Regulatory Guide 7.11

Fracture Toughness Criteria of Base Material for Ferritic Steel Shipping Cask Containment Vessels with Maximum Wall Thickness of 4 Inches (0.1 M)

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U.S. NUCLEAR REGULATORY COMMISSION

R E GUlaTORY

June 1991 GUIDE

OFFICE OF NUCLEAR REGULATORY RESEARCH

REGULATORY GUIDE 7.11 FRACTURE TOUGHNESS CRITERIA OF BASE MATERIAL

FOR FERRITIC STEEL SHIPPING CASK CONTAINMENT

VESSELS WITH A MAXIMUM WALL THICKNESS OF 4 INCHES (0.1 m)

(Previously issued as Drafts MS 144-4 and DG-7001)

A.

INTRODUCTION

Part 71, "Packaging and Transportation of Ra dioactive Material," of Title 10 of the Code of Fed eral Regulations requires that packages used to trans port radioactive materials withstand the conditions in

§ 71.71, "Normal Conditions of Transport," and

§ 71.73, "Hypothetical Accident Conditions."

In this guide, the terms packaging, shipping cask, and shipping container are used interchangeably.

The regulations require that accident conditions with an initial temperature as low as -20'F (-29°C)

be considered. At this temperature, several types of ferritic steels are brittle and subject to fracture. This guide describes fracture toughness criteria and test methods acceptable to the NRC staff for use in evalu ating Type B (U) and Type B (M)l ferritic steel ship ping cask containment vessel base material having a maximum thickness of 4 inches (0.1 m) and having a maximum static yield strength of 100 ksi (690 kPa).

The containment vessel is a major component of the containment system as defined in § 71.4 of 10 CFR

Part 71. This guide is applicable to the containment vessel only and not to other components of the pack age.

Alternative fracture toughness criteria and test methods may be used provided the applicant can

,'Type B(U) and Type B(M) packages are defined in 10 CFR 71.4.

USNRC REGULATORY GUIDES

Regulatory Guides are issued to describe and make available to the pub lie methods acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate techniques used by the staff in evaluating specific problems or postulated accidents, or to pro vide guidance to applicants. Regulatory Guides are not substitutes for regulations, and compliance with them Is not required. Methods and solutions different from those set out in the guides wilf be acceptable if.

they provide a basis for the findings requisite to the issuance or continu ance of a permit or license by the Commission.

This guide was Issued after consideration of comments received from the public, Comments and suggestions for improvements In these guides are encouraged at all times, and guides will be revised, as ap propriate, to accommodate comments and to reflect new Information or experience.

Written comments may be submitted to the Regulatory Publications Branch, DFIPS, ADM, U.S. Nuclear Regulatory Commission, Washing ton, DC 20555.

demonstrate that their use will ensure equivalent safety.

Any information collection activities mentioned in this regulatory guide are contained as requirements in 10 CFR Part 71, which provides the regulatory ba sis for this guide. The information collection require ments in 10 CFR Part 71 have been cleared under OMB Clearance No. 3150-0008.

B.

DISCUSSION

This guide presents fracture toughness criteria and test methods that can be used for evaluating ferritic steel containment vessel base material having a maximum wall thickness of 4 inches (0.1 m) with a maximum static yield strength of 100 ksi (690 kPa).

Section III of the ASME Boiler and Pressure Vessel Code (Ref. 1) contains requirements for mate rial fracture toughness; however, these requirements were developed for reactor components only and do not address hypothetical accident conditions appro priate for packaging (e.g., severe impact loads at low temperatures). Therefore, the code requirements are not directly applicable to shipping container design.

NUREG/CR-1815, "Recommendations for Pro tecting Against Failure by Brittle Fracture in Ferritic Steel Shipping Containers up to Four Inches Thick"

(Ref. 2), contains background and other information The guides are issued in the following ten broad divisions:

1. Power Reactors

2. Research and Test Reactors

3. Fuels and Materials Facilities

4. Environmental and Siting

5. Materials and Plant Protection

8. Occupational Health

9. Antitrust and Financial Review

10. General Copies of issued guides may be purchased from the Government Printing Office at the current GPO price. Information on current GPO prices may be obtained by contacting the Superintendent of Documents, U.S.

