This standard is the revision of GB/T 13286-1991 "Criteria for Independence of Class 1E Equipment and Circuits in Nuclear Power Plants". This standard is equivalent to American National Standard ANSI/IEEE Std 384-1992 "IEEE Standard Criteria for Independence of Class 1E Equipment and Circuits". Revised contents concerned in this standard mainly include:
a) Adoption of the latest results of separation testing completed on electrical faults in America. Separation distance criteria had been adjusted to make it more applicable to the actual conditions;
b) According to the various combination of types and structures of all kinds of cable wiring channels likely to be presented in engineering practice, the applicable minimum separation distance had been determined respectively to make more operable of the standard;
c) Relevant provisions of "use of fuses as isolation devices" were added;
d) The definition of "maximum current and voltage transient" was added for much easier understanding;
e) Inappropriate wording in the original standard had been adjusted, to make it more succinct, definite and in conformity with the industry practice.
This standard supersedes GB/T 13286-1991 from the implementation date hereof.
This standard was proposed by China National Nuclear Corporation.
This standard is under the jurisdiction of the Institute for Standardisation of Nuclear Industry.
The drafting organization of this standard: Shanghai Nuclear Engineering Research and Design Institute.
Drafting staff of this standard: Feng Yuping and Gu Shenjie.
National Technical Committee on Nuclear Instruments of Standardization Administration of China is entrusted to in charge of the explanation of this standard.
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IEEE Foreword
This foreword is not a part of IEEE Std 384-1992 IEEE Standard Criteria for Independence of Class 1E Equipment and Circuits.
This standard provides criteria and requirements for establishing and maintaining the independence of Class 1E equipment and circuits and auxiliary supporting features by physical separation and electrical isolation.
This 1992 revision of IEEE Std 384-1981, IEEE Standard Criteria for Independence of Class 1E Equipment and Circuits, reflects the results of separation testing completed by the nuclear industry on internally generated electrical faults. The working group has performed the following activities:
(1) Assessed completed industry test reports to determine their applicability in support of changes in separation distances and reported these results to the Nuclear Power Engineering Committee (NPEC).
(2) Conducted a panel discussion on the test results at the 1988 Institute of Electrical and Electronics Engineers (IEEE) Winter Power Meeting.
(3) Presented a technical paper on the test results at the 1989 IEEE Winter Power Meeting (IEEE Paper No. 90 WM 254-3EC).
The working group’s review has resulted in changes to Chapter 4. of the standard as follows:
(1) Separation distance criteria for configurations identified in IEEE Std 384-1981 have been reduced in some cases. In other cases, insufficient testing data were available to support reducing the distances in IEEE Std 384-1981.
(2) Separation distance criteria for configurations not addressed in IEEE Std 384-1981 have been added to the standard based on test results. These configurations include cable trays and conduits, cable trays and cable in free air, and conduits and cable in free air.
Other sections of this standard have been reviewed, and many editorial improvements have been made. As part of this work, the working group assessed Nuclear Regulatory Commission (NRC) Regulatory Guide 1.75, Revision 2, which endorses IEEE Std 384-1974.
A Request for Interpretation of IEEE 384-1977 was received by the working group regarding the phrase “maximum credible voltage or current transient.” A definition of this phrase has been added to the standard.
A request for proposed revision from the DC Auxiliary Power Working Group (Nuclear Power Subcommittee of the Power Generation Committee) was received regarding the use of fuses as isolation devices in power circuits. The standard has been revised to permit the use of fuses as isolation devices in power circuits.
Section 8 of IEEE Std 384-1981 was previously included to provide interim criteria for implementation of independence requirements for safe shutdown systems required for exposure fires. 10 CFR 50, Appendix R has since been issued to provide the requirements for safe shutdown; consequently, Section 8 has been eliminated from the present issue of this standard.
The Working Group has received suggestions and recommendations regarding the application of fiber optic cabling to Class 1E circuits. However, to date, there have been no analyses or test programs submitted to the Working Group to support special criteria for separating these cables in a manner different than already provided by considering them equivalent to typical instrumentation cable. If sufficient information becomes available to justify special separation criteria, the Working Group will consider adding this criteria to the standard in a future revision.
The IEEE has developed these criteria to provide guidance in the determination of the independence requirements related to the class 1E systems of the nuclear facility. Adherence to these criteria may not suffice for assuring the public health and safety, because it is the integrated performance of the structures, the fluid systems, and the instrumentation and electric systems of the station that establish the consequences of accidents. Failure to meet these requirements may be an indication of system inadequacy. Each applicant has the responsibility to assure himself and others that this integrated performance is adequate.
The Working Group feels that the criteria herein represent an industry and government consensus for ascertaining the adequacy of the independence of Class 1E systems.
The revision to this standard was prepared by Working Group SC 5.5 of Subcommittee 6 under the NPEC.
