Neutron spectrum measurements near KAMINI reactor south beam vault door using nested neutron spectrometer

KAlpakkam MINI reactor (KAMINI) is a ²³³U fuelled research reactor has various neutron irradiation locations for experimental purposes. The pit at the south beam end of KAMINI reactor is being extensively utilized for neutron attenuation experiments in prospective shielding materials as well as for neutron radiography. During reactor operation, it will be closed by a movable shield. A vault door is located above the shield and the movable shield is used to attenuate streaming neutrons and gammas during reactor operation. Even with the shield, there exists significant dose due to streaming neutrons and gamma rays. It varies depends on the power of the reactor. The neutron and gamma dose rates close to the south beam vault door have recently been found to be 275-300μSv/h and 175-200μSv/h respectively, when the reactor is operating at 10kW. In order to characterize the streaming neutron spectra of vault door place for the first time, measurements are done using the Nested Neutron Spectrometer (NNS). Along with that neutron flux, neutron mean energy and ambient dose equivalent rate are also measured and compared with earlier measurements carried out inside the south beam pit. It is observed that the presence of paraffin shield reduces the neutron average energy from 370 keV to 178 keV. Apart from energy reduction, 10kW normalized neutron flux of south beam pit is also attenuated by the shield by 25,000 times and it is found that the neutron spectrum of the measured location is also more thermalized. Neutron reference data of the location is generated. (author)