Government Printing Office, Post Office Box 37082, Washington, DC

20013-7082, telephone (202)275-2060 or (202)275-2171, Issued guides may also be purchased from the National Technical Infor mation Service on a standing order basis. Details on this service may be obtained by writing NTIS, 5285 Port Royal Road, Springfield, VA 22,161.

pertinent to the development of the criteria in this guide. These criteria are divided into three categories that are associated with the levels of safety appropri ate for the radioactive contents being transported.

Table 1 in this guide identifies the radioactivity limits for each of the three categories. Tables 4, 5, and 6 in NUREG/CR-18152 (reproduced along with Table 3 in the Appendix to this guide) list the fracture tough ness criteria associated with each category. A qualita tive description of the margins of safety against brittle failure for each of the three categories is given in Ap pendix C to NUREG/CR-1815 (Ref. 2).

Additional information regarding the basis for the criteria is contained in Appendix B of NUREG/

CR-1815 (Ref. 2).

Regulatory Position 1 endorses a portion of the criteria contained in Section 5 of NUREG/CR-1815.

These criteria identify material properties in accor dance with the standards specified in Tables 4, 5, and

6 of NUREG/CR-1815, as appropriate.

For Category II and III containers, the highest nil ductility transition temperature (TNDT)

specified for the material in Table 3 of NUREG/CR-1815 (repro duced in the Appendix to this guide) may be used in lieu of conducting tests to determine the actual TNDT of the material.

Table 1 Category I

Category II

Category III

Low Greater than Less than Specific

30,000 Ci or

30,000 Ci Activity greater than and less than

3,000 A,* or

3,000 A,

greater than and less than

3,000 A,-

3,000 A,

Special Greater than Between Less than Form

3,000 A,

3,000 A, and

30 A, and or greater than 30 A, and not less than

30,000 Ci greater than

30,000 Ci

30,000 Ci Normal Greater than Between Less than Form

3,000 A2

3,000 A2 and

30 A2 or greater than 30 A2 and not and less than

30,000 Ci greater than

30,000 Ci

30,000 Ci

• Defined in 10 CFR 71.4 Although NUREG/CR-1815 (Ref. 2) addresses the use of ferritic steels only, it does not preclude the Mrhe following corrections should be made to the NUREG: Table 1, Category III revise to read "...Fine Grain Practice..."; Table 4, Crite ria .... third line "has ays a 70 ksi, either."; Figure 6, vertical scale should be "...0, 20, 40..."; Section 5.3.1, subsection 1, "By se lecting a normalized steel ...."

use of austenitic stainless steels. Since austenitic stain less steels are not susceptible to brittle failure at tem peratures encountered in transport, their use in con tainment vessels is acceptable to the staff and no tests are needed to demonstrate resistance to brittle fail ure.

NUREG/CR-3019, "Recommended Welding Cri teria for Use in the Fabrication of Shipping Contain ers for Radioactive Materials" (Ref. 3), and NUREG/

CR-3854, "Fabrication Criteria for Shipping Contain ers" (Ref. 4), also contain information applicable to shipping containers, as does a related Regulatory Guide 7.12, "Fracture Toughness Criteria of Base Material for Ferritic Steel Shipping Cask Contain ment Vessels with a Wall Thickness Greater than 4 Inches (0.1 m) But Not Exceeding 12 Inches (0.3 m)" (Ref. 5).

C. REGULATORY POSITION

1. The criteria contained in Section

5 of NUREG/CR-1815 (Ref. 2), other than for full-scale destructive testing (5.1.4 and 5.2.4) and qualifying procedures for reduced stress levels (5.1.2), are ac ceptable to the NRC staff for assessing the fracture toughness of thin-wall base material (up to and in cluding 4 inches (0.1 m)) ferritic steel containment vessels for the categories identified in Table 1 of this guide. In 5.1.2, only a value of a/Uyd equal to I is acceptable.

2. A Category I container qualified in accor dance with this guide is acceptable for transporting either Category II or Category III radioactive materi als. Similarly, a Category II container qualified in ac cordance with this guide is acceptable for transporting Category III materials.

D. IMPLEMENTATION

The purpose of this section is to provide informa tion to applicants and licensees regarding the NRC

staff's plans for using this regulatory guide.

Except in those cases in which an applicant or licensee proposes an acceptable alternative method for complying with specified portions of the Commis sion's regulations, the methods described in this guide (which reflects public comments) will be used by the NRC staff in evaluating base material for all applica tions for new package designs and all requests that existing package designs be designated as Type B(U)

or Type B(M) packages submitted after Septem ber 30, 1991.

