Accuracy of neutron dosimetry system by Helium accumulation method

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Accuracy of the Helium Accumulation Fluence Monitor (HAFM) developed by Power Reactor and Nuclear Fuel Development Corporation (PNC) was experimentally estimated by using neutron irradiated HAFM samples. Samples were irradiated by neutrons in the standard neutron spectrum fields of the Fast Neutron Source Reactor of "YAYOI" at university of Tokyo. The amount of Helium produced in the samples was measured by the Helium Atoms Measurement System (HAMS) at Kyushu University and by the HAFM measurement system at PNC. Both experimental results and the values estimated by the multi-foil activation method were compared. The neutron irradiated samples measured by the HAMS were two 1 mg enriched boron HAFM samples (boron chips were enveloped in a vanadium capsule), two 10mg natural boron HAFM samples, two 40 mg enriched boron HAFM samples, two natural boron chips and two TLD chips. Several dummy samples, which were not irradiated by neutrons, were also measured to estimate the amount of background helium at sample measurements. The overall errors for the helium measurements of samples by the HAMS were estimated to be less than 3%. The amount of background helium determined by the dummy sample measurements was less than 1% of helium contained in the neutron-irradiated samples. Our results by the HAMS were mostly in good agreement with the results by PNC. The estimated values supported our results. Reliance of helium measurement by the HAMS and by the HAFM measurement system, and validity of the neutron dosimetry by the helium accumulation method were consequently confirmed.