ML101450123
| ML101450123 | |
| Person / Time | |
|---|---|
| Issue date: | 06/17/2010 |
| From: | Dan Dorman NRC/NMSS/FCSS |
| To: | Schuleter J Nuclear Energy Institute |
| michael raddatz, 301-492-3108 | |
| References | |
| Download: ML101450123 (6) | |
Text
June 17, 2010 Ms. Janet R. Schlueter, Director Fuel & Material Safety Nuclear Generation Division Nuclear Energy Institute 1776 I Street NW Suite 400 Washington, DC 20006-3708
SUBJECT:
DESIGN FEATURES ASSOCIATED WITH THE INTEGRATED SAFETY ANALYSIS
Dear Ms. Schlueter:
This responds to your letter dated January 22, 2010, and our subsequent meeting on April 27, 2010, regarding the use of design features in lieu of designated items relied on for safety (IROFS) in the Integrated Safety Analysis (ISA). The U.S. Nuclear Regulatory Commission (NRC) appreciates the Nuclear Energy Institutes (NEIs) perspective on this issue.
The staff has reviewed the industry consensus paper transmitted by your January letter, as well as the proposed path forward discussed during the April 27, 2010, meeting.
At the April meeting, the NRC staff committed to provide a written response to the January consensus paper. Specifically, you requested that we address NEIs proposed definition for Bounding Assumptions/Design Features and the examples presented in the paper.
As the staff emphasized in the April meeting, the NRCs regulations specify that any engineered or administrative control or control system necessary to comply with performance requirements in Title 10 of the Code of Federal Regulations (10 CFR) Part 70 shall be designated as an IROFS.
In the paper, NEI proposes that Bounding Assumptions and Design Features be defined as,
[p]assive engineered features of the facility/process configuration that have insignificant possibility of failure, the safety aspect is not easily altered or degraded and do not require periodic testing or verification to ensure they remain available and reliable to perform their intended function. According to NEI, these passive engineered features would be used to establish the creditability, frequency, or consequence of the accident/criticality sequences and events identified in 10 CFR 70.61. In addition, NEI provided general descriptions of example categories of structures, systems, components and attributes of components that it believed fit the proposed definition and therefore should not be designated as IROFS.
Staff has reviewed the paper and concludes that NEIs proposed definitions, as applied through the examples, may not ensure compliance with 10 CFR Part 70. As defined in 10 CFR 70.4, IROFS are structures, systems, equipment, components and activities of personnel that are relied on to prevent potential accidents at a facility that could exceed the performance requirements in 10 CFR 70.61 or to mitigate their potential consequences, and that are designated as such in the licensees ISA. The staffs review identified that under some
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circumstances many of NEIs examples may be relied on to achieve the performance requirements of 70.61(d) and therefore would constitute IROFS under 10 CFR Part 70.
In the enclosure to this letter, the staff has provided comments on NEIs examples and when those features may be relied upon to meet the performance requirements of 10 CFR 70.61, and should therefore be designated as IROFS pursuant to 70.61(e). Whether any specific item is actually relied on at a particular facility will depend on that facilitys design and ISA.
In addition, the staff is reviewing your letter dated June 10, 2010, on this subject. In that letter, you provided an industry proposal regarding a path forward to resolve these issues. The industry proposal includes emphasis on defining the terms design features and bounding assumptions. Based on the discussion above and in the enclosure, the staff concludes that additional issues will require resolution to ensure a consistent understanding and application of regulatory requirements. Specifically, a proposed definition of new terms such as design features must be reconciled with the existing rule language regarding engineered controls in the context of compliance with performance requirements. Finally, additional guidance may be warranted to ensure the right safety focus in implementation and to prevent unnecessary burden. Examples include management of changes related to sole IROFS and graded application of management measures.
The NRC staff proposes to focus the June 28, 2010, public meeting on defining a process for resolving these issues. We will contact you in the next few days as we develop the agenda for that meeting.
In accordance with 10 CFR 2.390(d) of the NRCs Rules of Practice, a copy of this letter will be available electronically for public inspection in the NRC Public Document Room or from the Publicly Available Records component of NRCs document system (ADAMS). ADAMS is accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html (the Public Electronic Reading Room).
If you have any questions, please contact Michael G. Raddatz of my staff at (301) 492-3108 or via e-mail at michael.raddatz@nrc.gov.
Sincerely,
/RA/
Daniel H. Dorman, Director Division of Fuel Cycle Safety and Safeguards Office of Nuclear Material Safety and Safeguards
Enclosure:
Examples from Industry White Paper
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circumstances many of NEIs examples may be relied on to achieve the performance requirements of 70.61(d) and therefore would constitute IROFS under 10 CFR Part 70.
In the enclosure to this letter, the staff has provided comments on NEIs examples and when those features may be relied upon to meet the performance requirements of 10 CFR 70.61, and should therefore be designated as IROFS pursuant to 70.61(e). Whether any specific item is actually relied on at a particular facility will depend on that facilitys design and ISA.
In addition, the staff is reviewing your letter dated June 10, 2010, on this subject. In that letter, you provided an industry proposal regarding a path forward to resolve these issues. The industry proposal includes emphasis on defining the terms design features and bounding assumptions. Based on the discussion above and in the enclosure, the staff concludes that additional issues will require resolution to ensure a consistent understanding and application of regulatory requirements. Specifically, a proposed definition of new terms such as design features must be reconciled with the existing rule language regarding engineered controls in the context of compliance with performance requirements. Finally, additional guidance may be warranted to ensure the right safety focus in implementation and to prevent unnecessary burden. Examples include management of changes related to sole IROFS and graded application of management measures.
The NRC staff proposes to focus the June 28, 2010, public meeting on defining a process for resolving these issues. We will contact you in the next few days as we develop the agenda for that meeting.
