Gas expansion modules

KALIMER has enhanced safety features with the use of metallic fuel, Self-Actuated Shutdown System (SASS), Gas Expansion Module (GEM) in the core, and Passive Safety Decay Heat Removal System (PSDRS). Utilization of these enhanced safety features eliminates the need for diverse and redundant engineered safety systems and KALIMER accommodates unprotected anticipated transients without scram (ATWS) events without operator action, and without the support of active shutdown, shutdown heat removal, or any automatic system without damage to the plant and without jeopardizing public safety. 

To enhance the negative reactivity feedback at elevated temperatures, gas expansion modules (OEMs) were added at the core periphery to compensate for the large positive Doppler feedback associated with the decreasing fuel temperature of oxide cores during fission shutdown. The gas expansion modules have a vapour space which will expand with loss of core inlet pressure to increase the core neutron leakage. 

The summary of reactivity feedbacks resulting from Doppler effect, uniform radial expansion, and various sodium voidings in the equilibrium core and during the startup cycle are given in Table XX-4. This table also includes the reactivity worths of the control rod system, the GEM (gas expansion module), and the USS (ultimate shutdown system). The gas expansion module is a device that introduces negative reactivity through gas expansion under temperature increase. Its position in the core is shown in Fig. XX-7 no additional details are provided. The USS is explained further in this section. 

Enhanced safety following ATWS. Gas expansion modules. Experiment for the response time required. 

In some advanced pool type reactors, the consequences of a postulated break of the primary coolant pipe can be mitigated by the inherent safety functions. This is achieved through the reactivity feedbacks induced by the Doppler, as well as sodium, radial and axial expansion reactivity effects. The control rod driveline length increase, and the operation of gas expansion modules (GEM) are also important reactivity feedback mechanisms. 

The inherent safety characteristic against postulated events is the most remarkable superiority of a liquid metal cooled reactor (LMR) to other type of reactors. One of the major threats to the safety of LMR is a loss of flow event accompanied a failure of reactor shutdown systems. This situation is usually referred to as an unprotected loss of flow (ULOF). The inherent safety of the Korean Advanced Liquid Metal Reactor (KALIMER) during the ULOF [I] has been assessed for the situation of all pump trips followed by coastdown. It was assumed that the decay heat is removed by four intermediate heat exchangers (IHXs) and the safety grade system of passive safety decay heat removal system (PSDRS). The results showed that the power was stabilized by the reactivity feedback of the system even though the effect of the gas expansion module (GEM) was not taken into account. 

The core consists of driver fuel assemblies, internal blanket assemblies, radial blanket assemblies, control rods, ultimate shutdown system (USS) assembly, gas expansion modules (OEMs), reflector assemblies, B4C shield assemblies, shield assemblies, and in-vessel storages (IVSs). There are no upper or lower axial blankets surrounding the core. A fission gas plenum is located above the fuel slug and sodium bond. The bottom of each fuel pin is a solid rod end plug for axial shielding. The reflector assemblies contain solid Inconel-600 rods. The control assemblies use a sliding bundle and a dashpot assembly within the same outer assembly structure as the other assembly types. 

The reactivity and power control rod system consists of two identical clusters. Each control rod unit consists of an array of tubes containing B4C to provide a gravity-driven rod drop and a powered drive-in. Gas expansion modules (OEMs) located at the periphery of the active core are passive reactivity feedback assemblies that insert negative reactivity into the core during the loss of flow events. 

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