GB/T 13286-2021 in English
VALIDCriteria for independence of class 1E equipment and circuits in nuclear power plants
- Issued on:2021-12-31
- Implemented on:2022-07-01
- File Format:PDF
- Delivery:Via email within 5 business days
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《GB/T 13286-2021核电厂安全级电气设备和电路独立性准则》由TC30（全国核仪器仪表标准化技术委员会）归口，TC30SC2（全国核仪器仪表标准化技术委员会反应堆仪表分会）执行，主管部门为国家标准化管理委员会。
Introduction
Core changes in the standard revision
| 2008 version | New content in the 2021 version | Technical impact |
|---|---|---|
| Optical cable requirements are not included | New optical fiber loop isolation specifications | Adapt to the development needs of digital instrumentation and control systems |
| Simple EMC requirements | Improve the electromagnetic interference evaluation system | Improve the reliability of anti-interference design |
| Retain supplementary requirements | Delete redundant requirements in Chapter 7 | Coordinate and unify with other standard systems |
Key terminology system analysis
Safety level (1E level): Equipment and systems that complete the six major safety functions such as reactor emergency shutdown and containment isolation, special attention should be paid to the fact that their functional definition does not rely on voltage levels.
Three elements for determining related circuits: 1) electrical connections are not isolated 2) physical spacing is insufficient 3) shared signal sources, any of the three is considered a related circuit.
Key points for the implementation of physical separation
Regional management
| Regional type | Judgment standard | Typical separation distance |
|---|---|---|
| Non-hazardous area | Instrument control circuit + limited power supply only | Horizontal 2.5cm/vertical 7.5cm |
| Low-hazardous area | Contains power cables below 70mm² | Horizontal 15cm/vertical 30cm |
| Hazardous area | Existence of high-energy pipelines/projectiles | Special analysis required |
Containment penetration arrangement example: Redundant penetrations need to be distributed circumferentially, and the minimum spacing refers to the cable channel requirements. When passing through non-safety-level circuits, they need to be handled according to the relevant circuits.
Innovative Practices in Electrical Isolation
Isolation Device Selection Matrix
| Device Type | Applicable Scenarios | Special Requirements |
|---|---|---|
| Optical Coupler Relay | Digital Signal Transmission | Contact Fusion Risk Needs to be Assessed |
| Fiber Optic Coupler | Cross-Regional Signal Isolation | Exemption from Isolation Distance Requirements |
| Current-Limited Charger | DC System | Current-Limiting Characteristics Need to be Verified Regularly |
Typical application misunderstanding: When the circuit breaker is used as an isolation device, its fault current interruption capability must be verified before the upper protection is activated, and the diesel generator must ensure transient current supply.
Special treatment of optical fiber circuits
The standard innovatively establishes the triple exemption principle for optical fiber circuits: 1) No isolation requirements between safety-grade optical fibers 2) No isolation requirements with non-safety-grade optical fibers 3) No impact when used as a fault source. Only when used as an affected circuit, it is necessary to maintain a distance from the energized circuit (see Table 3).
Implementation difficulties: At present, the rated operating temperature of optical fiber is conservatively taken as 40℃. In the future, the spacing requirements need to be optimized through test data. At this stage, the metal bracket fixation method can be used to reduce the vertical spacing to 2.5cm.
Recommendations for the implementation of the standard
- Establish a circuit correlation traceability system to realize the visualization of safety-level sequence identification
- Develop a three-dimensional spacing verification tool to automatically detect the compliance of cable laying
- Implement dynamic classification management for hazardous areas, and adjust measures in combination with pipeline identification status
- Fiber optic loops use a differentiated identification system, which is different from traditional cables
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