Reactor emergency system

Hard-wired interlocks should be provided to prevent opening of the SOj/air isolation valve until the reactor emergency system is primed. The system should be activated by a hard-wired interlock to an organic flow sensor. 

Another strategy would involve design of the reactor vessel for a pressure rating in excess of any likely emergency system pressure. This assumes we can adequately predict all possible worst case situations, which is doubtful. 

S. S. Grossel, Design and Sizing of Knockout Drums/Catchtanks for Reactor Emergency Relief Systems, Plant /Operations Progress (July 1986). 

In most cases, a two-phase (vapour/ liquid or gas/ liquid) mixture is vented from a reactor emergency relief system. The relief system required for a two-phase mixture is very often larger (by, in some cases, several times the flow area) than for gas or vapour alone. It is therefore essential to take account of two-phase relief to size a relief system properly. J ... 

S S Grossel, "Design and Sizing of Knock-out Drums/ Catchtanks for Reactor Emergency Relief Systems", Plant/Operations Prog, 5 (3), 129-135,1986... 

The primary system is intended to isolate the major equipment in order to prevent reverse flow and exhaust oxides in a gaseous state. It consists of a special restraint type valve (check) and two motorised shutdown valves, arranged in series. The system includes a low pressure detector on the main pipe that trips the sulphuric acid pumps, isolates the process and stops the helium flow into the reactor and heaters (emergency system EAS-200). 

The high impedance is usually a resistance chosen to limit the earth current to about 20 mA. A current detector is used in conjunction with the resistance to raise an alarm if a line-to-earth fault occurs. A zig-zag transformer, or reactor, is sometimes used with three-wire supplies such as used in drilling rigs and emergency systems. It is specially designed and internally connected to create a very low zero sequence impedance to earth currents. Therefore, the current is limited only by the resistance of the neutral earthing resistor. Some special purpose earth current alarm systems are available that inject a small DC current into the three-phase system, which is used to identify the actual location of the fault. 

The two first events are associated with the reactor start-up tests. However, the two last ones, although they initiated an emergency shut-down thank to the "fail-safe" design of the reactor protection system, present the problem of its reliability. 

Totally 104 failures have occurred over a total operation period. The abnormal operation events due to equipment and system failures resulted in 28 plant shutdowns of which 18 shutdowns involved reactor scrams (5 events involved manual reactor emergency shutdowns). In the remainder the plant power reductions took place. 

Common requirements for the reactor protection system, engineered safety features actuation system and emergency load sequencer on one side, and for the reactor limitation system on the other side have been set forth in the following areas ... 

Apart from differences of approach between world regions, in this period of time and in all the countries with nuclear reactors, the systems installed in the plants according to the requirements of the safety bodies and having the sole purpose of accident mitigation, were frequently the subject of heated debates in particular, the emergency core cooling systems and the containment systems were often discussed. 

On the upper unit of V-392 reactor 121 nozzles are provided for the members of reactivity control system and reactor emergency protection (CPS) in comparison with 61 nozzles in V-320 reactor. This gives a possibility to vary the number and arrangement of CPS members and to optimise each fuel cycle for reaching the best characteristics of the core safety and efficiency. 

Such blockage might occur rapidly under emergency conditions such as an earthquake. Therefore, a second safety system has been provided for the Hanford Production Reactors. In order to minimize the possibility of the control medium not being able to enter the reactor, this system depends only on gravity for insertion and is fluid in nature. 

Phase II, i.e. the time between 2005 and 2020 approximately, encompasses the forecasted doubling of today s world-wide installed nuclear capacity along with evolutionary reactors, innovative Systems like AP600, PIUS, MHTGR, EFR will emerge. 

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. 

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