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Results of Radioecological Survey at the Accident Site of the Nuclear Submarine Kursk Using ANFEZH Sorbent

The article presents the results of radioecological survey at the accident site of the nuclear submarine Kursk in the Barents Sea about 80 km from the coast. Water samples were taken at a distance of 0.2 to 7 km from the submarine on 21 and 22 September 2000. The water was passed through the cesium selective sorbent ANFEZH®. After being dried, the sorbent was measured at the Institute of Global Climate and Ecology with a high-sensitivity semiconductor gamma spectrometer.

A radionuclide analysis of the samples has well documented that the amounts of cesium-137 in the sea water corresponds to its background content before the accident with the nuclear submarine Kursk. Other radionuclides (at the survey site) which could be released from the submarine reactors (i.e. cesium-134, cesium-136, zirconium-95, etc.) were not detected.   On 12 August 2000, the nuclear-powered submarine Kursk (Northern Fleet of the Russian Navy) sank in the international waters of the Barents Sea at a depth of 108 m, about 80 km from the coast. The third generation nuclear submarine Kursk (Project Antey) had been in operation since January 1995. The submarine had two pressurized water reactors (PWR) also classified as third-generation reactors [2]. Nuclear reactor cores at third-generation nuclear-powered submarines consist of fuel assemblies with different enrichment levels. Uranium in the fuel assemblies in the center of the reactor core and in the outer part of the reactor core is enriched with uranium-235 up to 21% and 45%, respectively. Nuclear reactor cores at third-generation nuclear-powered submarines contain 115 kg of uranium-235 and the total amount of uranium is 350 kg [2]. The sinking of the nuclear-powered submarine Kursk near the Southern Murmansk bank, an area with intensive fishing, raised understandable concerns associated with potential radioactive contamination of sea water. For this reason, during the last ten days of August the Russian Academy of Sciences initiated an independent radioecological examination of the area where the submarine sank. During the preparations for such works, it was proposed to study the content of radionuclides of artificial origin in the sea water in the area of the Barents Sea immediately adjacent to the accident site, at the depth where the submarine lay.

Of all the radionuclides listed in the table, several groups can be distinguished: 1) Cesium radioisotopes; 2) Strontium and yttrium radioisotopes; 3) Radionuclides which, according to the table, have the highest activity accumulated over the reactor lifetime, that is, 95Zr, 95Nb, I03Ru, 140Ba + 140La, I41Ce, I43Pr, and 144Ce. During the initial discussions, it was decided to filter all sea water samples through a sorbent which absorbs cesium. This is why the cellulose inorganic sorbent ANFEZH® was selected for this purpose. This iron/potassium ferrocyanide-based sorbent is highly specific to cesium in sea water and had already been used in the Barents Sea to determine the background level of cesium-137 in water [3]. The plan was to quantify the content of cesium-137 in sea water, as well as to estimate the content of cesium-134, cesium-136 and, possibly, some radionuclides from the third group, e.g. zirconium-95, following the analysis of the samples on a highly sensitive semiconductor gamma spectrometer. The latter could be in the water only if at least one reactor was depressurized and the strong hull of the submarine was damaged. The research vessel Dalnie Zelentsy departed from the city of Murmansk on 19 September 2000 to perform field operations at the accident site. The vessel carried a multidisciplinary scientific team on board, which performed the field operations required for water sampling and associated hydrological measurements directly on the accident site and in the reference areas. The operations area near the sunken submarine was selected on the basis of recent hydrological and hydrodynamic data obtained by Russian and Norwegian researchers. The meridional sections performed by the team crossed a near bottom water flow around the submarine. According to the existing diagram of warm currents in the Barents Sea, the operations area is under the influence of an east-south-east branch of the Nordkapp Current with maximum velocities in the bottom waters ranging from 0.3 to 0.5 m/s. During the operations, high-volume sea water samples (100 to 550 L) were taken from the research vessel from a depth of 100 m: on 21 September at a distance of 5-7 km and on 22 September at a distance of 0.2 to 1.5 km from the submarine. For comparison purposes, sea water samples of the same volume were taken in the reference areas located far away from the sunken submarine. 

Taking into account other tested samples, the results suggest that cesium-137 is present in sea water in the amount of (1.9-2.8) Bq/m3, which is consistent with the data obtained during the water studies in the Barents Sea prior to the Kursk submarine disaster. It was therefore concluded that there were no significant traces of cesium-134, zirconium-95, niobium-95, and other radionuclides in the tested samples, which could possibly indicate the presence of radioactive products from the submarine reactors (at the survey site).

Based on:

Yu. Izrael*, E. Stukin*, V. Soyfer**, S. Konstantinov*, V. Solovyev*, V. Averkov*, A. Smetankin***  

Results of Radioecological Survey at the Accident Site of the Nuclear Submarine Kursk // Meteorologiya i Gidrologiya (Meteorology and Hydrology), 2000, No. 10