ESTIMATION OF THE GENERATION OF 13C AND 14C IN THE REACTOR GRAPHITE USING MCNP6 MODELLING, ISOTOPE RATIO MASS SPECTROMETRY AND 14C MEASUREMENT TECHNIQUE

摘要

Characterization of irradiated graphite in terms of~(14)C activity is crucial for the optimization of treatment technology: geological disposal, landfill storage, recycling, etc. The main contributor to~(14)C generation in the RBMK reactor graphite is~(14)N(n, p)~(14)C reaction. The generation of carbon isotopes~(13)C and~(14)C in the virgin RBMK graphite samples irradiated at the LVR-15 research reactor (Research Centre ?e?, Ltd.) were investigated in order to obtain the impurity concentration level of~(14)N. Afterwards the modeling of graphite activation in the RBMK-1500 reactor was performed by computer code MCNP6 using obtained~(14)N impurity concentrations and new nuclear data libraries. The irradiation parameters – neutron fluence have been checked by method based on coupling of stable isotope ratio mass spectrometry and computer modelling. The activity of~(14)C in the different constructions of irradiated graphite of the RBMK-1500 reactor has been measured by the β spectrometry technique (LSC) and has been compared with the simulated one. Obtained results have indicated the importance of~(14)C production from~(14)N in the RBMK-1500 reactor and in the LVR-15 neutron spectrum. Measured~(14)C specific activity values in the samples varied from 130-700 kBq/g in the RBMK-1500 irradiated samples and from 3-12.5 Bq/g in the LVR-15 irradiated graphite samples. This corresponds to 15±4 - 80±10 ppm impurity of~(14)N in various graphite samples of RBMK reactor.