No abstract
One of the most important parameters indicating contamination of the environment by a radioactive contaminant (radioactive gases, aerosols), entering the atmosphere as a result of emissions from the ventilation pipes of nuclear power and other plants in the nuclear power industry, is the intensity of emission eemts [Ci/sec], defined as the product of the flow rate G [cm3/sec] in the ventilation pipe by the volume activity Qv [ Ci/cm3] [1]. For the standard operation of a nuclear power plant, the design and off-design accidents in the case when an automated system for monitoring the radiation conditions (ASMRC) is used, this parameter should be evaluated in the automatic regime. At the present time the per second flow rate is determined as the sum of the flow rate of separate ventilation systems that are part of the automated system; this is an inconvenient and expensive procedure in automating the measurements of the flow rate. The volume activity of the impurity in the automatic regime is measured with aspiration plants of the "Kalin" type and the nuclide composition of the standard emissions is measured under laboratory conditions in accordance with the technological regulations. If the rate of gas flow in the ventilation pipe is known as a function of the radius of the pipe, then, by normalizing the velocity function to the value measured at a point, i.e., by determining the velocity in absolute units, the flow rate can be found as an integral of the velocity of the flow over the cross section of the pipe at constant density, and the volume activity can be measured according to the dose rate produced by the radioactive contaminant.Therefore, if the velocity of the air flow at some point in the pipe and the dose rate of/3 and ,,/-radiation of the radioactive contaminant can be measured with a sensor, then the problem posed above can be solved. The construction of such a sensor and a method for determining the intensity of emission of a radioactive contaminant is presented in [2]. The sensor is based on a measurement of the induction and ionization currents produced by the ionized gas (air) flow, moving in the transverse (relative to the direction of flow) electric field in the interelectrode gap of the channel of the sensor (Fig. 1). In the present paper we consider the theory of the method and present the results of measurements of the induction and ionization currents as a functions of the velocity of the air flow or the external voltage, which indicate operation of the sensor.The physical crux of the method consists of the following. A gas flow, formed in the ventilation pipe as a result of ionziation of the air flow by the radioactive contaminant and separated in the electric field of the interelectrode gap, produces a current, the concentration of ions of one sign in the regions near the electrodes being much higher than that of ions of the opposite sign. But, just as the longitudinal air flow in the ventilation pipe also drags ions, so it produces a longitudinal component of their velocity that determine...
Methods of radiological monitoring of the environment that can be used on objects utilizing atomic energy, including NPP, are examined. The methods are based on the indications of sensors measuring the dose rate and the spectral characteristics of photon radiation. The sensors can be placed in the opening of a vent stack as well as on unmanned radio-controlled aircraft and underwater apparatus. Radiological monitoring is accomplished in real-time by transmitting information along a radio channel to the pilot's and dosimetrist's consoles. A method of remote radiological monitoring where the diagnostics apparatus is a radar station operating in a definite wavelength range is briefly described. The use of cryogenic technologies for recycling radioactive inert gases discharged into the atmosphere is briefly described.The methods of radiological monitoring by means of the ASKRO system as well as its hardware in some cases do not permit obtaining information in real-time. This pertains to, for example, the radiation characteristics of gas-aerosol impurity propagating in the atmosphere during emissions from an NPP, radioactive contamination of the underlying surface and the bottom regions of reservoirs located in the contamination zone, and so forth.The present article proposes unconventional methods and means for performing radiological monitoring which, if adopted, will make it possible with a small measurement error, as is characteristic for the sampling method, to increase considerably its operational efficiency and reliability, to reduce the risk of making an incorrect decision, and ultimately to optimize decision making. One such method is measurement of the intensity of the emission of gas-aerosol radioactive impurity into the atmosphere from vent stacks at an NPP in the standard regime and in preventative maintenance regimes [1,2]. The means for implementing this method are free-air (open at the ends) and sealed (with isolated working body (air)) ionization chambers with identical dimensions. In the first chamber, the ionization current in the working volume is created as a result of the ionization (of the working body) by the photons from the gas-aerosol radioactive impurity flowing into the vent stack as well as by ions carried into the working volume by air flow; in the second chamber, the ionization current is created solely as a result of the ionization of air (working body) by the photons of the gas-aerosol radioactive impurity.The air flow velocity can be determined from the relation U 0 = (i free /i seal -1)(S n /S 0 )μE 0 . Here i free and i seal are the ionization currents of the free-air and sealed ionization chambers, respectively; S n and S 0 are the areas of the electrodes and transverse section of the chamber, respectively; and μ is the mobility of the charge carriers. The flow rate can be determined from the expression where U(r) is the radial velocity distribution of the air flow in the opening of the vent stack, approximated by the expression G U r rdr r = π − ∫ 2 0 0 ( ) , δ
The use of radar stations (RSs) as a means for detecting atmospheric radioactive emissions from nuclear power plants is based on the characteristics of the propagation of electromagnetic waves in plasma, which have been quite well studied for the ionosphere. But the propagation of electromagnetic waves in plasma, arising in the boundary layer of the atmosphere accompanying the spreading of a radioactive impurity due to emissions from a nuclear power plant, until recently, has not been given the attention it merits because of the fact that the sources of the plasma are of a technogenic origin. In the present work we attempt to fill this lacuna by providing both the experimental data on the detection of ionized formations arising in the atmosphere, either directly as a result of the emissions of a radioactive impurity or as a result of ionization of the air medium by "t--/3 radiation from different surfaces (ventilation pipes, roofs, radioactive waste burial sites) at nuclear power plants and other radiation hazardous enterprises, with the aid of the radar station as well as an examination of the theoretical questions regarding the formation and dynamics of plasma in the boundary layer of the atmosphere and the propagation of electromagnetic waves.In what follows, by plume of radioactive "emissions" we shall mean plasma formations (plasmoids), which arise primarily as a result of the ionization of air by 3'--B emission from the contaminated surfaces of radiation hazardous objects, especially plasma formations arising around the plume or cloud of radioactive impurity entering the atmosphere accompanying emissions from ventilation pipes in nuclear power plants. In this case, the quotation marks in the phrase "plume of radioactive emissions" will be dropped.The experimental works on the investigation of the possibility of ~etecting and identifying a radioactive cloud, arising as a result of the dissemination of an impurity in the atmosphere accompanying emissions from a nuclear power plant and other radiation hazardous objects, with the aid of radars were first undertaken immediately after the Chernobyl accident and then in 1989-1992 at Ukrainian and some Russian nuclear power plants [1]. The works were performed using radar stations operating in the centi-, deci-, and meter-wavelength ranges.The emission plumes were observed at distances in the range 11-65 km, and they were observed at a maximum range of 500 km with a limiting sensitivity for emissions of a radioactive impurity from a nuclear power plant up to several Ci per day. The results of the experimental investigations are presented as an illustration in Fig. 1 and consist of the following:1. The structure of the emission plume, which is the target of the radar, consists of a long cylinder or elongated frustum of a cone (their projections onto a plane) with a height ranging from several hundreds of meters up to several kilometers and in diameter from several tens of meters up to 400-500 m, the bottom (wide) part of the cone lying above the ventilation pipe of ...
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