1 Copies may be obtained from the American Society of Mechanical Engineers, Three Park Avenue, New York, NY 

10016-5990; phone (212) 591-8500; fax (212) 591-8501; www.asme.org.

This regulatory guide lists the Code Cases that the NRC has determined not to be acceptable for use on a generic basis. Licensees may submit a request to implement

one or more of the Code Cases listed in this regulatory guide through 10 CFR 50.55a(a)(3), which permits the use of alternatives to the ASME Code requirements

referenced in 10 CFR 50.55a provided that the proposed alternatives result in an acceptable level of quality and safety.

This guide was issued after consideration of comments received from the public. The NRC staff encourages and welcomes comments and suggestions in connection

with improvements to published regulatory guides, as well as items for inclusion in regulatory guides that are currently being developed. The NRC staff will revise existing

guides, as appropriate, to accommodate comments and to reflect new information or experience. Written comments may be submitted to the Rules and Directives Branch,

Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001.

Regulatory guides are issued in 10 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; and 10, General.

Requests for single copies of draft or active regulatory guides (which may be reproduced) should be made to the U.S. Nuclear Regulatory Commission, Washington, DC

20555, Attention: Reproduction and Distribution Services Section, or by fax to (301) 415-2289; or by email to Distribution@nrc.gov. Electronic copies of this guide and

other recently issued guides are available through the NRC’s public Web site under the Regulatory Guides document collection of the NRC’s Electronic Reading Room

at http://www.nrc.gov/reading-rm/doc-collections/ and through the NRC’s Agencywide Documents Access and Management System (ADAMS) at

http://www.nrc.gov/reading-rm/adams.html, under Accession No. ML052140501. Note, however, that the NRC has temporarily suspended public access to ADAMS so

that the agency can complete security reviews of publicly available documents and remove potentially sensitive information. Please check the NRC’s Web site for updates

concerning the resumption of public access to ADAMS.

U.S. NUCLEAR REGULATORY COMMISSION Revision 1

August 2005

REGULATORY GUIDE

OFFICE OF NUCLEAR REGULATORY RESEARCH

REGULATORY GUIDE 1.193

(Draft was issued as DG-1126, dated August 2004)

ASME CODE CASES NOT APPROVED FOR USE

A. INTRODUCTION

In Title 10, Part 50, of the Code of Federal Regulations (10 CFR Part 50), “Domestic Licensing of

Production and Utilization Facilities,” Section 50.55a(c), “Reactor Coolant Pressure Boundary,” requires, in part,

that components of the reactor coolant pressure boundary be designed, fabricated, erected, and tested in accordance

with the requirements for Class 1 components of Section III, “Rules for Construction of Nuclear Power Plant

Components,”1

 of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code

(B&PV Code) or equivalent quality standards. Section 50.55a(f), “Inservice Testing Requirements,” requires,

in part, that Class 1, 2, and 3 components and their supports meet the requirements of the “Code for Operation

and Maintenance of Nuclear Power Plants” (OM Code) of the ASME OM Code or equivalent quality standards. 

Finally, 10 CFR 50.55a(g), “Inservice Inspection Requirements,” requires, in part, that Classes 1, 2, 3,

MC (metal containment), and CC (concrete containment) components and their supports meet the requirements

of Section XI, “Rules for Inservice Inspection of Nuclear Power Plant Components,” of the ASME B&PV Code

or equivalent quality standards.

The ASME publishes a new edition of the B&PV and OM Codes every 3 years and new addenda every year. 

The latest editions and addenda of Section III, Section XI, and the OM Code that the U.S. Nuclear Regulatory

Commission (NRC) has approved for use are referenced in 10 CFR 50.55a(b). The ASME also publishes 
2 Revision 32 to Regulatory Guide 1.84 combined Regulatory Guides 1.84 and 1.85 to list all the Section III Code Cases

in one guide. The title of Regulatory Guide 1.84 has been modified to reflect this.

RG 1.193, Rev. 1, Page 2

Code Cases for Section III and Section XI quarterly and Code Cases for the OM Code yearly. 

