Analysis of the Fallback Values of Digital Control Systems in Nuclear Power Plants †
Abstract
:1. Background
2. DCS Description
2.1. Structure
2.2. Invalidity Management
2.3. Failure Mode of Signals
- (1)
- Failure in level 0, which includes sensor failure, disconnection, signal shaking, etc.; this kind of failure is detected by input modules. After a failure, the corresponding input module detects an abnormal change in input electrical signals and then informs CPUs to set the quality state of the signal as “invalid”.
- (2)
- Failure in the level 1 component, which includes failure of input modules, power loss in the level 1 component, and so on. A CPU periodically monitors the working state of the level 1 component; after detecting a failure, the CPU sets the corresponding signal quality state as “invalid”, and the physical value of the signal in the CPU is not refreshed any more. Typical functions of a level 1 failure diagnosis include an input and output (IO) module watchdog timer diagnosis, IO module and CPU communication failure mode diagnosis, etc.
- (3)
- Communication failure within the level 1 cabinet, which includes network failure, gateway failure, etc. After a communication failure, the receiving cabinet detects the signal transmission failure and sets the network signal quality state as “invalid”, and the physical value of the signal is not refreshed any more.
3. Analysis of Fallback Values
3.1. Scope
3.2. Analysis Method for Fallback Values
- (1)
- The monitoring of signal failure, whether the failure can be monitored by operators in the main control room, and how difficult it is;
- (2)
- The consequence of signal failure, the influence on process systems and plant operation, if it will lead to automatic actions, and what the behavior of the systems involved is;
- (3)
- The functional redundancy of the signal; if there is any substitution of functions relative to the signal;
- (4)
- The safe position of the actuators, which mainly considers whether the fallback value setting is consistent with the safe position of the actuators, as long as the actuators are involved in the control logic the signal participates in.
3.3. Implementation of Fallback Values
3.4. Engineering Application
3.5. Verification and Validation
4. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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Wang, Z.; Liu, L.; Liu, Z.; Huang, Y.; Hu, M.; Ma, T. Analysis of the Fallback Values of Digital Control Systems in Nuclear Power Plants. Eng. Proc. 2023, 49, 2. https://doi.org/10.3390/engproc2023049002
Wang Z, Liu L, Liu Z, Huang Y, Hu M, Ma T. Analysis of the Fallback Values of Digital Control Systems in Nuclear Power Plants. Engineering Proceedings. 2023; 49(1):2. https://doi.org/10.3390/engproc2023049002
Chicago/Turabian StyleWang, Zhenying, Liu Liu, Zhiyun Liu, Yu Huang, Mingxin Hu, and Tingwei Ma. 2023. "Analysis of the Fallback Values of Digital Control Systems in Nuclear Power Plants" Engineering Proceedings 49, no. 1: 2. https://doi.org/10.3390/engproc2023049002