Instrumentation radiation level detection

The Instrumentation and Control Fundamentals Handbook was developed to assist nuclear facility operating contractors provide operators, maintenance personnel, and the technical staff with the necessary fundamentals training to ensure a basic understanding of instrumentation and control systems. The handbook includes information on temperature, pressure, flow, and level detection systems position indication systems process control systems and radiation detection principles. This information will provide personnel with an understanding of the basic operation of various types of DOE nuclear facility instrumentation and control systems. 

Measurements of the radiation levels in an area are a vital aspect of radiation safety. Every laboratory using radioisotopes should have ready access to the means to measure the ambient activity in the facility. In areas where there are fixed sources of substantial radiation such as a °Co irradiator, some types ofaccelerators,ora nuclearreactor, fixed radiation monitoring systems usually are installed. Thesepermanently installed systems need to be supplemented by portable instruments to be used to detect radiation levels in localized areas that might not be seen by the fixed system, or arising from movable sources. 

Higher-range instruments are used to determine radiation levels and dose rates to those exposed, and are not useful for detecting contamination. These instruments are normally handheld with no probe. 

The sensitivity should be considered as the ability of an instrument to detect and quantify low concentrations of the target compound. In absorption spectrometry, low concentration of the analyte means high transmitted radiation levels. This is the reason why the poorer sensitivity of silicon-based photodiodes compared to photomultipliers or coupled charge detectors is in fact not so important. The relatively lower sensitivity of photodiodes is also compensated... 

Ageing effects may be detected by a change in measurable parameters. For example, increase in temperature or pressure may be an indication of die accumulation of corrosion products in the tube of a heat-exchanger and instrument drift may be an indication of electronic component degradation. Parameters should be measured periodically in a consistent manner and the readings should be compared and assessed. Physical parameters, such as temperature, pressure, flow rate, control rod drop times, radiation level (e.g. neutron and gamma), water quality, are indicators of the state of a system, structure or component. 

A survey counter is a gas filled detector used to detect spilled radioactive materials that can be hazardous for the operators or may disturb accurate dose measurements. Survey counters can be mounted at critical places to measure the radiation level in rooms continuously. A hand-foot-clothing monitor is a suitable and obligatory instrument to detect possible contamination before leaving the area where radioactive materials are handled. 

The Ulchin Units 3 and 4 are equipped with monitoring instrumentation to detect inadequate core cooling (ICC) and Post Accident Monitoring Instrumentation (PAMI). Examples of parameters monitored are reactor coolant system pressiure, temperature, primary safety valve position, containment pressure and site radiation level, etc. 

In practice, using a CW instrument, the absorption of energy may be detected by subjecting the sample to radiation of varying frequency at a fixed value of the applied field or vice versa until the conditions required by equation (9.24) are met. At this point, the system is said to be in resonance, both upward and downward transitions occur, and a net absorption of energy is observed because of the small excess of nuclei in the lower level. 

A majority of traditional NIR measurements are made on solid materials and these involve reflectance measurements, notably via diffuse reflectance. Likewise, in the mid-IR not all spectral measurements involve the transmission of radiation. Such measurements include internal reflectance (also known as attenuated total reflectance, ATR), external reflectance (front surface, mirror -style or specular reflectance), bulk diffuse reflectance (less common in the mid-IR compared to NIR), and photoacoustic determinations. Photoacoustic detection has been applied to trace-level gas measurements and commercial instruments are available based on this mode of detection. It is important to note that the photoacoustic spectrum is a direct measurement of infrared absorption. While most infrared spectra are either directly or indirectly correlated... 

Another instrument often used to detect levels of radioactivity is a scintillation counter, which takes advantage of the fact that certain substances, such as zinc sulfide, give off light when they are struck by high-energy radiation. A photocell senses the flashes of light that occur as the radiation strikes and thus measures the number of decay events per unit time. 

A radioactive method has also been developed for determination of catalyst levels in reactors, hoppers, and catalyst-feed lines of moving-bed units (331). The equipment consists of one or more radiation sources (radium chloride), a Geiger tube, and associated electronic instruments. The radium sources are mounted within the vessel at intervals over the range of levels to be measured, with the Geiger tube at the top. The exact amounts and locations of the radium sources are so proportioned that radiation from each source is no longer detected when covered by a 2-ft. layer of catalyst. Thus the counter receives maximum radiation when the vessel is empty and decreasing intensities as catalyst level rises. 

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