Inherent safety simplicity

Safety concept and design philosophy Provisions for simplicity and robustness of the design Active and passive systems and inherent safety features Structure of the defence-in-depth Design basis accidents and beyond design basis accidents Provisions for safety under seismic conditions... 

The philosophy behind the 4S safety concepts is to put an emphasis on simplicity achieved by strong reliance on passive and inherent safety features as a major part of the defence in depth strategy. The ultimate objective of the 4S safety concept is to eliminate the requirement of evacuation as an emergency response measure. The 4S safety concept provides for three functions to be shouldered by the defence in depth in each phase of the abnormal operation or an accident these three functions are the following ... 

Incorporation of several passive and inherent safety features, such as low power density in the core, good thermal characteristics of the metal fuel bonded by sodium, negative reactivity coefficients by temperature, passive shutdown heat removal by both natural circulation of the coolant and natural air draft, and a large coolant inventory are some important provisions for simplicity and robustness of the 4S design. 

Provisions for simplicity and robustness of the design inherent safety features... 

Based on the abovementioned considerations, the features targeted for a small reactor include long-life core, design simplicity (resulting in easy maintenance and operation), small size and transportability, strong reliance on inherent safety features, and enhanced proliferation resistance achieved through the operation with a sealed reactor vessel. 

The merits for this case may be outstanding, but the problem for small reactors appears to be very difficult. The criticality requirement can be satisfied by adding some plutonium to fresh fuel of a small reactor. However, the requirement that infinite neutron multiplication factor of fresh fuel should be less than or nearly unity is difficult to be met. On the other hand, strict implementation of CANDLE bumup strategy may be not needed for these reactors, once several other important characteristics are ensured, such as long-life core, simplicity and inherent safety. In this paper the application of CANDLE bumup strategy to small fast reactor with plutonium-admixed natural uranium as fresh fuel is investigated. 

Low operating parameters, low specific fuel power, a limited number of in-tank components, use of passive systems and inherent safety features contribute to simplicity and robustness of the RUTA-70 design. 

Accident prevention (Inherent safety features) Design simplification Simplicity is emphasized in all aspects of the design, construction, operation, and maintenance complexity of plant designs has been one of the main sources of high capital costs. 

Significant improvements in yields or reaction conditions can be achieved, together with considerable simplification of operating procedures. The powerful synergistic combination of PTC and microwave techniques has certainly enabled an ever increasing number of reactions to be conducted under clean and mild conditions. The inherent simplicity of the method can, furthermore, be allied with all the advantages of solvent-free procedures in terms of reactivity, selectivity, economy, safety, and ease in manipulation. 

The simplicity and robustness of the MARS design under long-term operation is ensured by an appropriate selection of the structural materials and by the incorporation of certain inherent and passive safety features in the original design concept. 

Incorporation of several inherent and passive safety features, good thermal characteristics of the liquid metal coolant and metal fuel, and large coolant inventory are some of the important provisions for the simplicity and robustness of the KALIMER design. 

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