ML20199L670

for Comment Issue of Draft Reg Guide,Task Ms 501-4, Fracture Toughness Criteria for Ferritic Steel Shipping Containers W/Wall Thickness Greater than Four Inches (0.1m)

ML20199L670
Person / Time
Issue date:	06/30/1986
From:	NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:
References
RTR-REGGD-7.012, TASK-MS-501-4, TASK-RE REGGD-07.XXX, REGGD-7.XXX, NUDOCS 8607090545
Download: ML20199L670 (8)

Text

PD6 June 1986

[e aeg'o U.S. NUCLEAR REGULATORY COMMISSION Division 7

!" {n 0FFICE OF NUCLEAR REGULATORY RESEARCH Task MS 501-4 9 *****

/ DRAFT REGULATORY GUIDE AND VALUE/ IMPACT STATEMENT

Contact:

H. Graves (301)443-7709 FRACTURE TOUGHNESS CRITERIA FOR FERRITIC STEEL SHIPPING CONTAINERS WITH A WALL THICKNESS GREATER THAN FOUR INCHES (0.1 m)

A. INTRODUCTION ,

Part 71, " Packaging and Transportation of Radioactive Mat [ rial," of Title 10 of the Code of Federal Regulations requires that, packages'used to transport radioactive materials withstand the conditions in S 71.717" Normal Conditions of Transport," and S 71.73, " Hypothetical Accident Conditions." The regulations require that accident conditions with an initiai 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 acceptable to the NRC staff fo'r use in evaluating Type B(U) and N Type B(M)1 ferritic steel shipping cask containment vessels with a wall thick-Kj ness greater than 4 inches (0.1 m).' The guide is applicable to the containment vessel only and not to other components of the package.

Other fracture toughness criteria may be used provided the applicant can s

demonstrate that their use will~ ensure equivalent safety.

Any information collection activities mentioned in this draft regulatory guide are contained asp requirements in 10 CFR Part 71, which provides the regulatory basis for this' guide. The.information collection requirements in 10 CFR Part 71 have.been' cleared under OMB Clearance No. 3150-0008.

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', 8607090545 860630 PDR REGGD 07.XXX R PDR ,

tType B(U) and Type 8(M) are defined in S 71.4 of 10 CFR Part 71.

Yhts regulatory guide and the associated value/ impact statement are being issued in draf t form to involve the pubite in the early states of the development of a regulatory position in this area. They have not received complete staff review and do not represent an official MRC staff position.

rublic Cossaents are being solteited on both draf ts, the guide (including any implementation schedule) and the value/ impact

'~~' s statement. Consaents og the value/ impact statement should be accompanied by supporting data, written co.imaents may be sutattted to the Rules and Procedures Branch. ORR. A0ft. U.S. Nuclear Regulatory Comission. Washington. OC 20555. Convaents

/ may also be delivered to Room 4000. 'taryland National Bank Building 1735 Old f.eergetown Road. 8ethesda, *taryland from

- ' a:is a.m. to 5:00 p.m. Coptes of coav,ents received may be eiseined at the meC Pubite cocument noon 1717 H street nW.,

Washington OC. Coasnents will be most helpful if received by August 29, 1986.

Requests for single copies of draft guides (which may be reproduced) or for placement on an automatic distribution Itst for single copies of future draft guides in specific divisions should be yde in writing to the U.S. Nuclear Regulatory Comission.

Washington CC 20915. Attent ton : Of rector. 01viston of Technical Information and Document Control.

B. DISCUSSION This guide presents fracture toughness criteria that can be used for evaluating ferritic steel containment vessels with a wall thickness greater than 4 inches (0.1 m).

Section III of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code 2 (ASME B&PVC) contains requirements for material frac-ture toughness. However, these requirements were developed for reactor compo-nents only and do not address hypothetical accident conditions (e.g., severe impact loads). Therefore, the ASME code requirements are not directly applicable to shipping container design.

NUREG/CR-3826, " Recommendations for Protecting Against Failure by Brittle Fracture in Ferritic Steel Shipping Containers Greater than Four Inches Thick,"3 contains background and other information pertinent to the development of the criteria in this guide. The criteria studied involved four approaches, which are summarized as follows:

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

2. A fracture arrest criterion based on an asymptotic extrapolation of the Pellini fracture toughness reference curve.

3. A fracture initiation criterion based on the allowable flaw sizes specified in Table IWB-3510-1 of Section XI of the ASME B&PVC.

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 the drop test to be more costly, but there is no significant difference in cost impact between the two fracture arrest criteria and the fracture initiation criterion at yield stress levels.

However, the staff believes that fracture arrest is a more appropriate method 2 Copies may be obtained from the American Society of Mechanical Engineers, United Engineering Center, 345 47th Street, New York, NY 10017.

3 Copies are available for purchase from the Superintendent of Documents, U.S.

Government Printing Office, P.O. Box 37082, Washington, DC 20013-7982.

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G for licensing shipping containers because of the inspection requirements asso-

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v ciated with fracture initiation and the level of safety it provides in rela-tion to the drop test and the fracture initiation criterion.

The regulatory position identifies a fracture arrest criterion for demonstrating adequate toughness of containment vessels. The criterion states that materials selected should have sufficient toughness to preclude extensions of a through-wall crack irrespective of the crack size at yield strength levels of dynamic stress.

The nil ductility transition temperature (TNDT) for lowest service tem-perature (LST) of -20 F specified for the material in Table 2 of this guide may be used in lieu of conducting tests to determine the actual T f the material.

NDT Materials not listed need to be tested in accordance with ASTM Standard E208-84a,

" Standard Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic Steels,"4 to determine the T NDT' l Although the use of ferritic steels is addressed, the guide does not I

preclude the use of austenitic stainless steels. Since austenitic stainless steels are not susceptible to brittle fracture at temperatures encountered in transport, their use in containment vessels is acceptable to the staff and no

\ tests are needed to demonstrate resistance to brittle fracture.

