Reactor control systems

Open-Loop versus Closed-Loop Dynamics It is common in industry to manipulate coolant in a jacketed reacdor in order to control conditions in the reacdor itself. A simplified schematic diagram of such a reactor control system is shown in Fig. 8-2. Assume that the reacdor temperature is adjusted by a controller that increases the coolant flow in proportion to the difference between the desired reactor temperature and the temperature that is measured. The proportionality constant is K. If a small change in the temperature of the inlet stream occurs, then depending on the value or K, one might observe the reactor temperature responses shown in Fig. 8-3. The top plot shows the case for no control (K = 0), which is called the open loop, or the normal dynamic response of the process by itself. As increases, several effects can be noted. First, the reactor temperature responds faster and faster. Second, for the initial increases in K, the maximum deviation in the reactor temperature becomes smaller. Both of these effects are desirable so that disturbances from normal operation have... 

Our examples above demonstrated this quantitatively. For this reason, it is vital to design a reactor control system with very fast measurement dynamics and very fast heat-removal dynamics. If the thermal lags in the temperature sensor and in the cooling jacket are not small, it may not be possible to stabilize the reactor with feedback control. 

Open-Loop versus Closed-Loop Dynamics It is common in industry to manipulate coolant in a jacketed reactor in order to control conditions in the reactor itself. A simplified schematic diagram of such a reactor control system is shown in Fig. 8-2. Assume that the reactor temperature is adjusted by a controller that increases the coolant flow in proportion to the difference between the desired reactor temperature and the temperature that is measured. The proportionality constant is Kc. If a small change in the temperature of the inlet stream occurs, then... 

An actuator fault can be generated by a malfunction of the cooling system, such as electric-power failures, pomp failures, valves failures, and leaking pipes. Without loss of generality, actuator faults may be modeled as an unknown additive term affecting the state equation in (6.5), due to unexpected variations of the input u with respect to its nominal value, i.e., the value computed by the reactor control system. 

The area of reactor design has been widely studied, and there are many excellent textbooks that cover this subject. Most of the emphasis in these books is on steady-state operation. Dynamics are also considered, but mostly from the mathematical standpoint (openloop instability, multiple steady states, and bifurcation analysis). The subject of developing effective stable closedloop control systems for chemical reactors is treated only very lightly in these textbooks. The important practical issues involved in providing reactor control systems that achieve safe, economic, and consistent operation of these complex units are seldom understood by both students and practicing chemical engineers. 

Implementation of the method of Spent Nuclear Fuel (SNF) unloading from unwatered NS reactors represents a crucial solution of the nuclear safety challenge because removal of moderator eliminates the risk for reactor core to attain critical condition under any design-basis/beyond-the design-basis operations with reactor control systems. 

Considerable work was done prior to commissioning on the MTG reactor control system and the cooling water system. Simulation code was written for the MTG control to model the heat/mass transfer effects during reactor switching and various trip scenarios. As a result no serious control problems have been experienced in the MTG plant. 

Two other systems are connected to the protection system The technological protection of steam generators and its peripheral functions are included in the SAS function. The Reactor Control System (RCS) performs the regulating function to operate the reactor in a predefined diagram according the power of the reactor. This system replaces the existing ARM function. 

Reactor Control System (RCS) which is a replacement of the existing ARM system... 

The preceding three chapters of the Handbook have described the reactor, its use, and the physics of its design. In this chapter the reactor control system and some of the-philosophy behind-it will. be discussed Like that of the rest, of the MIB, the development of the controls has gone on over the last five years therefore no separate historical development is attempted. 

Mounted in the concrete pipe line leading to the Blower and Fan House is a venturi tube for determining the flow rate through the system. The flow rate is indicated on a panel in the Blower and Fan House. Since the Blower and Fan House is an unattended station which will have periodic inspections only, the information for operation of thd reactor air system is transmitted to the Process Water Building and the Reactor Control Boom. The Process Water Building serves, as the center for operational infoi mation. on the reactor air system. The flow rate is therefore recorded at the control panel in the Process Water Building, and there ar.e low flow rate alarms at both this panel, and the panel in the Reactor. Control Boom., Besides the. above, the ye nturi information is transmitted >to. the reactor control system to automatically shut the reactor down on failureof the air system. 

I. Kliger, Synthesis of an optimal nuclear reactor control system. Atomic Energy Comm. Symp. Series, Vol. 7, Neutron Dynamics and Control, pp. 110-136 (1967). 