Criteria for Independence of Class IE Equipment and Circuits in Nuclear Power Plants
1 Scope
This standard specifies criteria for the independence that can be achieved by physical separation and electrical isolation of equipment and circuits that are redundant.
This standard is applicable to the class 1E equipment and relevant electrical equipment and circuits in nuclear power plants.
This standard is not applicable to the determination of what equipment and circuits are redundant.
2 Normative References
The following standards contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below.
GB/T 12790 Method for Identification of Documents Related to Safety Class 1E Equipment and Systems for Nuclear Power Plants
EJ/T 534-1991 The Design and Installation of Cable Systems for Class 1E Circuits in Nuclear Power Plants
EJ/T 590-1991 Criteria for Design, Installation, and Qualification of Raceway Systems for Class 1E Circuits in Nuclear Power Plants
EJ/T 705-1992 Type Test of Class 1E Electric Cables and Field Splices for Nuclear Power Plants
3 Definitions
For the purposes of this standard, the following terms and definitions apply.
3.1 Acceptable
Demonstrated to be adequate by the safety analysis of the station.
3.2 Associated circuits
Non-Class 1E circuits that are not physically separated or are not electrically isolated from Class 1E circuits by acceptable separation distance, safety class structures, barriers, or isolation devices.
Note: Circuits include the interconnecting cabling and the connected loads.
3.3 Auxiliary supporting features
Systems or components that provide services (such as cooling, lubrication, and energy supply) that are required for the safety system to accomplish its safety functions.
3.4 Barrier
A device or structure interposed between redundant Class 1E equipment or circuits, or between Class 1E equipment or circuits and a potential source of damage to limit damage to Class 1E systems to an acceptable level.
3.5 Cable in free air
That portion of a cable not routed in either a raceway or an enclosure.
3.6 Class 1E
The safety classification of the electric equipment and systems that are essential to emergency reactor shutdown, containment isolation, reactor core cooling, and containment and reactor heat removal, or are otherwise essential in preventing a significant release of radioactive material to the environment.
3.7 Design basis events
Postulated abnormal events used in the design to establish the acceptable performance requirements of the structures, systems, and components.
3.8 Division
The designation applied to a given system or set of components that enables the establishment and maintenance of physical, electrical, and functional independence from other redundant sets of components.
3.9 Enclosure
An identifiable housing, such as a cubicle, compartment, terminal box, panel, or enclosed raceway, used for electrical equipment or cables.
3.10 Flame retardant
Capable of limiting the propagation of a fire beyond the area of influence of the energy source that initiated the fire.
3.11 Independence
The state in which there is no mechanism by which any single design basis event, such as a flood, can cause redundant equipment to be inoperable.
3.12 Isolation device
A device in a circuit that prevents malfunctions in one section of a circuit from causing unacceptable influences in other sections of the circuit or other circuits.
3.13 Maximum credible voltage or current transient
That voltage or current transient that may exist in circuits, as determined by test or analysis, taking into consideration the circuit location, routing, and interconnections combined with failures that the circuits may credibly experience.
3.14 Raceway
Any channel that is designed and used expressly for supporting or enclosing wires, cable, or busbars. Raceways consist primarily of, but are not restricted to, cable trays and conduits.
3.15 Redundant equipment or system
Equipment or system that duplicates the essential function of another piece of equipment or system to the extent that either may perform the required function regardless of the state of operation or failure of the other.
3.16 Safety class structures
Structures designed to protect Class 1E equipment against the effects of the design basis events.
Note: For the purposes of this standard, separate safety class structures can be separate rooms in the same building. The rooms may share a common wall.
3.17 Separation distance
Space that has no interposing structures, equipment, or materials that could aid in the propagation of fire or that could otherwise disable Class 1E systems or equipment.
3.18 Exposure fire
The fire caused by non-electrical causes or the burning materials are not cable insulation.
4 General Independence Criteria
4.1 Required independence
Physical separation and electrical isolation shall be provided to maintain the independence of Class 1E circuits and equipment so that the safety functions required during and following any design basis event can be accomplished.
4.2 Methods of achieving independence
The physical separation of circuits and equipment shall be achieved by the use of safety class structures, separation distance, or barriers or any combination thereof. Electrical isolation shall be achieved by the use of separation distance, isolation devices, shielding and wiring techniques, or combinations thereof.
4.3 Equipment and circuits requiring independence
Equipment and circuits requiring independence shall be determined and delineated during the plant design and shall be identified on documents and drawings in a distinctive manner (see GB/T 12790).
4.4 Compatibility with auxiliary supporting features
The independence of Class 1E circuits and equipment shall not be compromised by the functional failure of auxiliary supporting features. For example, an auxiliary supporting feature (such as Class 1E switchgear room ventilation) shall be assigned to the same division as the Class 1E system it is supporting in order to prevent the loss of mechanical function in one division from causing loss of electrical function in another division.
