ML12125A405
| ML12125A405 | |
| Person / Time | |
|---|---|
| Issue date: | 05/03/2012 |
| From: | Poole B NRC/NMSS/SFST |
| To: | Mccullum R Nuclear Energy Institute |
| Sampson M | |
| References | |
| Download: ML12125A405 (3) | |
Text
May 3, 2012 Mr. Rod McCullum, Director Used Fuel Programs Nuclear Energy Institute 1776 I Street N.W., Suite 400 Washington, DC 20006-3708
SUBJECT:
RESPONSE TO NEI JUNE 2011 LETTER REGARDING INDUSTRY POSITION ON HELIUM LEAKAGE TESTING OF DRY STORAGE SYSTEM CONFINEMENT BOUNDARIES
Dear Mr. McCullum:
By letter dated June 13, 2011, to the U.S. Nuclear Regulatory Commission (NRC), the Nuclear Energy Institute (NEI) provided an Industry Position on Helium Leakage Testing of Dry Storage Systems Confinement Boundaries (ADAMS Accession No. ML111950121). The NEI letter addressed several issues, including: (1) that Interim Staff Guidance (ISG) -25 has been used to establish new regulatory requirements through an extra-regulatory process; (2) NRC lacks adequate technical basis for the guidance provided in ISG-25, which recommends helium leakage testing for the entire confinement boundary; and (3) ANSI N14.5-1997, Radioactive Materials - Leakage Tests on Packages for Shipment, may not be appropriate for assessing dry storage system confinement boundaries. The NEI letter further stated that a revision to 10 CFR Part 72 is an appropriate regulatory process to establish a new requirement; however, development of a Regulatory Guide would be an appropriate vehicle to inform industry of one or more alternative approaches that the staff considers acceptable for meeting the regulations. By letter dated August 4, 2011, the staff acknowledged your letter and addressed the first concern regarding the role of interim staff guidance (ML112170116). NRC subsequently conducted a public meeting with NEI on September 21, 2011, to further discuss the issues identified in NEIs June letter (ML11285A013).
The staff has determined that ISG-25 continues to provide appropriate staff guidance for review of dry storage system designs. The staff reviewed the industry position, as identified in your letter and further clarified at the public meeting, considered operational experience, and performed an additional literature survey. The staff found no technical basis which would support establishing a generic exception for leakage testing of base material for all potential types of confinement materials and designs. The review indicated that confinement base materials and welds are not universally immune to flaws and unexpected failures. The staff acknowledges that ANSI N14.5 was specifically developed for demonstrating containment effectiveness of transportation packages. However, a consensus standard specifically addressing demonstration of confinement integrity for a dry storage system does not exist. Dry storage system vendors historically have adopted and specified ANSI N14.5 as the leakage testing standard for the fabrication and closure of various portions of the dry storage system confinement boundary. ANSI N14.5 provides a comprehensive method to demonstrate that no leakage exists at required test sensitivities, including the criterion for demonstrating a leak-tight containment boundary through testing (i.e., leakage rate less than or equal to 1.0 x 10-7 ref-cm3/sec). The staff notes that applicants may specify allowable leakage rates greater than the
R. McCullum ANSI N14.5 defined leak-tight criterion and perform dose analyses to demonstrate that assumed leakage does not exceed the limits specified in 10 CFR §§ 72.104 and 72.106. Staff guidance for reviewing such an approach is provided in ISG-5, Confinement Evaluation. The staff finds that helium leakage testing according to the examination criteria established by ANSI N14.5 provides a proven design-neutral method to verify confinement effectiveness of the dry storage system, including base material.
Applicants may propose other means for satisfying the applicable regulatory requirements. The staff currently is reviewing applications for dry storage system designs in which the applicant has proposed to demonstrate confinement integrity by analyses based on the unique design features and materials characteristics of the design. The staff evaluates such approaches on a case-by-case basis, given the variability in confinement designs (e.g., ML12054A791 and ML120400687). Such applications should address factors including the specific design configuration, characteristics of the selected materials of construction, resistance to defects caused by fabrication (e.g., inclusions, non-uniform concentrations, cracks, porosity, stringers, etc.), procurement and fabrication quality, and any applicable data validating the confinement performance of the design. Elements of these analyses may be specified as key design or administrative features in the technical specifications accompanying NRC approval.
As noted at the public meeting, the staff acknowledges that industry could pursue development of a new consensus standard for demonstrating integrity of the entire confinement system in the context of specific regulatory requirements in 10 CFR Part 72. The staff has participated in working groups and on Code committees for the development of consensus standards in the past and would welcome the opportunity to be involved with development of a new standard in this area.
Thank you for sharing your perspectives on this matter. If you have any questions or comments, please contact Michele Sampson of my staff at 301-492-3300.
Sincerely,
/RA/
Brooke D. Poole, Acting Director Division of Spent Fuel Storage and Transportation Office of Nuclear Material Safety and Safeguards
R. McCullum ANSI N14.5 defined leak-tight criterion and perform dose analyses to demonstrate that assumed leakage does not exceed the limits specified in 10 CFR §§ 72.104 and 72.106. Staff guidance for reviewing such an approach is provided in ISG-5, Confinement Evaluation. The staff finds that helium leakage testing according to the examination criteria established by ANSI N14.5 provides a proven design-neutral method to verify confinement effectiveness of the dry storage system, including base material.
Applicants may propose other means for satisfying the applicable regulatory requirements. The staff currently is reviewing applications for dry storage system designs in which the applicant has proposed to demonstrate confinement integrity by analyses based on the unique design features and materials characteristics of the design. The staff evaluates such approaches on a case-by-case basis, given the variability in confinement designs (e.g., ML12054A791 and ML120400687). Such applications should address factors including the specific design configuration, characteristics of the selected materials of construction, resistance to defects caused by fabrication (e.g., inclusions, non-uniform concentrations, cracks, porosity, stringers, etc.), procurement and fabrication quality, and any applicable data validating the confinement performance of the design. Elements of these analyses may be specified as key design or administrative features in the technical specifications accompanying NRC approval.
As noted at the public meeting, the staff acknowledges that industry could pursue development of a new consensus standard for demonstrating integrity of the entire confinement system in the context of specific regulatory requirements in 10 CFR Part 72. The staff has participated in working groups and on Code committees for the development of consensus standards in the past and would welcome the opportunity to be involved with development of a new standard in this area.
Thank you for sharing your perspectives on this matter. If you have any questions or comments, please contact Michele Sampson of my staff at 301-492-3300.
Sincerely,
/RA/
Brooke D. Poole, Acting Director Division of Spent Fuel Storage and Transportation Office of Nuclear Material Safety and Safeguards G:SFST\Sampson\ISG25-Response Letter to NEI-05-02-12 final.doc ML12125A405 OFC: SFST SFST SFST SFST SFST SFST SFST SFST NAME: LCruz SDePaula MDeBose MSampson DPstrak DWeaver BPoole DATE: 5/1/12 5/1/12 5/1/12 5/1/12 5/1/12 5/2/12 5/3/12