor coolant pumps is provided by tie rods made of ASTM A-108 Grade 1018 steel.

Although this material specification is not explicitly assigned a fracture-toughness ranking by NUREG 0577, companion steels of similar characteristes (e.g., AISI 1017 and AISI 1020) are rated Group II (intermediate fracture toughness). In FRC's judgment, ASTM A-108 Grade 1018 likewise merits a Group II ranking.

As a Group II steel ASTM A-108 Grade 1018 can be expected to meet the NUREG 0577 NDT screening criteria if used in thin sections, and fail these criteria if used in thick sections.

The tie rods are 4 3/4-in in diameter, which is clearly thick-section use. Consequently, the 4 3/4-in ASTM A-108 Grade 1018 tie rods must be regarded as candidates for possibi.e brittle behavior, particularly if they were to experience the dynamic loadings from a LOCA. Therefore, a definitive assessment of the fracture-toughness adequacy of these tie rods is needed.

5.4 LACK OF INFORMATION, WELDING The information submitted with respect to welding practice and inspection was reviewed but found insufficient to permit assessment of the fracture-toughness adequacy of the welding.

5.5 COMMENTS ON THE STRESS

SUMMARY

A computerized stress analysis of the support structures for both the S/G and the RCPs was carried out for normal, upset, and faulted loading conditions.

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Item 2 of the NRC's generic letter to the licensee requested maximum stresses in each principal element of the support structure. The licensee provided tabular data showing the maximum stresses for the most severely stressed ele- l i

ments in each group members of a similar type. This simplification provided ,

useful information for general overall appraisal of fracture-toughness in-tegrity.

The stresses shown for normal loading conditions are everywhere low; for upset conditions, stresses are generally moderate. For the faulted loading condition, which is a major concern in assuring fracture-toughness adequacy, the stresses shown are almost all high as compared to yield strength. With few exceptions, the tabulated stresses under faulted conditions are near or above the elastic limit. This indicates that at least one member of nearly every structural type till be highly stressed under the postulated conditions.

It is not entirely clear from the tabular presentation whether the stresses shown for the faulted loading condition are primary stresses only or whether they represent primary plus-secondary stresses. It is clear, however, that the criteria used for qualification of support members under faulted loading conditions allow members to operate well into the inelastic regime.*

i The support structures have a number of major members manufactured from materials that are not particularly fracture tough (e.g., A-53 seamless pipe, A-36 shapes, A-108 Grade 1018 rods). It appears that certain of these members under faulted conditions will be highly stressed. The possibility that some members of unexceptional fracture toughness may be highly stressed by dynamic load indicates that a detailed assessment of fracture-toughness adequacy is needed.

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l *Part II AISI criteria were used, which permits members to be loaded to their theoretical ultimate strength when stresses are computed using the conser- I vative assumption that material behavior is elastic-perfectly plastic. l i l l

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6. CONCLUSIONS Information received from PASNY relating to the fracture-toughness design of the S/G and RCP pump supports for Indian Point Unit 3 has been reviewed at FRC and evaluated in accordance with the criteria of NUREG 0577.

It was found that the supports include members made of steels ordered to specifications classified by NUREG 0577 as Group I, the fracture toughness of which is relatively poor. In Indian Point Unit 3, such products are ASTM A-53 seamless pipe used as major members of the RCP frame, and ASTM A-307 nuts, which appear on the materials list provided by the licensee for principal structural members. The specific applications for these nuts do not appear to be identified further in the drawings or documents submitted.

In addition, steels ranked (either explicitly or implicitly) by NUREG 0577 as possessing intermediate fracture toughness (Group II materials) were used  ;

in members having thick sections. Such applications occur in the thick flanged I-beams of ASTM A-36 steel used for the main verticals and cross support members of the S/G support and the 4 3/4-in diameter tie rods of ASTM A-108 Grade 1018 steel used to provide horizontal restraint for the RCPs. When the NDT screening criteria of NUREC 0577 are applied to these steels, it is found that the criteria permit their use r: thin S/G and RCP support members but not (without additional qualifications) in thick members.

The information supplied concerning veld designs, welding practices, and wald-inspections was also reviewed but found to bc insufficient to permit fracture-toughness evaluation.

Based upon (1) the use of Group I materials, (2) use of Group II materials in thick sections, and (3) provision of information insufficient to demonstrate the fracture toughness adequacy of welding FRC recommends that a tentative Group I plant ranking for fracture toughness of S/G and RCP supports be assigned to PASNY's Indian Point Unit 3 nuclear power station.

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Further in-depth evaluation of these concerns should be undertaken. It is possible that the fracture-enughness adequacy of some or all of the areas in question can be demonstrated by methods described in NUREG 0577 as acceptable to the NRC.

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