Code Cases provide alternatives to the ASME Code. 

Revision 33 of Regulatory Guide 1.84, “Design, Fabrication, and Materials Code Case Acceptability,

ASME Section III,”2

 and Revision 14 of Regulatory Guide 1.147, “Inservice Inspection Code Case

Acceptability, ASME Section XI, Division 1,” which the NRC published concurrently with this guide,

identify the Code Cases that the NRC has determined to be acceptable alternatives to applicable parts of

Sections III and XI of the ASME B& PV Code. This regulatory guide does not approve the use of the

Code Cases listed herein. Section III and Section XI Code Cases listed in Supplement 12 to the 1998

Edition of the ASME B&PV Code through Supplement 6 to the 2001 Edition were reviewed by the NRC

during the revision of these regulatory guides.

Because this regulatory guide does not approve the use of the Code Cases listed herein, it does

not contain new or amended information collection requirements subject to the Paperwork Reduction Act

of 1995 (44 U.S.C. 3501 et seq.). The NRC may neither conduct nor sponsor, and a person is not required

to respond to, an information collection request or requirement unless the requesting document displays

a currently valid OMB control number.

B. DISCUSSION

This regulatory guide lists the Code Cases that the NRC has determined not to be acceptable

for use on a generic basis. A brief description of the basis for the determination is provided with each

Code Case. Licensees may submit a request to implement one or more of the Code Cases listed below

through 10 CFR 50.55a(a)(3), which permits the use of alternatives to the Code requirements referenced

in 10 CFR 50.55a provided that the proposed alternatives result in an acceptable level of quality

and safety. A licensee must submit a plant-specific request that addresses the NRC’s concern about

the Code Case at issue.
RG 1.193, Rev. 1, Page 3

C. REGULATORY POSITION

For this guide, the NRC staff reviewed the Section III and Section XI Code Cases listed in

Supplement 12 to the 1998 Edition of the ASME B&PV Code through Supplement 12 to the 2001

Edition. Licensees must not implement Code Cases listed in this guide without prior NRC approval. 

Periodic updates to this regulatory guide are planned to accommodate new Code Cases and any revisions

of existing Code Cases.

1. Unacceptable Section III Code Cases

The NRC determined that the following Section III Code Cases are unacceptable for use by

licensees in their Section III design and construction programs. The ASME issues a new edition of

Section III every 3 years, and publishes quarterly supplements to the edition containing Section III Code

Cases. Hence, there are 12 supplements to each edition. To assist users, the third column of Table 1 lists

the date of approval by the ASME, or for new Code Cases, the supplement and edition in which each

Code Case was published (e.g., 3/01E means Code Case Supplement 3 to the 2001 Edition).
RG 1.193, Rev. 1, Page 4

Table 1. Unacceptable Section III Code Cases

Code Case

Number

Table 1, Unacceptable Section III Code Cases Date or

Supplement/Edition Summary

N-284-1 Metal Containment Shell Buckling Design Methods, Section III,

Division 1, Class MC

10/2/00

(1) The following errata, misprints, recommendations, and

errors have been identified:

• Fig. -1511.1, The curve for αθL should not exceed 0.8 for

any value of (R/t).

• - 1512, The statement “See Fig.-1512-1 then see

-1713.1.2 for method of calculating M” should be

rephrased as: “See -1713.1.2 for method of calculating

M, then see Fig. -1512-1.”

• - 1513, Recommend “Use the value of αil given for

spherical shells in accordance with -1512.”

• - 1521, (i) In (a) Axial Compression, “αθG = αθL” should

be changed to “αφG = αφL.” (ii) The source of the

equations shown under “(a) Axial Compression”

provided separate instability equations for

stringer-stiffened and ring-stiffened cylindrical shells.

The Code Case adopted the instability equations

pertaining to ring-stiffened shells, which are less

conservative than those for stringer instability, for both

ring and/or stringer stiffened cylindrical shells. Is this the

intent? (Ref. “Summary of Buckling Tests on Fabricated

Steel Cylindrical Shells in USA,” by C. D. Miller, in

“Buckling of Shells in Offshore Structures,” 1982.)

