ML19292A930
| ML19292A930 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/1983 |
| From: | Weidenhamer G NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | |
| References | |
| RTR-REGGD-7.011, TASK-MS-144-4, TASK-RE REGGD-07.XXX, REGGD-7.XXX, NUDOCS 8307120105 | |
| Download: ML19292A930 (11) | |
Text
/
of U.S. NUCLEAR REGULATORY COMMISSION June 1983 y
0FFICE OF NUCLEAR REGULATORY RESEARCH Division /
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E Task MS 144-4
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DRAFT REGULATORY GUIDE AND VALUE/ IMPACT STATEMENT 9
Contact:
G. H. Weidenhamer (301)443-5860 FRACTURE TOUGHNESS CRITERIA FOR FERRITIC STEEL SHIPPING CASK CONTAINMENT, VESSELS WITH A MAXIMUM WALL THICKNESS OF FOUR INCHES",(0.1 m) ys
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INTRODUCTION 4
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Title 10,CodeofFederalRegulations,Part71{p1jPackagingofRadioactive w..
s Material for Transport and Transportation of Radic, active" Material Under Certain e-Conditions," requires that packages used to trin' sport radioactive materials osw withstandthenormalconditionsandhypotheh1 cal 7 accident conditions of Appen-v These accident cofiditions may occur at an initial dices A and B of Part 71.
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temperature of -20 F (-29 C).
At this temperature, several types of ferritic n
steels are brittle and subject to fracture,;; This guide describes fracture toughness criteria and test methods? acceptable to the NRC staff for use in n
evaluating Type B(U) and Type B(M)2 ferritic steel shipping cask containment vessels having a maximum thickness"of 4 inches (0.1 m) and having a maximum staticyieldstrengthofIb0,ksi[(690kPa).
The guide is applicable to the containment vessel only and not to other components of the package.
Alternative fracture toughness criteria and test methods may be used provided the applicant can demonstrate that their use will ensure equivalent c, 'n safety.
Anyguidance}rin this document related to information collection activities m
has been cleared under OMB Clearance No. 3150-0008.
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to 2All references to 10 CFR Part 71 in this draft regulatory guide refer to the n04 proposed version that was published for comment on August 17, 1979 (44 FR 48234).
@@x 2 Type B(U) and Type B(M) are defined in 9 71.4 of 10 CFR Part 71.
-a:x b X Q
This regulatory guide and the associated value/ impact statement are being issued in draf t f orm to involve CD Q.0 the public in the ear;/ stages of the development of a regulatory position in this area. They have not received complete staf f review and do not represent an official NRC staf f pnsition.
Public comments are being solicited on both drafts. the guide (including any implementation schedule) and the value/ impact statement, Comments on the valee/ impact statement should be accompanied by supporting fata. Comments on both drafts should be sent to the Secretary of the Commission, 0.5. Nuclear Regulatory Commission, washington. 3.C. 20555, Attention: Oncketing and Service Branch by Q p 7 Requests for single copies of draft quices (which may be reproduced) or for placement on an sutomatic distribution list for single copies of future draft guides in specific divisions should be made i, writing to the U.S. Nuclear Regulatory Commitsion, ' Washington. D.C. 20555, Attention: Diractor, Division of Technical Information and Jocument :ontr ol.
B.
DISCUSSION This guide presents fracture toughness criteria and test methods that can be used for evaluating ferritic steel containment vessels having a maximum wall thickness of 4 inchas (0.1 m) with a maximum static yield strength of 100 ksi (690 kPa).
Section III of the ASME Boi'ar and Pressure Vessel Code 3 contains require-ments for material fracture toughness; however, these requirements were devel-oped for reactor components only and do not address hypothetical accident condi-tions (e.g., level D service limits or severe impact loads).
Therefore, the code requirements are not directly applicaole to shipping container design.
