Recirculation flow control

The BWR is unique in that reactor power output can be varied over a power range of approximately 25% of the operating power level by adjustment of the reactor recirculation flow without any movement of control rods. This is the normal method used for load following and maneuvering the reactor and allows for load following at rates of up to 1% of 

Reactor power change is accomplished by using the negative power coefficient. An increase in recirculation flow temporarily reduces the volume of steam in the core by removing the steam voids at a faster rate. This increases the reactivity of the core, which causes the reactor power level to increase. The increased steam generation rate increases the steam volume in the core with a consequent negative reactivity effect, and a new constant power level is established. When recirculation flow is reduced, the power level is reduced in a similar manner. 

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The integration of the turbine pressure regulator and control system with the reactor water recirculation flow control system permits automated... 

The BWR operates at constant pressure and maintains constant steam pressure similar to most fossil boilers. The integration of the turbine pressure regulator and control system in conjunction with the reactor water recirculation flow control system permits automated changes in steam flow to accommodate varying load demands on the turbine. Power changes of up to 25% of rated power can be accomplished automatically by recirculation... 

Above approximately 65% of rafed core flow, the recirculation flow control is automatic. 

After passing through the core, the coolant steam-water mixture enters the bank of centrifugal steam separators mounted above the core, where the water is separated out by vortex action and flows down to join the recirculation flow through the annulus. The steam passes upwards into the steam driers in which the moisture is further reduced, and thence to the turbine. The steam leaving the core is at a temperature of 286°C, at a pressure of 1040 psi (73 kg cm The total thermal output from the core is 3833 MWt. Recirculation flow control is used to provide automatic load following power changes of up to 25% of full power can be accommodated in this way. 

Air control louvers or dampers, popular in the past for air flow control, are used primarily for only very low scale air flow control. Louvers are used in many winterized heat exchangers in extremely low ambient temperature locations to retain and recirculate warm air in completely enclosed heat exchangers, sometimes in very compHcated control schemes. The use of louvers on the discharge side of a fan to control air flow is inefficient and creates mechanical problems in the louvers because of the turbulence. A fan is a constant volume device, thus use of louvers to control flow is equivalent to... 

Air-Flow Control Process operating reqmrements and weather conditions are considered in determining the method of controlling air flow. The most common methods include simple on-off control, on-off step control (in the case of multiple-driver units), two-speed-motor control, variable-speed drivers, controllable fan pitch, manually or automatically adjustable louvers, and air recirculation. 

At 0119 10, the operator began to increase the rate of feedwater return to reduce the recirculation flow to increase the water level in the steam drums. At 0119 45, the reduced inlet water. stopped water from boiling in the core. The absence of the steam voids reduced the reactivity, and control rods were withdrawn, such that only 6 to 8 rods were in the reactor, rather than the required 30. Then, to avoid reactor trip from steam drum or feedwater signals, their scram circuils v ere locked out (a safety regulation violation). 

Embedded in such models, in which variations were developed [12] are further detailed. The laminar burning velocity is expressed as a function of fuel type, fuel/ air ratio, level of exhaust gas recirculation, pressure, temperature, etc. Furthermore, submodels have been developed to describe the impact of engine speed, port-flow control systems, in-cylinder gross-flow motion (i.e., swirl, tumble, squish), and turbulent fluctuations u. Thus, with a wider knowledge base of the parametric impact of external variables, successful modeling of... 

Figure 2.22 [2.6] demonstrates the method of a cooling circuit with recirculated flow An injector pump operated with just evaporated LN2 aspirates the warmer N2 coming from the condenser and feeds the mixture back in the condenser. The desired condenser temperature can be controlled by a throttle valve. To achieve a uniform temperature distribution, the gas mixture is alternately fed to one or the other end of the condenser. No results of such a system are given. 

The reactor core, the source of nuclear heat, consists of fuel assemblies and control rods contained within the reactor vessel and cooled by the recirculating water system. A 1,220-MWe BWR/6 core consists of 732 fuel assemblies and 177 control rods, forming a core array 16 feet (4.8 meters) in diameter and 14 feet (4.2 meters) high. The power level is maintained or adjusted by positioning control rods up and down within the core. The BW R core power level is further adjustable by changing the recirculation flow rate without changing control rod position, a feature that contributes to excellent load-following capability. 

The key to smooth operation of a CFB system is the effective control of the solids recirculation rate to the riser. The solids flow control device serves two major functions, namely, sealing riser gas flow to the downcomer and controlling solids circulation rate. Both mechanical valves or feeders (see Figs. 10.1(a) and (d)) and nonmechanical valves (see Figs. 10.1(b) and (c)) are used to perform these functions. Typical mechanical valves are rotary, screw, butterfly, and sliding valves. Nonmechanical valves include L-valves, J-valves (see Chapter 8), V-valves, seal pots, and their variations. Blowers and compressors are commonly used as the gas suppliers. Operating characteristics of these gas suppliers which are directly associated with the dynamics and instability of the riser operation must be considered (see 10.3.3.2). 

An electrical resistance heater with more turns at the tube ends (to compensate for heat losses) surrounds each tube. There is a vertical laminar flow hood over the loading area to minimize particle contamination of the wafers being loaded. As we can see, there are temperature controls for the furnace tubes, and a power module to provide the electrical power. When operated as a LPCVD system, a unit including both the gas flow and vacuum systems is positioned on the right side. Such a unit is shown in Figure 8. Here we can see the vacuum pumps on the left, and the mass flow controllers on the right. The vacuum pump oil recirculation systems are shown in the slide out drawers. As can be seen in Figure 9, this system, as well as most current similar systems, operate under computer control. 

Step 8. Several control valves now remain unassigned. Steam flow to the trim heater controls reactor inlet temperature. Cooling water flow to the trim cooler is used to control the exit process temperature and provide the required condensation in the reactor effluent stream. Liquid recirculation in the absorber is flow-controlled to achieve product recovery, while the cooling water flow to the absorber cooler controls the recirculating liquid temperature. Acetic acid flow to the top of the absorber is flow-controlled to meet recovery specifications on the overhead gas stream. Cooling water flow to the cooler on this acetic acid feed to the absorber is regulated to control the stream temperature. Cooling water flow in the column condenser controls decanter temperature. 

The pilot plant contained three flowmeters (FI) to measure the permeate, concentrate, and recirculation streams. The flows of the recirculation and concentrate streams could be controlled by means of valves to provide the flows wanted for the experiment, while the permeate stream was a function of the other two. The recirculation flow was fixed at 2.4 m /h and it remained constant in all the experiments. 

A recirculating Moyno-type (screw) [Himp with independent flow control. 

In the bubble column the velocity profile of recirculating liquid is shown in Fig. 27, where the momentum of the mixed gas and liquid phases diffuses radially, controlled by the turbulent kinematic viscosity Pf When I/l = 0 (essentially no liquid feed), there is still an intense recirculation flow inside the column. If a tracer solution is introduced at a given cross section of the column, the solution diffuses radially with the radial diffusion coefficient Er and axially with the axial diffusion coefficient E. At the same time the tracer solution is transported axially Iby the recirculating liquid flow. Thus, the tracer material disperses axially by virtue of both the axial diffusivity and the combined effect of radial diffusion and the radial velocity profile. 

Recirculation from seal chamber through a flow control orifice to the seal and simultaneously from the seal chamber through a control orifice (if required) to pump suction. Plan 14 is a combination of Plan 11 and Plan 13. 

Fluxes of 25 l/m -hr were consistently achieved through permeate flow controlled operation of the hollow fibers. Further optimization of recirculation rates might lead to higher flux performance. 

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