• - 1712.1.1, The equation “Cθh = 0.92/(Mθ - 0.636)” should

be changed to “Cθh = 0.92/(Mφ - 0.636).”

• Fig. -1712.1.1-1, The leftmost curve should be labeled

Cθh

• - 1712.2.2, (a) Axial Compression, (i) In the formula for

σφej, the denominator should be (mπ/Lj

)

2 C tφ . 

(ii) The expressions for Cφ and Cθ should be separated.

• - 1712.2.3, (i) The factor 1.944 in an older edition has

been changed to 2.00. No basis is apparent. (ii) The

misprint “t 1

1⁄4” should be corrected to “t11⁄4.”

• - 1713.1.1, (i) The equation “στa=αφθCσφθel/FS” should be

changed to “στa=αφθLCσφθel/FS”. (ii) The title of (c) should

be changed to “Axial Compression Plus In-Plane Shear.”

• Fig. -1713.1-1, In (b), the lower value “Ks=σra” on the

vertical axis should be changed to “Ks=σha”

• - 1713.2.1, (i) The headings for (b) and (c) should include

the words “In-Plane.” (ii) In (b) “Axial Compression

Plus Shear,” “σθ” should be changed to “σφ”.

(2) Applicants intending to use Code Case N-284-1 shall submit

a request to the NRC staff for its review and approval on a

plant-specific basis.
Code Case

Number

Table 1, Unacceptable Section III Code Cases Date or

Supplement/Edition Summary

RG 1.193, Rev. 1, Page 5

N-483-2

N-483-3

Alternative Rules to the Provisions of NCA-3800, Requirements

for Purchase of Material, Section III, Divisions 1 and 3

5/7/99

2/25/02

The Code Case lacks sufficient detail to ensure that the supplied

material is as represented by the Certified Material Test Report.

N-510

N-510-1

Borated Stainless Steel for Class CS Core Support Structures and

Class 1 Component Supports, Section III, Division 1

12/9/93

8/14/01

No technical basis was provided for expanding the Code Case to

include borated stainless steel Types 304B, 304B1, 304B2, and

304B3. A considerable amount of information was required to

support the types presently contained in the Code Case. The

revised Code Case would permit borated stainless steel to be used

for component supports within the reactor vessel. The technical

basis to support the Code Case only addresses the use of these

materials as component supports in spent fuel racks and

transportation casks.

N-519 Use of 6061-T6 and 6061-T651 Aluminum for Class 1 Nuclear

Components

2/23/00

Code Case is applicable to only one DOE aluminum vessel.

N-530 Provisions for Establishing Allowable Axial Compressive

Membrane Stresses in the Cylindrical Walls of 0-15 Psi Storage

Tanks, Classes 2 and 3

5/5/00

There are numerous errors in the equations. The errors must be

corrected before the Code Case can be approved for use.

N-565 Alternative Methods of Nozzle Attachment for Class 1 Vessels 12/3/99

The Code Case essentially requires a design using a seal to protect

the threads from the contained fluid, and seals are not a Code

item. The seal, which plays a very important part in the integrity

of the joint, imposes too great a vulnerability in the design. The

supporting information for the Code Case does not demonstrate

the resulting threaded nozzle configuration is equivalent in

integrity to that of a welded connection.
Code Case

Number

Table 1, Unacceptable Section III Code Cases Date or

Supplement/Edition Summary

RG 1.193, Rev. 1, Page 6

N-595

N-595-1

N-595-2

N-595-3

Requirements for Spent Fuel Storage Canisters, Section III,

Division 1

2/26/99

9/24/99

12/8/00

Regulatory approval for the use of multi-purpose casks is 6/01E

presently addressed by the NRC Spent Fuel Project Office Interim

Staff Guidance No. 4, Rev. 1 (ISG-4, Rev. 1). The interim staff

guidance provides a framework to ensure that the cask system, as

designed, and when fabricated and used in accordance with the

conditions specified in its Certificate of Compliance, meets the

requirements of 10 CFR Part 72. The ASME is presently

developing Code Case N-717 to replace Code Case N-595-3. 

