ANSI/ANS 2.26 Draft 0 Revision #12
March 26, 2003
American Nuclear Society
Categorization of Nuclear Facility
Structures, Systems and Components
For Seismic Design
an American National Standard
published by the
American Nuclear Society
555 North Kensington Avenue
La Grange Park, Illinois 60525 USA
Foreword
This standard has been developed based on methods used by the U.S. Department of Energy (DOE) for performance categorizing and designing structures, systems and components (SSCs) in nuclear facilities to withstand the effects of natural phenomena [1, 2, 3, 4].
The standard provides criteria and guidance for selecting a seismic design category (SDC) and Limit State for the SSCs important to safety in a nuclear facility. The SDC and Limit State are to be used with standards ANS 2.27, “Guidelines for Investigations of Nuclear Facility Sites for Seismic Hazard Analysis,” ANS 2.29 “Probabilistic Seismic Hazards Analysis,” and ASCE xx, “Seismic design Criteria for Structures and Seismic Input for Systems and Components in Nuclear Facilities”[5, 6, 7]. These standards together establish the level (peak ground acceleration and design spectra) of the Design Basis Earthquake and the design and construction practices to be applied to the SSCs. The objective is to achieve a risk consistent design that protects the public, the environment and workers from potential consequences of earthquakes. The referenced standards and their procedural relationship to this standard are discussed in Appendix A.
Working Group ANS 2.26 of the Standards Committee of the American Nuclear Society had the following membership at the time of approval of this standard:
Neil W. Brown, Chairman, Lawrence Livermore National Laboratory
Steve Additon, Kaiser Hill
Harish Chander, U.S. Department of Energy
Dan Guzy, U.S. Department of Energy Asa Hadjian, Defense Nuclear Facilities Safety Board
Quazi Hossain, Lawrence Livermore National Laboratory
George B. Inch, Niagara Mohawk
Calvin Morrell, Stone a& Webster
Andrew Persinko, U.S. Nuclear Regulatory Commission
Howard C. Shaffer, Consultant
John Stevenson, Consultant
Charles M. Vaughan, Global Nuclear Fuel
Contents
Foreword 2
List of Acronyms 5
1. Scope 6
2. Applicability 6
3. Definitions 7
4. Seismic Categorization 9
5. SSC Limit States 11
6. Analyses to Support Selection of SDC and Limit States 13
Appendix A Risk Informed Basis for Seismic Design Categorization and Associated Target Performance Goals 21
Appendix B Examples of SSC Placement in Limit States 29
References 34
List of Acronyms
AEGL Acute Exposure Guideline Level
ANS American Nuclear Society
ANSI American National Standards Institute
ASCE American Society of Civil Engineers
ASME American Society of Mechanical Engineers
DBE Design Basis Earthquake
DOE Department of Energy
DRS Design Response Spectra
ERPG Emergency Response Planning Guide
HEPA High Efficiency Particulate
HVAC Heating Ventilating and Air Conditioning
IBC International Building Code
NRC Nuclear Regulatory Commission
SDB Seismic Design Basis
SDC Seismic Design Category
SSC Structures, Systems and Components
USGS United States Geological Survey
UHRS Uniform Hazard Response Spectra
1. Scope
(a) This standard provides: (i) criteria and guidelines for selecting an SSC Limit State based on its safety and performance requirements and (ii) criteria for selecting the Seismic Design Category[1] (SDC) for nuclear facility structures, systems, and components (SSCs) for the purpose of designing SSCs to withstand earthquakes using methods specified in ASCE XX.
(b) The standard outlines the essential facility data and safety analyses necessary to support the seismic design categorization process.
(c) The SSC seismic design categories that this standard establishes shall be used by the facility owner and the facility designer, in conjunction with ANS 2.27, “Guidelines for Investigations of Nuclear Facility Sites for Seismic Hazard Analysis”, ANS 2.29 “Probabilistic Seismic Hazards Analysis”, and American Society of Civil Engineers standard ASCE XX, “Seismic design Criteria for Structures and Seismic Input for Systems and Components in Nuclear Facilities”. Application of these standards will produce: (i) the design basis earthquake response spectra; (ii) SSC Limit State necessary to achieve adequate safety performance during and following earthquakes; and (iii) SSC designs that achieve the desired Limit States.
