Safety analysis scope

Progress has been made recently in the scope and quality of safety analysis reports for NPPs in the region and significant activities related to LPS conditions are ongoing in several NPPs. However, the reports are still neither systematic nor complete regarding LPS conditions. This is inconsistent with the relatively high probability of the corresponding events. The situation does not differ considerably between eastern and western countries. 

As already mentioned, the scope and depth of the analyses may differ. If only the left-hand side of the bow-tie diagram is treated, we are dealing with a probabilistic safety analysis. Its results are the expected frequencies of undesired events. The objectives then are to identify weak points and imbalances in the engineered safety systems as weU as to indicate ways for eliminating them. This is the most work-intensive part of a risk analysis. 

As illustrated in Fig. 3.2, before proceeding with a detailed System Safety Assessment (SSA), the FHA is often used to determine the need for and scope of any subseqnent analysis. An FHA may contain a high level of detail in some cases (such as for a Flight Guidance and Control System with many functional modes), but many installations may need only a simple review of the system design [AMC25.1309 para 10b(3)]. If further safety analysis is not required, then the FHA could itself be used as a complete safety assessment. 

This section identifies the codes, standards, regulations, and Department of Energy (DOE) Orders that are required for establishing the safety basis for the HCF. Only those requirements that are pertinent to the safety analysis and scope of this chapter are provided. 

DOE Order 5480.23, Nuclear Safety Analysis Reports (DOE 1992b), This order specifies the requirements for nuclear facilities to document the safety analyses that establish the adequacy of the facility safety bases. A Safety Analysis Report (SAR) is required to document the results of the safety analysis for the facility. Furthermore, as part of the SAR, the contractor is responsible for addressing the Derivation of TSRs as indicated in Section 8 under Requirements, Part b, "Scope and Content of the SAR", subsection (p). The Attachment to the Order, "Interim Guidance for DOE Order 5480.23 - SARs," Section 4, "Interpretation," Part f. Subsection d.16, provides additional guidance on the content. 

Part II of this Basic Guide to System Safety presents and briefly discusses some of the more common system safety analytical tools used in the performance of the system safety function. Through example analyses of hypothetical mechanical and/or electrical systems, the reader should become familiar with each type of system safety analysis method or technique discussed. However, it must be understood that it is not within the limited scope of this volume to provide a detailed explanation of each of these methods and/or techniques. The intention is to merely introduce the reader to the various tools associated with the system safety process. The value of each concept in the analysis of hazard risk will vary according to the individual requirements of a given organization or company. 

The scope of the safety assessment is to check that the design meets the requirements for management of safety, the principal technical requirements, the plant design and plant system design requirements given in Sections 3-6 of Safety of Nuclear Power Plants Design [1], and that a comprehensive safety analysis has been... 

The safety analysis, part of the safety assessment used in plant licensing, should proceed in parallel with the design process, with iteration between the two activities. The scope and level of detail of the safety analysis should increase as the design programme progresses so that the final safety analysis reflects the final plant design as constracted. 

The general scope of safety analysis for HWRs, covering the accident categories considered, safety barriers challenged, and the technical disciplines involved are summarized in Table 4.2. Failures in safety support systems (such as instrument air) are addressed in the PSA. 

The application must cover fhe design basis the limits on operation and a safety analysis of structures, systems, and components (SSC) of the plant as a whole. The scope and contents of the application are equivalent to the level of detail foimd in an FSAR for a currently operating commercial nuclear power plant. The NRC staff prepares an SER that describes its review findings of the plant design and how such a design meets all applicable regulations. 

As stated in DOE-STD-3009-94, a preparation guide for U.S. DOE Nonreactor Documented Safety Analysis reports, "It is not the intention of the DSA to cover safety as it relates to the common industrial hazards that make up a large portion of basic OSHA regulatory compliance." Therefore, in the context of 10 CFR 830, Subpart B requirements, the scope of HAZWOPER is taken to include those hazards, associated controls, and safety and health (S H) programs that must be identified and maintained within a Hazard Category 1, 2, or 3 facility s safety basis. 

