Equipment containment design principles

This section summarises some of the important factors which have been considered and debated within the IBP and the industry and provides examples of equipment design and operation. The potential for releasing significant quantity of biological material either inadvertently as a consequence of an accident, or routinely during its operation, are both important considerations. 

The use of a back-up secondary seal may offer additional security against release. A steam flush, or another barrier fluid, offers a higher level of security. 

Chapman suggested a simple framework for relating mechanical design to the level of operational containment. Table 11.1 illustrates this framework for static and dynamic seals (using the contained use regulations terminology). 

Double mechanical seal Double mechanical seal with steam flush 

Double mechanical seal in ventilated housing Double mechanical seal with steam flush in ventilated housing 

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During the evolution of the BWRs, three m or types of contaiiunents were built Mark 1 (page 3-16), Mark 11, and the Mark 111 (page 3-18). Unlike the Mark HI, that consists of a primary containment and a dry well, the Mark 1 and Mark n designs consist of a drywell and a wetwell (suppression pool). All three containment designs use the principle of pressure suppression for LOCAs. The primary containment is designed to condense steam and to contain fission products released from a LOCA so that offsite radiation doses specified are not exceeded and to provide a heat sink and water source for certain safety related equipment. 

Reactors are designed to be inherently safe based on physical principles, supplemented by redundant equipment and special procedures. Nuclear power benefits from the appHcation of the concept of defense in depth, ie, by using fuel form, reactor vessel, building containment, and emergency backup procedures to ensure safety. 

In designing the process and equipment, use chemical engineering principles to minimize the accumulation of energy or materials and to contain the energy and materials ... 

Plant layout is a crucial factor in the safety of a process plant because of e.g. segregation of different risks, containment of accidents and limitation of exposure. Safe plant layout is designed on the basis of design standards and local regulations. These are often expressed as minimum clearances between equipment. Safety distances between plant items can in principle be calculated by estimating the size of possible leaks, the probability of ignition and explosion... 

The plate separator is a major configuration of gravity separators. This equipment uses differences in densities between oils and water as a principle separation technique. The module can be a single plate or three plates or may contain a nest of parallel plates, which is typically 10-20 mm wide. The operational principles of plate separators are to allow oil droplets rise to a plate surface where coalescence can occur and to form larger oil droplets, which are easier to separate. The performance of the plate separator can be enhanced by selecting appropriate plate designs or by the use of a coalescer. 

Commercial equipment. The Welsbach Corp., Ozone Process Division, offers Laboratory Ozonators which produce ozone concentrations up to 4% by weight in air and up to 8% by weight in oxygen. Accessory units are as follows. An ozone concentration meter based on the principle of the thermal conductivity cell continuously measures ozone concentration in the carrier gas. A strip-chart recorder is designed specifically for use with the ozone meter. A portable air dryer is a self-contained unit consisting of a compressor and dryer on a common portable base no attendance is needed. 

The concept of passive safety meant the use of systems based on simple physical laws more than on complex equipment. One example is represented by safety injection systems on water reactors which use gravity as a motive force and not pumps. This principle was, for example, adopted in the passive PWR AP600, certified by the NRC in 1999. It comprises a voluntary fast depressurization system of the primary circuit and the provision of a water reservoir in the containment located at an elevated position with respect to the reactor vessel. Passive cooling of the containment was also incorporated in the design. Evidently, however, neither of these new concepts nor the industrial weight of the NRC certification are sufficient to immediately convince the investors because, up to now (2005), no new AP600 has been ordered. 

Allner, K. (1985). Laboratory and equipment design for containment of biohazards. In. Comprehensive Biotechnology. The Principles, Application and Regulations of Biotechnology in Industry, Agriculture and Medicine. (Cooney, C.L. and Humphry, A.E. eds). Pergamon Press New York, pp. 468-485. 

The main steam and feedwater lines is equipped with three system-fluid-operated isolation valves, one of every three being of a different design from that of the other two valves. Closure of the main steam valves to isolate the containment is based on the fail-safe principle employing solenoid pilot valves or through passive actuation. 

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