2. Applicability
This standard is applicable to the design of SSCs of nuclear facilities (see definition in Section 3.) that include: nuclear fuel manufacturing facilities, nuclear material waste processing, storage, fabrication, and reprocessing facilities, enrichment facilities; tritium facilities; radioactive materials laboratories; and nuclear reactors other than commercial power reactors.
3. Definitions
Design Response Spectra: The ground motion spectra used to design the facility SSCs. For SDC-3, 4 and 5 Design Response Spectra (DRS) are defined at the base of the structure and are equal to the product of the Uniform Hazard Response Spectra (UHRS) [defined in ANS 2.29)] and the Design Factor defined in ASCEXX [described in terms of the mean peak ground acceleration at specified annual frequencies of occurrence, the Uniform Hazard Response Spectrum (UHRS), both obtained using ANS 2.27 and ANS 2.29 and a design factor used in ASCE XX.] The DRS for SDC-1 and SDC-2 are defined in IBC.
Failure Consequence: A measure of the adverse radiological and toxicological exposure of the public, the environment and workers that may result from failure of an SSC by itself or in combination with other SSCs.
Graded Approach: The process of assuring that the level of analysis, documentation and actions used to comply with requirements in this standard are commensurate with: (1) The relative importance to safety, safeguards and security; (2) The magnitude of any hazard involved: (3) The life cycle stage of the facility; (4) The programmatic mission of a facility; (5) The particular characteristics of the facility; (6) The relative importance of the radiological and non-radiological hazards; and (7) any other relevant factor.
Life Safety Function: This term is used in the same context as used in the IBC. When an SSC in a facility is designed to provide Life Safety Function, the occupants of the facility are expected to avoid serious injury and escape through the damages that might result from a design basis earthquake.
Limit State: The limiting acceptable deformation, displacement or stress that an SSC can experience during or following an earthquake and still perform its safety function. Four Limits States are identified and used by this standard and ASCE XX.
Mitigation: The process for reducing or eliminating the adverse effects or consequences of earthquake caused failures.
Nuclear Facility: A facility that stores, processes, tests, or fabricates radioactive materials in such form and quantity that a nuclear risk to the workers, to the offsite public, or to the environment exists. (Large commercial power reactors are excluded because they are covered by other standards.)
Seismic Design Basis: The combination of Seismic Design Category (1, 2, 3, 4, or 5) and Limit State (A, B, C, or D) determine the Design Basis Earthquake and acceptance criteria for designing the SSCs. For example, Seismic Design Basis 3C would use criteria given in this Standard for Seismic Design Category 3 and Limit State C.
Safety Function: An SSC shall be considered to perform a safety function if its failure, by itself or in combination with other SSCs, could result in any of the consequence levels given in Table 1 being exceeded. Also, an SSC, the failure of which may impair or adversely effect an operator action that is required for restoring another SSC safety function or for preventing or mitigating the consequences of a design basis earthquake (DBE) during and following the event shall also be considered to have a safety function.
Target Performance Goal: Target annual frequency of failure (i.e., exceeding a specified Limit State). Performance goals of 1x10-4, 4x10-5 and 1x10-5 per year are have been chosen in accordance with ASCE XX for Seismic Design Categories 3, 4, and 5 respectively. For example, the expected probability of exceeding a Limit State in Seismic Design Category 3 in any given year is less than 1x10-4. The role of Target Performance Goals in this standard is discussed in Appendix A.
Unmitigated Consequences: Consequences of failure of an SSC predicted by a safety analysis in which no credit is taken for the mitigating effects of any engineered features of the facility. The selection of a Seismic Design Category of an SSC is performed on the basis of an Unmitigated Consequence Analysis as described in Section 6.1 below.
4. Seismic Categorization
(a) The placement of an SSC in a Seismic Design Category (SDC) is based on the objective of achieving acceptable risk to the public, the environment and workers resulting from the consequences of failure of the SSC (See Appendix A for additional discussion.). Each SDC has a defined consequence severity level that shall not be exceeded. Proper placement of the SSCs in the SDCs and constructing[2] the SSCs in accordance with ASCE XX will provide an acceptably low risk to the public, the environment and workers from seismic induced SSC failures.