The reactor control system consists of four rods located in the radial reflector and in the lower movable end reflector. Two rods are used for automatic and manual control, whereas the other two, together with the movable reflector, are used for the protection in case of emergency. The negative temperature coefficient of the reactor reactivity allows operating for a long time without the interference of the control system. Only some deterioration of electric power necessitated increasing of thermal power up to a new level. 

On-power refuelling provides the principal means for controlling reactivity in the CANDU 3. Additional reactivity control, independent of the safety system, is achieved through use of reactivity control mechanisms. These include absorber rods, mechanical zone control units, and adjuster rods all are located between fuel channels within the low pressure heavy water moderator and do not penetrate the heat transport system pressure boundary. The overall reactor control system is described in Section 5.8.2.3. 

Load following without operation of reactor control system,... 

Hanford Production Reactor operations will be carried on within limits aimed toward assurance of total available control strength of the combined reactor control systems adequate to avoid development of a reactivity state which would significantly Increase the consequences of an accident In the event of any credible combination of events or complete and permanent loss of coolant. 

In the operation of the Hanford Production Reactors every reasonable effort vlU be made to assure a sufficiently rapid response of the reactor control system to avoid development of an energy state during any power excursion which would significantly Increase the consequences of the accident. 

The principal natural phenomena that influence transient operation are the temperature coefficients of the moderator and fuel and the buildup or depletion of certain fission products. Reactivity balancing may occur through the effects of natural phenomena or the operation of the reactor control system using the RCCs or chemical "shim." A change in the temperature of moderator or fuel (e.g., due to an increase or decrease in steam demand) will add or remove reactivity (respectively) and cause the power level to change (increase or decrease, respectively) xmtil the reactivity change is balanced out. RCC assemblies are used to follow fairly large load transients, such as load-follow operation, and for startup and shutdown. 

On-power fueling means that there is very little reactivity hold-up needed in the reactor control system (and no need for boron in the coolant to hold down reactivity, resulting in a simpler design). The control rod reactivity worth can therefore be kept quite small (2 mk per rod or less). 

The rupture of any process tube In a manner to Introduce large qiuantitles of water will result in flow and pressure transients resulting in a reactor scram. The time required to flood a large fraction of the reactor core with water from one process tube would be sufficient to allow all reactor control systems to be fully inserted. In the remotely possible case of multiple tube rupture the flooding time for a significant fraction of the pile may be short. 

Reactor control systems, innovative continuous reactor technologies including the variable geometry reactor and micro CSTRs. 

Vessel system 2 - Reactor core 3 - In-vessel cavity 4 - Tube block 5 - Probe unit of in-reactor control system 6 - Upper unit 7 - Two SGs 8-2 MCPs 9 - CPS drives. 

The output can be varied by control of the turbine-water system alone using a negative coolant temperature reactivity coefficient of the core, which makes it possible to abandon the traditional reactor control system ... 

Nearly constant fissile fuel content and neutron multiplication factor hence, very small excess reactivity built-in and very simple reactor control system that requires adjustment for burn-up only once every few years ... 

Non-divergent power oscillations resulting from normal control systems response are not of significant concern. The primary safety concern is for divergent power oscillations and the ability of the power reactor control system to detect and suppress the oscillations before they can challenge the fuel safely limits and damage fuel cladding. 

Load rejections requiring greater than a fifty percent reduction of rated thermal power initiate the rapid power reduction system. This trips preselected rod cluster control assembfies into the reactor core to rapidly reduce reactor power into a range where the rod control and reactor control systems can maintain stable plant operation. 

Do the Hanford reactor control systems satisfy these requirements ... 

A polymerization reactor often produces several grades (in terms of composition and viscosity) of the same polymer and therefore the control strategy must be easily adapted to a multi-product plant and in some cases to on-line grade transitions. In the case of a multi-product plant it may be necessary to operate the reactor in terms of rather short campaigns in order to noinimize the finished-product inventory and thus the working capital. In these cases the reactor control system must be designed in such a way as to achieve fast startups while minimizing off-specification polymer formation. 

Tritium targets are normally prepared by allowing tritium gas to be absorbed into a thin layer of titanium on a suitable base such as copper. Using this reaction, miniature accelerator tubes have been designed which are small enough to be completely inserted into a reactor. These devices can be operated in the pulsed mode the rate of decay of the neutron flux following a rapid injection of neutrons into the reactor can be measured and used to obtain information on parameters such as the effectiveness of the reactor control system. 

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