7.11-2

REFERENCES

1. ASME Boiler and Pressure Vessel Code, Sec tion III, "Rules for Construction of Nuclear Power Plant Components," American Society of Mechanical Engineers, New York, updated frequently.

2. W. R. Holman and R. T. Langland (under Lawrence Livermore National Laboratory contract to the NRC), "Recommendations for Protecting Against Failure by Brittle Fracture in Ferritic Steel Shipping Containers Up to Four Inches Thick," U.S. Nuclear Regulatory Commission, NUREG/CR-1815, *August

1981.

3. R. E. Monroe, H. H. Woo, and R. G. Sears (under Lawrence Livermore National Laboratory contract to the NRC), "Recommended Welding Cri teria for Use in the Fabrication of Shipping Contain- ers for Radioactive Materials," NUREG/CR-3019,*

U.S. Nuclear Regulatory Commission, March 1985.

4. L. E. Fischer and W. Lai (under Lawrence Livermore National Laboratory contract to the NRC),

"Fabrication Criteria for Shipping Containers,"

NUREG/CR-3854,* U.S. Nuclear Regulatory Com mission, March 1985.

5. U.S. Nuclear Regulatory Commission, "Frac ture Toughness Criteria of Base Material for Ferritic Steel Shipping Cask Containment Vessels with a Wall Thickness Greater Than 4 Inches (0.1 m) But Not Exceeding 12 Inches (0.3 m)," Regulatory Guide

7.12,* May 1991.

• Copies may be purchased from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161.

7.11-3

APPENDIX

Tables 3 through 6 from NUREG/CR-1815, "Recommendations for Protecting Against Failure by Brittle Fracture in Ferritic Steel Shipping Containers Up to Four Inches Thick," are reproduced here for the reader's convenience.

TABLE 3.

NDT temperatures for steel plates.

NDT

Group Thickness temperature ASTM

Group treatment (in.)

range (*F)

specification I. PEARLITIC:

Low and intermediate strength steels (oys = 30 to 70 ksi)

A As rolled

0.625 to 3

0 to 70

A36, A516, A709,

3 to 4

20 to 90

A442, A662 B Normalized (fine

0.625 to 3

-50 to 10

A516, A442, A662, grain practice)

3 to 4

-30 to 30

A709 C Normalized (high

0.625 to 3

-70 to -10

A441, A537, C.I 1, strength, low alloy)

3 to 4

-50 to 10

A533, A588, A736

11. MARTENSITIC AND BAINITIC: High strength steels (47y3 = 80 to 120 ksi)

D Quenched and tempered

0.625 to 4a

-90 to -30b A514, A517 (low alloy)

E Quenched and tempered

0.625 to 4

-160 to -80b HY-80, HY-100,

(high alloy)

A-508-CL 4 & 5, A543 Ill. CRYOGENIC STEELS:

(ays = 37 to 120 ksl at room temperature)

F See ASTM specifications

0.625 to 4

<-70OFc A203 G See ASTM

0.625 to 4

<-100Fc A353, A553, A645 aMaximum thickness depends on hardenability.

bManufacturer must certify that the NDT temperature Is within this range.

CThese steels are special cases. Each product should be tested by the DT test to determine the NDT temperature.

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TABLE 4.

Category I fracture toughness requirements and criteria for ferritic steels with yield strength no greater than 100 ksi.

Required degree Safet*y Very large margin of safety.

(-e Appeadh C)

Reqrueed amevnt of fracture toughme Sufficient to arrest large cracks under dynamic loading; gemeral (see Sec. 5.1)

yielding will precede fracture.

Thicknke (B)

(I-.)

Criteria for meeting toughness requirementsa

0.625 to 40

• NDT temeratureb must be iss than a maximum value.

See FIg. 3, and Secs. 5.1.1 and 5.1.2.

Additlonally, if the steel has y < 70 ksl, either: *

0 5/9 in. thick DTr mast be greater than 400 ft-4b at upper shelf temperatures.

See Sec. S.I.I.

Or

• CVd mist be greater than 45 ftl.b at upper sbelf temperatures.

See See. 5.1.1.

0.19 to 0.625

• Use DT Test E-604-80. 80% or greater shear fracture appearsace required at LST.

See See. 5.1.3.

Or

"me DWTT Test E.-436 80% or greater Asear fracture appearance required at LST.

