Design margin

The core design scope of the Super LWR can be roughly defined by the considerations of the design margins, criteria, boundary conditions, and targets. How these four items affect the Super LWR core design is explained in this section. 

Generally, the following three points are considered to be the fundamental requirements of all kinds of reactors  

A sufficient design margin is kept from the fuel failure limit during normal operatiOTi 

The reactor can be brought to a cold shutdown state with a sufficient margin (shutdown margin) 

The reactor retains inherent safety features (e.g., negative feedbacks to reactivity insertions) 

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Design Margins. The heat-transfer surface area determined usiag the siting or rating methods is considered the minimum required area. 

There are additional surface-area requirements for design margins ia the final siting of a heat exchanger. 

Develop practical test program to demonstrate components ability to meet structural and performance criteria. Extent of such test program, if any, depends on economic value of component, number of units to be produced, consequences of failure, accuracy of structural analysis and design, margins of safety used in design, knowledge about service loads and environments, and difficulty of duplicating service loads and conditions in test... 

The following two equations usually provide an adequate design margin between (NPSH)a and (NPSH)jj ... 

Figure4.3 Effect of design margins [13] (by courtesy of S. Hasebe, Kyoto University).

The situation with heat transfer varies. The gas heat transfer coefficient increases with velocity, so existing exchangers are often adequate as the capacity is increased. Whether or not extra heat transfer capacity is needed will depend on the service, the design margins and the operating flexibility86. 

O Connell derived his correlation from binary systems in distillation service with bubble-cap trays. Calculated values are slightly conservative for sieve and valve trays. Credit for the slight improvement in valve and sieve tray efficiency should be ignored and counted as a design margin. A separate correlation was developed for absorption services. 

The value of constant k depends on system complexity, design margins, and design objectives for rehabUity, whereas the value of growth factor fi depends on the development effort... 

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