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Temporal and spatial variations of Cs-137 in the waters off a nuclear fuel reprocessing facility in Rokkasho, Aomori, Japan (by means of sorbent ANFEZH)

Takahiro Nakanishi • Tatsuo Aono • Masatoshi Yamada • Masashi Kusakabe

Extracted from source: // J Radioanal Nucl Chem (2010) 283 : 831–838

Five survey cruises were carried out from 2004 to 2007 to determine 137Cs concentrations in the water columns off Rokkasho Village, Aomori Prefecture, Japan, where the spent nuclear fuel reprocessing plant of Japan Nuclear Fuel Ltd has been undergoing test operation since March 2006. Seawater samples were collected with a large volume in situ filtration and concentration system at different depths in the water column. 137Cs in particulate form could not be detected in the survey area. Dissolved 137Cs showed temporal variation, especially in the surface water. Based on the results, it was concluded that no observable 137Cs contamination was present in the investigated area. The distribution of 137Cs concentrations was influenced by the mixing between the Tsugaru and Oyashio Currents.

Collection of dissolved 137Cs was done using a Large Volume Filtration and Concentration System (LV-FiCS)…

The system consists of filtration and concentration modules installed in an electromechanical cable at different depths… Each module consists of the main and auxiliary filtration and concentration units (main-FC and aux-FC units, respectively). Several tons of seawater are filtrated through the main-FC unit (which uses a 70 lm-mesh Teflon filter and two 1 lm-pore-size glass fiber filters), and then dissolved constituents are concentrated onto adsorbents in the main housings. At the same time, several hundred liters of seawater are filtrated through a cartridge filter with 1 lm pore size, and then dissolved nuclides are concentrated onto other adsorbents in the auxiliary housings…

Minor modification of the LV-FiCS was made…

Dissolved 137Cs was concentrated onto two housings in series in the auxiliary unit; each housing contained a polyvinyl chloride tube (4 cm ID - 20 cm length) sealed with nylon net and was packed with approximately 40 g of Anfezh ™ (Eksorb Ltd, ... Russia).

Anfezh is a coarse-grained adsorbent made of ferric potassium hexacyanoferrate(II) on a cellulose support. An important attribute of this adsorbent is that it has very low distribution coefficients for the major and minor salts commonly present in seawater. This means that large volumes of seawater can be processed to extract radioisotopes without loading the adsorbent with unwanted salts. Therefore, Anfezh has been used for many years for removal of Cs from the large volumes of seawater…

In most cases, sample collection was conducted for 4 h at each station and could filter ca. 314–1391 L of seawater through the auxiliary line...

The 137Cs concentrations were corrected for decay to the date of sample collection. The recovery of 137Cs via the Anfezh adsorbent on the LV-FiCS ranged from 31 to 96% with an average of 62 ± 16%.

original paper