Reactivity temperature coefficient

Temperature Coefflelenf. As the temperature of the reactor rises, the reactivity falls. The reactivity temperature coefficient, defined as the change in Ak/k per degree centigrade temperature rihe in the reactor, is the sum of three partial coefficients These partial coefficients arise from... 

The void reactivity and all reactivity temperature coefficients are negative. 

The core and fuel are designed to eliminate the need for refuelling during approximately thirty years and to make all reactivity temperature coefficients negative. Metal fuel, which has an excellent thermal conductivity, is applied. The core is shaped as a cylinder its main dimensions are given in Table XIV-6. The core can be operated during thirty years by axially... 

The coupled neutronics/thermo-hydraulic/thermo-structural reactivity feedback design approach for the STAR-H2 reactor has achieved the proper ratio between that reactivity which is vested in the coolant temperature rise relative to inlet temperature vis-a-vis that reactivity which is vested in the fuel temperature rise above the coolant, and at the same time in having designed an overall coolant flow circuit pressure drop tailored to cause coolant flow rate to adjust properly to changes in pressure driving head caused by source/sink temperature difference. A non-conventional open-pitch ductless fuel assembly structural design coupled with a non-conventional core support approach (the assemblies tend to neutral buoyancy in the dense Pb coolant) has been proposed to simultaneously provide low pressure drop, structural reliability of grid spacers, and an appropriate value for coolant power/flow reactivity temperature coefficient. 

The stabilizing reactivity feedback caused by negative reactivity temperature coefficients for the fuel and coolant as well as the void reactivity coefficient mean that heating up the core structural components, including fuel, or water boiling in the core would eventually result in a spontaneous reduction or self-limitation of the reactor power irrespective of the positions of control rods, including scram rods. 

Usually as a safety feature and for stability reasons, the overall reactivity temperature coefficient is designed to be negative. In this core the temperature of a critical reactor increases, k becomes less than one and... 

The reactivity temperature coefficient can then be calculated from the foregoing data for each of the several increments and for the overall change. 

In a solid homogeneous fuel moderator reactor such as Triga, would you expect the reactivity temperature coefficient to be more or less negative than that of the Argonaut Why ... 

The Brayton unit compressor inlet temperature (CIT) is affected by varying the HRS flow rate (pump speed). Changes in the compressor inlet temperature influence reactor power and thus reactor outlet temperature and Brayton unit electric power output. This change in reactor power is caused by the change in reactor inlet temperature (Tcold) coming from the compressor and the resultant change in reactivity due to the reactivity temperature coefficient. It is desirable to operate at the lowest compressor inlet temperature for maximum plant efficiency. Control of the plant based on HRS flow rate thus prevents the system from operating at maximum efficiency. As such, this control scheme is not envisioned for use for normal operation. 

Relative reactivity wiU vary with the temperature chosen for comparison unless the temperature coefficients are identical. For example, the rate ratio of ethoxy-dechlorination of 4-chloro- vs. 2-chloro-pyridine is 2.9 at the experimental temperature (120°) but is 40 at the reference temperature (20°) used for comparing the calculated values. The ratio of the rate of reaction of 2-chloro-pyridine with ethoxide ion to that of its reaction with 2-chloronitro-benzene is 35 at 90° and 90 at 20°. The activation energy determines the temperature coefficient which is the slope of the line relating the reaction rate and teniperature. Comparisons of reactivity will of course vary with temperature if the activation energies are different and the lines are not parallel. The increase in the reaction rate with temperature will be greater the higher the activation energy. 

More recently, Silva et a/.447,448 have found that the temperature coefficients of dEa /dT for a number of stepped Au surfaces do not fit into the above correlation, being much smaller than expected. These authors have used this observation to support their view of the hydrophilicity sequence the low 9 (rs0/97 on stepped surfaces occurs because steps randomize the orientation of water dipoles. Besides being against common concepts of reactivity in surface science and catalysis, this interpretation implies that stepped surfaces are less hydrophilic than flat surfaces. According to the plot in Fig. 25, an opposite explanation can be offered the small BEod0/dT of stepped surfaces is due to the strong chemisorption energy of water molecules on these surfaces. 

Therefore further progress in this area depends on the measurement of equilibrium constants. At this stage I simply cannot say how much of the difference of two powers of 10 between the k+Bpl of the alkenes and the styrenes is to be attributed to an intrinsic difference in reactivity and how much to the existence of the P+ G complexes. The negative temperature coefficient of the rate constant for a-methyl styrene found by Chawla Huang (1975) is a strong indication in favour of my view that the propagation is not a simple bimolecular reaction. 

Control of Temperature and Pressure. Diffusion coefficients in aqueous solution have a temperature coefficient of about +2% deg 1,42 which means that polarographic diffusion currents or voltammetric peak currents increase about 1-2% deg-1. The rates of follow-up chemical reactions of reactive species produced at the electrode surface depend even more strongly on temper-... 

The adsorption of each of the reactants and products on cobalt molybdate was studied under conditions as close as possible to reaction conditions. Butene and thiophene both showed strong temperature dependence, adsorption of the latter in particular being slow at the lower reaction temperatures. The temperature coefficients were 8.5 and 9.5 kcal. per mole, respectively. H2S adsorbed quickly and desorbed at a rate proportional to coverage, and hydrogen apparently behaved in the same way. Only relatively weakly bound or free hydrogen appeared to be reactive, but adsorbed hydrogen probably modified the adsorption of thiophene and of butene. 

Relative reactivity will vary with the temperature chosen for comparison unless the temperature coefficients are identical. For example, the rate ratio of ethoxy-dechlorination of 4-chloro- vs. 

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