The process for the specification of human subsystem safety requirements is no different to software or hardware although it is ai uably considerably harder due to the difficulties associated with the immense scope and variety of issues affecting the reliable performance of human tasks. This paper has examined issues relating to the consideration of human subsystem safety and has outlined the scope and activities necessary for a comprehensive human factors safety analysis. A pragmatic method was introduced that advocates the application of focused Human Factors techniques to the assurance of safety for human subsystems. 

Unusual, non-routine, non-production work, work where high energy exposures are contemplated, and maintenance projects for which the scope of the work requires a determination that pre-job planning and safety analysis would be beneficial... 

The scope of safety analysis ranges from a rough qualitative appraisal of sources of hazards, via detailed qualitative analysts, to quantitative analysis with figures concerning the expected frequency and consequences of incidents. The scope must be governed by the definition of the task. Here the following must be taken into account ... 

EOPs should be consistent with the design basis of the plant. EOPs may impact the final safety analysis report (FSAR), limits and conditions/ technical specifications and other safety documents, since the scope of EOPs extends from expected plant transients to BDBAs ... 

The functional FMEA is used to evaluate failures in one or many subsystems that function within a larger system, while the hardware FMEA examines failures in the assemblies, subassemblies, and components within those subsystems. The FMEA, therefore, has great versatility in the system safety process. The analysis can either be specialized, without regard for other subsystems which are not within the scope of the analysis, or it can be generalized to encompass total subsystem or system effects of a given failure condition. However, because the FMEA does not consider the human factors element or multiple failure analyses within a system, other types of system safety analysis tools and techniques should also be utilized. 

The frequency of in-service testing should be determined on the basis of the safety analysis in which the necessary test interval has been determined. The scope and coverage of in-service testing shotrld be determined in the computer system design and should be shown to be adeqrrate for its purpose. 

Regulatory guidelines on the requirements for safety analysis are under development in the Russian Federation and Ukraine which include requirements on the scope and methodology for DBA and BDBA analysis. ... 

The applicative case-study that supports the evaluation of the methodology and its associated tools is a system function called Compute traction orders . While being limited to one single system function, this case-study is representative of the system since it contains both critical and non-critical sub-functions and considers both realtime and operational constraints. The use-case will allow to structure and strengthen the development platform and framework of such systems, especially in the scope of multi-viewpoint system modelling (e.g. operational, functional, constructional, dysfunctional...). A simplified view of interoperability needs between system model, safety analysis and requirement management is represented in the following workflow ... 

In addition to the re-planning mentioned above, applying the RAMS validation process to each increment will also give risk and hazard analyses a gradually evolving scope. This will improve the quality of these analyses. Even if the increments cannot be installed at the customer s site, they can still be tested and run as part of a system simulation. In addition, safety analysis performed on small increments can be more focused and thus give better results [19]. 

Elements of the PSI are Safety Status Analysis (SSA) and Probabilistic Safety analysis (PSA). A security analysis to evaluate measures against external influences is not at the moment included in the scope of PSI. 

Within the scope of PSI, the safety-related status of a plant is evaluated integrally by means of PSI elements, i.e. Safety Status Analysis (SSA), Probabilistic Safety Analysis (PSA) and evaluation of performance in operational practice. 

Safety Status Analysis (SSA) provides a deterministic evaluation to verify that the requirements oriented to safety objectives have been satisfied. If this is not fully the case, operational experience gained in the plant itself and similar plants may also be used for evaluation. The extent of evidence required depends, amongst other things, on the frequency of occurrence of the respective events or their consequences. That is to say, probabilistic criteria determined within the scope of Probabilistic Safety Analysis (PSA) already play an important role in this area too. 

Quantitative assessment of plant safety and the balanced nature of the plant concept taking into account all influencing factors is effected within the scope of Probabilistic Safety Analysis (PSA). The PSA includes human error/failure events as far as they are included in the operational manuals. Human actions described in the emergency manuals are not included. 

The scope, extent and detail of the safety analysis for low power research reactors may be significantly less than is required for high power research reactors because certain accident scenarios may not apply or may need only a limited analysis. For example, the treatment of loss of coolant accidents may differ significantly, depending on the power and design of the reactor. Paragraphs 6.72-6.78 establish requirements for the scope, factors and process to be considered in the safety analysis. 

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