Sodium — Coolant for nuclear power plants with fast reactors

Abstract

The adoption of mercury as a coolant has a long history. But, the main scientific-technical results in this field were obtained in connection with the development of nuclear power plants with fast reactors when sodium was chosen as the main coolant on the basis of a comprehensive analysis and comparison of the properties of different coolants. Operations with the coolant, including production and loading into the apparatus, up to shutdown of the nuclear power plant were examined (see Fig. I). As a result, a comprehensive approach was formulated for studying the system sodium --impurity --constructional materials --shielding gas. On account of the high chemical activity of sodium, special attention was devoted to safety.The path from the laboratory stands to adoption of sodium as a coolant and the development of experimental setups with fast reactors of the BR-5 type up to the demonstration commercial nuclear power plants with and BN-600 reactors has now been traversed.Analysis of more than a 40-year period of scientific-research, and experimental-constructional works and experience in operating experimental and commercial plants, shows that the sodium coolant technology which has been developed and adopted permitted long term operation of nuclear power plants at nominal parameters and with deviations from the nominal parameters (sodium leakage and sodium burnup, water leaks in the steam generators, anomalous comamination of the coolant and the shielding gas, and others).Impurities in Sodimn. The composition of the impurities in the initial sodium and the impurities appearing during operation of the systems is diverse. The greatest attention is devoted to oxygen, hydrogen, carbon, products of corrosion of the constructional materials, and radionuclides [1, 2]. The main difficulties with the initial sodium were associated with carbon (hydrocarbons and carbon electrodes, employed in production) and calcium. The development of a special apparatus for producing reactor-purity sodium at the Bereznikov soda plant solved this problem. However, this sodium was several times more expensive. It seems that under current conditions the final purification of sodium is best done at the nuclear power plant. Optimization of this process requires additional scientific-research reactors, which will more than pay for themselves.The constant sources of impurities, acting under normal operating conditions, are corrosion hydrogen from the steam generator, tritium from the core, oxygen and hydrogen from the shielding gas and from maintenance work, and products of corrosion of the constructional materials (see Table 1).It should be noted that the corrosion processes occurring in sodium are much less intense than in water or lead-based coolant [3]. However, it has been found that the rate of corrosion at the location of a water leak in the sodium through defects in the constructional material separating the sodium and water is several times higher than the corrosion rate in sodium under normal conditions [4]. For this reason, secondary d...

Development of Sodium Coolant Technology for Fast Reactors

“…The specifications for methods of monitoring performance, concentration range and sensitivity take account of not only the development of conditions for long-time incident-free operation of industrial facilities and their prototypes, maintaining the radiation conditions and minimizing dose loads but also the need for experimental work [14].…”

Sodium as a coolant for fast reactors

“…When water flows into the sodium, the corrosion rate of the wall material increases many-fold in the outflow zone. As a result, a small leak grows and becomes a large leak, a high-temperature plume forms and actively interacts with and destroys neighboring tubes of the steam generators [10,11].…”

“…The disadvantages inherent to sodium are high chemical activity in an oxidative medium and intense interaction with water (with formation of hydrogen gas), induced radioactivity of 24 Na and 22 Na with half-life 15 h and 2.6 yr, respectively -resulted in a second loop, also with sodium, in the reactor facility. The second loop prevents the products of the interaction of water with sodium from entering the core and the effect of high pressure on the first loop.The experimental and computational-theoretical studies led to an understanding of the liquid-metal system of nuclear power facilities as a complex heterogeneous multicomponent system whose components react with the structural materials and with one another [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. …”

“…The experimental and computational-theoretical studies led to an understanding of the liquid-metal system of nuclear power facilities as a complex heterogeneous multicomponent system whose components react with the structural materials and with one another [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].…”

“…Safe techniques for performing various operations were developed by means of studies and generalization of experience: removal of residues of sodium for and sodium decontamination of equipment, protection of sodium from oxidation during opening of the loop, extraction and installation of loop equipment, elimination of wastes, and salvaging of spent coolant [8,11]. Different methods of removing coolant residues and eliminating wastes were investigated: steam-gas, alcohol and water-alcohol, water-vacuum, vacuum distillation, and washing with water mist.…”