Reactor shut-down

Account must be taken in design and operation of the requirements for the production and consumption of xenon-135 [14995-12-17, Xe, the daughter of iodine-135 [14834-68-5] Xenon-135 has an enormous thermal neutron cross section, around 2.7 x 10 cm (2.7 x 10 bams). Its reactivity effect is constant when a reactor is operating steadily, but if the reactor shuts down and the neutron flux is reduced, xenon-135 builds up and may prevent immediate restart of the reactor. 

Mixed oxide (MOX) fuel, 21.0-wt% Pu in 18.0-wt% enriched uranium, was irradiated from the 16 to 35 cycle at the 3" row in the experimental fast reactor JOYO. Tire effective full power days were 1019.33, and the peak bumup was 143.8 GWd/t. Atotal of 1560 days have passed from the reactor shut down to analysis. 

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... 

An Intermediate Event is an event that is one that has been designated for further development as the analysis progresses. For example, when developing the fault tree to do with the loss of production just discussed, an intermediate event could be Reactor shuts down. It is likely that, as the tree is developed, this simple phrase will be expanded as various reasons for reactor shutdown are considered. The reasons for reactor shutdown could include loss of feed, loss of flow of heating medium, or instrument malfunction. 

Result. No radiation released to environment reactor shut down and not reused. 

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. 

In the meantime the reactor shuts down (even if the power could initially increase slightly if the void coefficient is positive) and the safety injection through the accumulators and then through the high and low pressure pumps, starts. 

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 design of the check valves has been refined, and the valves in the primary loops have been replaced by advanced ones. An algorithm by which reactor power is automatically reduced by a preset value without reactor shut-down at switching-off of one of the primary pumps has been introduced. 

The main gate valves have adequate operating characteristics they assure such a tightness level of a disconnected loop that operations on withdrawal of removable parts of the main pumps and check valves can be carried out without reactor shut-down. 

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 is carried out by means of deenergizanion of control rod drives and... 

Reactor shut down by controlled insertion of control rods into the core by the CRDMs. Reactor shut down by simultaneous insertion of all absorber rods into the core under gravity following de-energization of the CRDMs. This is done automaticaliy and diversely from normal movements of CRDMs in response to changes in physical conditions such as power or water level. 

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... 

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. 

In case of reflector rods failure inherent reactor shut down by negative temperature coefficient for all physically possible reactivity insertions without fission product release and component damages (L)... 

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... 

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... 

---