Calibration of CFUL01 fission chambers in the standard neutron fields of the BR1 reactor at SCK CEN

Recent subcritical VENUS-F experiments showed that fission chambers with a threshold deposit like U-238 can essentially improve the on-line sub-criticality measurments beam interruption method, which is currently supposed to be main method for ADS MYRRHA. To suppress uncertainty caused by fissions in U-235 impurities, fraction of U should accurately known. Three PHOTONIS CFUL01 type were purchased sub-critical reactor. verify purity their deposits, effective masses measured empty cavity BR1 reactor well-known thermal neutron spectrum. It turned out mass two lower than declared (as it be), but this not case third chamber. Then, these FCs was fast spectrum MARK-III convertor Finally, isotopic composition obtained and found agreement values certificates As length bigger convertor, necessary corrections calculated MCNP. The developed procedure using standard irradiation fields applied calibration impurity determination large chambers.