Event based procedures

Historically, the first sets of emergency procedures used at nuclear power plants before TMI consisted entirely of event based procedures. This means that all the procedures in the package were scenario dependent. Behind any set of event based procedures is a triple initial assumption that  

Procedures which use plant symptoms/states for the operator to diagnose the actual status of the plant are termed symptom/state based procedures. The concepts of symptoms/states have been introduced in order to respond to the need for reliable and continuous plant diagnosis. The operators in the control room monitor the evolution of the accident by means of the major plant symptoms/states  

In modern EOF packages the following implicit assumptions are applied 

The advantage of these EOF packages is continuous or repetitive diagnosis, which helps to correct any initial misdiagnosis and to ensure that the operators respond to changing plant conditions that could be more threatening to the core integrity than the initial event. Experience indicates that events can also evolve differently than predicted by pure analysis because they can evolve into a combination of events and operator errors over time. 

---

Steady-state procedures that require routine operator intervention can be either event- or time-based. Event-based procedures are usually performed in response to a system change or condition. For example, with regard to the cooling tower example, the facility may have event-based procedures to handle issues such as adding chemicals to the water, or controlling the temperature of the water. Time-based procedures are those that are to take place at a specified time interval. For example, the operator may have to catch a sample of the cooling water every 4 hours in order to check the chemical concentrations in the water. Many maintenance-related activities, such as checking the lube oil level in pumps, are time based. 

The Paks Nuclear Power Plant (NPP) experience with respect to development of symptom-based emergency operating procedures (EOPs) was reported. These symptom based EOPs improve the performance of the plant in the event of an incident or accident because they provide a framework within which all critical safety functions can be monitored and appropriate actions taken. They provide a complement to event-based procedures because it isn t possible to anticipate all plant events, particularly combinations of individual events. The Paks NPP staff have integrated the existing event-based procedures with symptom-based EOPs to provide a comprehensive framework to appropriately respond to all abnormal and emergency conditions. 

Event based procedure a procedure that contains actions which are appropriate only for a specific accident sequence (or set of sequences), which must be diagnosed before applying the procedure. An event based procedure may or may not be symptom based. 

In almost all nuclear power plants there is a series of old event based procedures that respond to a wide range of events. Since the effort associated... 

The verification process supports comparison of the EOFs with all of the documents used as sources in EOF development. These would include the plant specific writer s guide, the reference/generic set of EOFs, plant difference documents, plant technical specifications, FSAR, event based procedures used in writing EOFs, etc. Additionally, the verification guide will provide for preparation of the verification, assessment, resolution of problems and documentation of the verification process ... 

Technical accuracy means that the EOPs are consistent with the EOP source documents. These include all of the reference documents used to develop the EOPs. Examples are the EOP technical bases document, FSAR, limits and conditions, event based procedures, etc. The verification of technical accuracy requires that evaluation criteria be developed. These criteria should encompass entry conditions/symptoms/states, sequences/steps/notes/warnings, quantitative information and hardware ... 

Consideration should be given to the inherent limitations of event based procedures. These are ... 

The periodic reviews will be event-based or time-based exercises. Event-based reviews will normally be carried out if there is a controlled change made to the computerized operation that is outside the scope of the original validation and could impact on process or product quality attributes. This will normally be conducted in conjunction with the change control procedure (see Sec. IX.C), and should include a review of all relevant validation documentation to determine the extent of revalidation that may be required. 

Even with access to both a viable chemical system and a routine procedure for monitoring interfacial events based on electrochemistry, it is necessary to develop appropriate strategies for attachment of the chemical sites to electrode surfaces. We have investigated three different approaches based on a) chemical links using covalent bond formation, b) physical adsorption of premade polymers, c) electropolymerization at the electrode surface. All three techniques have their own particular nuances and will be discussed in more or less the chronological order in which they were applied to the attachment of Ru-bpy complexes. 

Procedural, object-oriented, visual, symbolic, pipeline-based, event-based... 

