Guidelines for reliability assurance This case study includes examination of ways to defend against three types of hazards:
The hazards triggering this accidence were due to hardware failure, namely, two valves that were stuck open. The common practice to prevent this kind of fault is by choosing components of high reliability.
Guidelines for reliability assurance
Not always we can find components of high reliability. This is especially true about the PORV
state indicator, which had to work in high temperatures. This implies that we should focus on early detection of faults.
It is possible and quite easy to define operational rules about the desired vs. forbidden relationships between the primary operational
mode and those of sub-systems. For example, such a rule may be that maintenance
activities regarding the safety add-ons (such as secondary and auxiliary pumps) are allowed only when the system is in any primary
mode other than production.
These rules can be implemented in the Scenario analyzerand stored in a scenario database. In the recommended architecture, the compliance with the rules can be checked by the scenario center.
Guidelines for scenario-situation compatibility assurance
In this case study, the operators did not perceive properly the system situation, and consequently, they made the wrong action, turning off the auxiliary pumps.
The guide suggests that rules about the proper system behavior should be defined and implemented also for exceptional situations.
The system had the data, based on various sensors, which enable analysis of the system
situation better than that obtained by reading the pressure.
The rules could be applied to provide better information to the operators, to prevent the mistake.
Updated on 20 Apr 2016.