The sources of impurities entering the sodium in fast reactors were investigated. The analysis showed that oxygen and hydrogen can be removed from the sodium by using cold traps in all operating regimes of a nuclear power plant as well as hot traps. An operating regime preventing hydrogen accumulation in the first-loop cold trap is proposed for a system purifying the first two loops. A computer code for calculating the impurity mass transfer is perfected. Test calculations showed that the procedure developed and the code are both serviceable. The deviation of the computational results from the experimental data is about 30% on average. For a built-in purification system, it is essential to develop a cold trap with a large impurity capacity. It is shown on the basis of experiments that such cold traps can in principle be developed. Thermohydraulic and mass-transfer codes must be developed in order to realize this possibility.Sodium-coolant purification systems in nuclear power plants with fast reactors must provide the required purity in all operating regimes taking account of all sources of impurities and must have the capacity required to handle the impurities accumulating in the purification system (it is permissible to replace the elements of the system during purification but the number of such replacements must be minimal). When significant contamination is present (routine maintenance, refueling, and accidental contamination), their capacity must ensure that impurities will be removed from the coolant as quickly as possible before the power reaches the operating level and the accumulation of suspensions in the first loop must be prevented.At the present stage of development of nuclear power, considering that safety, cost-effectiveness, and environmental compatibility must be improved, the requirements for the equipment in a nuclear power facility have been raised. Specifically, it has been decided that all systems with radioactive sodium be placed inside the reactor tank. This limits the dimensions of the first-loop systems. Therefore, the positive experience gained in placing purification systems outside the reactor tank cannot be fully utilized.For optimization, the purification characteristics were analyzed for the first loop. The analysis is based on evaluating the possible sources of impurities: their composition, amount, and rate of flow into the coolant in all possible operating regimes of a nuclear power plant. The relationship between the first-and second-loop purification systems and their effect on the distribution of impurities and the possibility and desirability of using not only cold traps but also other methods of purification, for example, hot traps, the structural implementation of the purification system, and the operation regime were all examined.The sources of impurities in systems with sodium coolant are oxygen, hydrogen (determining amount by mass and volume), products of corrosion of the structural materials, tritium, cesium if fuel-elements become depressurized, gaseous fission prod...
The characteristics of sodium permeation through graphite and the accompanying swelling of the graphite are examined for the central rotating column of a BN-600 reactor. The sodium transport parameters when sodium comes into contact with graphite at 350-500°C for up to 400 h are determined experimentally. Under these conditions, the permeation parameter is (0.13-1.3)·10 -11 m 2 /sec, which corresponds to an effective diffusion coefficient (0.2-2)·10 -11 m 2 /sec. The ratio of the increment to the graphite volume and the sodium mass there is ~0.85.It is of scientific and practical interest to investigate the interaction of graphite with sodium. Specfifically, graphite is present inside the central column of a BN-600 reactor. This column is in direct contact with liquid sodium.Graphite is characterized by a layered structure. The parameters of the crystal lattice are: a = 2.46·10 -10 m in closepacked layers with a hexagonal structure and c = 6.7·10 -10 m (twice the distance between layers) [1, 2].The interaction of sodium and graphite is determined by the degree of ordering of the carbon structure and the presence of impurities and porosity in the system [3][4][5]. When the graphite is permeated, metal from the pores penetrates into the ordered structure of the carbon framework, forming layered compounds (graphitides) of the form MeC n . This increases the distance between the planes with the close-packing of atoms, causes the framework to swell, and results in the formation of cracks. The maximum degree to which sodium penetrates into the graphite matrix corresponds to the chemical formula NaC 8 [3].It is known that at their melting temperatures metals such as Cu, Ag, Sn, Pb, and Sb, in contrast to carbide-forming group IV-VI transition metals, do not wet the surface of graphite [6]. The transport of liquid metal in the pores in graphite is described by the relation (analog of the Washburn permeation equation [7]) where l is the permeation depth; r is the average capillary radius; ρ is the density of the metal; k is a coefficient that takes account of the rate of carbonization of the liquid metal; η is the viscosity; ∆λ is force driving the permeation (this force is associated with the surface tension); m is a coefficient that depends on the radius of the capillary; τ is the permeation time; g is the acceleration of gravity; and the exponent n is usually close to 0.5.We shall study the transport of liquid sodium into graphite under the following conditions: • initially, the sodium does not wet the graphite;• after a certain period of time the sodium interacts with the carbon material on the surface of the graphite, including at the openings of the pores, forming in the pores the initial front of meniscuses; l r k m r g n = − − ( ) ln ( ) , πρ η λ π ρ τ ∆ 2
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