Radyasyon Ölçüm Tekniği İle Tanklarda Akışkan Seviyesi Tayini

Abstract

Radyoizotopların endüstriyel uygulamalarında önemli bir yeri, radyosyon ölçümleme ve değerlendirme prensibine dayanan teknikler tutmakta ve bu teknikler içinde de seviye ölçümü amacıyla geliştirilen uygulamalar ayrı bir önem taşımaktadır. Bu tez çalışmasında, nükleer uygulamalar içinde yaygın kullanımı olan radyoizotop kaynakla tanklarda akışkan seviyesi tayini yapılması amaçlanmıştır. Bu amaçla önce laboratuvarda kaynak-su tankı-dedektör ve ilgili malzemelerden oluşan sistem kurulmuş. noktasal ve lineer kaynak olarak Na-24. kaynağının kolimasyonu ve analitik zırhlama hesabı yapıldıktan sonra, tank içerisindeki sıvı seviyesinin sabit aralıklarla izlenmesi sağlanmıştır. Sodyumun ışınlanması ÎTU Nükleer Enerji Enstitüsündeki TRIGA Mark-II Reaktöründe gerçeklenmiştir. Bu tez içinde esas olarak, gama geçirgenlik tekniği kullanılmıştır. Deneylerde ölçümler için en basit hal olan tek kaynak - tek dedektör durumu çeşitli geometrik konfigurasyonlarıyla ile birlikte incelenmiştir. Ayrıca, tek kaynak - çift dedektör, çift kaynak tek dedektör ve çift kaynak - çift dedektör halleri yine çeşitli geometrik konfigurasyonlarıyla gözlenmiştir. Bunlardan ayrı olarak daha çok devamlı seviye ölçümlerinde kullanılan lineer kaynak kullanımı için lineer kaynak hazırlanmış ve lineer kaynağın tank içine veya dışına yerleştirilmesi hallerinde tek ve çift dedektör kullanımı geometrik konfigurasyonlarıyla incelenmiştir. Her hal için deneyler en az üç kez tekrarlanarak standart sapmaları hesaplanmıştır. Elde edilen sayımların, su seviyesine göre zamandan bağımsız grafikleri çizilerek genel bir değerlendirmeye gidilmiştir. Bu tez çalışması, ÎTU Araştırma Fonunca Yüksek Lisans Tez Araştırma Projesi olarak desteklenmiştir.

