Application of remote gamma spectrometry in automated systems for monitoring emissions from nuclear power plants

Abstract

Methodological questions concerning the application of remote gamma spectrometry for radiation monitoring of air emissions from nuclear power plants and detecting trans-boundary transport of products of an accident are examined for the example of the development and experimental operation of the components of the Spaider data-acquisition system produced by the KonverSia company. A system of collimated γ spectrometers arranged along the monitoring contour at the site boundary of a nuclear power plant makes it possible to increase the accuracy of the computational predictions and to obtain and accumulate, during normal operation of a nuclear power plant, emissions data for radioactive inert gases and iodine in a continual monitoring regime.Integral dosimeters are used to monitor radioactive emissions in most automated radiation monitoring systems operating in nuclear power plants. The low dose sensitivity (~600 µR −1 ) and impossibility of autonomous classification of any anomalies detected are forcing developers of such systems to switch to more sensitive γ-spectrometric means for performing measurements (55000 µR −1 and more) [1]. Assessments of the predicted irradiation dose in the case of accidental emission are based on the accepted model of impurity transport and dissemination in the atmosphere near the ground, making it possible to assess the radionuclide concentration field near the ground. Such calculations require as initial information data on the amount and composition of technogenic radionuclides which have entered the environment. Today, many spectrometers are installed in the technological equipment of nuclear power plants to monitor emissions [2]. More accurate assessments of the actual emissions as well as monitoring of the radiation parameters of the emission stream in an on-line regime for use in models can be performed by using the results of remote spectrometry of streams [1]. This makes it possible to increase the accuracy of the computed forecast, obtain and accumulate data during normal operation of a nuclear power plant on the emission of radioactive inert gases and iodine in a continual regime, and to monitor the time and radiation parameters of legally allowed emissions, radiation incidents, and accidents.The present article examines the methodological questions concerning the use of remote gamma spectrometry for radiation monitoring of emissions from nuclear power plants and detecting trans-boundary transport of the products generated by an accident. This method has been tested during development and experimental operation of the components of the Spaider data-acquisition system produced by the KonverSia company [1].Requirements for the Main Characteristics of Gamma Spectrometers. In remote gamma spectrometry performed for the purpose of monitoring emissions, the radiation characteristics of the γ field generated by the radionuclides in a stream, which at short distances (up to 1.5 km) from the exhaust stack of a nuclear power plant has well-defined transverse dimensions, which are only ...

Use of model sources for measuring radiation emissions and calculation of gamma spectrometer characteristics

“…As an example, the SEG-017 spectrometer used in the Spider data acquisition system with an 80 × 80 mm NaI(Tl) crystal, allowing a maximum input statistical mode of no more than 10000 counts·sec -1 , is examined [5].…”

“…This is ordinarily done by using a collimator directed toward the stream [5]. Comparing the sensitivity of a spectrometer with and without a collimator (hollow lead cylinder 20 cm in diameter and 20 cm high, wall thickness 3 cm, angular aperture 120°) makes it possible to assess the situation in the zone where the emission stream touches the surface of the ground.…”

Metrological support for the ASKRO spectrometric channel

“…The information of the spectrometric channel ASKRO serves for establishing a correspondence between the volume activity of the ith technogenic radionuclide q i and control levels (control correspondence), its variation in time (monitoring), the probability of evaluating the presence in the ground layer of the atmosphere (discovery). The δq i error in evaluating the concentration is related with, first and foremost, the accuracy δS ij with which the sensitivity of the spectrometer with respect to the jth line of the ith radionuclide is evaluated in the geometry used for the measurements:where ΔX ij is the excess count rate above the background in the region of the total absorption peak of the jth characteristic line of the radionuclide [2].If the concentration q i of a radionuclide is less than the minimum measured value, the relative estimate of the excess of the count in the jth energy range N ij above the a posteriori average count N ij , calculated on the stationariness interval, (N ij -N ij )/N ij 1/2 is used to calculate the probability of its presence in the ground layer of the atmosphere [3]. The sensitivity of the spectrometer with respect to the ith radionuclide in explicit form does not enter into the relation used to calculate the…”

“…If the concentration q i of a radionuclide is less than the minimum measured value, the relative estimate of the excess of the count in the jth energy range N ij above the a posteriori average count N ij , calculated on the stationariness interval, (N ij -N ij )/N ij 1/2 is used to calculate the probability of its presence in the ground layer of the atmosphere [3]. The sensitivity of the spectrometer with respect to the ith radionuclide in explicit form does not enter into the relation used to calculate the…”

“…However, the minimum detectable activity of a radionuclide is determined by the sensitivity of the spectrometer used [3]. The determination of the sensitivity of the ASKRO spectrometer in measuring 2π sources and the certification scheme are not regulated at the present time.…”