Coolants for reactors

The recognition in 1940 that deuterium as heavy water [7789-20-0] has nuclear properties that make it a highly desirable moderator and coolant for nuclear reactors (qv) (8,9) fueled by uranium (qv) of natural isotopic composition stimulated the development of industrial processes for the manufacture of heavy water. Between 1940 and 1945 four heavy water production plants were operated by the United States Government, one in Canada at Trail,... 

To slow down and control the rate of reaction, a moderator is also required. Typically, the moderator is boric acid, graphite, or heavy water (D20) and is present in the high-purity water, which also serves as a primary coolant for the fuel and the reactor vessel. The tremendous heat generated by nuclear fission is transferred to this closed-loop coolant, which is contained within a reactor primary-coolant circulation system. The high-purity water coolant also contains a suitable pH buffer such as lithium hydroxide, which has the additional effect of limiting the corrosion of fuel-cladding and other components. 

Further away in time are possibilities of using fast reactors, though, at least for some decades, not as breeders. The Soviet navy has been using such reactors, using a lead/bismuth eutectic mixture as coolant, for some decades in some of their high performance submarines and it is understood that work is now going on to see whether this design could be made suitable for small commercial power production... 

Because the melting point of sodium metal is about 98° C (a bit lower than the boihng point of water), it is heated into a liquid phase and then transported in rail tank cars, where it cools and solidifies. When it arrives at its destination, heating coils in the tanks warm it back to the liquid stage, and it is then stored for use. Because sodium has a high specific heat rating, a major use is as a liquid coolant for nuclear reactors. Even though sodium (both solid and liquid) is extremely reactive with water, it has proven safe as a coolant for nuclear reactors in submarines. 

Uses. Coolant for heat exchange in nuclear reactors... 

Coolant -for molten steel [IRON BY DIRECT REDUCTION] (Vol 14) -for nuclear reactors [NUCLEARREACTORS - REACTOR TYPES] (Vol 17)... 

Both sodium and potassium are so reactive that they have to be stored under oil to prevent them from coming into contact with water or air. However, because they have low melting points and are good conductors of heat, they are used as coolants for nuclear reactors. 

Effect Of Throughput Figures 2.3 and 2.4 show what happens when the feed flow-rate is increased by 50% from the base case production rate. The 50% conversion design requires very large coolant flowrates for reactor temperatures above 340 K. At this temperature the reactor volume of 16.2 m3 with a heat transfer area of 29.8 m2 requires a jacket temperature of 297.6 K. The fraction of the total available AT is... 

Results for the two reactors are given in Figure 5.27. In the adiabatic reactor, temperature increases down the reactor as chlorine is consumed and products are formed. In the constant-coolant temperature reactor, temperature reaches a maximum of 411 K at about 0.6 m from the inlet. Note that very little allyl chloride is formed in the cooled reactor because the temperatures are low. In the adiabatic reactor, the high temperatures increase the allyl chloride reaction rates because of the higher activation energy. 

Ignatiev, C., Pankratov, D., Toshinskiy G., et al. (2004) Nuclear and Radiation Safety during Spent Nuclear Fuel Storage of Land-based Stands Prototypes of Naval Liquid-metal Coolant Power Reactor Installations - Final Report under the ISTC Project 2710p between the Russian Research Center Institute for Physics and Power Engineering (RRC IPPE) and the Brookhaven National Laboratory of the US Department of Energy, Obninsk (in Russian). 

From the above table it follows that major works in different areas are to be performed in Gremikha including -management of SNF of Nuclear Submarines (NSs) with Liquid-Metal Coolant (LMC) reactors and WER -management of Solid and Liquid Radioactive Waste (SRW and LRW) -removal of SNF and Spent Removable Units (SRUs) to Mayak for reprocessing -rehabilitation of buildings, constructions, terrestrial and aquatic systems. 

Parametric Sensitivity. One last feature of packed-bed reactors that is perhaps worth mentioning is the so-called "parametric sensitivity" problem. For exothermic gas-solid reactions occurring in non-adiabatic packed-bed reactors, the temperature profile in some cases exhibits extreme sensitivity to the operational conditions. For example, a relatively small increase in the feed temperature, reactant concentration in the feed, or the coolant temperature can cause the hot-spot temperature to increase enormously (cf. 54). This sensitivity is a type of instability, which is important to understand for reactor design and operation. The problem was first studied by Bilous and Amundson (55). Various authors (cf. 57) have attempted to provide estimates of the heat of reaction and heat transfer parameters defining the parametrically sensitive region for the plug-flow pseudohomogeneous model, critical values of these parameters can now be obtained for any reaction order rather easily (58). 

Dangerous when heated it emits highly toxic fumes of Na20 and K2O. Used as a liquid coolant for nuclear reactor cores. See also SODIUM and POTASSIUM. 

A jacketed vessel, as shown in Figure 3.23, is often used for maintaining temperature however, it has limited surface area and low heat transfer coefficients. Sometimes internal reactor cooling coils are also used to provide additional heat transfer area. In order to manipulate the heat transfer, maximum flow is maintained in a circulation loop, while the jacket temperature is adjusted by bringing in and letting out coolant. The reactor temperature controller provides a setpoint to the jacket temperature controller. Heat transfer is linear and proportional to the temperature difference. 

Two cooling systems are needed. First, the moderator itself serves as a coolant for the reactor. It transfers fission-generated heat to a steam generator. This converts water to steam. The steam then goes to turbines that drive generators to produce electricity. Another coolant (river water, sea water, or recirculated water) condenses the steam from the turbine, and the condensate is then recycled into the steam generator. 

The heat transfer fluid will be a coolant for exothermic reactions and a heating medium for endothermic reactions. If the flow rate of the heat transfer fluid is sufficiently high with respect to the heal released (or adsorbed) by the reacting mixture, then the heat transfer fluid temperature will be constant along the reactor. 

Li hydroxide is now used in some water-cooled reactors to inhibit corrosion by control of hydrogen ion concentration. Because the thermal-neutron absorption cross sections of the lithium isotopes are Li, 940b, and Li, 0.037 b, it is necessary to use Li contaiiting less than 0.01 percent Li. Li metal, which melts at 180°C, was proposed as coolant for an aircraft-propulsion reactor, because of its low vapor pressure at high temperature and low neutron-absorption cross section. 

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