1、Graded Approaches toSetpoint DeterminationApproved 15 October 2005ISATR67.04.092005TECHNICAL REPORTISA The Instrumentation,Systems, andAutomation Society TMISA-TR67.04.09-2005 Graded Approaches to Setpoint Determination ISBN: 1-55617-968-5 Copyright 2005 by ISA The Instrumentation, Systems, and Auto
2、mation Society. All rights reserved. Not for resale. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic mechanical, photocopying, recording, or otherwise), without the prior writ
3、ten permission of the Publisher. ISA 67 Alexander Drive P.O. Box 12277 Research Triangle Park, North Carolina 27709 - 3 - ISA-TR67.04.09-2005 Copyright 2005 ISA. All rights reserved. Preface This preface, as well as all footnotes and annexes, is included for information purposes and is not part of I
4、SA-TR67.04.09-2005. This document has been prepared as part of the service of ISA the Instrumentation, Systems, and Automation Society toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Toward
5、 this end, the Society welcomes all comments and criticisms and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; Fax (919) 549-8288; E-mail: standardsisa.org. The ISA Sta
6、ndards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA standard
7、s of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical rep
8、orts to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing although their need to function may be the same, there is less need to know exactly how accurately they will function. Applying a
9、level of rigor and documentation commensurate with the safety significance of the instrument channel can save significant resources. Since these resources can then be applied to issues of higher safety significance, the overall effect is an increase in plant safety. ISA-TR67.04.09 -2005 - 12 - Copyr
10、ight 2005 ISA. All rights reserved. This paper describes a basic three category graded approach for addressing instrument uncertainties associated with indications, interlocks, setpoints, test criteria, allowable values, and action points. The strongest recommendation for this approach is its simpli
11、city. Obviously, there are indications, interlocks, setpoints, test criteria, and action points that need to be as accurate as possible and all reasonable care should be taken to estimate their performance. Also obviously, there are indications, interlocks, setpoints, test criteria, and action point
12、s that have no relationship to nuclear or personnel safety, and an experienced engineer can safely allow sufficient margin for expected performance without formal documentation. Lastly, there are the difficult-to-classify indications, interlocks, setpoints, test criteria, and action points that fall
13、 between the two clearly defined extremes. That sets up a basic three category system. Note that some instrument channels perform multiple functions, such as a channel that supports both a Reactor Trip function and a Post Accident Monitoring Function. The different functions may result in the channe
14、l being in multiple categories, since not all channel components would be used to support all functions. Other approaches may be used; its not the intent of this paper to require the use of any specific approach. However, the classification scheme used should be clearly described and controlled in p
15、lant procedures. Specific plant licensing commitments may require items to be upgraded to a more rigorous Category then the classification scheme would normally require; such individual commitments should not result in changes to the classification scheme, but should be understood to be exceptions t
16、o the classification scheme. 6 Classifying Functions Functions can be broadly classified into “Important to Safety“ and “Not Important to Safety.“ Instrumentation that supports functions that are “Important to Safety“ should be classified as either Category 1 or Category 2, depending on the rigor ne
17、eded to gain assurance that the instrument uncertainty will support the safety function. Instrumentation that supports functions that are “Not Important to Safety“ should be classified as Category 3. The paragraphs below give more detailed guidance; Annex 1 gives a graphical presentation of the proc
18、ess. Although specific classifications are plant unique, Annex 2 includes some examples of the classification process. NOTE: The basis of the classification should be consistent with the licensing basis of the facility, and should be the result of multidiscipline reviews. Licensing submittals may be
19、 required to implement a graded approach. 6.1 Category 1 Stringent Criteria Category 1 should be the default category for all nuclear safety related instrumentation as defined in ISA-67.04.01, Section 3.13. Downgrades to Category 2 or Category 3 may be appropriate as discussed below. Although specif
