1、Copyright 2011 ISA. All rights reserved. AMERICAN NATIONAL STANDARD ANSI/ISA-67.04.01-2006 (R2011) Setpoints for Nuclear Safety-Related Instrumentation Reaffirmed 13 October 2011 ANSI/ISA-67.04.01 - 2006 (R2011) Copyright 2011 ISA. All rights reserved. 2ANSI/ISA-67.04.01-2006 (R2011) Setpoints for N
2、uclear Safety-Related Instrumentation ISBN: 978-1-937560-15-7 Copyright 2011 by ISA The International Society of Automation. 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 a
3、ny form or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher. ISA 67 Alexander Drive P. O. Box 12277 Research Triangle Park, North Carolina 27709 USA ANSI/ISA-67.04.01 - 2006 (R2011) Copyright 2011 ISA. All rights rese
4、rved. 3Preface This preface, as well as all footnotes and annexes, is included for information purposes and is not part of ANSI/ISA-67.04.01-2006 (R2011). The standards referenced within this document may contain provisions which, through reference in this text, constitute requirements of this docum
5、ent. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this document are encouraged to investigate the possibility of applying the most recent editions of the standards indicated within this document. Members of I
6、EC and ISO maintain registers of currently valid International Standards. ANSI maintains registers of currently valid U.S. National Standards. This document has been prepared as part of the service of ISA toward a goal of uniformity in the field of instrumentation. To be of real value, this document
7、 should not be static but should be subject to periodic review. Toward 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 (91
8、9) 549-8411; Fax (919) 549-8288; E-mail: standardsisa.org. The ISA Standards 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 De
9、partment is further aware of the benefits to USA users of ISA standards 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 a
10、ll new and revised standards, recommended practices, and technical reports 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 b) provide containment isolation; c) provide reactor core co
11、oling; d) provide for containment or reactor heat removal; or e) prevent or mitigate a significant release of radioactive material to the environment or is otherwise essential to provide reasonable assurance that a nuclear power plant or nuclear reactor facility can be operated without undue risk to
12、 the health and safety of the public. 3.11 Performance test: a test that evaluates the performance of equipment against a set of criteria. The results of the test are used to support an operability determination. 3.12 Reference accuracy (also known as Accuracy Rating as defined in ANSI/ISA-51.1-1979
13、 1993): a number or quantity that defines a limit that errors will not exceed when a device is used under specified operating conditions. (See ANSI/ISA-51.1-1979 R1993.) 3.13 Safety limit (SL): a limit on an important process variable that is necessary to reasonably protect the integrity of physical
14、 barriers that guard against the uncontrolled release of radioactivity. (See 10CFR, 50.36c1iA.) 3.14 Sensor: the portion of a channel that responds to changes in a process variable and converts the measured process variable into an instrument signal (See ANSI/ISA-51.1-1979 R1993). 3.15 Trip setpoint
15、 limiting (LTSP): the limiting value for the nominal trip setpoint so that the trip or actuation will occur before the AL is reached, regardless of the process or environmental conditions affecting the instrumentation. 3.16 Trip setpoint nominal (NTSP): a predetermined value for actuation of a final
16、 setpoint device to initiate a protective action. 3.17 Uncertainty: the amount to which an instrument channels output is in doubt (or the allowance made for such doubt) due to possible errors, either random or systematic. The uncertainty is generally identified within a probability and confidence le
17、vel. Additional definitions related to instrumentation terminology and uncertainty may be found in ANSI/ISA-51.1-1979 (R1993) and ANSI/ISA-37.1-1975 (R1982). 4 Establishment of setpoints Setpoints of nuclear safety-related instruments shall be selected such that resultant actions will correct the mo
18、nitored condition or mitigate the consequences of the monitored condition. The importance of the various types of setpoints differs, and as such it may be appropriate to apply setpoint determination requirements of different levels of rigor. For automatic setpoints that have a significant importance
19、 to safety, a rigorous setpoint methodology should be used, for example, those ANSI/ISA-67.04.01 - 2006 (R2011) Copyright 2011 ISA. All rights reserved. 11required by the plant safety analyses and related to Reactor Protection System, Emergency Core-Cooling Systems, Containment Isolation, and Contai
