Authors & Affiliations
Zagorulko Yu.I., Ganichev N.S., Konovalov M.A., Ilicheva N.S.
A.I. Leypunsky Institute for Physics and Power Engineering, Obninsk, Russia
Zagorulko Yu.I. – Leading Researcher. Contacts: 1, Bondarenko sq., Obninsk, Kaluga region, Russia, 249033. Tel.: +7 (484) 399-80-84; e-mail:
Ganichev N.S. – Head of Laboratory.
Konovalov M.A. – Junior Researcher.
Ilicheva N.S. – Senior Researcher.
Abstract
At carbon concentration in sodium of 30 ppm in temperature interval 400–550 °C the system
«sodium-carbon» is two-phase system, consisted of carbon solution in sodium
(with share from 0.005 to 0.12 of overall concentration) and particulate carbon
phase, transported by sodium flow. The latter will be subjected to phase
transitions (dissolution or crystallization) in circuits with temperature
gradients. Except, mechanisms of carbon phase transitions could be dependent on
scale factor, defined as ratio of sodium mass flow rate to specific wetted
surface of the circuit pipelines and equipment units. It follows, that carbon
activity in sodium circuit should be considered as an essentially local
characteristic.
To carry out adequate experimental investigation of structural
materials carburization/decarburization processes it is necessary to provide
stable carbon activity in sodium in the test zone of the material.
The results of investigation on austenitic stainless steels
carbonization in high-temperature sodium in dependence on the carbon
thermodynamic activity in sodium are presented in the article. It was demonstrated, that at carbon activity
near to 0.1, carburization of austenitic steels in sodium at
700–750 °C exceeds ~ 1.2 mass %. An equilibrium carbon activity in
st. steels 04Cr16Ni15Mo3Nb, 08Cr16Ni15Mo3Nb at 700–750 °C is close to 5·10–3,
that is characteristic to st. steels 304, 316.
It was
established experimentally time irreversibility in kinetic of st. steels
carburization/decarburization processes. It follows that at elevated
temperatures short-time carbon activity «shocks», e.g. at
abnormal or accidental sodium coolant pollution could cause st. steels very
high carburization, which could be reserved subsequently for a long time in
sodium with low-level carbon activity.
Keywords
fast reactor,
mass transfer, carbon-containing impurities, sodium, carbon source, carbon
activity, suspensions, carburization, austenitic steel, equilibrium
samples-standards, diffusion sensor of carbon activity