NB/Z 20250-2013Guidance for the decision on modernization for instrumentation and control system important to safety in nuclear power plants (English PDF)

Foreword

This document was issued on 8 June 2013 by the National Energy Administration of the PRC and takes effect on 1 October 2013.

It is a NB/Z guiding technical document: it does not oblige, it guides.

It is classified under ICS 27.120.20, Chinese classification F 83.

This guiding technical document was drafted in accordance with the rules given in GB/T 1.1-2009.

This guiding technical document is a modified adoption, by the redrafting method, of IEC/TR 62096:2009 Nuclear power plants - Instrumentation and control important to safety - Guidance for the decision on modernization.

Compared with IEC/TR 62096:2009 there is an adjustment of the text structure, reflected mainly in Clause 3: because former subclause 3.9 has been deleted, the former 3.10 and 3.11 have been renumbered 3.9 and 3.10.

The technical differences with respect to IEC/TR 62096:2009, and the reasons for them, are as follows: Figure 1 and the associated description have been deleted in order to satisfy the drafting requirements of Chinese standards; as regards the normative references, technically significant adjustments have been made in order to suit the drafting requirements and the technical conditions of Chinese standards, the adjustments being concentrated in Clause 2.

The specific adjustments are: EJ/T 1143, a modified adoption of the international standard, replaces IEC 61839, see Clause 7; NB/T 20026, an identical adoption, replaces IEC 61513, see 6.4.2; NB/T 20027, an identical adoption, replaces IEC 62241, see 7.14; NB/T 20054, a modified adoption, replaces IEC 60880, see 6.4.2; NB/T 20060, a modified adoption, replaces IEC 60709, see Clauses 6 and 7; NB/T 20072, a modified adoption, replaces IEC 61888, see 7.17; references to EJ/T 529, GB/T 11684, GB/T 12727 and GB/T 13625 have been added, see 6.4.2; and the references to IEC 60050-191:1990, IEC 60300-3-3:2004, IAEA-TECDOC-1066:1999 and IAEA:2007 have been deleted.

The term nuclear safety and its definition, formerly 3.9, have been deleted in order to satisfy the drafting requirements of Chinese standards.

The Chinese documents having a corresponding relationship with the international documents normatively referenced in this guiding technical document are: EJ/T 529 Digital computers for systems important to safety in nuclear power plants (EJ/T 529-1990, IEC 60987:1989, eqv); EJ/T 799-2006 Determination and maintenance of trip setpoints for safety system instrumentation in nuclear power plants (IEC 61888:2002, EQV); EJ/T 1143-2002 Nuclear power plant control room design - Function analysis and assignment (IEC 61839:2000, MOD); GB/T 11684 Electromagnetic environmental conditions and test methods for nuclear instruments (GB/T 11684-2003, IEC 61000 series, NEQ); GB/T 12727 Quality qualification of electrical equipment of the safety system of nuclear power plants (GB/T 12727-2002, IEC 60780, MOD); GB/T 13625 Seismic qualification of electrical equipment of the safety system of nuclear power plants (GB/T 13625-1992, IEC 60980:1989, eqv); NB/T 20026-2010 General requirements for instrumentation and control systems important to safety in nuclear power plants (IEC 61513:2001, IDT); NB/T 20027-2010 Alarm functions and displays of the main control room of nuclear power plants (IEC 62241:2004, IDT); NB/T 20054-2011 Computer software performing category A functions in instrumentation and control systems important to safety in nuclear power plants (IEC 60880:2006, MOD).

This guiding technical document was proposed by the Nuclear Power Standardization Technical Committee of the Energy Industry.

This guiding technical document is under the administration of the Nuclear Industry Standardization Research Institute.

Drafting organizations of this guiding technical document: CGN Engineering Co., Ltd.; Shenzhen CGN Engineering Design Co., Ltd.; Nuclear Power Institute of China.