Systems theory provides a much better foundation for safety engineering than the classic analytic reduction approach underlying event-based models of accidents. It provides a way forward to much more powerful and effective safety and risk analysis and management procedures that handle the inadequacies and needed extensions to current practice described in chapter 2. 

Detailed investigation of accident scenarios modeled in Czech PSA projects has led to the conclusion that, at least for major subset of aU actions performed in response to initiating event occurrence and driven by symptom based procedures, lack of time should not be relevant issue. Thus, the time-versus-reliabiUty curves (for short time windows) are used just in some few very special cases of potential lack of time (with time windows shorter than 30 minutes), mostly connected with necessity to recover plant critical safety functions. 

Symptom based procedures can be directly used as the best information source for building of accident scenarios models and accident sequences logic covering the phase of control room crew response to initiating event. According to current requirements, the symptom based procedures set developed for specific plant should cover response to all initiating events defined in plant PSA. 

Quantitative methods in AET rely on localization techniques to determine the coordinates of the emission souree, to image cracks in the material. The method used to localize AE events depends on the geometry of the object being tested, and whether the resolution is required in one, two or three dimensions. Although a detailed description of these methods is the focus of Chap. 6, basic concepts - in particular using full waveforms - are described in this chapter for completion and to understand signal-based procedures. 

Either event based or symptom based procedures shall be developed for abnormal conditions and design basis accidents. Emergency operating procedures or guidance for managing severe accidents (beyond the design basis) shall be developed . ... 

Scenario dependent procedure is a general term apphcable to any event based (i.e. event specific) procedure. These procedures are developed and optimized to respond to a specific event or category of events, as would typically be the case for design basis accidents. It should be noted that the event specificity applies to individual procedures within the EOF package. 

For anticipated operational occmrences and accident conditions, the OPs should provide instructions for the recovery. For design basis accidents (DBAs), these procedures to keep the plant state within specified limits may be event based or symptom based. For beyond design basis conditions, the instractions will be symptom based that is, they will use parameters indicating the plant state to identify optimum recovery routes for the operator without the need for accident diagnosis. 

Symptom based EOPs can resolve some of the limitations of the event based approach by formally defining and prioritizing the major critical safety functions. In symptom based procedures, the decisions for measures to respond to events should be specified with respect to the symptoms and the state of systems of the plant (such as the values of safety parameters and critical safety functions). This allows the operator to maintain optimal operating characteristics without the need to be concerned with the continuing accident scenario. The method for monitoring plant parameters used in the symptom based approach is in accordance with the needs of the plant staff in severe accident conditions. 

Since the Three Mile Island accident, considerable effort has been devoted to the development of "symptom-based" procedures to replace (or at least significantly augment) the event-specific procedures. The basic premise underlying these symptom-based procedures is that there is a limited set of critical safety functions (CSFs), which, if successfully performed by either automatic plant response or manual action, result in a "safe" condition for the plant. The basic goal of the plant safety systems and the ultimate goal of operator actions is to ensure the performance of these critical safety functions. Symptom-based operating procedures relate critical safety function performance to specific plant/control room instruments. 

Symptom-Based Procedures Simulator Training Math Fundamentals Reactor Event Reports... 

The staff has determined that it is not necessary to issue symptom-based status trees when adequate event-based Abnormal Condition Control (ACC) procedures are in place in the control room. This is due to the significant amount of development and operator training required prior to issuing EOPs. This waiver is, however, conditional on WSRC demonstrating that the event-based ACCs are adequate for response to accident conditions. Reactor Training and Procedures (RTAP) has endeavored to evaluate the acceptability of the ACCs by the use of the simulator. Event-based ACCs that are delineated in SAR Chapter 15 Accident Condition Categories 11, III, and IV, with the exception of the Loss of All AC Power procedure, were reviewed and simulator malfunction codes were identified for each accident that could be performed on the simulator. The ACC procedures required for use in responding to each accident were evaluated by operators who respond to each of these accident scenarios. Only those ACC procedures necessary for response to specific... 

---