Possible Solutions for Improving Operational Safety of NPP by Dr.-Ing. Juri Tsoglin The Society of Sciences & Engineering „KIW- Gesellschaft e. V“, Dresden, Germany, Diese E-Mail-Adresse ist vor Spambots geschützt! Zur Anzeige muss JavaScript eingeschaltet sein!
Following the accident in Fukushima Daiichi NPP stability of NPP against external conditions was verified by applying stress-tests and achievement of high-level operational safety satisfying “international requirements” was declared all over the world.
Nevertheless, given the experience of at least two accidents – Armenian NPP in 1982 and Chernobyl in 1986 (the author had been involved in elimination of consequences of the latter) – we shouldn’t have made this declaration with such confidence. Internal latent factors remained out of sight – appearing to become possible sources of accidents or of their progressing. These factors did not make themselves known before the specific situation and therefore don’t appear in any document type of “Probabilistic Safety Analysis” or “Safety Analysis Report” and can’t be discovered using stress-tests.
Some of the hidden factors and possible ways of overcoming them have been investigated in the present paper.
1.One is In-core Monitoring Systems (IMS) based on the ideology of the neutron monitoring and neutron detectors acting as primary transducers. A hidden defect, not taken into account in the safety analysis could be caused on one hand by the absence of a reliable metrological maintenance of neutron detectors and on the other hand by the influence of the processes of burning out detector fuel and materials (processes burnout) on the reliability of the measurements and the resulting information. Accounting for these factors is associated with the large volume of related assumptions, additional data and auxiliary computing operations [1, 2]. This leads to the presence of software of huge complexity in today’s ICMS, which may result in failure of standard systems in an emergency situation to give the information necessary for adequate decision-making.
The defect can be eliminated if we include in neutron IMS a system based on monitoring thickness of the gamma radiation flux, which is accurately connected to quantify the fission rate.