C. REGULATORY POSITION The brittle fracture acceptance criteria outlined below are acceptable to the NRC staff for assessing the fracture toughness of thick-wall (over 4 inches (0.1 m)) ferritic steel containment vessels.

The T NDT criteria for ferritic steels to meet the fracture arrest criteria should be as summarized in Table 1.

l 4 Copies may obtained from the American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103.

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Table 1. T NDT Criteria for LST = -20 F Thickness (in.) TNDT ( I) 4 -123 8 -135 12 -140 16 -144 20 -146 NOTE: Interpolation may be used 'to determine T NDT values for differ-ent thicknesses.

The T NDT criteria for the materials listed in Table 2 are acceptable to the staff for containment vessels. Materials not listed should be tested in accordance with ASTM E208-84a,4 using specimen type P-2 or P-3.

Table 2. T NDT Criteria Material TNDT ( f)

SA-508-4A -158.33 SA-508-4B -148.00

• SA-350-4B -120.00

• Acceptable for forged section 5 4 in. thick.

D. IMPLEMENTATION I

The purpose of this section is to provide information to applicants and licensees regarding the NRC staff's plans for using this regulatory guide.

This draft guide has been released to encourage public participation in its development. Except in those cases in which an applicant proposes an accept-able alternative method for complying with specified portions of the Commis-sion's regulations, the methods to be describrd in the active guide reflecting public comments will be used by the NRC staff in evaluating applications for new package designs and requests for existing package designs to be designated as Type B(U) or Type B(M) packages.

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BIBLIOGRAPHY v

ASME Boiler and Pressure Vessel Code,Section XI, " Rules for Inservice Inspec-tion of Nuclear Power Plant Components," American Society of Mechanical Engi-neers, New York, updated frequently.

Holman, W. R. , and R. T. Langland, " 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.

Available for purchase from National Technical Information Service, Springfield, VA 22161.

Schwartz, M. W., " Recommendations for Protecting Against Failure by Brittle Fracture in Ferritic Steel Shipping Containers Greater than Four Inches Thick,"

U.S. Nuclear Regulatory Commission, NUREG/CR-3826, July 1984. Available for purchase from National Technical Information Service, Springfield, VA 22161.

U.S. Nuclear Regulatory Commission, " Fracture Toughness Criteria for Ferritic Steel Shipping Cask Containment Vessels with a Maximum Wall Thickness of Four Inches (0.1 m)," Draft Regulatory Guide MS 144-4. Single copies are avail-able from the USNRC Division of Technical Information and Document Control, Washington, DC 20555.

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REGULATORY ANALYSIS

1. STATEMENT OF THE PROBLEM Sections 71.71 and 71.73 of 10 CFR Part 71 identify normal and acci-dent conditions that a shipping container must withstand without releasing radioactive materials that exceed specified limits. One of the accident condi-tions requires that containers be able to withstand a drop from a height of 30 feet (9 m) onto an unyielding surface when the ambient temperature is -20 F

(-29 C). At this temperature, many steels are brittle and are subject to frac-ture under certain conditions of flaw size, flaw location, and stress level.

Therefore, it is necessary that the containers have sufficient toughness at

-20 F (-29 C) to withstand the impact loads.

There is currently no published guidance on design criteria regarding frac-ture toughness of thick-wall shipping containers. The possible use of ferritic steels for thick-wall container configurations makes it important that guidance on fracture toughness criteria be issued as soon as possible. It is important to issue this guidance to aid and support the evaluation of thick-wall containers for licensing decisions.

2. OBJECTIVES The objectives are to establish guidance on fracture toughness design criteria that would ensure the structural integrity of shipping containers sub-jected to accident conditions representative of those that may occur during transport. These criteria would also aid in expediting the licensing process by providing a set of consistent levels against which fracture safety margins of specific designs can be evaluated.

3. ALTERNATIVES The alternative is to take no action to issue guidance, but to inform applicants and licensees about the p*oposed guidance on an individual basis as interchanges occur between applicants and licensees and the staff during the review process.

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4. CONSEQUENCES Since the release of radioactive materials must not exceed specified limits in the event of an accident during transport, it is necessary that containers be designed to resist fracture. Fracture toughness design criteria for thick ferritic steels have been developed with NRC funds; therefore, it is important that these criteria be made available for use. Publication of these criteria and associated guidelines will aid in expediting the design process.

If no action is taken, applicants and licensees must continue to be informed on a case-by-case basis of the staff's position regarding fracture toughness design criteria, thus expending staff and industry resources that could be conserved.

5. DECISION RATIONALE In light of the above discussion, it is concluded that the criteria should '

be published in a regulatory guide to inform applicants and licensees of the

'O current staff position regarding fracture toughness criteria for thick-wall

\ casks in order to reduce review time and expedite the design process. This l proposed action would be an addition to a series of regulatory guides on the subject of shipping containers.

6. IMPLEMENTATION This guide will be used by the staff in evaluating all new container designs received after the final guide is issued. Licensees and applicants may use the guide in discussions with the staff on currently pending applications or modifi-cations to existing container designs to be designated either Type B(U) or B(M).

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UNITED STATES ,ostcesswas NUCLEAR REGULATORY COMMISSION Postas e reis paio WASHINGTON, D.C. 20555 w fs','. "o' c.

PERMIT No G 47 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE. $300 12 0NRC US 5 55 0 6 421 *= 1 IGPIS41s71RT ADH-DI V 0F TICC hp VMENT CONTROL DESK-RECSB WASHINGTON DC 20555 l

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