20、nment Heat Removal. However, for setpoints that may not have the same level of importance, the setpoint determination methodology could be less rigorous, for example, those that are not credited in the safety analyses or do not have limiting values. In all cases, the methodologies utilized shall be
21、documented, and appropriate justification for their use shall be provided. The discussions in the remainder of Section 4 are written for safety-related trip or actuation setpoints with rigorous requirements; the discussions are applicable in general for setpoints with less rigorous requirements. NOT
22、E: Although the scope of this standard is limited to nuclear power plants and nuclear reactor facilities, the same principles apply to setpoints for other nuclear facilities. 4.1 Safety Limits Nuclear power plants and nuclear reactor facilities include physical barriers that are designed to prevent
23、the uncontrolled release of radioactivity. Safety limits (SL) are chosen to maintain the integrity of these physical barriers. Safety limits can be defined in terms of directly measured process variables such as pressure or temperature. Safety limits can also be defined in terms of a calculated vari
24、able involving two or more measured process variables, such as departure from nucleate boiling ratio. 4.2 Analytical limits The analytical limit (AL) is the value of a given process variable at which the safety analysis models the initiation of the instrument channel protective action. ALs are docum
25、ented in the safety analysis calculations and/or the Updated Final Safety Analysis Report (UFSAR). Performance of the safety analyses with conservative ALs demonstrates that the established Safety Limits and other acceptance criteria are not exceeded during normal plant transients, Anticipated Opera
26、tional Occurrences, and other design basis transients. Note that only specific trip functions and/or safeguard features are required to operate for each postulated event. 4.3 Trip setpoint Trip setpoints are chosen to assure that a trip or safety actuation occurs before the process reaches the AL. T
27、rip setpoints are also chosen to assure that the plant can operate and experience expected operational transients without unnecessary trips or safeguard actuations. The limiting trip setpoint (LTSP) is the least conservative value of the nominal trip setpoint that still protects the AL. The nominal
28、trip setpoint (NTSP) can be more conservative than the LTSP due to plant conditions or as a compensatory action. The actual trip setpoint is known only at the time of measurement, as instrument uncertainty (including drift) will cause the actual trip setpoint to vary over a small range. It is the as
29、-found or as-left value when measured. See the figure for a graphical relationship between these values. ANSI/ISA-67.04.01 - 2006 (R2011) Copyright 2011 ISA. All rights reserved. 124.4 Choosing trip setpoints The choice of an LTSP requires determining the total loop uncertainty (TLU). The TLU repres
30、ents the expected performance of the instrumentation under any applicable process and environmental conditions. Note that the trip or actuation is only required to mitigate certain postulated events; only the process and environmental conditions that occur during those postulated events need be cons
31、idered. The LTSP and NTSP for a trip or actuation on an increasing process would be: LTSP = AL TLU NTSP = AL TLU Margin where margin is discretionary or may be chosen based on the methodology applied. Data used to calculate the TLU should be obtained from appropriate sources, which may include any o
32、f the following: operating experience, equipment qualification tests, equipment specifications, engineering analysis, laboratory tests, and engineering drawings. The TLU shall account for the effects of all applicable design-basis events and the following process instrument uncertainties unless they
33、 were included in the determination of the analytical limit, considering as a minimum the following: a) Instrument calibration uncertainties caused by: 1. calibration standards; 2. calibration equipment; 3. calibration method; and 4. setting tolerance. b) Instrument uncertainties during normal opera
34、tion caused by: 1. reference accuracy, including conformity (linearity), hysteresis, dead band, and repeatability; 2. power supply voltage changes; 3. power supply frequency changes; 4. temperature changes; 5. humidity changes; 6. pressure changes; 7. vibration; 8. radiation exposure; 9. process eff
35、ects; 10. instrumentation transfer functions; 11. analog-to-digital conversion; and 12. digital-to-analog conversion. c) Instrument drift All instruments may not have the same calibration interval. The drift used should be based on instrument specific calibration intervals. d) Instrument uncertainti
36、es caused by design-basis events Only uncertainties specific to the event and required period of service should be used. The use of different uncertainty components for the same process equipment for different events is permitted. Any residual effects of a design-basis event shall also be included.
