[en] The service life of the absorber rods is extended by 1) exchanging the absorber rods used for controlling the output for absorber rods in the end position, depending on the irradiation dose absorbed, 2) by driving the absorber rods used for controlling the output to the same depth in the fuel element pebble bed, for temporary fast shutdown of the reactor, 3) by inserting all absorber rods into the fuel element pebble bed for long term shutdown. (orig./HP)

[en] The fast shutdown effect is based on an intervention into the operative connection between control rod and control rod drive mechanism. During operation of the LMFBR the coolant sodium is developing sufficient differential pressure on the separating plate and on the seal of the control rod to press the rod against the separating plate and to keep it above the neutron high-flux region of the core. If the flow rate of the coolant is reduced (accident, leak or rupture in the primary loop, earthquake) or the control rod is moved laterally the differential pressure on the separating plate decrases. The control rod drops because of gravity. A scramwill follow. (DG)

[en] KERENA is a medium capacity boiling water reactor. The SCRAM system of KERENA is based on the concept of German BWR power plants where the energy for the fast hydraulic control rod insertion is provided via pressure vessels. In contrast to the existing SCRAM systems, where nitrogen is used to provide the pressure as driving force, for KERENA electrically heated water/steam tanks will be used. The advantage of this design is, that in case of a scram, non-condensable gases are prevented from entering the RPV. Therefore negative impact on the heat transfer capacity of the Emergency Condenser (passive safety system for residual heat removal from the RPV) is avoided. Another difference compared to existing systems is that the two ring manifolds (ring lines) are not connected. Each ring line is supported by three scram vessels and each vessel can insert 50 % of the control rods at the required time. To avoid thermal loads in the piping system and the control rod drives hot water should not reach the piping system. So, the steady state temperature profile and the amount of cold water which is available is of special interest. In order to stop the leakage mass flow into the RPV as soon as possible after a scram a pressure suppression system is installed in the KERENA scram vessels. To study the temperature profile in the scram vessel as well as the pressure reduction 1:1 scaling tests were carried out. Beyond that, the operating behavior, e.g. how long does it take to reach steady state conditions, how long does it take to bring the vessel back into operational conditions can be analyzed as well. (authors)

[en] Minimization of safety rod actuator operating time is studied. The rods are held out of the core by electromagnets and springs are used to insert them in. An optimal relationship is derived between start-up time of the holding electromagnets and motion time of safety rods. Two basic variants of safety rod motion are considered: in a gaseous and liquid medium. Minimum operating time of the actuator is found to occur if the start-up time of the electromagnets equals half the motion time of the safety rods

[en] The control process described is for a protection system, particularly of a nuclear reactor, according to which, as from N measurements of one or several physical values measurements are processed by N adaptation members and/or calculations. The median value is selected of the N signals corresponding to N determinations, and the median value is compared with a reference value so that this comparison initiates the triggering off of the desired protective action. This process can be used to carry out the emergency shutdown of a nuclear reactor by dropping safety absorbers into the core

[en] The method of operating the linear drive devices to increase reliability to scram involves first raising and holding the control elements using the drive means and first holding means for each of the linear drive devices. Then, for a first portion of the linear drive devices, the control elements associated therewith are further raised, the second holding means actuated, and the first holding means de-actuated to place the control elements in engagement with the second holding means of the portion of linear drive devices. De-actuation and disengagement of the first holding means of the first portion of linear drive devices is then detected to ensure that the first holding means will not interfere with the release of the control elements by the second holding means to scram the control elements into the nuclear core. The linear drive devices of the present invention comprise a magnetic jack type drive having a second type of holding means which is operative to engage and hold the control element drive extension in a fully withdrawn position with respect to the nuclear core

No abstract available

No abstract available

[en] Purpose: To moderately stop control rods upon completion of scram by effectively utilizing the axial length of the damping component to thereby increase the damper section. Constitution: A damper cylinder is secured to a guide roller support to form a second damper space surrounded with a hollow cylinder, the guide roller support and a damper cylinder, and a second damper piston is threaded into the upper end of the damper sleeve in the inside of the second damper space. The provision of the damper piston and the damper space above the damper sleeve increases the damper effect, enabling to stop the control rods more slowly upon completion of scram. (Yoshino, Y.)

No abstract available