Thus, Code Case N-595-3 will be retained in Regulatory Guide

1.193, and the NRC staff will review Code Case N-717 when it is

published.

N-645

N-645-1

Use of Rupture Disk Devices on Nuclear Fuel Storage Canisters,

Class 1, Section III, Division 1

6/14/00

4/01E

The NRC does not permit the use of rupture disk devices in spent

nuclear fuel storage canister designs.
RG 1.193, Rev. 1, Page 7

2. Unacceptable Section XI Code Cases

The following Section XI Code Cases were determined to be unacceptable for use by licensees in

their Section XI inservice inspection programs. The ASME issues a new edition of Section III every

3 years, and publishes quarterly supplements to the edition containing Section III Code Cases. Hence,

there are 12 supplements to each edition. To assist users, the third column of Table 1 lists the date of

approval by the ASME, or for new Code Cases, the supplement and edition in which each Code Case was

published (e.g., 3/01E means Code Case Supplement 3 to the 2001 Edition).

Table 2. Unacceptable Section XI Code Cases

Code Case

Number

Table 2. Unacceptable Section XI Code Cases Date or

Supplement/Edition Summary

N-465

N-465-1

Alternative Rules for Pump Testing, Section XI, Division 1 11/30/88

8/14/97

The draft standard referenced in the Code Case is outdated. The

requirements contained in the OM Code, “Code for Operation and

Maintenance of Nuclear Power Plants,” should be used. Note that

Revision 12 of RG 1.147 approved N-465 for use. The

disapproval of N-465 for use applies only to new users.

N-473

N-473-1

Alternative Rules for Valve Testing, Section XI, Division 1 3/8/89

8/14/97

The draft standard referenced in the Code Case is outdated. The

requirements contained in the OM Code, “Code for Operation and

Maintenance of Nuclear Power Plants,” should be used. Note that

Revision 12 of RG 1.147 approved N-473 for use. The

disapproval of N-473 for use applies only to new users.

N-480 Examination Requirements for Pipe Wall Thinning Due to Single

Phase Erosion and Corrosion, Section XI, Division 1

Annulled on 9/18/01

Code Case has been superseded by Code Case N-597,

“Requirements for Analytical Evaluation of Pipe Wall Thinning,”

implemented in conjunction with NSAC-202L,

“Recommendations for an Effective Flow Accelerated Corrosion

Program.” 

N-498-2

N-498-3

Alternative Requirements for 10-Year System Hydrostatic Testing

for Class 1, 2, and 3 Systems, Section XI, Division 1

6/9/95

5/20/98

Code Case N-498-4 is conditionally approved in Revision 13 to

Regulatory Guide 1.147. Those licensees choosing to implement

this Code Case are to implement Revision 4.
Code Case

Number

Table 2. Unacceptable Section XI Code Cases Date or

Supplement/Edition Summary

RG 1.193, Rev. 1, Page 8

N-532-2 Alternative Requirements to Repair and Replacement

Documentation Requirements and Inservice Summary Report

Preparation and Submission as Requested by IWA-4000 and

IWA-6000

5/01E

The following concerns were identified during review of the

Code Case:

(1) Clarification is needed relative to the intent of Footnote 1

and Table 4 regarding the applicable edition and addenda;

and

(2) Submission of Form OAR-1 is at the end of each inspection

period rather than 90 days following the outage.

N-542 Alternative Requirements for Nozzle Inside Radius Section Length

Sizing Performance Demonstration, Section XI, Division 1

Annulled on 3/28/01

Code Case N-542 was subsumed by Code Case N-552,

“Alternative Methods–Qualification for Nozzle Inside Radius

Section from the Outside Surface,” which is being implemented

by licensees. Thus, there is no need to approve N-542.