4.5 Associated circuits
4.5.1 General
Non-Class 1E power, control, and instrumentation circuits become associated in one or more of the following ways:
a) Electrical connection to a Class 1E power supply without the use of an isolation device (see Figure 1);
b) Electrical connection to an associated power supply without the use of an isolation device (see Figure 1);
c) Proximity to Class 1E circuits and equipment without the required physical separation or barriers (see Figure 2);
d) Proximity to associated circuits and equipment without the required physical separation or barriers (see Figure 2);
e) Sharing a Class 1E or associated signal source without the use of an isolation device (see Figures 3 and 8).
4.5.2 Criteria
Associated circuits shall comply with one of the following requirements.
4.5.2.1 They shall be uniquely identified as such or as Class 1E and shall remain with (traceable to the associated Class 1E division), or be physically separated the same as, those Class 1E circuits with which they are associated. They shall be subject to the requirements placed on Class 1E circuits, unless it can be demonstrated by analysis or testing that the absence of such requirements cannot degrade the Class 1E circuits below an acceptable level.
4.5.2.2 They shall be in accordance with above from the Class 1E equipment to and including an isolation device. Beyond the isolation device, such a circuit is non-Class 1E provided that it does not again become associated with a Class 1E system.
4.5.2.3 They shall be analyzed or tested to demonstrate that Class 1E circuits are not degraded below an acceptable level.
Note: Preferred power supply circuits from the transmission network and those similar power supply circuits from the unit generator that become associated circuits solely by their connection to the Class 1E distribution system input terminals are exempt from the requirements for associated circuits.
4.5.3 Qualification requirements
Associated circuits, including their isolation devices or the connected loads without the isolation devices, shall be subject to the qualification requirements placed on Class 1E circuits to assure that the Class 1E circuits are not degraded below an acceptable level. Associated circuits need not be qualified for performance of function, since the function is non-Class 1E.
4.6 Non-Class 1E circuits; general criteria
The independence of non-Class 1E circuits from Class 1E circuits or associated circuits shall be achieved by complying with the following requirements:
4.5.1 Non-Class 1E circuits shall be physically separated from Class 1E circuits and associated circuits by the minimum separation requirements specified in 5.1.3 to 5.1.5, or 5.6, except as permitted in 4.5.4, or the non-Class 1E circuits shall be associated circuits (see Figure 2);
4.5.2 Non-Class 1E circuits shall be electrically isolated from Class 1E circuits and associated circuits by the use of isolation devices, shielding, and wiring techniques or separation distance, except as permitted in 4.5.4, or the non-Class 1E circuits shall be associated circuits (see Figure 1.)
4.5.3 The effects of less than minimum separation or the absence of electrical isolation between the non-Class 1E circuits and the Class 1E circuits or associated circuits shall be analyzed to demonstrate that Class 1E circuits are not degraded below an acceptable level or the non-Class 1E circuits shall be associated circuits.
4.5.4 Non-Class 1E instrumentation signal and control circuits are not required to be physically separated or electrically isolated from associated circuits provided that:
a) the non-Class 1E circuits are not routed with associated cables of a redundant division;
b) the non-Class 1E circuits are analyzed to demonstrate that Class 1E circuits are not degraded below an acceptable level. As part of the analysis, consideration shall be given to potential energy and identification of the circuits involved.
4.7 Mechanical systems
Class 1E circuits shall be routed or protected so that failure of the mechanical equipment of one division cannot disable Class 1E circuits or equipment essential to the performance of the safety function by the systems of the redundant division(s). The effects of failure or misoperation of a mechanical system on its own division shall be considered when the Class 1E circuits or equipment are required to mitigate the consequences of such failure or misoperation. The effects of pipe whip, jet impingement, water spray, flooding, radiation, pressurization, elevated temperature, or humidity on redundant electrical systems caused by failure, misoperation, or operation of mechanical systems shall be considered. The potential hazard of missiles resulting from failure of rotating equipment or high energy systems shall be considered.
4.8 Structures and equipment
Independence and redundance of required Class 1E systems shall be maintained during and subsequent to failure of structures and equipment not qualified for design basis events.
4.9 Fire protection systems
In areas where redundant division equipment and circuits must be placed within the area of influence of a fixed fire protection system, the design of the equipment and circuits and the fire protection system shall be coordinated so that the independence of the Class 1E system will not be compromised.
4.10 Fire
4.10.1 An electrically generated fire in one Class 1E division shall not cause a loss of functions in its redundant Class 1E division.
4.10.2 The independence of redundant Class 1E circuits and equipment shall be such that a fire in a fire hazard area shall not prevent the capability to perform safety functions.
Foreword II
IEEE Foreword III
1 Scope
2 Normative References
3 Definitions
4 General Independence Criteria
5 Separation Criteria
6 Electrical Isolation Criteria
7 Class 1E Equipment and Circuits of Safe Shutdown
