![]() ![]() Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983). It must be noted, the change in density is not linear with temperature, because the volumetric thermal expansion coefficient for water is not constant over the temperature range. It has a maximum of density at 3.98 ☌ (1110 kg/m 3), whereas the density of its solid form ice is 1017 kg/m 3. Also heavy water differs from most liquids in that it becomes less dense as it freezes. Pure heavy water (D 2O) has its highest density 1110 kg/m 3 at temperature 3.98 o C (39.2 o F). The molar mass of water is M(H 2O) = 18.02 and the molar mass of heavy water is M(D 2O) = 20.03 (each deuterium nucleus contains one neutron in contrast to hydrogen nucleus), therefore heavy water (D 2O) has a density about 11% greater (20.03/18.03 = 1.112). Since about 89% of the molecular weight of water comes from the single oxygen atom rather than the two hydrogen atoms, the weight of a heavy water molecule, is not substantially different from that of a normal water molecule. This difference is caused by the fact, the deuterium nucleus is twice as heavy as hydrogen nucleus. Pure heavy water (D 2O) has a density about 11% greater than water, but is otherwise physically and chemically similar. Due to the different relative power of fuel assemblies in a core, these fuel assemblies have different hydraulic resistance and this may induce local lateral flow of primary coolant and it must be considered in thermal-hydraulic calculations. The pressure loss due to the coolant acceleration in an isolated fuel channel is then:
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