(b) An SSC shall be placed in one of the SDCs listed in Table 1 by comparing the unmitigated consequences listed in the table with those that may result from the failure of the SSC by itself or in combination with other SSCs. If the SSC failure consequences are the same as or less severe than those listed in Table 1 for a given SDC, the SSC shall be placed in that SDC. The comparison shall be performed for all three types of consequences listed in the table, i.e., consequences to the public, the environment and workers, and the SSC shall be placed in the highest SDC determined from these comparisons. Section 6 provides guidance on performing unmitigated consequence evaluations. An SSC will also be assigned one of four Limit State levels defined in Section 5. Thus, each SSC important to safety will be assigned to an SDC and have its Limit State identified. This set of conditions is identified as the Seismic Design Basis (SDB) used by ASCE XX.
(c) SDC 1 and 2 in conjunction with IBC and SDC 3 through 5 in conjunction with ANS 2.27, ANS 2.29 and ASCE XX shall establish the Design Response Spectra and SSC design and analysis requirements.
(d) The latest issue of ASCE XX, ANS 2.29, ANS 2.27, and IBC shall be used.
Table 1
Seismic Design Categories Based on the Unmitigated Consequences of SSC Failure
Unmitigated Consequence of SSC FailureCategory / Worker / Public / Environment
SDC-11 / No radiological or chemical release consequences but failure of SSCs would place facility workers at risk of physical injury.4 / No consequences. / No consequences.
SDC-22 / Radiological or chemical exposures to workers will have no permanent health effects. Will place more facility workers at risk of physical injury, or place emergency facility operations at risk. / Radiological or chemical exposures of public areas are small enough to require no public warnings concerning health effects. / No consequences.
SDC-33 / Radiological or toxicological releases that would place facility workers long- term health in question. / Would require off-site emergency preparedness plans to be implemented to protect the public. / No long term environmental consequences are expected but environmental monitoring may be require for a period of time.
SDC-43 / Radiological or toxicological effects that would cause long-term health problems and possible loss of life for a worker in proximity of the source of hazardous material, or place workers in nearby on-site facilities at risk. / Radiological or toxicological effects that would cause long- term health problems to an individual at the exclusion area boundary for 2 hours or more. / Environmental monitoring required and potential temporary exclusion from selected areas for contamination removal.
SDC-53 / Radiological or toxicological effects that would cause loss of life of workers in the facility. / Radiological or toxicological effects that would possibly cause loss of life to an individual at the exclusion area boundary for 2 hours or more. / Environmental monitoring required and potentially permanent exclusion from selected areas of contamination.
Notes:
1. SSCs placed in SDC-1 with Limit States A, B, and C may be designed to IBC(using Group I, II, and III, respectively in accordance with ASCE XX).
2. SSCs placed in SDC 2 with Limit States A and B may be designed to IBC (using Group I, II, and III, respectively in accordance with ASCE XX).
3. SSCs placed in SDC-3, SDC-4, and SDC-5 shall be designed to the requirements of ASCE XX and ANS 2.29.
4. SSCs in a facility with a human occupancy rate of more than 72 person hours per 24 -hour period shall be placed, as a minimum, in SDC-1. SSC failures that result in no consequence to the public or environment and present only a physical threat to the workers and therefore placed in SDC-1, shall be designed to IBC using Group I in accordance with ASCE XX.
5. SSC Limit States
SSCs that require seismic design shall be assigned to one of four Limit States defined below based on the information or data obtained from the safety analysis outlined in Section 6 and the guidance provided here and in Appendix B.
Limit State A: An SSC designed to this Limit State may sustain large permanent distortion short of collapse and instability (i.e., uncontrolled deformation under minimal incremental load), but can still perform its life safety function and will not generate missiles.
Examples of SSCs that may be designed to this Limit State are:
· Building structure that must perform a Life Safety Function.
· Systems and components designed to be pressure retaining but can perform their safety function even after developing some significant leaks following an earthquake.
Limit State B: An SSC designed to this Limit State may sustain moderate permanent distortion but still can perform its safety function. The safety function may include both structural and leak tight integrity of an SSC designed to retain fluids under pressure. Damage can be repaired.
Examples of SSC that may be designed to this Limit State are:
· Building structures that must perform a passive system or component support functions.
· Systems and components designed to be pressure retaining but can perform their safety function even after developing some minor leaks following an earthquake (i.e. they either do not contain hazardous material or the leakage rates associated with minor leaks do not exceed consequence level of assigned SDC).