Vol 125, No 1 (2018)

Next-generation apparatus for monitoring the neutron flux (NFMA) has been developed for use in the generation-3+ reactor installations of project NPP-2006. The apparatus is a component of the control and protection system in the power generating units of Novovoronezh NPP-2. Technical and algorithmic innovations making the apparatus more competitive relative to world analogs, including from the standpoint of safety, reliability, diagnostics, convenience of service, and methodological characteristics, are used. The apparatus was put into commercial operation in the No. 1 unit of Novovoronezh NPP-2. The basic principles of the NFMA design are presented, innovative and conservative (conventional) solutions adopted in the development of the apparatus are described, and the results of physical measurements performed in the course of the startup procedures are presented.

The functions, structure, and basic characteristics of the Hindukush-F equipment as part of the in-reactor monitoring system of NPP with VVER-1200 reactor are described. An analysis of the technical solutions used in the design is presented from the standpoint of the modern safety requirements of the equipment of this class and information on currently operating plants and plants under construction where this equipment is used is presented. It is concluded that the subsequent development of the in-reactor monitoring system is driven by increasing informatization and requires the use of modern computer technology and means of automation but the safety requirements must also be taken into account.

The results of development work on experimental samples of small fission ionization chambers for recording fast neutrons (E_n ~ 1–20 MeV) in a reactor core are presented. A technological solution for obtaining a radiator based on ThO₂ as a result of nonstationary low-temperature consolidation of an oxide coating from a solution of thorium carboxylate was developed and realized. Samples of ThO₂-based radiators on the surfaces of multichannel electrodes of diameter 3 and 5 mm and coatings based on the isotope ²³⁸U (in the form U₃O₈ based on uranium with ²³⁵U content 0.00002%) were fabricated and small fission chambers based on them were assembled. Sample radiators were bench tested for stability during thermal cycling (15 cycles, heating to 750°C) and under vibration loads (to 200 Hz). Physico-mechanical and reactor tests of the fission chambers were conducted and the discrimination characteristics of samples and their sensitivity to heat and fast-neutron fluxes were determined. A comparative analysis of the conditions of effective application of small ²³⁸U- and ²³²Th-based fission chambers in long-time operation as well as in single neutron measurements is made.

During studies performed in 2010–2014, in the under-reactor rooms and deaerator stack of the sarcophagus at the Chernoby NPP, the average volume activity of radon was ~100 Bq/m³ and the average coefficient of equilibrium of radon and its daughter products was ~0.7. The maximum volume activity of radon reached 666 Bq/m³. The daughter products complicate radiation monitoring of the aerosol situation. In the inspected rooms of the under-reactor space and deaerator stack, the radiation exposure of workers due to inhalation of radon, thoron, and their daughter products can exceed 10% of the maximum admissible effective dose. It was determined that the carrier aerosols of the daughter products are submicron aerosols with active median aerodynamic diameter ~0.1 μm. The arch erected above the sarcophagus at the end of 2016 can degrade the radon radiation situation because of reduction of the natural ventilation.

It was necessary to determine the possibility of expanding the range of working distances used in calibrating spectrometric standards of activity for radionuclides, which will make it possible to reduce number of standard measures needed for calibration. The approach proposed here consists in checking the shape integrity of the total absorption peak and the stability of the photon detection efficiency in the total absorption peak in a given geometry of the standard spectrometric gamma sources (SSPGS) and makes it possible to extend the lower bound of the activity range of the radionuclides of the calibrated SSPGS.