Selection criteria for technical options

Selection of appropriate technologies for nuclear fuel handling is a function of economics, physical constraints, process volume, flexibility needed, maintenance, system reliability and consequences of failure. A summary of the criteria and their categories is given in Table III.

Remote hand tools have been used more readily in unique, relatively low volume or one-time operations. They are relatively inexpensive and rapidly fabricated, require little maintenance, and are generally highly specialized. Such tools are generally reliable and as effective as the skills of the operator within the constraints of a given environment. Examples of remote manual tooling development and applications in the USA and Iraq were presented.

Remote hand tools are less desirable where a high radiation dose potential exists; necessary human presence requires extra shielding and/or extra-long handles, making manual manipulation more difficult. Because of specialization, a large number of hand tools may be required to complete a sequence of operations. For these reasons, remote hand tools are used less frequently in production facilities, where economies of scale permit cost effective means of speeding operations and reducing radiation exposure. Telemanipulators have been used worldwide in production modes, fuel movement and other handling activities in production, reprocessing and reactor facilities, inspections and destructive evaluation of spent fuel.

Table III Criteria for selection of technical options

CATEGORIES CRITERIA

• Capacity /throughput

• Location of system application (1) Functional requirements

• Technical alternatives • Performance

• Cost of implementation • Lead-time / Lifetime

• Reliability / Availability / Maintainability (RAM) (2) Selection factors • Simplicity / Flexibility • Experience • Licensing • Safety (3) Others • Safeguard ability (1) Remote versus hands-on operation

In nuclear technology the radioactivity, of the items handled usually determines whether remote technology needs to be employed. In accordance with the ALARA principle, remote technology is encouraged in order to reduce the collective radiation doses to the operating staff. There may be factors such as low radiation level, low frequency, or ready access (by the operator), which can make hands-on operation the preferred option.

There are many factors that determine whether a manual or automated process is the optimum solution. Manual operations are less desirable where high throughput and/or high radiation protection are required. Automation provides enhanced productivity and can realize higher quality standards if required, but require more complex machinery. Flexible automation can rapidly respond to low volume, high radiation protection requirements. The higher capital investment must be justified e.g. by less dose exposure and/or by higher process efficiency. (2) Location of process

Where processes must be designed into existing facilities, many constraints are placed on the design. Such constraints include available space, process interfaces, limitations on changing the existing process and operating philosophy. If a new facility is being designed, it is

important to minimize the volume of such a facility in order to minimize costs and environmental impact. It is important, however, to also consider flexibility for future uses and to provide adequate space for maintenance.

(3) Throughput and capacity

Two of the most influential factors in process selection are throughput and capacity. These govern the size and overall cost of the solution. High throughput requirements can justify higher investment. A process designed for higher throughput generally requires logistically optimized solutions with high reliability and provision of buffer stores.

(4) Quality

The quality to be achieved in the process is fundamental. High quality is often achieved through a high degree of automation. Another aspect is the way in which the desired quality is to be achieved. The traditional technique of final testing requires a different approach than more modern techniques such as statistical process control.

(5) Lifetime

The lifetime of the process equipment to be considered is of major influence to the design. Process equipment for long-term use must fulfill different design criteria than those for short- term use since design lifetime often dictates materials of construction, safety margins and choice of components. The present experience is that facilities often operate longer than the original design lifetime.

(6) Lead time

Whatever the lead-time is, the process equipment must fulfill all necessary design and safety criteria. However, if the available time to prepare the process equipment is very short, less optimized solutions might have to be adopted. If the lead-time allows for more detailed design, better-optimized equipment with better technical performance and economy can be provided.

(7) Licensing and safety

Licensing requirements are one of the major influencing design parameters. The safety requirements differ from country to country, thus sometimes preventing direct transfer of equipment or processes already in operation in another country. However, a positive licensing statement in one country may be used to support licensing elsewhere.

(8) Experience

Experience is a very valuable factor when designing a remote technology process. It is usually gained through the process of designing, building and operating facilities. Designs guides published by the IAEA, ANS, BNES, etc. are also useful references. Although new technology may seem beneficial, proven technology is sometimes chosen to provide a higher degree of confidence. A regulator who may wish to see a working example of the process involved can influence choice of solutions.

(9) Flexibility

When designing a process it is important to build in flexibility for current and anticipated future needs. The degree of flexibility depends entirely upon the application and in certain cases for very specific tasks; however, it may not be necessary to take flexibility into account.

(10) Maintainability

Each process must be designed with specific consideration of maintainability. Even processes, which are essentially maintenance free, should have provision made for possible failure. If such provisions are made then the impact of failures on operational cost and plant outage are reduced. A wide variety of remote technologies are available for specific maintenance operations.

(11) Simplicity

Simplicity of a process is often an advantage since it usually results in fewer failures of the process, lower capital cost and easier maintenance. This is a particularly important factor of consideration for contamination environments where human intervention for repair work is costly or robotic intervention is failure prone.

Another benefit of simplicity consideration is that parts are readily available off the shelf which makes replacement work faster and cheaper than the case of special fabrication of the parts.

(12) Costs

The price of procurement is of course a primary consideration for selection of a remote system, in compromise with other associated criteria. Because of the production costs, standard products off-the-shelf from the market are usually much cheaper than producing in- house and therefore, this aspect of economics is a useful criterion in the selection.

Lifetime costs (including consideration of decommissioning and waste processing) should be the basis of cost comparisons rather than initial capital outlay alone. A preferred solution may not always be possible to realize due to financial constraints on the project.

(13) Safeguards

It is of great advantage to incorporate safeguard requirements at an early stage of design since this can avoid costly rework that can happen after completion of facility design, or even worse after construction, should any requirement associated with safeguards is found not implemented or not in compliance.