Typical reactor coolants, physical

Physical Properties of Some Typical Reactor Coolants... 

Unlike water, sodium, or helium, liquid fluoride salts are a family of coolants with similar general properties. The choice of a specific molten salt for a specific application is determined by functional requirements and costs. Many salts have been examined. Table XXVI-3 shows the properties for several different liquid salts and traditional reactor coolants under typical conditions. Table XXVI-4 lists leading candidates for various nuclear liquid salt applications and their key physical properties. The remainder of this Appendix discusses the various salts and the constraints that limit the choice of salt. 

A relevant aspect of the implementation of defence in depth is the provision in the design of a series of physical barriers to confine the radioactive material at specified locations. The number of physical barriers that will be necessary will depend on the potential internal and external hazards, and the potential consequences of failures. The barriers may, typically for water cooled reactors, be in the form of the fuel matrix, the fuel cladding, the reactor coolant system pressure boundary and the contaimnent. 

The desired product is P, while S is an unwanted by-product. The reaction is carried out in a solution for which the physical properties are independent of temperature and composition. Both reactions are of first-order kinetics with the parameters given in Table 5.3-2 the specific heat of the reaction mixture, c, is 4 kJ kg K , and the density, p, is 1000 kg m . The initial concentration of /I is cao = 1 mol litre and the initial temperature is To = 295 K. The coolant temperature is 345 K for the first period of 1 h, and then it is decreased to 295 K for the subsequent period of 0.5 h. Figs. 5.3-13 and 5.3-14 show temperature and conversion curves for the 63 and 6,300 litres batch reactors, which are typical sizes of pilot and full-scale plants. The overall heat-transfer coefficient was assumed to be 500 W m K. The two reactors behaved very different. The yield of P in a large-scale reactor is significantly lower than that in a pilot scale 1.2 mol % and 38.5 mol %, respectively. Because conversions were commensurate in both reactors, the selectivity of the process in the large reactor was also much lower. 

A violent vapor explosion can result when a cold volatile liquid is suddenly brought into contact with a hot liquid. The explosion is due to the rapid vaporization of the cold liquid from heat transfer from the hot liquid. Such explosions are referred to as vapor, steam, physical, or thermal explosions rapid-phase-transitions (RPTs) (typically when referring to explosions involving cryogenic liquids) and molten fuel-coolant interactions (FCIs) when applied to nuclear reactor accidents. Accidental vapor explosions are frequent occurrences in the metallurgical, pulp and paper, and cryogenic industries. General reviews of the various aspects of vapor explosions can be found in Reid [1] and Corradini et al. [2]. 

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