Contamination by other radionuclides

As has been discussed above in detail, °Co and Co are usually the radionuclides that determine the radiation dose rates at the primary circuit surfaces. In isolated cases, however, other radionuclides, usually activation products of other primary circuit materials, may also be of significance. Fission products normally do not contribute to a significant extent to contamination buildup. 

Jarnstrom (1982) reported that in the first operating cycles of the VVER plants Loviisa 1 and 2 the radionuclides Sb, Sb and ° Ag were chiefly responsible for the radiation dose rates at the primary circuit. The most important sources for antimony were identified to be the ammonia solutions added, which contained antimony impurities in the range of 10 to 50pg/kg for silver the main source was KOH used for alkalizing the coolant which contained silver impurities in the range of 5 to lOmg/kg. Both impurity elements, as well as their radioisotopes, were removed with a low efficiency from the primary coolant by the action of the purification system. In the course of plant shutdown, a marked increase in the concentrations of these radionuclides in the primary coolant was observed, which was counteracted by a change in the cooldown procedure the purification system was 

Concerning the On Ag activity in the primary coolant of several plants, silver-containing sealings were identified as the main source, from which traces were released to the coolant by corrosion or mechanical wear. Usually, does not 

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Some of the experimental results are shown In Table I. Contaminations by other radionuclides are very small. 

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