Automatic Power Level Control

The power level can be switched from 10 to 650 W by the chosen cycle time. The temperature can be preset and subsequently controlled automatically between 0 and 120°C. Vacuum is generated by a built-in vacuum pump (operating at 12 V), producing 0.0-0.3 bar vacuum. The vacuum level is indicated by an automatic meter. Since the oven provides a sealed and ventilated system, the evaporation of formalin, ethanol, isopropanol, and other reagents does not affect the operator. Vapors and fumes are extracted by continuous ventilation. The oven weighs about 21 kg. Its use is awaited. 

To fine-tune the cavity, the spectrometer is put in the operate mode. Adjust the microwave frequency, the iris position (resonator parameter), and the reference arm current ( bias ) so that the analog indicators for the automatic frequency control ( AFC ) and the diode always stay at the center as the microwave power is increased from minimum (e.g., 50 dB, 2 fiW) to maximum (e.g., 0 dB, 200 mW). This indicates that at all power levels, the majority of microwave power is stored in the resonator and very little is reflected. Adjust the signal phase to let the diode indicator reach the maximum, and then decrease the bias if necessary to put diode back to center again. 

There have been two major accidents (Three Mile Island in the United States and Chernobyl in the former Soviet Union) in which control was lost in nuclear power plants, with subsequent rapid increases in fission rates that resulted in steam explosions and releases of radioactivity. The protective shield of reinforced concrete, which surrounded the Three Mile Island Reactor, prevented release of any radioactivity into the environment. In the Russian accident there had been no containment shield, and, when the steam explosion occurred, fission products plus uranium were released to the environment—in the immediate vicinity and then carried over the Northern Hemisphere, in particular over large areas of Eastern Europe. Much was learned from these accidents and the new generations of reactors are being built to be passive safe. In such passive reactors, when the power level increases toward an unsafe level, the reactor turns off automatically to prevent the high-energy release that would cause the explosive release of radioactivity. Such a design is assumed to remove a major factor of safety concern in reactor operation, see also Bohr, Niels Fermi, Enrico AIan-HATTAN Project Plutonium Radioactivity Uranium. 

In the reactor core, shown in Fig. 19.15, uranium that has been enriched to approximately 3% (natural uranium contains only 0.7% is housed in cylinders. A moderator surrounds the cylinders to slow down the neutrons so that the uranium fuel can capture them more efficiently. Control rods, composed of substances that absorb neutrons, are used to regulate the power level of the reactor. The reactor is designed so that should a malfunction occur, the control rods are automatically inserted into the core to stop the reaction. A liquid (usually water) is circulated through the core to extract the heat generated by the energy of fission the energy can then be passed on via a heat exchanger to water in the turbine system. 

For a short time just after refueling, 25 percent of full power is achieved before the inner group of rods is fully withdrawn. During this brief period and at power levels below 25 percent, some of the inner control rods may be partially inserted to control core reactivity. Also, these inner rods may occasionally be used to control reactor power at other levels. However, in most circumstances the automatic operation will be limited to the outer control rod drives. 

Automatic continuous reduction of power level through servo control as long as the unsatisfactory coolant or power level situation exists or until the power level is reduced to 1% of. full power. 

Full-scale test of the servo mechanism as an automatic control device was accomplished during the low—power nuclear experiments described in Section A4.5.7. The system performed satisfactorily for several months at power levels from 100 watts to 175 kilowatts. 

The control rod system provides for automatic control of the required reactor power level and its period reactor startup manual regulation of the power level and distribution to compensate for changes in reactivity due to burn-up and refuelling automatic regulation of the radial-azimuthal power distribution automatic rapid power reduction to predetermined levels when certain plant parameters exceed preset limits automatic and manual emergency shutdown under accident conditions. A special unit selects 24 uniformly distributed rods from the total available in the core as safety rods. These are the first rods to be withdrawn to their upper cut-off limit when the reactor is started up. In the event of a loss of power, the control rods are disconnected from their drives and fall into the core under gravity at a speed of about 0-4 m/s, regulated by water flow resistance. 

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. 

The computer system of the station control and data acquisition is a distributed micro processer based systems. A digital multiplexed control system takes the place of hard wired analogue control. This accounts for a significant reduction in cable usage. Built-in diagnostics and board level maintenance makes restoration of operability of any fault in the system a matter of replacement of printed circuit cards. Automatic control systems and procedures are deployed to simplify these procedures and power level manoeuvers. In case of unsafe conditions the reactor protection system (PMS) takes over and automatically scrams the reactor and actuates the relevant safety systems. Diverse methods are used to assure the shutdown of the reactor in hypothetical situations. The systems also provide for post-accident monitoring. 

Control equipment is provided to allow the reactor to respond automatically to load changes and abnormal operational transients. Reactor power level is manually controllable. 

Capable of automatically controlling the unit at startup and at any pre-selected power level within the normal loading range... 

The nuclear flux level and rate of change of flux is monitored in the sub-critical range, in the intermediate power level range, and in the operating range by multiple sensing and control systems, each consisting of multiple fail-safe components. Any one of these systems, except for the subcritical instruments, will automatically shut down the reactor complex in the event that process limits are exceeded. 

The horizontal rod system in the RPR provides the following functions a Normal reactor control (IC circuit) b. Automatic slow setback of power level (2C circuit) c Automatic (or manual) fast scram (IX circuit)... 

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