NUREG/CR-1815, " Recommendations for Protecting Against Failure by Brittle Fracture in Ferritic Steel Shipping Containers Up to Four Inches Thick,"* con-tains background and other information 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 for the types of containers and radio-active contents being transported.
Table 1 in this guide identifies the radio-activity limits for each of the three categories.
Tables 4,5 5, and b in NUREG/
CR-1815 list the fracture toughness criteria associated with each category.
A qualitative de!.;ription of the margins of safety against brittle failure for each of the three rategories is given in Appendix C to NUREG/CR-1815.
Addi+.ional information regarding the basis for the criteria is contained in Appendix B of NUREG/CR-1815.
The Regulatory Position endorses the criteria contained in Section 5 of NUREG/CR-1815.
These criteria identify the following two options, either of which will demonstrate adequate toughness of containment vessels.
1.
Material properties in accordance with the standards specified in Tables 4,5 5, or 6 of NUREG/CR-1815, as appropriate.
aCopies may be obtained from the American Society of Mechanical Engineers, United Engineering Center, 345 East 47th Street, New York, N.Y.
10017.
4A copy of this document can be obtained by writing the Division of Technical Information and Document Control, Document Sales Office, U.S. Nuclear Regula-tory Commission, Washington, D.C.
20555, or by phoning (301) 492-9530.
'The third line in the criteria in Table 4 should read:
" Additionally, if the steel has a g 7r, ksi, either:"
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2.
Full-scale drop tests in accordance with paragraohs 5.1.4 and 5.2.4 i
of NUREG/CR-1815.
For Category II and III containers, the highest nil luctility transition temperature (TNDT) specified for the material in either Figure 1 or Table 3 of NUREG/CR-1815 may be used in lieu oi conducting tests to determine the actual T
f the material.
NDT Use of Option 2 (full-scale drop tests) for demonstrating the toughness of the containment vessel requires introduction of one or more flaws into the test specimen.
Determination of proper flaw size, location, and orientation depend on several variables (e.g., container test orientatit., stress magnitude and distribution, NDE orocedures).
Therefore, the technical details for con-ducting full-scale drop tests under Option 2 must necessarily be considered on a case-by-case basis.
Although NUREG/CR-1815 addresses the use of ferritic stec.ls only, it does not preclude the use of austenitic stainless stee'-
Since austenitic stain-less steels are no+ susceptible to brittle fail' ire. at temperatures encountered in transport, their use in containment. vessels is acceptable to the staff and no tests are needed to demonstrate resistance to crittle failure.
C.
REGULATORY POSITION The criteria contained in Section 5.0 of NUREG/CR-1815 are acceptable to the NRC staff for assessing the fracture toughress of thin-wall (up to and including 4 inches (0.1 m)) ferritic steel containment vessels for the cate-gories identified in Table 1.
A Category I container qualified in accordance with this guide is accept-able for transporting either Category II or Category III radioactive materials.
Similarly, a Category II container qualified in accordance with this guide is acceptable for transport ^ng Category III materials.
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Table 1 Categories and Associated Radioactivity Limits for Shipping Containers CATEGORY I CATEGORY II CATEGORY III Applies if quantity Applies if quantity Applies if quantity per package is:
per package is:
rer package is:
greater than or equal to less than 3(10)4 Ci and less than 30A and 2
3(10)4 Ci,3(10)aAE,or 3(10)3A but greater 30A.
2 1
3(10)aAI.
than or equal to 30A and less than Also applies if con-2 3(10)3A but greater tents are (1) low 1
than or equal to 30A.
specific activity mate-1 rials or (2) objects with fixed contamina-tion (not readily dispersible) and the total quantity per package is less than 3(10)4 Ci, 3(10)3A, and 3(10)sA.
2 2
Defined in S 71.4 of 10 CFR Part 71.
D.
EPl.EMENTATION The purpose of this section u to provMe information to applican's and licensees regarding the 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 acceptable alternative method for complying with specified portions of the Commission's regtlations, the metheds to be described in the active guide reflecting public comments will be used by the NRC staff in evaluatirg appli-cations for new package designs and requests for existing package designs to be designated as Type B(U) or Type B(M) packages.
