Reactor shut-down system

The two reactor shut down systems which are consisted of 10 control rods and 7 small absorber ball holes are all positioned in the side reflector. The in core control rods are not needed. 

The reactor shut-down system includes 6 independent control rod groups (CGs) which can be inserted into the core by electric drives or under gravity in the case of de-energization of the drives. The drives are also equipped with a special mechanism for hand-operated insertion of each CG. In addition, a liquid absorber injection system is provided. 

The reactor shut down system (RSS) is a constituent part of the CPS and is designed in such a way that a CPS failure does not affect operability of the RSS. An important feature of the reliabili of the RSS actuation is the fact that apart from 6 RSS clusters all 19 clusters of the CPS fall to their ultimate lowest position under gravity. 

CIRS - completely independent reactor shut-down systems... 

The results of calculation for a scenario with total NPP blackout accompanied by simultaneous failure of the reactor shut down system are shown in Fig. X-6. Similar results obtained for an NPP with standard WER-IOOO reactor [X-2] are presented for reference. 

The control and safety SAs have the same structure, and the reactor is controlled or shut down by their movement in the tubes. There are two separate reactor shut-down systems, both of which can quickly shut down the reactor. The compensation and regulating SAs form the first shut-down system whereas the safety SAs form the other shut-down system. 

Wide use of self-actuated devices for initiation of safety system operation, including reactor shut down, when the most important safety related parameters exceed their design limits. 

In the normal operation manual, the reactor decay heat after the reactor shut down is to be removed through the steam generator and the residual heat removal system like the land based PWRs. When this normal procedure is not available due to an accident, the decay heat is removed passively by helps of the EDRS and the CWCS as shown in Fig. 5. The decay heat is transferred from the primary coolant to the water of the containment through the heat exchanger of EDRS, and... 

February 1989, the safety injection system was erroneously actuated with the reactor shut down and depressurized. A motor-operated valve opened but its electrical operator didn t succeed in closing it (it was closed manually later) against the forces caused by the full flow in the line. It was later determined that the torque limiter had erroneously been actuated, although its setting was the prescribed one. The method for the determination of the intervention... 

The reactor is equiped with two independoit shut down systems, first of which is composed of 3 compensation and 2 regulation subassonblies with a rrqiid drop down time less than 1.5 seconds, the second shut down system includes 3 safety subassemblies widi a rqrid drop down time less than 0.7 seconds. 

The appropriate combination of inherent safety features and engineered ones should be necessary to prevent the extension of anticipated transients and also postulated accidents within the system. As an example of inherent safety features, one should mention Doppler reactivity that is effective against criticality events, which is a basis to ensure the reactor shut down function. Natural circulation is also an inherent safety feature to enhance the cooling capability of the reactor core. The nuclear energy system should be designed in such a way that severe core damage leading to the release of massive amounts of radioactive materials could be avoided. 

Residual Heat Removal System The residual heat removal sy stem (RHRS) of the NHR 5 consists of two independent trains which assigned to two groups of primary heat e.xchangers. There are three natural circulation cycle for each train. Figure 4 show s the schematic s stem diagram of the RHRS. After reactor shut-down the decay heat will be transferred to the... 

Reactor shut down by injection of liquid absorber (boron solution) through the active and/or passive channels of the back-up system for transferring the reactor into the "cold" state. 

Loss ofelectnc sources - passive systems for reactor shut down, residual heal removal, and radioactive discharges localizalKui... 

Extreme insertion of reactivity Negative temperamre coefficient Passive Perturbation initiated by the malfunction of the reflector rods or of the small absorber spheres system (KLAK) Inherent reactor shut down by negative ten ierature coefficient limits the maximum core temperature to < 1300°C Ejection of the shut down devices not possible due to their integration within the pressure vessel... 

CCS-Cavity Cooling System, CPV-Connecting Pressure Vessel KLAK-Small absorber spheres shut down system, RB-Reactor Building RPV-Reactor Pressure Vessel, SGPV-Steam Generator Pressure Vessel StrSchV - Strahlenschutzverordnung (German Radiation Protection Ordinance)... 

There is a diverse emergency shut down system which is initiated manually if it is not possible to insert the control rods. It allows for injection of boron into the reactor. Since inadvertent operation of this system must be completely prevented, it requires insertion of a spool piece to connect the boron tank to the reactor. The negative moderator temperature coefficient is sufficient to maintain the reactor in a hot shut down condition for several days until the spool piece can be inserted. 

When operating parameter is departing from the safe region the task of safety systems is to return the safe conditions by actuating the safety functions, such as reactor fast shut-down-system or emergency core-cooling-system. 

Several inherent and passive safety features are incorporated in compact high temperature reactor. Due to negative temperature coefficient of reactivity, the power of the reactor comes down without necessitating any external control in case of increase in core temperature. The reactor also adopts passive systems like removal of core heat by natural circulation of liquid metal coolant in the main heat transport circuit, passive regulation and shut down systems. The reactor is also able to remove heat passively by way of conduction in the reactor block and by radiation and natural convection from the outer surface of the reactor during loss of heat sink. The paper deals with the details of passive systems incorporated in the AHWR and CHTR and the analysis performed for these systems. 

With the reactor shut down and the PORV open, the pressure in the primary circuit fell. The PORV was designed to close automatically when the pressure dropped to 2205 psi, which it did 13 s after the initial feedwater pump trip. Although the control room panel indicated that the valve had closed, it had in fact stuck open, so that the coolant was draining off into the reactor s let down system. This was to continue for almost two and a half hours before the circuit was eventually sealed by the closure of a backup valve. 

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. 

It must be possible to shut down the nuclear installation at any given time. In addition to the reactivity shut down system a strong negative temperature coefficient of reactivity should be able to shut the reactor down from any operational condition, i.e. by physical means alone. 

Schulenberg and Starflinger (2012) reported about a constant pressure start-up and shut-down system for the three-pass core design of the HPLWR, trying to keep the feed-water temperature constant to minimize thermal stresses of the reactor pressure vessel. This concept also includes a warm-up procedure for the deaerator during startup from cold conditions. A battery of cyclone separators is foreseen outside of the containment to produce some steam from depressurized hot coolant of the reactor. 

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