Safety ultimate shutdown system

Number of IHTS Loops Safety Shutdown Heat Removal Ultimate Shutdown System Fuel Handling Seismic Design... 

In addition to the inherent safety features, there are two independent systems for reactor shutdown. The primary shutdown system provides for a drop of several sectors of the reflector, and the back-up shutdown system provides for insertion of the ultimate shutdown rod, located as a central subassembly on a stand-by in a fully out condition. 

Ultimate safety systems are, by definition, only required in extremis. When they are required, they really must work - that is so obvious it should not have to be said. And yet, at Chernobyl (the reactor shutdown system). Deepwater Horizon (the blow out preventer) and Fukushima (the tsunami barrier), the ultimate safety system in each case was woefully inadequate and unable to prevent disaster when called for. 

Control systems will play a key role in future distributed plants ]139,145]. As a rule of thumb, plants will be smaller and simpler, but the control systems will be much more advanced, of a standard not known today. Plant personnel for operation and managing will ultimately no longer be required, except for start-up, shutdown, and services. This is a shift from a regulatory to a servo role, supported by a sophisticated sequence control. Control is needed for safety issues, operability, and product quality control. Sensors have a central role to provide the information needed for control and modeling and simulation is needed for process models. 

The ultimate objective for fast reactors has always been to maximise the utilisation of the natural uranium resource and in common with the main development programmes world wide, EFR has pursued the sodium coolant technology. The safety approach recognises the differing requirements of a sodium cooled fast reactor core compared to the established water and gas cooled thermal reactors which has resulted in a different balance between prevention and mitigation with consequences for the shutdown, decay heat removal and containment systems. 

The SSWS cools the Component Cooling Water System (CCWS) through the Component Cooling Water Heat Exchangers and rejects the heat to the ultimate heat sink during normal, transient, and accident conditions. The CCWS in turn provides cooling water to those safety-related components necessary to achieve a safe reactor shutdown, as well as to various non-safety reactor auxiliary components. 

Apart from this automatic shutdown function which is an "ultimate safety" feature, there is a conventional protection system which initiates scram when operation limits are exceeded. Such scrams are performed by means of a scram valve, letting pool water in to the recirculation pump suction side. In addition, the reactor can be shut down by boron Injection via the normal control system. 

Heat sink could be defined as the complex of sources of service water necessary to operate, shutdown and cool-down a nuclear plant safely. The issue is to deal widi the reliability of the sources themselves such as rivers, lakes, ponds and the reliability of systems and components intended to transfer heat ifom safety related systems to the cold sources. The ultimate heat sink must be shown to be capable of dissipating the heat following normal or abnormal situations, under unfavorable meteorological conditions, for periods long enough to guarantee the safety of the plant. 

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