Correlation between Tritium and 152Eu Induced in Various Types of Concrete by Thermal Neutron Irradiation.

Tritium induced in BWR reactor shielding wall and PWR biological shielding wall irradiated by thermal neutrons is considered to be the critical radionuclide for trench disposal management in Japan. For the purpose of tritium quantification, preparing a specimen of activated concrete without letting tritiated water scatter away is, however, practically impossible. This calls for an alternative means of tritium quantification through indirect estimation from measurement of a substitute radionuclide, such as Eu-152, that is easy to quantify. Many types of concrete and their raw materials were sampled and irradiated by thermal neutrons of the JRR-4 reactor to find out the correlation existing in irradiated concrete between the specific activities of tritium and of Eu-152. The induced activity of for Eu-152 was measured by Ge detector, and that of tritium by liquid scintillation counter. From the results measured on the various types of concrete, the formula obtained empirically between H-3 and Eu-152 was H-3(Bq/g) =Eu-152(Bq/g) x (5-27). Another noteworthy finding is that the ratio of the quantity of tritium induced by thermal neutrons is 1:46 between low-activation concrete and ordinary concrete.