N-547 Alternative Examination Requirements for Pressure Retaining

Bolting of Control Rod Drive (CRD) Housings, Section XI,

Division 1

Annulled on 5/20/01

Code Case N–547 states that the examination of CRD housing

bolts, studs, and nuts is not required. However,

10 CFR 50.55a(b)(2)(xxi)(B) requires the examination of CRD

bolting material whenever the CRD housing is disassembled and

the bolting material is to be reused. Examination of CRD bolting

material is required to verify that service-related degradation has

not occurred, or that damage such as bending and galling of

threads has not occurred when performing maintenance activities

that require the removal and reinstallation of bolting.

N-560

N-560-1

N-560-2

Alternative Examination Requirements for Class 1, Category B-J

Piping Welds, Section XI, Division 1

8/9/96

2/26/99

3/28/00

(1) The Code Case does not address inspection strategy for

existing augmented and other inspection programs such as

intergranular stress corrosion cracking (IGSCC), flowassisted corrosion (FAC), microbiological corrosion (MIC),

and pitting.

(2) The Code Case does not provide system-level guidelines

for change in risk evaluation to ensure that the risk from

individual system failures will be kept small and dominant

risk contributors will not be created.
Code Case

Number

Table 2. Unacceptable Section XI Code Cases Date or

Supplement/Edition Summary

RG 1.193, Rev. 1, Page 9

N-561

N-561-1

Alternative Requirements for Wall Thickness Restoration of Class 2

and High Energy Class 3 Carbon Steel Piping, Section XI,

Division 1

12/31/96

3/28/01

Neither the ASME Code nor the Code Case have criteria for

determining the rate or extent of degradation of the repair or the

surrounding base metal. Reinspection requirements are not

provided to verify structural integrity since the root cause may not

be mitigated.

N-562

N-562-1

Alternative Requirements for Wall Thickness Restoration of Class 3

Moderate Energy Carbon Steel Piping, Section XI, Division 1

12/31/96

3/28/01

Neither the ASME Code nor the Code Case have criteria for

determining the rate or extent of degradation of the repair or the

surrounding basemetal. Reinspection requirements are not

provided to verify structural integrity since the root cause may not

be mitigated.

N-574 NDE Personnel Recertification Frequency, Section XI, Division 1 8/14/97

Based on data obtained by the NRC staff during its review of

Appendix VIII, “Performance Demonstration for Ultrasonic

Examination Systems,” to Section XI, the NRC staff noted that

proficiency decreases over time. The data does not support

re-certification examinations at a frequency of every 5 years.

N-575 Alternative Examination Requirements for Full Penetration

Nozzle-to-Vessel Welds in Reactor Vessels with Set-On Type

Nozzles, Section XI, Division 1

8/14/97

The supporting basis for the Code Case applies to the specific

configuration of one plant and is not applicable on a generic basis. 

In addition, there are insufficient controls on stress and operating

conditions to permit a generic reduction in examination volume. 

Finally, the boundaries of the volume of the weld, cladding, and

heat affected zone from Figure 2 are ambiguous. 

N-577

N-577-1

Risk-Informed Requirements for Class 1, 2, and 3 Piping,

Method A, Section XI, Division 1

9/2/97

3/28/00

(1) The Code Case does not address inspection strategy for

existing augmented and other inspection programs such as

intergranular stress corrosion cracking (IGSCC), flowassisted corrosion (FAC), microbiological corrosion (MIC),

and pitting.

(2) The Code Case does not provide system-level guidelines for

change in risk evaluation to ensure that the risk from

individual system failures will be kept small and dominant

risk contributors will not be created.
Code Case

Number

Table 2. Unacceptable Section XI Code Cases Date or

Supplement/Edition Summary

RG 1.193, Rev. 1, Page 10

N-578

N-578-1

Risk-Informed Requirements for Class 1, 2, and 3 Piping,

Method B, Section XI, Division 1

9/2/97

3/28/00

(1) The Code Case does not address inspection strategy for

existing augmented and other inspection programs such as

intergranular stress corrosion cracking, flow-assisted

corrosion, microbiological corrosion, and pitting.

