Identification of Initiating Events

Based on the incident reports for all units, Kozloduy NPP has completed the identification of initiating events which occurred during shutdown conditions for inclusion in the PSA studies. These initiating events are classified into five groups according to the IAEA recommendations. The most important events are ... 

The identification of initiating events for process plants is difficult because of their great variety. As pointed out before chemical processes involve both physical and chemical hazards. Physical hazards derive from operating conditions which may be extreme, such as very low or very high temperatures and pressures. Chemical hazards are those associated with the materials present in the process, which may be toxic, flammable or explosible, or exhibit several of these properties at the same time. A further complication stems from the fact that some of these... 

Risk assessment - Identification of initiating events Cause analysis and consequence analysis - Risk picture... 

Identification of initiating event Various hazard identification techniques... 

One of the issues identified in the sample review of LOPAs in HSE s research report RR716 was that the identification of initiating events was not comprehensive and therefore that the frequency of demands on protection layers may have been underestimated. It is important that the process for identifying initiating events is comprehensive and that it is carried out with the involvement of those who have to perform the tank-filling operation. 

The purpose of this annex is to provide an exampie of an outiine methodoiogy for the systematic identification of initiating events that can iead to hazardous events. This methodoiogy can be used with any SiL determination (such as LOPA, fauit tree anaiysis) or other techniques used for identification of the initiating events ieading to a specific hazardous event. 

The risk picture for the regional RVA was established based on the identification of initiating events (hazards/threats) and the cause and consequence analysis (cf Section 4.3, 4.4). From an initial number of several hundred adverse events, the filtering, merging and aggregation process described in Section 4.4 resulted in 51 events in the final risk picture. 

The top event, interpreted as loss of control lead to the identification of initial events and possible end consequences. From this stage the bow-tie models functioned more as a tool for identifying failure causes and thus, the barrier elements against accident sequences. Both preventive and mitigating barriers were highlighted. 

Clarification has been given on the specification of operating conditions for Low Power and Shutdown (LPSD) states. A precise definition and identification of initiating events with special consideration of erroneous human actions before such an event occurred has been provided. In addition, a clear definition of the end states of event sequences during low power and shutdown is available. Last not least, Fire PSA methods have been adapted to these Plant Operational States (POS). 

Identification of hazards and selection of initiating events are the first steps in any risk analysis. Hazards are generally related to the physical properties of the material being transported. The properties represent the inherent risk and the potential adverse consequences if the material were released. The hazards to be considered when evaluating different movements may include ... 

Detailed identification of initiating cause causing the impact event. 

Identification of hazards and listing of initial events such as gas leakage. This work is based on generic information about the type of concept, and operational experience plays a minor role. 

An important part of hazard analysis and risk assessment is the identification of the scenario, or design basis by which hazards result in accidents. Hazards are constandy present in any chemical faciUty. It is the scenario, or sequence of initiating and propagating events, which makes the hazard result in an accident. Many accidents have been the result of an improper identification of the scenario. 

The first step-in plant-system and accident-sequence analysis is the identification of earthquake-induced initiating events. This is done by reviewing the internal analysis initiating events to identify initiating events relevant to seismic risk. For example. Table 5,1 -5 shows the initiating events that were used in the Seismic Safety Margins Research Program for a PWR plant (Smith et al., 1981)... 

Hazard Identification, the main sources of ammonia that could release are identified and the initiating events (IE) that can cause accidents leading to the release of ammonia are determined. Three methods used for IE identification were Master Logic Diagram, checklists, and HAZOP... 

The case study has documented the investigation and root cause analysis process applied to the hydrocarbon explosion that initiated the Piper Alpha incident. The case study serves to illustrate the use of the STEP technique, which provides a clear graphical representation of the agents and events involved in the incident process. The case study also demonstrates the identification of the critical events in the sequence which significantly influenced the outcome of the incident. Finally the root causes of these critical events were determined. This allows the analyst to evaluate why they occurred and indicated areas to be addressed in developing effechve error reduchon strategies. 

In April 1982, a data workshop was held to evaluate, discuss, and critique data in order to establish a consensus generic data set for the USNRC-RES National Reliability Evaluation Program (NREP). The data set contains component failure rates and probability estimates for loss of coolant accidents, transients, loss of offsite power events, and human errors that could be applied consistently across the nuclear power industry as screening values for initial identification of dominant accident sequences in PRAs. This data set was used in the development of guidance documents for the performance of PRAs. 

The model also allows quick identification of die various hazards diat result from die single initial event. 

In Section 21.4 tlie effects of the release of toxic vapors were considered in connection witli an accident sequence initiated by the failure of a plant programmable automatic controller. In tliis study, event tree analysis and fault tree analysis led to identification of tlie glycol cooling system circulation pumps as components meriting high priority for inspection. 

Regardless of the initiating process or processes leading to the development of hypertension, the ultimate goal is to reduce the risk of cardiovascular events and minimize target organ damage. This clearly requires the early identification of risk factors and treatment of patients with hypertension. 

Conduct initial screening for events of concern through identification of materials and conditions at site. 

Identification of the critical factors that may affect the initiating event evolution... 

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