See Sec. 5.1.3.

0.025 to 0.19

• Use Notc Tensile Teat E-33&

Notch temnlle strength

> 1.0 at ISr.

YW strenogth see sec 5.13.

aFgnl scale destructive tesding a

case-by-case basis may be weed as an alternate to requirements listed below. See Sec. 5.1.4.

bNDT Is mea*lred according to ASTM E-208, or an equivalext NDT cam be establisbed by subtracting 50*F from the midpoint of the

5/1 hi. DT eegy transition crve measured accordiag to ASTM E-604.

CDT measured according to ASTM E-604.

dcv measured according to ASTM E-23.

• Editor's Note: This line should read, "Additionally, if the steel has orys Ž

70 ksi, either:" to cor rect a typographical error.

7.11-5

TABLE 5.

Category II fracture toughness requirements and criteria for ferritic steels with yield strength no greater than 100 ksi.

Required degree *I safety Large margin of safety.

(see Appendix C)

Required amount of fracture toughness Sufficient to prevent fracture Initiation of cracks under dynamic (see Sec. 5.2)

loading.

Thickness (B)

(in.)

Criteria for meeting toughness requirementsa

0.625 to 4.0

• With full dynamic loading rates, NDT temperatureb must be less than a maximum value.

See Fig. 6 and Sec. 5.2.1.

• With reduced loading rates, NDT temperature can be determined from Fig. 7.

See Sec. 5.2.2.

0.19 to 0.625

" Use DT Test E-644-80. 50% or greater shear fracture appearance required at LST.

See Sec. 5.2.3.

Or

"0

Use DWTT Test E-436. 50% or greater shear fracture appearance required at LST.

See Sec. 5.2.3.

Or

• Use any normalized steel made to "Fine Grain Practice" or betterc.

See Sec. 5.2.3.

Less than 0.19

• No requirements wben B is less than 0.19 in.

See See. 5.2.3.

aFliI scale destructive testing on a case-by-case basis may be used as an alternate to requirements listed below. See Sec. 5.2.4.

bNDT is measured according to ASTM E-208, or an equivalent NDT can be established by subtracting 50*F from the midpoint of the

5/8 In. DT energy transition curve measured according to ASTM E-604 or the NDT temperature requirement can be met by selecting the maximum NDT temperature given in Fig. 1 or Table 3.

cSteei with an NDT temperature lower than steels made to a fine grain practice.

7.11-6

TABLE 6. Category III fracture toughness requirements and criteria for ferrtitc steels with yield strength no greater than 100 ksi.

Required degree of safety Adequate margin of safety.

(we Appendix C)

Required amouet of fracture toughness Sufficient to prevent fracture Initiation at minor defects typical of (see Sec. 5)

good fabrication practices.

Thickoess (3)

(I1.)

Criteria for meetlig toghnmess requremets

0.4 to 4.0

• Without testing, ue any normalized steel made to "Fine Grain Prctice" or bettera.

See Sec. 5.3.1.

Or

• Show that NDTh 4 10-F (B ; 0.625 in.).

Or

• Test to show that DTc > 50 ft-lb at 10*F, with test specimen 0.625 in. thick.

Or

• Test to show that CVd > 15 ft-lb at 10*.

Or

• Without testing, use as-rolled steel, provided the welds have been stress relieved and inspected by nondestructive evaluation techniques.

Less than 0.4

• No requirements when B is less than 0.4 in.

See Sec. 5.3.2.

aStee with an NDT temperature lower than steels made to a fine grain practice.

bNDT Is measured according to ASTM F,208, or an equivalent NDT can be established by subtracting 50*F from the midpoint of the

5/8 in. DT energy transition curve measured according to ASTM E-604 or the NDT temperature requirement can be met by selecting the maximum NDT temperature given in Fig. I or Table 3.

CDT measured according to ASTM E-604, for specimen thickness of 0.625 in.

dcv measured according to ASTM &-23.

7.11-7

VALUE/IMPACT STATEMENT

A draft value/impact statement was published with the draft of this guide when it was published for public comment (Task DG-7001, July 1989). No changes were necessary, so a separate value/impact statement for the final guide has not been prepared.

A copy of the draft value/impact statement is avail able for inspection or copying for a fee in the Com mission's Public Document Room at 2120 L Street NW, Washington, DC, under DG-7001.

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7.11-8