Monitoring and determination of actual power margine in WWER-440 type reactors

For the 1st time in DDR a morden in-pile monitoring system was used on the 3rd and 4th units of 'Bruno Leaschner' NPP in Greifswald. The work was aimed at the increase of density, lucidity and unambiguity of information from in-pile monitoring system to achieve reliability and economical reactor operation. The investigations should provide either total or as maximum as possible equipment availability in case of deviations from the nominal reactor operation. Data processing is carried out both in on-line andoff-line regimes. LEDI code identifies the tree-dimensional power density distribution in fuel rod bundles in accordance with the signals from electronic-emissive pickups. Besides this, using the hottest channel model, the power reserve is determined. Thereat the power capacity is identified takinginto account the reliable power supply for the main circulating pumps. The code consists of three components: a) temperature control monitoring system; b) monitoring system of power channel neutron flux control; c) calculation of power density distribution within the reactor corresponding to operating conditions. The monitoring systems of temperature and neutron flux control function constantly and independently from each other. As a result the code determines two experimental and one calculated values for the reactor permissible power reserve. Such an approach ensures the maximum loaded bundle indentification even in case of failure of one of the systems. An operator of the reactor has an ample opportunity to identify the value and location of the greatest heat load. The time variation of the power reserve is checked by the computer. If the power reserve decreases with intolerablyhigh gradient, the signalling system is activated