Supporting structures design considerations

Core support structure design with square grids at the central portion and radial stiffeners around the periphery has been recommended. Structural integrity assessment has demonstrated that even with the absence of the most critical radial stiffener, the reduction of rigidity of the structure is within the acceptable limits from reactivity insertion considerations. 

The volume is divided into fourteen sections. The introductory section gives the views of a practicing engineer and an experienced architect on the importance of these materials. Section II discusses the various materials that may be used to provide the physical strength, the supporting structure and the considerations involved in its selection and design. 

The design considerations of the supporting structure are covered in earlier sections of the book consideration of the selection of specific materials is discussed later in this section. 

Corrosion occurs in various forms and is promoted by a variety of causes, all related to process operating conditions to which equipment and support structures are subjected. It is a continuous problem that can lead to contaminated process streams. This subsequently leads to poor product quality and unscheduled equipment shutdowns, the consequence of which is reduced production, high maintenance costs, and equipment replacement costs. Minimizing corrosion is a key consideration for the designer and can be accomplished in two ways (1) proper material selection for apparatus, and (2) preventive nraintenance practices. Both of these approaches must be examined. 

Criterion 28 - Reactivity limits. The reactivity control systems shall be designed with appropriate limits on the potential amount and rate of reactivity increase to assure that the effects of postulated reactivity accidents can neither (1) result in damage to the reactor coolant pressure boundary greater than limited local 5uelding nor (2) sufficiently disturb the core, its support structures or other reactor pressure vessel internals to impair significantly the capability to cool the core. These postulated reactivity accidents shall include consideration of rod ejection (imless prevented by positive means), rod dropout, steam line rupture, changes in reactor coolant temperatme and pressure, and cold water addition. 

The lower portion of the evaporator section and the downcomer channel occupy only one-half of the steam generator cross-section. The effect of this non-symmetry is considered in calculation of recirculation ratio, internal flow considerations, and in design of tube support structures. 

There are three types of structures within the System 80+ Standard Design steam generators which support the tubes. These are the horizontal grid or "eggcrate , the vertical supports, and the diagonal supports, all of which are fabricated from Stainless Steel 409. One of the design considerations for these supports is prevention of dryout at support locations. With one exception, all tube supports in the System 80+ steam generator are constructed of flat strips which present a flat surface to the tube. The one exception is the flow distribution plate just above the entrance to the economizer section of the tube bundle. At this location secondary water is subcooled and, therefore, dryout will not be experienced. 

In most cases, the ability of the adhesive to support the design loads under service conditions for the planned life of the structure is considered first. Thus the mechanical properties, durability, and environmental resistance of the bonded structure are of obvious importance. But of equal concern are the nature of the adherends, the application technique, the cure conditions, the handling requirements, and, perhaps, the cost. A list of some of the factors considered in the selection process, together with the properties of the major generic classes of adhesives, are given in Table VI." It is important to remember that, even within a given class of adhesives, the performance may vary considerably, so that it is essential to consider the properties of each individual adhesive. It is apparent from this brief discussion that adhesive selection is far from simple. A computer-based selection program has become available recently." ... 

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