Radiogauging is the term that describes the use of radiation or emitted nuclear particles for the measurement of particular properties of a system. Actually, radiogauging is much older than the recent popular use of radioisotope sources. The primary advantages of radioisotopic sources over machine sources of radiation are: 1. They are less expensive, 2. They give a constant output, independent of such things as line-voltage fluctuations and fluctuations in ambient conditions that are troublesome with machine sources, 3. They are portable and do not need a power source, 4. They can be made quite 3mall, 5. They can be used by persons that are not highly trained in electronics. These advantages must be weighted against the disadvantages of not being able to "turn off" the radioisotope source and of having no control over the source energy and intensity except for initial choice. - xiv - The subject of radiogauging can be presented on the basis of at least three characterizations: 1. Function, i.e. what the gauge is used to measure, 2. Gauge configuration or principle, e.g. transmission type or backseat ter type. 3. Type of source. e.g. beta particle or gamma ray, Industrial applications of radioisotopes utilise the radiation of radioactive materials eradiation sources). Deending on the mode of industrial application, information is in most cases obtained through the effects of materials on radiation, about, e.g., the qualitative and quantitative material properties. The fundamental requirement to obtain and process the desired information about technological processes i 3 the detection and numerical evaluation of radiation. Radiogauges can be classified as static or continous according to their use. The static gauge is used to make one measurement at a time on individual samples; the continous gauge is used to monitor a product stream may vary with time. Certain radiogauge considerations are common to both types. Generally, the source- activity requirement for static gauges can be reduced by increasing the measurement time if the statistical source fluctuation is the controlling error. This is usually not possible with continous gauges since the rate of product movement and desired rate product control are the factors that largely determine the contionous radiogauge time constant. tAs long as the statistical source fluctuation is the controlling error, the relative accuracy of both types can be bettered by increasing the source intensity. - xv One often has several choices of radiogauge principle for the measurement of any given parameter. The optimum principle depends not only upon the accuracy Cand sensitivity) that is desired but also upon such practical considerations as; 1. Availability of a partinent radioisotope source, 2. Cost of radiogauge system, 3. Fredom from measurement interferences, 4.. Radiation safety considerations. The factors that affect the choice of a radioisotope are; 1. Availability. 2. Cost, 3. Half-life, 4.. Energy of emitted radiation. One radiogauging principle that is quite common is transmission of beta, gamma or X-rays through matter. It is worthwhile in this thesis to derive the optimum absorption cross section based on the best accuracy for this case. Gamma ray source is used more than any other in industrial measurements because of its versetility of appplication. By selecting different radiation energies, one can obtain a source that will barely penetrate a few desimeters of air or, at the other extreme, will penetrate several desimeters of concrete. The principles of measurement available are also quite varied. In this thesis, a gamma ray source as sodium- 24, is used for experimental cases. At first, appropriate souce activity level is calculated according to the experimental device in Radioisotope and Radiotracer Labratory in Nuclear Application Division of ITU Institute for Nuclear Energy. Irradiation of sodium have been done in ITU TRIGA Mark-II Reactor. Collimation and shielding design have been done with using nuclear safety criteria. - xvi - In industry a number of physical parameters are used to characterize material flow and product properties in technological processes.However, usually but a few physical ma ter ail parameters: - Level height, - Bulk density» - Thickness, - moisture, - Quantity are determined by radioisotope techniques, Level height is an important feature in several pieces of technological apparatus, in material storing or transportation systems, both from process control, either automatic or manual, and from quantity monitoring considerations. If the various methods applied in technology are compared with each other and with the isotope technique, t he t should be prefferred for problems where this more expensive method is safer from operational aspects and provides more reliable information than its conventional counterparts. Taking this into account, nuclear techniques have found wide applications for level monitoring problems under hard operational conditions like in mines, raw material transportation, ore processing, chemical technology, coal supply for power stations and closed tanks. Radioisotope level sensors contain a shielded radioactive source as a signal source (transmitter) and a detector converting radioactivee radiation to electrical pulses (receiver). The basic requirement of radioisotope level monitoring is the implementation of measurement configuration capable either of provoking abrupt changes or gradual variations (level indication and level measurement, respectively) in the radioactive radiation interacting with the measured material when the level has been altered. - xvii - Many measurement systems» called absorption types after the particular interaction process involved, offer an indication of appearance or disappearance of material level in the measuring line defined by the geometrical positions of radiation source and detector. The advantage of nuclear sensing in this case is that the indication depends only on relative absorption variations caused by material level changes. The influence of tank walls in the radiation path presenting a steady absorption can be compansated by increasing the radiation source activity. There are some versions for multipoint measuring systems. Also for a combined solution of n different measurement problems, one needs n radiation sources and n detectors. Generally» single or dual combinational systems are preferred for level height measurements. In this thesis. many of configurations are settle up and observed all their measurements i.e. single source - dual detector Cwith the gometrical configurations), and single source - dual detector and dual source - single detector Cwith the geometrical configurations), and dual source and dual detector cases. In addition of these cases, linear source is used for continous measurements. In this case, some conf igurational types are settle up and observed the measurements i.e., linear source is in the tank or not, and detector is single or dual. Graphs are drawn with observing counting rates via the fluid levels in the tank for every geometrical configuration and then they are evaluated according to each other. This thesis is supported by Research Foundation of Istanbul Technical University.