20、ic classifications are plant unique, Important to Safety channels would typically include: a) RTS and ESF setpoints, such as RTS Overpower Neutron Flux Trip and Reactor Coolant System High Pressure Trip b) TS LCOs and SRs, such as Core Flood Tank Pressure and Volume surveillance requirements c) Regu
21、latory Related setpoints, such as pressure a factor of 2 is generally considered acceptable. b) The margin between the setpoint or operating limit and the accident or safety analysis limit easily bounds the expected uncertainty; a factor of 2 is generally considered acceptable. c) The accident or sa
22、fety analysis is insensitive to changes in the parameter. d) PRA techniques show that the functions failure would not increases the probability of core damage by a more than a small amount. Although specific classifications are plant unique, typical candidates for downgrading from Category 1 to Cate
23、gory 2 include: a) RTS and ESF setpoints not credited in the accident or safety analyses as a primary trip for event mitigation, such as RTS anticipatory trips; b) TS LCOs and SRs that are not based on an analysis or safety limit, such as various radiation monitor setpoints; c) Regulatory Related se
24、tpoints that are not based on an analysis or safety limit, such as Appendix R requirements; d) Manually controlled actions associated with the control and operation of plant equipment where either the action is solely to prevent equipment damage; or the action controls the process at a point far bel
25、ow the analysis limit; or the action is to maintain an administrative limit, such as the minimum temperature at which LTOP administrative controls must be observed. 6.3 Category 3 Other Criteria Category 1 should be the default classification for channels performing any of the above functions. Howev
26、er, there are circumstances when downgrading to Category 3 is appropriate. Typically, functions considered for downgrade to Category 3 would include: a) All indications, interlocks, setpoints, test criteria, and action points that are not important to safety. b) Non-safety related, non-safety signif
27、icant plant control instrument channels. c) Instrument channels not included in Technical Specifications, but used to support operability of TS systems (by their exclusion from TS, these systems have already been judged less important) d) Parameters that define TS modes (these are nominal values) e)
28、 Parameters that define LCO applicability (these are nominal values) f) TS Surveillance Requirements that verify the rate of change of a parameter. ISA-TR67.04.09 -2005 - 14 - Copyright 2005 ISA. All rights reserved. Although specific classifications are plant unique, typical examples of Category 3
29、parameters include: a) Fire Protection alarm and action setpoints (not chosen quantitatively) b) Normal Operating Procedure actions points (nominal values) c) Radiation Effluent Monitor setpoints (release based on chemical sampling and volume measurements - radiation monitor only serves as a gross f
30、ailure indication) d) Decay heat removal mode minimum SG level requirements. e) Source Range and Intermediate Range neutron flux interlock setpoints. f) Jet Pump flow rate of change 7 Determining and Documenting Uncertainties 7.1 Category 1 - Stringent Criteria Instrument uncertainties should be app
31、lied. Uncertainties should be calculated in accordance with ISA 67.04.01 and ISA-RP67.04.02. All applicable uncertainty contributors should be considered. Formal documentation of the basis for classification and of the calculation should be developed and maintained. 7.2 Category 2 - Relaxed Criteria
32、 Instrument uncertainties should be considered. Uncertainties may be estimated using similarity, engineering judgment, and other less rigorous, less stringent methods, or an uncertainty calculation may be done. Alternately, a qualitative determination that the margin is large compared to the instrum
33、ent uncertainty is adequate in lieu of an uncertainty estimate or calculation. Formal documentation of the basis for classification and of the estimate or calculation or determination should be developed and maintained. The minimum recommended documentation for instrument channel functions under thi
34、s category should include the following: a) A description of the instrument channel and its required functions b) What makes this particular channel function safety significant (protects fission product barrier, mitigates the effects of design basis accidents, etc.) c) A qualitative or quantitative