1 Scope

NB/Z 20250-2013 is the Chinese guiding technical document for deciding whether, and how, to modernize the instrumentation and control systems important to safety in an operating nuclear power plant. It exists because of a mismatch of lifetimes: a reactor is built to run for sixty years, while the analogue cabinets, recorders and control computers installed with it become unsupportable in twenty. The trigger for replacing them is rarely the attraction of the new equipment; it is that spare parts for the old equipment have run out, that the vendor no longer exists, or that nobody left in the plant knows how to maintain it. But replacing the protection system of a running reactor is one of the most consequential projects a utility undertakes, because it touches the very systems that exist to make the plant safe, and because the analogue-to-digital move introduces failure modes the original design never contemplated, above all software common cause failure across redundant channels. This document is the framework for making that decision defensibly rather than by drift. Clause 5 separates the economic reasons from the safety reasons and requires them to be argued on a life cycle cost basis rather than on purchase price. Clause 6 sets out the decision process itself, from the long-term I and C strategy through the feasibility study to the tender specification and procurement, so that individual replacements add up to a coherent target architecture instead of a patchwork of vendors. Clause 7 is the substance: twenty-six considerations that a modernization has to answer, among them safety classification, equipment and software qualification, defence in depth and diversity analysis, reliability, human factors, isolation against fire and flood, setpoint and uncertainty recalculation, response time analysis, configuration management, interfaces with the systems that are not being replaced, and the retraining of the operators who will use the new interface. Clause 8 covers implementation and the sequencing of the upgrade steps, and Clause 9 gives the recommendations. The document is a modified adoption of IEC/TR 62096:2009, with the international normative references replaced by their Chinese equivalents. It was issued on 8 June 2013 by the National Energy Administration and took effect on 1 October 2013.

This guiding technical document provides guidance for making and preparing the decision to modernize all or part of the instrumentation and control (I and C) system of a nuclear power plant. Its content covers:

- the reasons for modernizing the I and C system;

- the main trade-offs to be considered between the different modernization options for the I and C system;

- the technical and economic principles for establishing a long-term I and C strategy;

- the main aspects to which a technical feasibility study has to pay attention.

This guiding technical document applies to the renewal or modification of all or part of the I and C system of a nuclear power plant, with the emphasis on improving the safety performance of the reactor and on improving the human-machine interface. It does not specify the design requirements of the I and C system.

2 Normative references

The following documents are indispensable for the application of this document. For dated references, only the edition cited applies to this document. For undated references, the latest edition, including all amendments, applies to this document.

EJ/T 529 Digital computers for systems important to safety in nuclear power plants (EJ/T 529-1990, IEC 60987:1989, eqv)

EJ/T 1143 Nuclear power plant control room design - Function analysis and assignment (EJ/T 1143-2002, IEC 61839:2000, MOD)

GB/T 11684 Electromagnetic environmental conditions and test methods for nuclear instruments (GB/T 11684-2003, IEC 61000 series, NEQ)

GB/T 12727 Quality qualification of electrical equipment of the safety system of nuclear power plants (GB/T 12727-2002, IEC 60780, MOD)

GB/T 13625 Seismic qualification of electrical equipment of the safety system of nuclear power plants (GB/T 13625-1992, IEC 60980:1989, eqv)

NB/T 20027 Alarm functions and displays of the main control room of nuclear power plants (NB/T 20027-2010, IEC 62241:2004, IDT)

NB/T 20054 Computer software performing category A functions in instrumentation and control systems important to safety in nuclear power plants (NB/T 20054-2011, IEC 60880:2006, MOD)

NB/T 20060 Separation criteria for instrumentation and control systems important to safety in nuclear power plants (NB/T 20060-2012, IEC 60709:2004, MOD)

NB/T 20072 Determination and maintenance of trip setpoints for safety system instrumentation in nuclear power plants (NB/T 20072-2012, IEC 61888:2002, MOD)

IEC 60964:2009 Nuclear power plants - Control room - Design

IAEA-TECDOC 1147:2000 Management of ageing of I and C equipment in nuclear power plants

3 Terms and definitions

3.1 availability

The ability of an item to perform its required function under given conditions at a given instant or over a given time interval, assuming that the required external resources are provided. Note: the availability of an item depends on the combined effect of its reliability, its maintainability and its maintenance support.

3.2 configuration management

The process of identifying and documenting the characteristics of the structures, systems and components of a facility, including computer systems and software, and of ensuring that changes to those characteristics are properly described, evaluated, approved, issued, implemented, verified, recorded and incorporated into the documentation of the facility.