(2) The Code Case does not provide system-level guidelines

for change in risk evaluation to ensure that the risk from

individual system failures will be kept small and dominant

risk contributors will not be created.

N-587 Alternative NDE Requirements for Repair/Replacement Activities,

Section XI, Division 1

12/12/97

The NRC believes this Code Case is in conflict with the review

process for approval of alternatives under 10 CFR 50.55a(a)(3). 

The Code Case would permit a licensee and the Authorized

Nuclear Inspector to choose unspecified alternatives to regulatory

requirements.

N-589

N-589-1

Class 3 Nonmetallic Cured-in-Place Piping, Section XI,

Division 1

4/19/02

5/01E

(1) The installation process provides insufficient controls on

wall thickness measurement.

(2) There are no qualification requirements for installers and

installation procedures such as those for welders and

welding procedures.

(3) Fracture toughness properties of the fiberglass are such that

the cured-in-place piping (CIPP) could crack during a

seismic event.

(4) Equations 4 and 5 in the Code Case contain an “i” term

[a stress intensification factor] that is derived from fatigue

considerations. Stress intensification factors, however, have

not been developed for fiberglass materials.

N-590 Alternative to the Requirements of Subsection IWE, Requirements

for Class MC and Metallic Liners of Class CC Components of

Light-Water Cooled Plants, Section XI, Division 1

Annulled on 4/8/02

The provisions of the Code Case were incorporated into the 1998

Edition which has been approved by the NRC. Thus, the

Code Case is no longer needed and was annulled by the ASME. 
Code Case

Number

Table 2. Unacceptable Section XI Code Cases Date or

Supplement/Edition Summary

RG 1.193, Rev. 1, Page 11

N-591 Alternative to the Requirements of Subsection IWL, Requirements

for Class CC Concrete Components of Light-Water Cooled

Plants, Section XI, Division 1

Annulled on 4/8/02

The provisions of the Code Case were incorporated into the 1998

Edition which has been approved by the NRC. Thus, the

Code Case is no longer needed and was annulled by the ASME. 

N-613 Ultrasonic Examination of Full Penetration Nozzles in Vessels,

Examination Category B-D, Item No’s. B3.10 and B3.90, Reactor

Vessel-To-Nozzle Welds, Fig. IWB-2500-7(a), (b), and (c),

Section XI, Division 1

7/30/98

The Code Case conflicts with and unacceptably reduces the

requirements of 10 CFR 50.55a(b)(2)(xv)(K)(2)(i). A revision to

the Code Case has been developed to address the concerns.

N-615 Ultrasonic Examination as a Surface Examination Method for

Category B-F and B-J Piping Welds, Section XI, Division 1

12/98E

The Code Case requires that the ultrasonic technique used be

demonstrated capable of detecting certain size flaws on the outside

diameter of the weld, but it does not specify any demonstration

requirements. To be acceptable, Section XI, Appendix VIII, type

rules for performance demonstration need to be developed and

applied.

N-622 Ultrasonic Examination of RPV and Piping, Bolts, and Studs,

Section XI, Division 1

R4/19/02

The Code Case was published in May 1999. Industry

Performance Demonstration Initiative efforts since that time have

made this Code Case obsolete. Issues associated with

supplements to Appendix VIII are being addressed individually in

separate Code Cases.

N-653 Qualification Requirements for Full Structural Overlaid Wrought

Austenitic Piping Welds, Section XI, Division 1

3/01E

(1) Section XI, Appendix VIII, Supplement 11, requires a

personnel performance qualification as part of the procedure

qualification. The detection acceptance criteria in the

Code Case do not require personnel performance

qualification as part of the procedure qualification. 

Personnel qualification is necessary to validate the

effectiveness of the procedure qualification.

