SPND Detectors Response at the Control Rod Drop in VVER-1000. Measurement and Modeling Results

V. Mitin, N. Milto, M. Kuzmichev, L. Shishkov, S. Tsyganov / RRC “Kurchatov Institute” / Russia

16th Symposium of AER on VVER Reactor Physics and Reactor Safety (2006, Bratislava, Slovakia)
Core Surveillance and Monitoring


The paper analyzes and discusses possibility of neutron flux inspection in the VVER core during fast dynamic processes applying existing in-core monitoring system.
The structure and functions of the system, basic principal of detector functioning and its temporal parameters are described briefly.
To assess the ability of such dynamic monitoring the event with control rod drop happened during operation of Kozloduy NPP Unit 5 is observed – at the level of power close to nominal one of the rod from control group shifted to the lowest position at ~2 seconds. In-core detectors readings at the process were registered and processed with mathematical methods that allow to single out only the prompt part of the signal. Results of the processing are presented.
Furthermore, the process observing have been modeled with 3D dynamic code NOSTRA. Results of modeling are presenting in a paper, and comparing with experimental ones. A good agreement achieved.
The analysis of measurements and its imitation give a hope that with an aggregate signal of detectors the measurement of control rod worth could be provided, and it allows to avoid of influence of spatial effects that are significant at standard technique with ex-core ion chambers.

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