37、The following are examples of these effects: 1) Temperature effects ANSI/ISA-67.04.01 - 2006 (R2011) Copyright 2011 ISA. All rights reserved. 13The uncertainties associated with event-specific temperature profiles shall be used where possible. If these are not available, use the uncertainty associat
38、ed with a bounding temperature. 2) Radiation effects The uncertainties associated with event-specific radiation exposure shall be used where possible. If these are not available, the uncertainty associated with a bounding radiation exposure (including Total Integrated Dose and rate effects) may be u
39、sed. 3) Seismic/vibratory effects The uncertainties associated with a safe shutdown or operating basis earthquake shall be used as appropriate. e) Process-dependent effects The determination of the trip setpoint allowance shall account for uncertainties associated with the process variable. Examples
40、 are (but are not limited to) the effect of fluid stratification on temperature measurement, the effect of changing fluid density on level measurements, and process oscillations or noise. f) Calculation effects The determination of the trip setpoint allowance shall account for uncertainties resultin
41、g from the use of a mathematical model to calculate a variable from measured process variables. An example is (but is not limited to) the determination of primary side power via the secondary side power calorimetric. g) Dynamic effects The behavior of a channels output as a function of the input wit
42、h respect to time shall be accounted for, either in the determination of the trip setpoint or included in the safety analyses. Normally, these effects are accounted for in the safety analyses. h) Calibration and installation bias accounting Any bias of fixed magnitude and known direction due to equi
43、pment installation or calibration method shall be either eliminated during calibration or accounted for in the uncertainty analysis. Additional guidance on determining TLUs can be found in ISA-RP67.04.02-2010, Methodologies for the Determination of Setpoints for Nuclear Safety-Related Instrumentatio
44、n. 4.5 Combination of uncertainties The uncertainty terms discussed above can be either deterministic, statistical, or some combination, and shall be combined using appropriate techniques. The result of the combination shall be a value that represents the performance of the instrumentation, either w
45、ith a 95% probability, or (where information is limited) with high probability as justified by reasonable basis. Square-root-sum-of-squares (SRSS) and arithmetic are appropriate techniques for combining uncertainties. Alternate techniques, including probabilistic modeling, stochastic modeling, or a
46、combination of these techniques may also be used. Additional guidance on combining instrumentation uncertainties can be found in ISA-RP67.04.02-2010, ANSI/ISA-67.04.01 - 2006 (R2011) Copyright 2011 ISA. All rights reserved. 14Methodologies for the Determination of Setpoints for Nuclear Safety-Relate
47、d Instrumentation. 4.5.1 Square-root-sum-of-squares method It is acceptable to combine uncertainties that are random, normally distributed, and independent by the SRSS method. When two independent uncertainties, ( a) and ( b), are combined by this method, the resulting uncertainty is ( c), where c =
48、 SQRT(a + b). 4.5.2 Arithmetic method It is acceptable to combine uncertainties that are not random, not normally distributed, or are dependent by the arithmetic method. In this method, the combination of two dependent uncertainties, (+a, -b) and (+c, -d), results in a third uncertainty distribution
49、 with limits + (a+c), - (b+d). 4.5.3 Test interval and scope The time between tests and the test scope may affect the magnitudes of some of the uncertainties. Therefore, the uncertainty analysis shall include consideration of the test scope and limiting test interval. 4.5.4 As-left limits The uncertainty analysis should determine an as-left band, bounding the equipment performance after calibration. This tolerance should be included in the TLU such that leaving the equipment anywhere in the as-left band will assure a trip before the AL is reached. 4.6
