Regulatory Guide 7.12

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(Previously Issued as Drafts Ms 501-4 & DG-7002) Fracture Toughness Criteria of Base Material for Ferritic Steel Shipping Cask Containment Vessels with Wall Thickness Greater than 4 Inches (0.1 M) But Not Exceeding 12 Inches (0.3 M
ML003739424
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Issue date: 06/30/1991
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RG-7.12
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U.S. NUCLEAR REGULATORY COMMISSION

KhUREULATOJRY C03hl

,el OFFICE OF NUCLEAR REGULATORY RESEARCH

SREGULATORY GUIDE 7.12 FRACTURE 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)

(Previously issued as Drafts MS 501-4 and DG-7002)

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 (-29eC)

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)* ferritic steel ship ping cask containment vessel base material with a wall thickness greater than 4 inches (0.1 m) but not greater than 12 inches (0.3 m). The containment ves sel 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 package.

"*Type B(U) and Type (M) packages are defined in § 71.4 of 10 CFR

Part 71.

USNRC REGULATORY GUIDES

Regulatory Guides are issued to describe and make available to the pub lic 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 will 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.

Alternative fracture toughness criteria and test methods may be used provided the applicant can 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 that can be used for evaluating ferritic steel contain ment vessel base material with a wall thickness greater than 4 inches (0.1 m) but not exceeding 12 inches

(0.3 in).

Section III of the American Society of Mechani cal Engineers Boiler and Pressure Vessel Code (ASME B&PVC) (Ref. 1) contains requirements for material fracture toughness. However, these require ments were developed for reactor components only and do not address hypothetical accident conditions appropriate for packaging (e.g., severe-impact loads at low temperatures). Therefore, the ASME B&PVC

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

6. Products

7. Transportation

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 22161.

June 1991 DE

requirements are not directly applicable to shipping container design.

NUREG/CR-3826, "Recommendations for Pro tecting Against Failure by Brittle Fracture in Ferritic Steel Shipping Containers Greater than Four Inches Thick" (Ref. 2), contains background and other in formation pertinent to the development of the criteria in this guide. The criteria studied involved four ap proaches, which are summarized as follows.

1. A fracture arrest criterion based on an expo nential extrapolation of the Pellini fracture toughness reference curve.

2. A fracture arrest criterion based on an asymp totic extrapolation of the Pellini fracture tough ness reference curve.

3. A fracture initiation criterion based on the al lowable flaw sizes specified in Table IWB-3510-1 of Section XI of the ASME

B&PVC (Ref. 3).

4. A drop test acceptance criterion based on the introduction of flaws at critical locations in a full-scale drop test specimen.

For each approach listed above, cost and safety analyses were performed. The results of the cost analyses showed that there is no significant difference in cost impact between the two fracture arrest criteria and the other two criteria. The staff believes that fracture arrest is a more appropriate criterion for ma terial selection for shipping containers because there is a wide variety of stresses that could occur during actual transportation accidents, and because inservice inspection for crack growth is not practical for ship ping containers.

The regulatory position identifies a criterion based on the fracture arrest method for demonstrat ing adequate toughness of containment vessels. The regulatory position was established to ensure that ma terials selected have sufficient toughness to preclude brittle fracture of a through-wall crack at yield strength levels of dynamic stress.

Although the use of ferritic steels is addressed, the guide does not preclude the use of austenitic stainless steels. Since austenitic stainless steels are not susceptible to brittle fracture at temperatures encoun tered in transport, their use in containment vessels is acceptable to the staff and no tests are needed to demonstrate resistance to brittle fracture.

NUREG/CR-3019, "Recommended Welding Cri teria for Use in the Fabrication of Shipping Contain ers for Radioactive Materials" (Ref. 4), and NUREG/

CR--3854, "Fabrication Criteria for Shipping Contain ers" (Ref. 5), also contain information applicable to shipping containers, as does a related Regulatory Guide 7.11, "Fracture Toughness Criteria of Base Material for Ferritic Steel Shipping Cask Contain ment Vessels with a Maximum Wall Thickness of 4 Inches (0.1 in)" (Ref. 6).

C.

REGULATORY POSITION

The criteria outlined below are acceptable to the NRC staff for assessing the fracture toughness of thick-wall base material (nominally over 4 inches (0.1 m), but not exceeding 12 inches (0.3 m)) of ferritic steel containment vessels.

The nil ductility transition temperature (TNDT)

for ferritic steels at a lowest service temperature (LST) of -20'F should be less than the value in Ta ble 1.

Table I

TNDT Criteria for LST = -20'F

Thickness (in.)

TNDT (OF)

4

-123

8

-135

12

-140

Note: Interpolation may be used to determine TNDT

values for different thicknesses.

Ferritic steels should be tested in accordance with ASTM E208-87a, "Standard Method for Conduct ing Drop-Weight Test To Determine Nil-Ductility Transition Temperature of Ferritic Steels" (Ref. 7),

using specimen type P-2 or P-3. Specimen locations should be in accordance with ASTM E 208-87a, paragraph 7.

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.

7.12-2

REFERENCES

1.

ASME Boiler and Pressure Vessel Code,Section III, "Rules for Construction of Nuclear Power Plant Components," American Society of Me chanical Engineers, New York, updated fre quently.

2.

M. W. Schwartz (under Lawrence Livermore National Laboratory contract to the NRC),

"Recommendations for Protecting Against Fail ure by Brittle Fracture in Ferritic Steel Shipping Containers Greater than 4 Inches Thick," U.S.

Nuclear Regulatory Commission, NUREG/

CR-3826,*July 1984.

3.

ASME Boiler and Pressure Vessel Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," American Society of Mechanical Engineers, New York, updated fre quently.

4.

R. E. Monroe, H. H. Woo, and R. G. Sears (un der Lawrence Livermore National Laboratory contract to the NRC), "Recommended Welding Criteria for Use in the Fabrication of Shipping Containers for Radioactive Materials," NUREG/

CR-3019,* U.S. Nuclear Regulatory Commis sion, March 1985.

5.

L. E. Fischer and W. Lai (under Lawrence Livermore National Laboratory contract to the NRC), "Fabrication Criteria for Shipping Con tainers,"

NUREG/CR-3854,*

U.S. Nuclear Regulatory Commission, March 1985.

6.

U.S. Nuclear Regulatory Commission, "Fracture Toughness Criteria of Base Material for Ferritic Steel Shipping Cask Containment Vessels with a Maximum Wall Thickness of 4 Inches (0.1 m),"

Regulatory Guide 7.11, May 1991.

7.

American Society for Testing and Materials, "Stan dard Method for Conducting Drop-Weight Tests To Determine Nil-Ductility Transition Tempera ture of Ferritic Steels," ASTM E208-87a, 1987.

  • Copies may be purchased from the National Technical In formation Service, 5285 Port Royal Road, Springfield, VA

22161.

7.12-3

REGULATORY ANALYSIS

A draft regulatory analysis was published with the draft of this guide when it was published for public com ment (Task DG-7002, July 1989). No changes were nec essary, so a separate regulatory analysis for the final guide has not been prepared. A copy of the draft regula tory analysis is available for inspection or copying for a fee in the Commission's Public Document Room at 2120

L Street NW, Washington, DC, under Task DG-7002.

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7.12-4