Plant Safety System Structure

FSLCM is a new technique designed to enable plant safety systems to be managed in a structured way. The technique has been designed to accommodate computer-controlled plants from start-up to shutdown, including emergency shutdowns. It aims to ensure that the safety related systems which protect and control equipment and plant are specified, engineered and operated to standards appropriate to the risks involved. The key concepts of tills technique are ... 

Safety Systems. Major expenditures here include the flare system (the flare structures and large lines extending throughout the plant) and the iirevvater system (high-capacity pumps and extensive piping). Safety systems, fortunately, are usually given particular attention. At this study phase, the main thrust should be to check the completeness of licensor equipment lists for cost estimation purposes. 

Every nuclear plant is also required to have an elaborate safety system to protect against the most serious potential problem of all, loss of coolant. If such an accident were to occur, the reactor core might melt itself down, possibly breaching the structures which contain it and releasing radioactive materials to the rest of the plant and, perhaps, to the outside environment. To prevent such an accident, the pipes carrying the coolant to and from the reactor are required to be very thick and strong. In addition, back-up supplies of the coolant must be available to replace losses in case of a leak. 

Hierarchical Approach is a simple but powerful methodology for the synthesis of process flowsheets. It consists of a top-down analysis organised as a clearly defined sequence of tasks grouped in levels. Each level solves a fundamental problem as, number of plants, input/output structure, reactor design and recycle structure, separation system, energy integration, environmental analysis, safety and hazard analysis, and plantwide control. At each level, systematic methods can be applied for the synthesis of subsystems, as chemical reaction, separations, or heat exchangers network. 

The Standard MHTGR plant is broken up into two major areas a Nuclear Island containing the four reactor modules and the Energy Conversion Area containing the two turbine generators. All "safety-related" structures, systems, and components are contained within the Nuclear Island portion of the plant. 

Table 3,2-4 lists the structures, systems, and major components of the plant and indicates the classification and, if "safety-related", the radionuclide control function of each. This correlation of equipment classified as "safety-related" to the radionuclide control function performed by each is also illustrated on Figure 3.2-2. The specific application of the classification process resulting in the indicated "safety-related" designations is discussed in Safety-Related Structures, Systems, and Components for the Standard MHTGR. (Ref. 6)... 

The SRDCs provide limiting design conditions for "safety-related" systems, structures, and. components (SSCs) and, as such, are included in the plant duty cycle. These conditions are used to ensure that the "safety-related" SSCs can be depended upon to respond to the design basis events (DBEs) to meet the dose limits of lOCFRlOO. Although the "safety related" design conditions (SRDCs) have been developed strictly as a licensing tool, they are included in the plant duty cycle to ensure that the "safety-related" SSCs can withstand the operating environment. 

The established system of three supervisory bodies has largely determined the structure of the whole complex of regulatory documents on nuclear power plant safety. 

The introduction and maintenance of a structured safety system will lead to a safety culture change within the organization. If one considers the effort, commitment, and change to the way safety is normally managed in a plant, the safety system will bring about a culture change. It will force leadership to become leaders and to create a positive environment where employees can feel comfortable participating in the safety activities. 

Every element of the safety system forms a building block of a strong safety culture. The system demands action and reaction in terms of safety, and these actions become integrated into the day-to-day activities of the plant or mine, and this culmination of actions, activities, and norms is the safety culture. The requiraneut of the structured safety system creates and maintains safety culture. 

A general agreement exists that classification of systems, structures and components of a plant from the point of view of safety and from the point of view of resistance to external actions (earthquake, and so on) is necessary to make decisions on the following ... 

The base scenarios are classified by initiating events or safety system availability which may impact on an accident progression. Left hand side of Fig. 2 represents sample database structure of analysis results for a loss of offsite power initiating event which can be applied to the OPR-1000 plant. There are 12 base scenarios depending on the operation status ofplant safety features. The operation status of safety systems are ... 

Compared with present-day LWR plants, the electric power supply systems of PIUS have been simplified significantly. The main reason for that is obviously the "inherent" self-protective functions of PIUS that eliminate many traditional safety-grade systems or reduce their importance to such extent that they can be declassified. Thus, a "two trmn" electrical supply system structure has been found fully acceptable with respect to safety and plant availability concerns. In order to improve the reliability of the power supply for important process functions, e.g. for protection of the capital investment, low voltage diesel generators are provided in the PIUS plant, but they are not safety-grade. The elimination of most of the DC distributions represents another major simplification of the electrical power supply system. 

The design of a nuclear power plant includes interdisciplinary reviews to assure the functional compatibility of the plant structures, systems, and components and compliance with licensing requirements. Safety reviews and accident analyses provide further assurance that system functional and licensing requirements will be met. Thus, the design and analyses of the plant take into account systems interactions. Nevertheless, the process may not consider all the interactions of various plant systems. Questions have been raised both as to the supporting roles such systems play and the effect one system can have on other systems, particularly with regard to the presumed redundancy and independence of safety systems. 

Concept Analysis of the Technical Plant after Planning. Preliminary hazard analysis and system structure analysis are intended to facilitate safety evaluation of the planned installation from the basic concept. Comprehensiveness of observation depends on the danger level of the installation. After concluding this work, basic changes in the technical procedure frequently become necessary and must be incorporated into the planning. 

Due to the need to check all safety measures, this part of the system analysis can become very voluminous. The method becomes difficult due to the constant change from the overall review of the plant to the review of individual components. For this reason it is important, in the case of major systems, to place preliminary hazard analysis and system structure analysis ahead of the evaluation of the planning concept. The advantages of this work plan are the following ... 

The system is the combination or interrelation of hardware, software, people, and the operating environment. In system safety engineering, you must look at the system from cradle to grave. In other words, the system life cycle is the design, development, test, production, operation, maintenance, expansion, and retirement (or disposal) of the system. A nuclear power plant is one large system with operators, pressure subsystems, electrical and mechanical subsystems, structural containment, safety systems, etc. A far simpler example is a boy riding his bike. The bike, the boy, the street (with all its traffic conditions), the weather, the time of day, and even other children make up the system of boy on his bike. 

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