(2) The minimum grading unit is 1.0 inch in the circumferential

direction. The acceptance tolerance, however, is 0.75 inch

root mean square error. Thus, the length sizing acceptance

criteria do not adequately prevent the use of testmanship

rather than skill to pass length sizing tests.
Code Case

Number

Table 2. Unacceptable Section XI Code Cases Date or

Supplement/Edition Summary

RG 1.193, Rev. 1, Page 12

N-654 Acceptance Criteria for Flaws in Ferritic Steel Components

4 in. and Greater in Thickness, Section XI, Division 1

4/01E

Licensees intending to apply the rules of this Code Case must

obtain NRC approval of the specific application in accordance

with 10 CFR 50.55a(3).

3. Unacceptable OM Code Cases

The following OM Code Cases were determined to be unacceptable for use by licensees in their

inservice testing programs. The ASME issues OM Code Cases annually with publication of a new

edition or addenda. No new OM Code Cases were added in this revision. To assist users of the

OM Code, Column 3 of Table 3 lists the edition or addenda to which each Code Case was attached

(E: edition; A: addenda).

Table 3. Unacceptable OM Code Cases

Code Case

Number

Table 3. Unacceptable OM Code Cases Date or Edition/

Addenda

Summary of Basis for Exclusion

OMN-10, Rev. 0 Requirements for Safety Significance Categorization of

Snubbers Using Risk Insights and Testing Strategies for

Inservice Testing of LWR Power Plants

July 1, 2000A

The method used for categorizing snubbers could result in

certain snubbers being inappropriately categorized as having

low safety significance. These snubbers would not be

adequately tested or inspected to provide assurance of their

operational readiness. In addition, unexpected extensive

degradation in feedwater piping has occurred which would

necessitate a more rigorous approach to snubber categorization

than presently contained in this Code Case.
RG 1.193, Rev. 1, Page 13

D. IMPLEMENTATION

The purpose of this section is to provide information to applicants and licensees regarding

the NRC staff’s plans for using this guide. No backfitting is intended or approved in connection

with the issuance of this guide.

Except when an applicant or licensee proposes or has previously established an acceptable

alternative method for complying with specified portions of the NRC’s regulations, the methods

described in this guide will be used in evaluating (1) submittals in connection with applications

for construction permits, design certifications, operating licenses, and combined licenses, and

(2) submittals from operating reactor licensees who voluntarily propose to initiate system modifications

that have a clear nexus with this guidance.

E. REGULATORY ANALYSIS

This regulatory guide lists only the Code Cases that the NRC staff has determined to be

unacceptable for use in the design and construction, inservice inspection, and inservice testing of nuclear

power plant systems and components. Therefore, the NRC staff did not prepare a regulatory analysis for

this guide.

Previous reviews of ASME Code Cases discussed only the Code Cases that the NRC staff

determined to be acceptable. The agency developed this guide at industry request to list the Code Cases

that the NRC staff has determined to be unacceptable for use in licensee design and construction,

inservice inspection, and inservice testing programs, including a summary of the basis for disapproval. 

Providing the basis for disapproval of a Code Case affords licensees the opportunity to address NRC staff

concerns through 10 CFR 50.55a(a)(3), which permits the use of alternatives to the mandated

ASME Code requirements, provided that the proposed alternatives result in an acceptable level of quality

and safety and their use is authorized by the Director of the NRC’s Office of Nuclear Reactor Regulation.

Providing the basis for disapproval of a Code Case in this guide also helps to conserve industry

resources. The cognizant ASME committees will be able to focus their attention on specific issues. 

In addition, licensees who choose to request alternatives under 10 CFR 50.55a(a)(3) will understand

the NRC staff concerns to be addressed. NRC resources will be saved because the 10 CFR 50.55a(a)(3)

process will be more efficient. When the ASME modifies a Code Case to address NRC staff concerns,

additional NRC resources will be saved because the agency will be able to generically approve the

Code Cases, thereby obviating the need for case-by-case approval. In addition, since many Code Cases

generally simplify implementation of ASME Code provisions, reduce radiological exposure, or

incorporate operating experience and technological improvements, it is anticipated that, when NRC staff

concerns have been addressed, licensees will still be able to further reduce allocated resources.