Non-accident-initiated event

Non-Accident-Initiated Event An event due to causes rmassociated with the movement-related aspects of transportation (e.g., improperly closed valves or pressure build-up due to contamination). 

Non-accident-initiated events differ in that the event is not associated with an external impact during transport. Typical non-accident-initiated events that may be reviewed as part of a transportation risk analysis may not be mode-specific, and could include ... 

Step 3 Selection of Consequence Measures Transportation risks arise from the release of hazardous materials as a result of accident- and/or non-accident-initiated events. The types of impacts that may be evaluated in a QRA include impacts to people, property, the environment, disraption of supply chain activities, and other financial concerns. 

The chance of an incident is generally a function of the distance traveled. Thus, the frequency of an accident is often expressed as an accident rate per mile. Contributions from non-accident-initiated events are typically expressed on a frequency-per-hour or per-year basis. Thus, the duration of the hazardous materials movement is a key parameter. Figure 5.3 illustrates the basic calculation sequence for one trip or movement. If multiple trips are made, the total risk is equal to the number of trips times the risk per trip. The basic calculation sequence will have minor variations for each mode of transport and can be broken down into greater detail as needed. Increased detail might include different accident rates and lengths for each segment of a route or might explicitly address the accident rates and release probabilities for different accident causes. Inputs to the analysis that may be altered or may influence the calculation include ... 

In a safety risk analysis, initiating transportation events may include both accidents and non-accidents. Depending on the mode of transport. Table 3.2 details some of the types of accident-initiated events that should be considered in the risk analysis process. 

Initiating Event Accident Non-Accident Direct Attack Theft/Diversion Tampering... 

The biggest differences between safety and security are the initiating events and the factors that make up the likelihood. For safety, the initiating events usually result from accidents or other non-accident causes. For security, however, the events are from a direct or opportunistic attack with the intent to release, steal, or contaminate the contents of a shipment. 

The failure of non-structural elements such as block walls, stairs and scaffolding could have consequences for SSCs. External hazards (such as earthquakes, high winds, explosions or impacts of aircraft) could be the cause of such a failure and they are usually evaluated on the basis of Ref [5]. However, there may be situations in which the failure of non-structural elements may be caused by internal initiating events such as operator error or accidents during maintenance. The consequences for SSCs should be evaluated in these cases. Care should be taken either to avoid such failures or to minimize the potential damage to SSCs by means of proper location and adequate barrier design. 

The possibility of repair during accident situation is yet to be included into Probabilistic Safety Assessment (PSA). A PSA method Includes Event tree (ET) to generate accident scenario and Fault Tree (FT) used to quantify the probability of failure of the Safety Barrier (SB). In literature, there are some examples in which FT analysis has been done for systems with repair components. A FT analysis of phased mission systems has been performed with repairable and non-repairable components (Vaurio 2001). The other FT models with repairable basic events have been proposed based on renewal intensity principle and inclusion-exclusion methods (Yuge et al. 2012 Yuge et al. 2013). However, ET analysis of Initiating Events (IE) with repairable SB has not been dealt before. Therefore this paper proposes a scheme of PSA level-1 for systems with repairable components using a simplified combination of Repairable Event Tree (RET) and Repairable Fault Tree (RFT). 

This paper deals with the PSA level-1 studies of a nuclear system with the possibility of recovery of some failed units during accident progressions. A scheme of PSA level-1 studies with the combination of partially dynamic repairable event tree and repairable fault tree is introduced. The quantification of repairable fault tree is performed based on the concept of up-time and down-time ratio for steady state system. A case study on the PSA of ASTRID DHR system with an initiating event is performed and found that repair of some units within the grace period during accident progression can reduce the CDF considerably. In future works, the proposed scheme would be implemented using dynamic reliability methods with the considerations of common cause failures and non-linear failure behaviors. 

The accident at TMI-2 was initiated at 4 am by a minor malfunction, or transient, in the non-nuclear part of the reactor. The main feed-water pumps stopped running, caused by either a mechanical or electrical failure, which prevented the steam generators from removing heat. This minor event would... 

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