Reduction of argon background in resonance ionization mass spectrometry for failed fuel detection and location of fast reactors

Iwata, Yoshihiro   ; Ito, Chikara   ; Aoyama, Takafumi*

For the fast reactors, rapid and accurate detection of fuel failures as well as subsequent identification of failed fuel location, if occurred, are essential to protect workers from radiation exposure and to reduce radiation contamination. A new type of failed fuel detection and location (FFDL) technique focused on the gas tagging method has been proposed by using resonance ionization mass spectrometry (RIMS) for the isotope analysis of the cover gas. Precise isotope analysis of ppt level Kr and Xe in Ar needed involves the two problems, which are the saturation of the output voltage by Ar ions and the Ar interference mainly with Kr. We proposed two methods, Brewster window and electrode with a slit-type hole, to decrease the adverse effect of Ar and Ar ions without any loss of Kr and Xe ion signals. The obtained measurement results using 100 ppt of Kr containing Ar standard gas show that we could successfully decrease the Ar ion yield by one to two orders of magnitude or more and that the mass peak of Kr corresponding to its nuclide concentration of 2 ppt was clearly observed without any obvious Ar peak. The precision of the isotope analysis seems to be about 10% for ppt level detection of Kr and slightly better for Xe, and is dominated by statistical errors. The next step is to increase the detection efficiency of our RIMS system to reduce statistical errors for further reliability improvement of RIMS in the FFDL system.