In accordance with 10 CFR 2.390(d) of the NRCs Rules of Practice, a copy of this letter will be available electronically for public inspection in the NRC Public Document Room or from the Publicly Available Records component of NRCs document system (ADAMS). ADAMS is accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html (the Public Electronic Reading Room).
If you have any questions, please contact Michael G. Raddatz of my staff at (301) 492-3108 or via e-mail at michael.raddatz@nrc.gov.
Sincerely,
/RA/
Daniel H. Dorman, Director Division of Fuel Cycle Safety and Safeguards Office of Nuclear Material Safety and Safeguards
Enclosure:
Examples from Industry White Paper DISTRIBUTION:
FCSS r/f ML101450123 OFFICIAL RECORD COPY OFFICE:
TSB TSB TSB SPTSD OGC FCSS NAME:
MRaddatz PJenifer PSilva MBailey BJones DDorman DATE:
5/25/10 5/24/10 6/4/10 6/8/10 6/7/10 6/17/10
Examples from industry white paperNone of the examples has enough context provided; the safety function they perform and the manner in which they are relied on to meet the performance requirements (e.g., whether safety is based on other controls) is not specified.
Example Comments 1
Most installation dimensions, e.g., spacing between favorable-geometry tanks that prevents significant neutron interaction If spacing and tank dimensions are included in the criticality safety models and it is determined that these dimensions are used as geometry control to meet the performance requirement of 10 CFR 70.61[d] and ensure subcriticality (under normal and credible abnormal conditions), they must be designated an item relied on for safety (IROFS) per 70.61(e).
2 Open-top cylindrical vessels whose outside diameter falls within the favorable-geometry requirement If the diameter of the vessel must be maintained to ensure subcriticality, in order to meet the performance requirements, it must be designated an IROFS.
3 A funnel break or break-tank between process vessels that protects against backflow, when it is designed so there exists no credible physical mechanism to force fluid in reverse through it, or to plug the atmospheric discontinuity in such a way as to allow backflow If the funnel break or break-tank is relied on to prevent backflow from favorable to unfavorable geometry, in order to meet the performance requirements it must be designated an IROFS.
4 Building structures that meet local building codes in effect at the time of construction If building structures are being credited to meet performance requirements then they may need to be identified as IROFS.
The fact that they are built to code may be the appropriate management measure. However, in either case they direct the reviewer (or ISA team) to the assumptions for wind load, snow load, seismic resistance, fire rating, etc., that the team would use later when evaluating the progression of a sequence.
The qualifier used in this example, in effect at the time of construction, would serve as a reminder to the reviewer that an existing buildings design attributes may differ from the current building code and a little more analysis may be required.
5 Flat, impermeable floors without deep collection points (e.g., sumps), such that credible liquid spills cannot reach the minimum depth or areal density required for nuclear criticality If the geometry of the floor is relied on to prevent exceeding a safe solution depth in order to meet the performance requirements, it must be an IROFS.
6 Routing of liquid-containing pipes far enough away from If the fact that there are no liquid-bearing pipes in the area is
2 Example Comments moderation-controlled areas that no credible leak or spray can adversely impact such areas credited to meet the performance requirements, it must be designated an IROFS.
7 Sealed buildings designed to prevent the dispersion of a source term beyond the containment area.
Buildings are designed for controlled ventilation, directing airflows from areas of low contamination toward areas of higher contamination to meet Part 20 requirements. This concept requires a ventilation system consisting of ductwork, fans, and usually HEPA filters, plus other accessories, and is for general radiation protection or contamination control, and not as mitigation for a high or intermediate consequence scenario.
The buildings are sealed within reason, so that leakage is limited, and a flow balance can be achieved, ensuring that about 1 WG pressure differential exists between zones. A flow velocity of 150 feet per minute is generally used to ensure particulate contamination flows into an area when a door or other opening exists. If the building were credited as a containment to reduce the consequences in order to meet performance requirements, then it would have to be designated an IROFS 8
Roofs, walls, floors and other physical barriers constructed to prevent water intrusion into moderation controlled areas If these items are credited to meet the performance requirements for credible sequences, they must be designated as IROFS.
9 Structural components such as concrete equipment bases, fixed geometry conveyor systems, rod tray storage cabinets, and fuel assembly storage racks If these items are relied on to maintain a minimum safe spacing between fissile-bearing equipment, in order to meet the performance requirements, they must be designated as IROFS.
The other listed items sound like ordinary criticality safety controls and do not seem robust enough, but this is unclear from the example provided. They could be bent or relocated so they are no longer at a safe spacing. In some ISA Summaries, the pellets or cans of powder are assumed to start on the safe geometry racks, but are knocked off in a seismic event 10 Spill control measures such as curbing, sumps, dikes, and sloped floors designed to collect or control liquid releases.
At some sites, curbing is installed to prevent excessive rainfall from flowing under the door slot into an area of moderator restriction.
3 Example Comments Curbs or dikes are installed under chemical storage tanks. The dike must be able to contain the entire contents of the tank in case of a leak. However, if the licensee then takes credit for them to meet 10 CFR 70.61(b) or (c), it then becomes an IROFS, and must be designated as such. These may be legitimate candidates for a Design Feature or Bounding Assumption. When evaluating the scenario, the reviewer would calculate the size of the leak, and the dike would be used when modeling the pool and its resultant evaporation rate.
The reviewer would need to examine the purpose of the sump -
collect liquid in a safe geometry, minimize surface area, provide suction head for a pump. One could agree that such plant features are resistant to change.
11 Geometrically safe piping If the dimensions of the piping are relied on the ensure subcriticality, i.e. to meet the performance requirements of 10 CFR 70.61 (d), they must be designated as IROFS.