Constant power reactor

Constant power reactors developed by Ashe Morris (see Appendix 4) employ variable geometry flow channels to regulate the process power at different stages within... 

For slower reactions a different kind of constant power reactor is used, known as the agitated cell reactor. The agitated cell reactor (ACR) shown in Figure 5.42 is a form of constant power reactor where the product flows through a series of agitated cells. The concept adapts a well-rooted meso-scaled technique of the continuously stirred tank reactor to the constant power notion for greater increase in process control and stability. 

As noted previously, the calculation of the poison concentrations is dependent on the time behavior of the flux. In the case of the constant-power reactor, the flux must be inversely proportional to the fuel concentration. Thus a complete description of the operating condition of this type of reactor will require, in addition to the differential equations for the poison concentrations, a statement of the mass balance for the fuel nuclei namely,... 

Example 1.7 predicted that power per unit volume would have to increase by a factor of 100 in order to maintain the same mixing time for a 1000-fold scaleup in volume. This can properly be called absurd. A more reasonable scaleup rule is to maintain constant power per unit volume so that a 1000-fold increase in reactor volume requires a 1000-fold increase in power. Use the logic of Example 1.7 to determine the increase in mixing time for a 1000-fold scaleup at constant power per unit volume. 

The pilot reactor is a CSTR. The large reactor will be geometrically similar to the small one, and the scaleup wiU be done at constant power per unit volume. This form of scaleup exploits the fact that small vessels typically... 

The critical feed time t it depends on the location and number of feed pipes, stirrer type, and mixing intensity, and increases with increasing reactor volume. When a constant power-to-volume ratio is preserved, ta-u is proportional to and where D., is the stirrer diameter and Vr the reactor volume (Bourne and Hilber, 1990 Bourne and Thoma, 1991). The productivity of the reactor expressed as the amount of product formed per unit time becomes almost independent of reactor volume. The reason is that the reaction goes to completion in the zone nearby the stirrer tip. The size of this zone increases independently of the tank size it only depends on the velocity of the liquid being injected, the location of the nozzle, and the stirrer geometry and speed of rotation. Accordingly, for rapid reactions, the feed time will also be the reaction time. 

Not surprisingly, the final temperature of the solvent relies on the volume used, especially if experiments are performed at constant power. In such experiments, a decrease of the final temperature was observed with increased volume. Obviously, it is not possible to directly compare single-mode experiments with multimode experiments at an identical output power. Due to the significantly higher power density, the heat transfer of single-mode reactors is substantially higher. 

The reactor parameters shown above are typical for commercial stirred alkylation units in H2S04-butylene service. It is important to emphasize that the mixer comparison was made at constant power. 

High flow of emulsion generated by the impeller should disperse the olefin feed more quickly throughout the reactor and thereby improve quality. Comparing the FBT and HIT impellers at constant power, the flow is 40% lower for the HIT impeller. Conventional wisdom would predict the product quality to be lower. Hence impeller pumping is not the key variable. 

The samples are irradiated in the reactor for a time between seconds and weeks, depending on the half-life of the radionuclide to be measured or the tolerable waiting time, whichever is shorter. Care must be taken to assure that the samples and standards receive equal exposure to neutrons, or that unequal doses be measured quantitatively by Irradiation of monitors. The flux in a reactor which operates at constant power can be stable to better than 1 from day to day, while that in a training reactor may vary greatly on a time scale of minutes. The very fact that the reactor core is a neutron source guarantees that there will be a spatial gradient in neutron intensity, which may amount to tens of percent or more across a large sample container (28). 

For constant power per unit volume with a factor of 10 scaleup in linear dimensions, the agitator speed in the large reactor must be = 0.6 times that in the small reactor. If the... 

Figure 3.5 illustrates the spatial variation of power density in one-quarter of the core of a 1060-MWe PWR when the enrichment of and the concentration of boron control poison are uniform throughout the core. The lines plotted are lines of constant power density expressed as kilowatts of heat per liter of reactor volume, and also as kilowatts of heat per foot of fuel rod. The maximum permissible value of the latter is around 16 kW/ft, to ensure against overheating the fuel or cladding. 

A small percentage of the fuel elements in a water-cooled reactor release gaseous fission products to the coolant. The insoluble noble gases are collected and stored for radioactive decay prior to their release to the atmosphere. Calculate the required storage time such that the radioactivity levels of Xe and Kr in the released gas are equal. Assume fissions at constant power only in an average irradiation time of 2 years, and assume that these noble gas radionuclides are released to the coolant in the same proportion as they exist within the fuel. Obtain mass yields from Table 2.9. Twenty-three percent of the fissions at mass 85 produces Ki. 

The original impetus to measure rate constants in vs ter at elevated temperatures provided by the development of nuclear power reactors but, as in many other innovations, there is a spin-off of value to wider fields of research. 

FIG. 16.2. Production of higher actinide isotopes by irradiation of mixed oxide fiiel (3% Pu, rest depleted U) at constant power in a boiling water reactor. 

In early 2000, 433 nuclear power reactors (349 GW ) were in operation 120 (108 GW ) in North America including the US, 3 ( 2 GW in South America, 2 ( 2 GW ) in Africa, 169 (146 GW ) in Europe, including the Russian federation, and 90 (66 GW ) in the Far East (mainly Japan). Presently 37 power reactors ( 31 GW ) are under construction, the majority in the Far East and most of the rest in Europe. As small old nuclear power plants are shut down and replaced by bigger new ones, the number of reactors may remain constant in a geographic area, or even decrease slightly, although the total installed nuclear g erating capacity often continues to increase. 

In the scaleup of a stirred reactor at constant power per unit volume, how do the following parameters change with vessel diameter if geometric similarity is maintained ... 

The second heat removal system is an independent cooling system (ICS), which includes, besides a part of primary and secondary circuit equipment, a loop separator-cooling condenser with natural circulation. Via this loop the heat is removed to the intermediate circuit water. This system ensures independent (from the turbine generator systems) reactor cooling and independent reactor plant operation at a constant power level up to 6 % N om at the nominal steam pressure. In case of total RI de-energizig the system ensures cooling of the reactor over several days. Connection/disconnection of ICS is realized with no operator action and without using external power supply systems. 

In nuclear reactors the fission rate is controlled to generate a constant power. The reactor core consists of fuel elements containing fissionable nuclei, control rods, a moderator, and a primary coolant. A nuclear power plant resembles a conventional power plant except that the reactor core replaces the fuel burner. There is concern about the disposal of highly radioactive nuclear wastes that are generated in nuclear power plants. 

The method of measurement consisted simply of insertion of ion chambers in the various holes provided, in the graphite for this purpose (see Fig. A4.C) and observation of the ion current with the reactor operating at a constant power level. For the purpose of normalization, ion chambers in two holes (8 and 13) were checked carefully against neutron (foil) measurements in the core, and thereafter all measurements were referred to chambers in these holes. 

Fig. 2. Power vs time for a reactor with constant power extraction and various initial reactivity jumps. The effeci of the delayed neutrons is disregarded. From W. K. Ergen and A. M. Weinberg, Physica, 20, 413 (1954).

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