Reactor automatic

The accident resulted from a routine safety test of some electrical control equipment at the start of a normal reactor shutdown for routine maintenance. The test was to determine the ability to continue to draw electrical power from a turbine generator during the first minute of coast-down following a station blackout. In a blackout, the reactor automatically scrams and diesel generators start to assume load (about 1 minute required). 

In addition, operator training is being overhauled and simulators will be more widely used. There will be increased security of the reactor automatic protection against unauthorised interference by operators and improved administrative arrangements to ensure that rules and regulations will be complied with. Research and development of the reactor physics and fuel element cooling of RBMK reactors will be increased. 

Nuclear and process control Instrumentation shall be provided to automatically scram the reactor when preset control limits are exceeded. Tables I, II, and III Indicate the Instrumentation, the number of monitored channels, the set points, and by-pass availability for each function capable of scramming the reactors automatically. 

System pressure drops reactor automatically scrams and emergency once-through system diesel punqps aixtomatlcally start ... 

Prevention of abnormal reactivity. Accidental withdrawal of control rods and passage of gas through the core during reactor operation were analyzed In both events, the reactor automatically shuts down, the event terminates safely and the maximum temperature of the fuel and fuel cladding remains within the limits with sufficient margin... 

The overall negative temperature feedback is assured under all conditions. The reactor nuclear design assures that the temperature reactivity coefficients of fuel and moderator are always negative under all operating and accident conditions. Together with the protection action of stopping the primary helium blower, this will lead to a reactor automatic shutdown in accident cases. 

PORV to open. The reactor coolant pressure continued to rise until, at about 8 s, the reactor automatically scrammed on high reactor coolant pressure. As a result of the reactor trip, the volume of the liquid reactor coolant began to contract, and the reactor coolant pressure began to fall as indicated in Figure 2.4-4. 

By approximately 11 00 pm Friday evening, the local electricity demand had subsided, and the load dispatcher gave permission for Chernobyl Unit 4 to continue with its power reduction. At this point, another step in a string of unfortunate events occurred when the automatic reactor control unit did not adjust for the new lower power level. The operators had reset the reactor monitoring system to the requested level, but had failed to reset the reactor automatic controller. The reactor s response was a dramatic drop in power, down to 30 MWt, 1 % of the normal operating level (US NRC, 1987). In effect, the automatic controller inserted control rods, which drove the overall core power dramatically lower than was intended. 

In service inspections of French nuclear Pressure Water Reactor (PWR) vessels are carried out automatically in complete immersion from the inside by means of ultrasonic focused probes working in the pulse echo mode. Concern has been expressed about the capabilities of performing non destructive evaluation of the Outer Surface Defects (OSD), i.e. defects located in the vicinity of the outer surface of the inspected components. OSD are insonified by both a "direct" field that passes through the inner surface (water/steel) of the component containing the defect and a "secondary" field reflected from the outer surface. Consequently, the Bscan images, containing the signatures of such defects, are complicated and their interpretation is a difficult task. 

Solvent Process. In the solvent process, or solvent cook, water formed from the reaction is removed from the reactor as an a2eotropic mixture with an added solvent, typically xylene. Usually between 3 to 10 wt % of the solvent, based on the total charge, is added at the beginning of the esterification step. The mixed vapor passes through a condenser. The condensed water and solvent have low solubiUty in each other and phase separation is allowed to occur in an automatic decanter. The water is removed, usually to a measuring vessel. The amount of water collected can be monitored as one of the indicators of the extent of the reaction. The solvent is continuously returned to the reactor to be recycled. Typical equipment for this process is shown in Figure 2. The reactor temperature is modulated by the amount and type of refluxing solvent. Typical conditions are ... 

Provide for addition of diluent, poison, or inhibitor directly to reactor. Provide for automatic or manual actuation of bottom discharge valve to drop batch into a dump tank with diluent, poison or inhibitor, or to an emergency containment area. 

Provide automatic or manual addition of diluent, poison, or inhibitor directly to reactor... 

Hydrochloric acid may conveniently be prepared by combustion of hydrogen with chlorine. In a typical process dry hydrogen chloride is passed into a vapour blender to be mixed with an equimolar proportion of dry acetylene. The presence of chlorine may cause an explosion and thus a device is used to detect any sudden rise in temperature. In such circumstances the hydrogen chloride is automatically diverted to the atmosphere. The mixture of gases is then led to a multi-tubular reactor, each tube of which is packed with a mercuric chloride catalyst on an activated carbon support. The reaction is initiated by heat but once it has started cooling has to be applied to control the highly exothermic reaction at about 90-100°C. In addition to the main reaction the side reactions shown in Figure 12.6 may occur. 

Humans control all chemical and nuclear processes, and to some extent all accidents result from human error, if not directly in the accident then in the process design and in the process inadequate design to prevent human error. Some automatic systems such used in nuclear power reactors because the response time required is too short for human decisions. Even in these, human error can contribute to failure by inhibiting the systems. 

In some BWR transient scenarios, the high pressure injection systems are postulated to fail. To make use of the low pressure injection system, it is necessary to depressurize the reactor coolant system, a function performed by the automatic depressurization system (ADS). In the scenario considered, ADS actuation is manual because the signals for automatic initiation of the system are not present. 

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