Determination of the mass fraction of 10B in boric acid by the measurement of thermal neutron flux depression

A thermal neutron absorption technique has been improved with the aid of Monte Carlo N-particle (MCNP) modelling and used for the determination of the mass fraction of 10B in boric acid. A relative standard deviation of that determination has been estimated to be below 0.12%. Owing to the good precision and simplicity, the presented technique could be helpful in nuclear plants with pressurized water reactors, where boric acid is added to the primary circuit coolant to control the chain reaction. Possible applications include the checking of the actual mass fraction of 10B in lots of boric acid delivered to nuclear power plants as well as calibration of instruments used for on-line monitoring the content of 10B in reactor coolants.