QUALITY ASSURANCE OF REACTOR INSTRUMENTATION

11- 2.1 Fundamentals of Quality Assurance

Industrial quality assurance has evolved from a policing function, consisting of final inspection and test, to a defect-prevention system that begins with product concep­tion and ends only when that product has satisfactorily fulfilled its intended function

At some quality level the balance between cost of failure and the cost of prevention and appraisal will be at a minimum. A successful quality system operates at or near that level In the nuclear industry the quality level must be higher than in most industries, this tends to result in higher costs for quality assurance

In specialized industries, such as those producing manned space vehicles and nuclear reactors, the level of quality has been set more by reliability requirements than by cost considerations However, as competition in the nuclear industry increases and as competition between nuclear energy and other energy sources increases, quality systems in the nuclear industry will have to meet plant safety and performance requirements at reasonable cost

(a) Modern Quality Systems. Modern quality systems prevent defects and substandard workmanship by exercising controls over design, materials, processes, and products at the appropriate place in the product cycle All modern quality systems contain three basic elements design con­trol, materials control, and process and product control

Design control consists in the preproduction efforts of Design Engineering, Manufacturing Engineering, and

Quality-Control Engineering* in developing a design and production and test methods that will ensure with a high degree of confidence that a quality product can be built and sold for reasonable profit to a customer who will accept the product and remain satisfied over its expected life Design control must be a joint effort of the three groups Properly conducted design reviews are essential during this phase

Materials control consists in the preproduction efforts of Quality Assurance, Materials, and Purchasing Quality Assurance must evaluate the vendor’s capability to perform and must ensure that quality requirements are included with purchase orders In addition, incoming material must be tested or inspected on a statistically valid basis An objective in materials control is to establish a certification program that puts the burden of quality control on the vendor rather than on Receiving Inspection This is essential for products that will be shipped directly to a site Materials control becomes extremely important whenever Boiler Code materials are involved Such materials must be traceable to their original heat number regardless of the state of manufacture This is accomplished by such tech­niques as color coding, electroetching, and tagging or by the use of move tickets, depending on the state of completion of the part All materials, whether raw stock or finished goods, must be controlled by Materials, and these controls should be audited periodically to ensure that they are being followed

Process and product control consists in the evaluation and control of manufacturing facilities (whether skilled workers or production machines) and the inspection and test of the product to ensure that the product meets all engineering specifications and quality standards Once control of manufacturing facilities has been accomplished through planning and the development of manufacturing and inspection or test equipment, training of operators, etc, process and product control must be maintained by implementing the quality plan This plan may require audits, automatic test, continuous sampling, or roving inspection It will specify the points in the manufacturing cycle where certain inspection or tests, or both, are necessary, the records to be kept, control charts, calibration and maintenance schedules of critical equipment, special handling techniques, etc Finally, there will be final inspection or tests, or both, to be performed and possible special packaging instructions and inspections to be per­formed at the site in many cases

(b) Justification of the Quality System. Since about 1950 most companies have incorporated a quality system containing the basic elements Given the talent, quality costs have been significantly reduced following the initial costs of putting the system in operation Costs have been reduced because the production lines have produced less

’Initial capitals are used m referring to groups m the industrial organization that is designing and manufacturing the product scrap and customers have returned fewer goods or de­manded less service The savings have more than paid for increased staff Savings have also been realized by reducing the number of policing inspectors and testers This reduc­tion has been made possible by detailed planning of inspection and testing and by using automated test equip­ment Cost savings have been experienced by large and small concerns, whether production-line or job-shop oriented

Positive side effects have been experienced following the institution of a well-planned quality system improved product design, better processes, and the development of quality mindedness in the production and engineering forces It is especially important that such systems be set up in the nuclear instrumentation industry and that the industry be organized in such a way as to foster the philosophy of total quality control The difficult, but not impossible, goal of increasing quality levels while reducing quality costs can be achieved when this happens

(c) Organization of the Quality System. The staffing of an organization to implement and operate a modern quality system depends on the size and resources of the company The number of engineers and test and inspection supervisors depends on three factors volume, variety, and complexity of product In brief, one or more quality control engineers, process-control engineers, test-equipment engineers, foremen, planners, inspectors, and testers are necessary In a small organization the process-control engineer can double as foreman, the quality-control engi­neer can do planning and specify commercially available test equipment, and inspector—testers can combine those two functions The quality-control engineer participates in design control, writes quality plans, including inspection and test instructions for a given product, evaluates vendor’s performance data, analyzes process and product measure­ments and product service reports, and applies the results to prevent poor-quality material and products in future purchases and production The process-control engineer is responsible for implementing the quality-control engineer’s quality plan (including control of incoming materials, processing equipment, and inspection or test equipment) He should be the leader in solving technical quality problems in the manufacturing area

Since this chapter is intended to detail quality assurance of nuclear instrumentation systems, the foregoing summary of a quality system and its staffing must suffice For additional information the reader is referred to Refs 1 to 3

(d) Special Aspects of Reactor Instrumentation Qual­ity Control Nuclear sensors are used to detect the presence and amount (intensity and energy) of neutrons and gammas (see Chaps 2 and 3) Sensors that are located in the nuclear-reactor core are considered an integral part of the pressure vessel and therefore fall within the scope of the ASME Boiler and Pressure Vessel Code As a consequence, manufacturing procedures and quality control of these sensors are stringent Many of the processes used in the manufacture of in-core sensors are peculiar to that product (e g, uranium and boron coating of electrodes, casting metal to ceramics, outgassing and backfilling with special mixtures, and pressures and purities of fill gases) In-process quality control procedures rely heavily on mechanical inspection techniques, especially where mechanical toler­ances are critical Helium mass-spectrometer leak testing is important after enclosure welds are made, and insulation — resistance checks are very important wherever parts are mechanically and electrically isolated from each other Final test and inspection depends on the end use Actual end-use operating conditions should be simulated as closely as is economically feasible

Nuclear-reactor readout instruments can be classified as any electronic system that accepts a signal from a nuclear sensor and converts it to usable information. Formerly, this category was normally typified by rack-mounted equip­ment However, recently the trend has been to integrate various instrumentation functions directly into panels and consoles, this has necessitated drastic changes in the in-process quality control With rack-mounted instruments, there are usually printed wire boards to be checked out either as boards or as a part of a system Obviously the quality of work by personnel who solder components or attach leads to the boards or to instrument chassis must be very high and should be monitored at carefully chosen points in the manufacturing cycle Quality-control prob­lems are different from those involved in sensor manufac­turing

Nuclear instrumentation systems can be classified as a group of instruments, including sensors, that together perform a specific function, such as the reactor protection system, the neutron monitoring system, the off-gas moni­toring system, the rod control system, or the area monitor­ing system Usually such systems are housed in one or two panels or a panel and a console so that systems check-out can be made without having to interconnect more than two panels These panels may house a multitude of instruments, or they may house switches, relays, and meters The degree to which in-process check-out (continuity, insulation, etc ) can be effected is determined by the configuration of the panel

Peripheral equipment is a catch-all term for the essential equipment involved in interfacing sensors and reactors or instruments It includes drive mechanisms, penetration seals, etc, and must be treated individually since each piece of equipment has its own peculiar problems

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