These applications should be accompanied by information demonstrating that the package design meets the criteria to be specified in the active guide.
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i DRAFT VALUE/ IMPACT STATEMENT
SUMMARY
Fracture toughness is one of the important safety issues that must be considered in the design and evaluation of shipping containers.
Since design criteria associated with fracture toughness of thin-wall ferritic steels have been developed, it is important that this information be documented to aid in the design and subsequent evaluation of these types of containers.
A regulatory puide has been determined to be the best procedural approach to document th's information since this is the most common vehicle for obtaining public comments.
The criteria were developed by considering information in the open literature.
NUREG/CR-1815, " Recommendations for Protecting Against Failure by Brittle Fracture in Ferritic Steel Shipp ng Containers up to Four Inches Thick,"
i which is the result of this development effort, serves as the basis for the regulatory guide.
Althougii the guide applies to ferritic steels only, it does not preclude the use of stainless steels for container application.
1.
PROPOSED ACTION 1.1 Description Establish staff positions on fracture tcughness design criteria and identify acceptable methods for assessing fracture toughness for thin-wall ferritic steci centainers.
- 1. 2 Need and Justification i
Appendices A and B of 10 CFR Part 71* identify normal and accident condi-tions that a shipping container must withstand without releasing radioactive
^All references to 10 CFR Part 71 in this draft regulatory guide refer to the
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materials that exceed specified limits.
One of the accident conditions requires that containers be able to withstand a drop from a height of 30 feet (9 m) onto an unyielding surface when the an.bient temperature is -20 F (-29 C).
At this temperature, many steels are brittle and are subject to fracture under certain conditions of flaw size, flaw location, and stress level.
Thtrefore, it is necessary that the containers have sufficient toughness at -20 F (-29'C) to withstand the impact loads.
There are currently no documented staff positions on design criteria regard-ing fracture toughness of shipping containers.
Since thin-wall designs comprise the majority of container configurations, it is important that guidance on fracture toughness criteria be issued as soon as possible to support licensing decisions and to be available for future designs.
1.3 Value/ Impact 1.3.1 NRC The fracture toughness design criteria are of value since the criteria are necessary for ensuring the structural integrity of shipping containers sub-jected to accident conditions that are representative of those that may occur during transport.
These criteria will also aid in expediting the licensing process by providing a set of consistent levels against which fracture safety margins of specific d(rigns can be evaluated.
1.3.2 Other Government Agencies These criteria may be beneficial to the Department of Energy, to the Department of Transportation, and to the International Atomic Energy Agency.
1.3.3 Industry The criteria and associated expected safety margins would provide a set of levels acceptable to the NRC staff that designers may use to meet the require-ments of 10 CFR Part 71.
Therefore, the design process should be ex;,cdited with the issuance of this guidance.
Also, methods that can be used to qualify the designs and materials for the specific applications would be identified.
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The guidance is intendad to apply to all new package designs and to requests for package designs to be designated as Type B(U)* or Type B(M).*
For new Category I containers, e.g.,
spent fuel containers, it is clear that high quality steels will be necessary to meet the criteria.
It is also clear that the criteria for new Categories II and III containers, although less than the Category I criteria, will require good quality steels.
With regard to the impact of these criteria on already approved container designs, the staff believes that many present designs would satisfy the criteria with little or no modification.
Although some designs would not meet the cri-teria, continued use of these containers would be permitted provided they are not to be designated either Type B(U) or Type B(M).
The basis for the approach used for specifying the toughiass is discussed in NUREG/CR-1815.
In addition, four experts in the field of brittle fracture have provided valuable input to the development of these criteria and all have concurred with the recommendations in NUREG/CR-1815.
Therefore, the staff believes that materials selected and qualified in accordance with the proposed guidance will result in containers with adequate safety margins to meet the normal and accident conditions identified in 10 CFR Part 71.
