Reactor period

Reverse-flow reactors Reactive distillation Reactive extraction Reactive crystalization Chromatographic reactors Periodic separating reactors Membrane reactors Reactive extrusion Reactive comminution Fuel cells... 

Reactor period is defined as that amount of time, normally in seconds, required for neutron flux (power) to change by a factor of e, or 2.718. 

Rate information is displayed on a meter in decades per minute, and since it is used by the operator to monitor the rate of change of power during startup, it is termed startup rate. Startup rate (SUR) equates to reactor period using Equation 6-10. 

SUR = startup rate in decades per minute 26.06 = constant x = reactor period in seconds... 

The determination of rate change of the logarithm of the neutron level, as in the source range, is accomplished by the differentiator. The differentiator measures reactor period or startup rate. Startup rate in the intermediate range is more stable because the neutron level signal is subject to less sudden large variations. For this reason, intermediate-range startup rate is often used as an input to the reactor protection system. 

Figure 5 shows the effect of phosphate concentration on crystallization rate Rg. Crystallization rate was obtained by weighing seeds in the reactor periodically, in which phosphate concentration drop in the bed was low enough, not to produce concentration distribution, by making the depth of the bed thin. Solubility of hydroxyapatite is so low, that the influent phosphate concentration is equal to super saturation dC. As shown in Figure 5, crystallization rate was proportional to 1.1th order of supersaturation. 

In this hydration process, high-purity acetylene under a pressure of 15 psi (103.4 kPa) is passed into a vertical reactor containing a mercury catalyst dissolved in 18 to 25% sulfuric acid at 70 to 90°C. Fresh catalyst is fed to the reactor periodically the catalyst may be added in the mercurous (Hg+)... 

While certain materials perform particularly well under certain conditions (e.g., titanium in the presence of chloride-containing feed), there appears to be no one material that is sufficiently corrosion resistant to all feeds of interest to SCWO. Material choices must therefore be made based on the most corrosive and/or most common feed component anticipated, and may vary for different parts of the SCWO system (including the reactor). Periodic replacement of components may be necessary as well. 

In the Chernobyl accident, reactor output increased from -20% to 100 times full power in about 4 seconds. Assume a constant reactivity excess during this time, a) What was the average reactor period b) How much energy was released during this time ... 

A typical Intermediate Range System for reactor scifety circuit use could consist of three Intermediate Range Monitors with log-level and reactor period readout and trips, through compensated ion chambers and associated power supplies and three reactor hole facilities with shield plug, bonnets, etc. 

Monitoring of the reactor period, neutron flux, thermal output of the reactor, rate of reactor power change, heat-up rate at the reactor vessel inlet, and the temperature difference between the overflow tank and the reactor vessel outlet ... 

A proper analysis of the tine dependent behavior of.a reactor operating on thermal neutrons must take into account the important effects on its criticality, reactivity, and stability which arise from such factors as fission i products of high thermal-neutron capture cross-section, depletion, temperature, average neutron lifetime in the reactor, flux level, and reactor period. As has been seen in the requirements placed on the.reactor, considerable excess reactivity must be built into the active core before start-up. The control rods must keep the reactivity below the critical value before and during start-up. 

The number defined hy T = 1/cu, where w is the largest root of (11), is called the stable reactor period. The reactor period is the enfolding time, the time required for the flux to increase by a factor e. 

The problem is separable for a bare homogeneous reactor. However, only the case of a step input of reactivity, i.e., the case of a constant value of p, is easily solved. In this case, the kinetic equations are readily reduced to a second order (for the case of one delayed neutron group) homogeneous linear differential equation with constant coefficients. For an input of positive reactivity two solutions arise, of the form and where o>i > 0 and 0)2 < 0. The first solution controls the persisting exponential rise of the flux, where it is recalled that T = l/o>i is the reactor period, and the second solution which rapidly becomes small is called the transient solution. 

The problem of immediate concern is that of the calibration of a control rod in a thermal reactor. By control rod calibration is meant the determination of the reactivity worth of a control rod per unit distance of travel, usually in a vertical direction. Such a calibration, particularly in experimental critical facilities, is of great importance in connection with a variety of reactor experiments. It is rather easy to calibrate a control rod, particularly in a low power critical assembly. A rod is withdrawn a few centimeters in a just critical reactor. As soon as the flux takes off on an exponential ascent the reactor period can be measured with the aid of appropriate detectors and recording devices. A relationship between the reactor period and reactivity is afforded from the inhour equation. Thus, the reactivity worth of a control rod per unit length of travel in a certain area of the reactor is determined. The rod may be calibrated over its entire length of travel by the expedient of maintaining criticality by the opposing... 

Stable and transient reciprocal reactor periods for a representative special case with large initial reactivity input... 

The quantity t/(fc — 1) is usually called the reactor period. It is given by the time of the neutron cycle (t), which is a constant for a given reactor and is determined mainly by the properties of the moderator. It is also determined by the criticality value k that varies, e.g., as a function of the position of the control rods. 

Over-all Instrument linearity and stability are better than 0.02%, and the instrument s dynamic rai is greater than. 4 decades. Qs excellent statistics and lack of counting losses have made it the instrument of choice lor reactor period and rod drop measurements. 

Void coefficients were measured through the use of thln-wall aluminum tubes. The reactivity differential between the void and no-void condition was evaluated by a measurement of the change in t e reactor period between the two conditions with the core fully reflected. 

The long prompt neutron lifetime (about 1 ms) means that for reactivity transients even above prompt critical, the rate of rise in power is relatively slow. For example, the reactor period for an insertion of 5 mk is about 0.85 s L whereas for 7 mk it is about 2.4 s 1. The SDSs are, of course, designed to preclude prompt criticality. 

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