Composition of the gas-plasma phase in the radioactive graphite - water vapor system

In this work, the composition and thermophysical properties of the “Reactor graphite-H2O” system at temperatures from 2123 to 3223 K are calculated. It was found that the main components of the vapor phase at a temperature of 2123-2923 K: carbon dioxide, carbon monoxide, water vapor, hydroxide, hydrogen, atomic hydrogen. At temperatures above 3223 K, oxygen and atomic oxygen are added to the gases present. The balances of uranium and plutonium are considered. Uranium at temperatures above 2123 K is present in the system in the form of gaseous and ionized uranium dioxide and trioxide. Plutonium at temperatures above 2123 K is present in the system in the form of gaseous and ionized plutonium oxide, gaseous plutonium dioxide. The calculation of thermophysical properties for the considered system is carried out.

Influence of vacuumetric pressure on thermal properties of high-temperature radioactive graphite-nitrogen system

To improve and specify the method proposed by the authors for high-temperature processing of reactor graphite in a nitrogen atmosphere, the thermodynamic data of the formed nitride compounds are supplemented and the system is calculated at a vacuum pressure of 0.5 atm. The data obtained are compared with the values at atmospheric pressure.

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

Characterization of irradiated graphite in terms of 14C activity is crucial for the optimization of treatment technology: geological disposal, landfill storage, recycling, etc. The main contributor to 14C generation in the RBMK reactor graphite is 14N(n, p)14C reaction. The generation of carbon isotopes 13C and 14C in the virgin RBMK graphite samples irradiated at the LVR-15 research reactor (Research Centre Řež, Ltd.) were investigated in order to obtain the impurity concentration level of 14N. Afterwards the modeling of graphite activation in the RBMK-1500 reactor was performed by computer code MCNP6 using obtained 14N 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 14C 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 14C production from 14N in the RBMK-1500 reactor and in the LVR-15 neutron spectrum. Measured 14C 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 14N in various graphite samples of RBMK reactor.

On In-Situ Disposal of ChNPP Facilities

The paper considers the possibility of applying in-situ disposal practice for Chornobyl exclusion zone facilities, in particular: ChNPP-1-3 that are under decommissioning, Shelter, RWDS ChNPP Stage III and RWDS Pidlisny. It was concluded that these facilities would not reach safety level over the next 300 years sufficient for clearance from regulatory control. In-situ disposal of ChNPP-1-3 would lead to a potential hazard related to a large amount of irradiated reactor graphite. Artificial barriers of concrete and bulk clay will not provide isolation of radionuclides, primarily radiocarbon, from the environment. The paper considers possible natural factors, the effect of which for the time required for the decay of radionuclides to acceptable level, can lead to destruction of surface storage facilities on ChNPP site. Such factors are as follows: probable transformation of Pripyat river valley; seismic influence related to both strong earthquakes in the Vrancea Zone (Romania) and the influence of local seismic centre. It raises issues connected with considering climate change, duration of and change in climate cycles for safety justification of in-situ disposal practices for ChNPP facilities. It was concluded that at this time it is impossible, to prove safety of surface burial on ChNPP site for the period of tens of thousands of years, since a number of external factors have probabilistic nature.

Xenon Behavior in Molten Salt Reactor Graphite

This article discusses the aspects of 135Xe behavior in molten salt reactor (MSR) graphite. Models of MSR graphite are described. The related mass transfer and mass diffusion coefficients are described and means by which they can be calculated are detailed. Xenon reactivity effects are explored. A method is presented to model the internal xenon distribution within the graphite stringers.