[en] The invention, which is an addition to patent application 2159196.8 relating to a device for reactivity control in nuclear reactors by means of changes of concentration of a more or less neutron-absorbing liquid, proposes to pass this liquid (e.g. boric-acid solution) through the control-rod guide tubes so that no additional vessels have to be applied and excessive liquid quantities do not become necessary. The guide tubes of several fuel elements may advantageously be interconnected by means of a circular pipeline. (RW)

[en] A burnable poison rod is described in which the displacement of the moderator coolant is minimized thereby increasing core moderation and burnable poison depletion, thus increasing the reactivity lifetime of the reactor core. (C.F.)

No abstract available

[en] Purpose: To improve the response function in the reactor scram with no wide space by injecting poisons in soluble poison guide tubes to such a liquid level as giving no effect on usual reactor operation. Constitution: Soluble poison guide tubes in a reactor are connected at their upper ends to a buffer tank and at their lower ends to a pressurizer by way of a header and an injection valve. The header is connected by way of a valve with a level meter, one end of which is connected to the buffer tank. During reactor operation, the injection valve is closed and the soluble poisons in the pressurizer vessel is maintained at a pressurized state and, while on the other hand, soluble poisons are injected by way of the header to the lower end of the soluble poison guide tubes by the opening of a valve, which is thereafter closed. Upon scram, a valve is closed to protect the level meter and pressurized poisons are rapidly filled in the guide tubes by the release of the injection valve. (Kawakami, Y.)

[en] Estimation of boron, used as neutron poison in power reactors in India is discussed. Two methods: (1) conductometric and (2) potentiometric are described. Boron concentration in ppm has been determined both during (1) normal operation and (2) initial approach to criticality. The results have been plotted in the form of curves. A third method, being developed at RAPP, to be used with an on-line monitoring of boron concentration has also been briefly mentioned. (K.B.)

[en] Purpose: To improve the safety and the operability of a nuclear reactor by adjusting the density of liquid poison. Constitution: The thermal expansion follow-up failure between cladding and a pellet upon abrupt and local variations of the power is avoided by adjusting the density of liquid poison during ordinary operation in combination with a high density liquid poison tank and a filter and smoothly controlling the reactor power through a pipe installed in the reactor core. The high density liquid poison is abruptly charged in to the reactor core under relatively low pressure through the tube installed in the reactor core at the time of control rod insertion failure in an accident, thereby effectively shutting down the reactor and improving the safety and the operability of the reactor. (Yoshihara, H.)

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[en] A process is described for monitoring reactivity effects due to the power changes in pressurized water nuclear reactors using the displacement in fuel assemblies of mobile bunches of absorbing material as well as soluble boron for correcting the long term effects of reactivity