Assay of nuclear grade primary sodium in the fast breeder test reactor for radionuclides and corrosion elements

摘要

Periodic assay of primary sodium used as a coolant in the fast breeder test reactor (FBTR) at Kalpakkam is necessary and pre-requisite for the safe and continuous operation of the reactor. Contamination of nuclear grade purity of the primary sodium is monitored either online or offline for the radionuclides and chemical impurities to ascertain the integrity of the various components. Chemical elements which can entrain into sodium due to the corrosion of structural materials is troublesome as they might clog the coolant channels resulting in to a reduced coolant flow which further leads to fuel clad failure. The corrosion elements present in the primary sodium were determined by ICP-OES and their activation products were assayed by high resolution gamma spectrometry. In case of fuel clad rupture, the fission products such as ~(137)Cs, ~(134)Cs, ~(136)Cs, ~(131)I, ~(90)Sr, ~(125)Sb etc. along with actinides U and Pu are released into primary sodium. This paper reports actinides, fission products, corrosion elements as well as their activation products and concentration levels present in the primary sodium of FBTR. Activity variation of one of the long-lived fission products, viz. ~(137)Cs over the period of time, before and after fuel clad rupture is profiled and discussed.