It is presented the results of analysis and interpretation of monitoring of the dynamics of neutron activity of a potentially nuclear-dangerous cluster of fuel-containing materials (that located in zone of penetrating of concrete slab of the reactor's vault) before and after installation of the new secure confinement (NSC) "Arka". It is shown that the constant growth (after the installation of the NSC) of neutron activity accompanies the process of water's quit from the over-moist multiplying environment and accordingly the NFD increasing is a result of positive reactivity's introducing that can lead to recurrent criticality and self-sustaining chain reaction with unpredictable consequences. Based on the results of experimental data and model calculations, the effectiveness of neutron monitoring (at the detection points) was estimated. A forecast (regarding the further neutron activity) was also made and it was obtained the criteria for expert assessment of dangerous changes of the level of sub-criticality of this cluster of FCM.
Keywords: nuclear-dangerous cluster, neutron activity, self-sustaining chain reaction, fuel-containing materials, nuclear safety monitoring system.
1. The investigation of nuclear-physical parameters and the development of methods for monitoring and controlling subcriticality in zones of risks of critical mass: (SRW final report) / IPB AES NAN Ukrainy; responsible executor. Ye. V. Vysotskij - Inv. № 3998. - Chernobyl, 2010. – 127 p. (Rus)
2. Frolov V. V. An abnormal incident on June 27 - 30 1990 inside the "Shelter" object of Chornobyl NPP/ V. V. Frolov // Atomnaya energiya. - 1996. - T. 80. - Iss. 3. - P. 216 - 219. (Rus)
3. Carrying out of calculations and the developing of technical proposals of methods for influencing on subcriticality of nuclear dangerous materials of “Shelter” Object: (SRW report) / IREP NAN Belarussia. - № 01/96-2 of 16.10.96. - Minsk, 1997. - P. 98 - 107. (Rus)
4. Investigation of neutron-physical and physically-chemical characteristics of nuclear-dangerous clusters and the development of methods of suppressing of their criticality parameters: (SRW final report) / IPB AES NAN Ukrainy. - Inv. № 4021. - Chernobyl, 2015. - 127 p. (Rus)
5. Vysotskij Ye. D. The methodical bases of control of subcriticality of fuel-containing masses / Ye. D. Vysotskij, V. G. Shevchenko. - Chernobyl, 1998. - 23 p. (Rus)
6. An assessment of changes during the evaporation-condensation dynamics of moisture inside the “Shelter” under the NSC, the behavior of FCM during changing of storage conditions, and the assessment of changes of dust formation: (SRW final report) / IPB AES NAN Ukrainy; responsible executor V. O. Krasnov. - Inv. № 374-17. - Chernobyl, 2017. - 222 p. (Rus)