35、discussion of the basis for classification of the conservatism in the analyses, the margin in the setpoint or limit, or the insensitivity of the analyses. 7.3 Category 3 - Other Interlock values, setpoints, test acceptance criteria, and action points should be chosen by engineering judgment, with ma
36、rgins for instrument uncertainties included and documented in appropriate procedures, databases, drawings, or other documents. Where the basis for classification into Category 3 is clear, the basis for classification and the estimate of instrument uncertainty do not need to be formally documented. D
37、ocumentation should be provided if there is a possibility that the instrument channels classification could come into question. This documentation should include: - 15 - ISA-TR67.04.09-2005 Copyright 2005 ISA. All rights reserved. a) A description of the instrument channel and its required functions
38、 b) A qualitative or quantitative discussion of the basis for classification - why each channel function is not safety significant. c) A qualitative or quantitative estimate of the instrument channels uncertainty. 8 Other Considerations The graded approach to determining appropriate levels of calcul
39、ation and documentation is one aspect of an overall instrument setpoint control program. Some elements of a full setpoint control program are: a) A methodology describing how to categorize instrument functions in a graded approach. b) A methodology on how to calculate Category 1 uncertainties. c) A
40、methodology on how to estimate Category 2 uncertainties. d) A methodology on how to determine interlocks, setpoints, test criteria, and action points. e) Documents that determine and control the uncertainties associated with all Category 1, all Category 2, and selected Category 3 functions. f) Docum
41、ents that determine and control the setpoints associated with all Category 1, all Category 2, and selected Category 3 functions. g) Documents listing and controlling all setpoints, including instrument setpoints and operating procedure action points. h) A process for adding, changing, and deleting s
42、etpoints from the program. i) A process for assuring that the setpoints determined and documented in the above documents are implemented in the plant. ISA-TR67.04.09 -2005 - 16 - Copyright 2005 ISA. All rights reserved. 9 References ISA ANSI/ISA-51.1 Process Instrumentation Terminology ANSI/ISA-67.0
43、4.01-2000 Setpoints for Nuclear Safety Related Instrumentation ISA-RP67.04.02-2000 Methodologies for the Determination of Setpoints for Nuclear Safety-Related Instrumentation Available from: ISA 67 Alexander Drive P.O. Box 12277 Research Triangle Park, NC 27709 Tel: (919) 990-9200 UNITED STATES NUCL
44、EAR REGULATORY COMMISSION NUREG-0800 Branch Technical Position HICB-1, Guidance on Establishing and Maintaining Instrument Setpoints Regulatory Guide 1.97 Instrumentation for Light-Water-Cooled Nuclear Power Plants to Assess Plant and Environs Conditions During and Following an Accident Regulatory G
45、uide 1.105 Instrument Setpoints for Safety-Related Systems Available from: U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Washington, D.C. 20555 - 17 - ISA-TR67.04.09-2005 Copyright 2005 ISA. All rights reserved. Annex A CLASSIFICATION FLOWCHART DOWNGRADE iF: a) The accident
46、 or safety analysis methods or assumptions can be shown to be conservative enough to easily bound expected uncertainties; a factor of 2 is generally considered acceptable. b) The margin between the setpoint or operating limit and the accident or safety analysis limit easily bounds the expected uncer
47、tainty; a factor of 2 is generally considered acceptable. c) The accident or safety analysis is insensitive to changes in the parameter. d) PRA techniques show that the functions failure would not increases the probability of core damage by a more than a small amount. Category 2 Default - Category 1
48、 DOWNGRADE IF: a) All indications, interlock values, setpoints, test acceptance criteria, and action points that are not important to safety. b) Non-safety related, non-safety significant plant control instrument channels. c) Instrument channels not included in Technical Specifications, but used to
49、support operability of TS systems (by their exclusion from TS, these systems have already been judged less important) d) Parameters that define TS modes (these are nominal values) e) Parameters that define LCO applicability (these are nominal values) f) TS Surveillance Requirements that verify the rate of change of a parameter. Category 3 This page intentionally left blank. - 19 - ISA-TR67.04.09-2005 Copyright 2005 ISA. All rights reserved. Annex B CLASSIFICATION EXAMPLES Example 1 Instrument channel function: PWR pressurizer pressure, normal surveill
