Monitoring of Xe and Kr radionuclides was conducted from August 2006 to 30 July 2008 within the framework of ISTC Project #2133. Cherepovets City in Vologda Province and St. Petersburg were chosen as monitoring locations. Kr-Xe concentrate samples were obtained as a result of processing of several thousand m 3 of atmospheric air. New results of 85 Kr monitoring show, that for last 15 years, the 85 Kr volumetric activity in the atmospheric air of the northwest region of Russia has increased approximately 50% and has achieved a level of 1.5 Bq/m 3 . This value correlates well with similar data for Western Europe and Japan. The xenon fraction (80-160 cm 3 under STP) is adsorbed on charcoal in the ampoule, which is measured in the well of HPGe gamma detector. Minimum detectable concentration (MDC) of 133 Xe for this technique is 0.008 mBq/m 3 , and it is the most sensitive method used today. The 133 Xe concentration in the atmospheric air of Cherepovets City varied in the monitoring period ranging from 0.09 to 2.5 mBq/m 3 . During the period of March 2007-30 July 2008, 133 Xe activity concentration in the atmospheric air of St. Petersburg changed from background values (0.2-0.3 mBq/m 3 ) to 185 mBq/m 3 and for approximately 20% of the samples 135 Xe was also measured with the 135 Xe/ 133 Xe activity ratio varied within the range of 0.03-3.5. -nuclides background in the air of St.-Petersburg, noble gas radionuclides release from nuclear power plants, high sensitivity methods of measuring Xe radionuclides.

A method was developed for determining radioactive Kr and Xe isotopes in air using liquid technical-grade oxygen prepared at air-separation plants. Kr and Xe are less volatile air components than N 2 and O 2 and are therefore accumulated in liquid oxygen in the course of its production. The method allows determination of background volumetric concentrations of Kr and Хе at short distances (~100 km) from the sources of radioactive noble gas (RNG) injection. The results of 85 Kr and 133,135 Xe monitoring in air of St. Petersburg in 2006-2008 are presented. For some air samples taken in St. Petersburg, back trajectories of the transfer of air masses were calculated, using HYSPLIT dispersion transport model developed by ARL, to determine possible sources of injection of Хе and 85 Kr radionuclides. Keywords: radioactive noble gas monitoring, volumetric concentrations of krypton and xenon isotopes in air, liquid technical-grade oxygen, transfer of air massesAn efficient method for monitoring safe operation of plants of nuclear power engineering is monitoring of gas-aerosol discharges in zones of location of such objects. In so doing, data on the concentrations of Хе and Kr in air are very valuable and bear important information. Direct isolation of Kr and Хе from air is very difficult, because their weight fraction in air is low: 1.14 × 10 -4 and 0.87 × 10 -5 vol %, respectively. Therefore, to determine background concentrations of Kr and Хе radionuclides, it is, as a rule, necessary to process large (no less than 5 m 3 ) air samples. These problems can be overcome by using those products from air-separation plants in which Kr and Хе are concentrated. A Kr-Xe mixture produced as by-product in oxygen production at metallurgical plants or liquid oxygen produced on smaller but more widespread airseparation plants can be used for this purpose. For monitoring of Kr and Хе radionuclides in St. Petersburg in 2006-2008, we used liquid technical-grade oxygen produced at an air-separation plant in the northern part of St. Petersburg near the Khlopin Radium Institute site.RNG adsorption on an inorganic sorbent, subsequent desorption, and transfer of Kr and Хе into a measuring ampule.Liquid oxygen samples were taken into a 5-l Dewar vessel from the liquid oxygen pouring system. Then the sample was delivered to a laboratory and processed into a spectrometric sample. The procedure was as follows: first step, gasification of liquid oxygen and sorption of Kr and Хе on an inorganic sorbent; second step, desorption of Kr and Хе from the inorganic sorbent and their transfer into a spectrometric ampule.Liquid oxygen gasification was performed in a specially fabricated gasifier. It was a ~1-l cylindrical metallic vessel with two welded-in gas-outlet pipes and a hole with a threaded stopper for filling with liquid oxygen. For gasification, liquid oxygen was poured into the vessel from which it spontaneously evaporated without special heating. With the progress of evaporation, oxygen was intermittently added into the gasifier until the oxyg...

A procedure was developed for determining radioactive isotopes of Kr and Xe in air using a krypton-xenon mixture (KXM) produced at air separation plants. The procedure allows determination of background volume concentrations of Kr and Хе at long distances from sites of their injection using common spectrometric apparatus. The results of monitoring volume concentrations of 85 Kr and 133 Xe in Cherepovets in 2006-2008 are presented.