Passive poison injection system

The passive poison injection system (PPIS) is an additional system in AHWRs to fulfill the shut-down function during a low-probability event of failure of wired SDSs [ie, anticipated transient without scram in the case of the SDS-1 and SDS-2 failure condition]. PPIS passively injects the liquid poison into the moderator by system fluid pressure during such transients to shut down the reactor. This situation may arise because of human-induced malevolent action caused by insider threat or compromise of functioning of both SDSs. 

In the KAMADO there are two independent and diverse systems of reactivity control. The mechanical control rods are used to compensate reactivity changes due to fuel bum-up and operational reactivity changes the primary reactor shutdown is assumed to be passive. A liquid poison injection system in the reactor pool is available as a secondary shutdown system. 

Two poison tanks which contain highly borated water (12,000 ppm of boron concentration) are installed in the CV for the passive reactor shutdown system (PRSS). Each poison tank (60 m ) is connected to the RPV by two pipes. The upper pipe has two normally closed hydraulic pressure valves. The pressure in the poison tank is maintained to be equal to that of the primary system under normal operation. The borated water in the tank is cooled by the C V water. The inside wall and the nozzle part of the poison tank have liners for mitigating a thermal stress due to temperature change during poison injection. 

Additional shutdown systems Two independent passive safety shutdown systems 28 shut-off rods and 6 liquid poison injection circuits... 

The reactor protection system comprises two independent fast acting shutdown systems. Shutdown system-1 (SDS-1) is based on mechanical shut-off rods with boron carbide based absorbers in forty lattice positions, providing a total negative reactivity worth of 75 mk with all rods inserted, and a worth of 47 mk with two maximum worth rods not available, shutdown system-2 (SDS-2) is based on a liquid poison injection into the moderator. In addition, a pressurized addition of poison, passively driven by steam pressure, takes place in the event of over pressure in the MHT system. 

Safety analysis included the analysis of 4 transients due to failure of wired systems of SDS-1 and SDS-2 and reactor shut down effected passively by injection of poison in the moderator by usage of system steam pressure. 

The technical basis for the RAPID includes general experience with sodium cooled fast reactors. Specifically, the RAPID concept includes no control rods but incorporates the passive lithium expansion modules, lithium injection modules and lithium release modules to enable an operator-free operation mode. These systems utilize Li as a liquid poison instead of B4C rods. To verify the reactivity worth of Li, the criticality test [XVII-5] using the fast critical assembly (FCA) of the Japan Atomic Research Institute (JAERI) has been conducted. Also, the manufacturing technology of the lithium modules was mastered, and the performance and neutron radiography tests of the lithium expansion and lithium injection module pilots were conducted. 

Further enhanced reliability of the shutdown, achieved by providing a passive shutdown device operated by steam pressure for injection of poison in case of extremely low probability case of failure of both mechanical shutoff rods and liquid poison shut down system,... 

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