1.3.4 Public A shipping container whose design satisfies the fracture toughness accept-ance criteria may be used with assurance that the public will not be exposed to unacceptable radiation levels if the container experiences an event encom-passed by the specified design conditions.
Therefore, no direct impact on the public is foreseen.
1.4 Decision Since the release of radioactive materials must net 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 thin A
As defined in S 71.4 of 10 CFR Part 71.
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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.
The proposed guidance is applicable to all new container designs and to existing container designs to be designated either Type B(U) or 3(M).
Although some existing containers will not meet these criteria, the containers can still be utilized for continued operation provided they are not to be designated either Type B(U) or B(M).
Therefore, the impa t of these criteria on current inventories will be small.
Although quality steels will be necessary to satisfy the appropriate criteria for each of the three categories of containers, it is important that adequate safety margins be demonstrated to meet the requirements of 10 CFR Part 71.
In light of the above discussion, it is concluded that the criteria should be published.
2.
TECHNICAL APPROACH The criteria were developed by the Lawrence Livermore National Laboratory under a technical assistance contract with the Office of Nuclear Materials Safety and Safeguards of the Nuclear Regulatory Commission.
Since the scope of the work was limited, the criteria were developed from the open literature.
NUREG/CR-1815 documents the results of the development effort and serves as the basis for the guidance.
The approach that is recommended is based upon principles of fracture mechanics.
Specifically, the nil ductility transition temperature (TNDT) is the parameter that is used to describe the toughness of the material.
Other methods such as the elastic plastic fracture mechanics approach based on such concepts as the J integral have not been considered.
The method also requires that the radioactive material being transported be categorized into one of three categories that depend on the consequences of failure.
Material fracture toughness capability is based on these categories.
In addition to the toughness criteria, methods for evaluating compliance with the criteria and procedures for qualifying the selected steels are identi-fied for each of the categories.
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3.
PROCEDURAL APPROACH The NRC staff determined that the best procedural approach for the docu-mentation of these criteria is a regulatory guide.
A regulatory guide pro-vidas the most. common vehicle for obtaining public input and also provides a convenient method for periodically upgrading the information if necessary.
The regulatory positions in the guide specifically identify the three categories of container radioactivity limits; however, because the associated fracture toughness criteria associated with these categories have already been published, the guide will incorporate the criteria by endorsing Section 5 of NUREG/CR-1815, in which they appear.
In order to ensure that recipients of the draft guide can review and provide comments on the criteria and the basis therefor, a copy of NUREG/CR-1815 will be furnished on request.
4.
STATUTORY CONSIDERATIONS 4.1 NRC Authority The authority for the proposed action is derived from the Atomic Energy Act of 1954, as amended, and tlw Energy Reorganization Act of 1974, as amended, and is implemented through the Commission's regulations, in particular 10 CFR Part 71.
4.2 Need for NEPA Asstasment Shipping containers designed in accordance with the information to be documented in the regulatory guide have no direct bearing on the environment.
Therefore, an environmental impact statement is not required.
5.
RELATIONSHIP TO OTHER EXISTING REGULATIONS OR POLICIES Conflicts with other agencies or other regulatory guides are not expected.
Rather, the toughness criteria will supplement Regulatory Guides 7.6, " Design Criteria for the Structural Analysis of Shipping Cask Containment Vessels,"
an'd 7.8, " Load Combinations for the Structural Analysis of Shipping Casks,"
that currently do not consider fracture toughness.
These guides address the 9
design criteria for structural ant. lysis of shipping containers and the loading combi..atic-is that must be considered to fulfill the requirements of 10 CFR Part 71, 6.
CONCLU, ION Fracture toughness design criteria, staf f positions, and niethods regarding the design of thin-wall ferritic steel shipping containers should be documented in a regulatory guide to provide a uniform basis for the design and the review of licence app 1' cations.
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