3.3 human machine interface

The interface through which the operating personnel exchange information with the I and C systems and the computer systems of the plant, including displays, controllers and the interfaces of the operator support systems.

3.4 I and C system

A system based on electrical, electronic and programmable electronic technology that performs I and C functions together with the service and monitoring functions related to the operation of the system itself. Note: the term is used as a collective name for all the components of the system, such as internal power supplies, sensors, other input devices, data buses and other communication links, actuator interfaces and other output devices. Different functions within the system may use dedicated resources or may share resources.

3.5 life cycle

The period from the conceptual phase of a product to its retirement.

3.6 life cycle cost

The cumulative cost of a product over its whole life cycle.

3.7 maintainability

The probability that, for an item used under stated conditions, a stated effective maintenance activity can be completed within a stated time using stated procedures and resources under stated maintenance conditions.

3.8 modernization

The renewal or modification of an existing system or of its components by means of a new system or new components. Renewal means the replacement of equipment carried out without changing the requirements of the existing system; modification means an upgrade carried out in order to add functional requirements or to raise performance requirements. Note 1: replacement and renewal have similar meanings and the two terms may be used interchangeably; both may apply to a single component or to a complete I and C system. Note 2: upgrade and modification have similar meanings and the two terms may be used interchangeably; both may apply to a single component or to a complete I and C system.

3.9 requirements

A statement in the content of a document concerning criteria that have to be satisfied; if the requirements are to be carried out in accordance with that document, no deviation from them is permitted. [ISO/IEC Directives, Part 2, 2004, 3.12.1] Note: requirements are divided into the following kinds: a) safety requirements, imposed by the nuclear safety regulatory authority on the basis of the effect of the nuclear power plant on the public, on society and on the environment during its lifetime; b) functional and performance requirements, the functional requirements specifying the response action that the system has to perform for a particular signal or condition, and the performance requirements specifying the characteristics of the system such as response time and accuracy; c) operating requirements, the mandatory requirements placed by the owner on the operating capacity and the operating capability of the plant; d) plant design requirements, the technical requirements placed on the overall design of the nuclear power plant in order to satisfy the safety requirements and the operating requirements; e) system design requirements, the design requirements placed on each of the systems that make up the whole nuclear power plant in order to satisfy the plant design requirements; f) equipment requirements, the requirements placed on each item of equipment in order to satisfy the system design requirements.

3.10 specification

A document that states the requirements, the design, the performance and the other characteristics of a system or component in a complete, accurate and verifiable manner. Normally the document also states the corresponding procedures for determining whether those provisions have been satisfied.

4 Abbreviations

The following abbreviations apply to this document.

CAD: Computer Aided Design

CDF: Core Damage Frequency

CMF: Common Mode Failure

DCS: Distributed Control System, or Digital Control System

EMC: Electromagnetic Compatibility

EMI: Electromagnetic Interference

FAT: Factory Acceptance Tests

HMI: Human Machine Interface

I/O: Input/Output

I and C: Instrumentation and Control

LOCA: Loss Of Coolant Accident

PAM: Post Accident Monitoring

PLC: Programmable Logic Controller

PSA: Probabilistic Safety Assessment

SAT: Site Acceptance Tests

SCC: Station Control Computer

V and V: Verification and Validation

VDU: Visual Display Unit

3D: Defence-in-Depth and Diversity

5 Reasons for modernization

5.1 General

The reasons for modernization arise mainly from consideration of the benefits in two respects: economics and safety. Replacing the existing I and C equipment with more advanced equipment can normally increase the functions of the system and improve its performance, but in most cases the main reason for upgrading the equipment is that there are problems with the old equipment, rather than the benefits that the new equipment may bring.

5.2 Economic reasons

5.2.1 General

The optimisation of the economic benefit should use the life cycle cost method, considering not only the reduction of cost but also the increase of output.

5.2.2 Reduction of cost

Cost can be reduced in the following respects:

a) operating costs: modernization can raise efficiency, so saving fuel, reducing energy consumption, saving consumables or reducing manpower requirements, and thereby reducing operating costs.