Safety whole system design

Compliance with this regulation was focused upon in establishing the design basis and system requirements both for the innovated plant I C system as a whole as well as for the I C portions of the individual plant safety and safety-related systems. Design and implementation of the refurbished I C systems important to safety will have to meet, in the first place, all the applicable requirements of this... 

To be able to systematically identify opportunities for reducing human error, it is useful to ask the question, What is human error One definition is that human error is an inappropriate or undesirable human decision or behavior that reduces, or has the potential for reducing safety or system performance (Rasmusssen 1979). There is a tendency to view errors as operator errors. However, the error may result from inadequate management, design, or maintenance of the system. This broader view which encompasses the whole system can help provide opportunities for instituting measures to reduce the likelihood of errors. 

Transportation should be considered when assessing risks associated with planned or existing plants. The design of new chemical processing units should include at the earliest opportunity a qualitative or quantitative risk assessment of the whole system including production, use, and transportation in order to minimize overall risk. A brief discussion of the inherent safety aspects of transportation is included in Chapter 5. 

Some I C system design do not include reliability analysis of hardware and software and the reliability impact of I C components on the whole plant safety. Such reliability analysis should include the behaviour before, during and after selected hypothetical severe accident conditions, including the instruments used in the reactor, thermocouples, pressure transducers, flow meters etc. 

It becomes necessary to regard the whole of the system as a single safety-related system. It thus becomes a high-demand system with a Maximum Tolerable Failure Rate (see Chapter 11) of 10 pa. This is at the far limit of SIL 4 and is, of course, quite unacceptable. Thus an alternative design would be called for. 

An integrated primary system design. The reactor vessel contains the whole primary circuit including steam generators (SGs) and control rod drive mechanisms (CRDMs). The design achieves a compact primary system and containment. It also eliminates initiating events for loss of coolant (LOCA) and control rod ejection accidents, which makes it possible to realize a simple safety design without safety injection and containment spray systems, Fig. VI-1. 

It provides researchers with an effective tool to make full use of the information generated at the lowest level in design to evaluate the safety of the whole system for resilience improvement of its operations. 

An emergent property is a novel system characteristics exhibited on the level of the whole system, but not by the components in isolation. It is a special attribute or characteristic, such as system safety and reliability, which result as a unique property of the final system design and manufacture. 

The SHA assesses the safety of the total system design by evaluating the integrated system. The primary emphasis of the SHA, inclusive of hardware, software, and HSI, is to verify that the product is in compliance with the specified and derived SSRs at the system level. This includes compliance with acceptable mishap risk levels. The SFLA examines the entire system as a whole by integrating the essential outputs from the SSHAs. Emphasis is placed on the interactions and the interfaces of all the subsystems as they operate together. 

As explored in Chapters 8 and 9, there is a clear need to address the whole system when considering safety implications (see Chapter 8). This is due to the inherent complexity of engineering systems today, as well as those of the future, and demands that safety knowledge be distributed throughout the systems supply chain, from the safety assessor to the designers, operators and maintainers. 

The safety system was designed with regard for the particular laboratory space and the building as a whole. 

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