Calculated safety justification of the VVER-1000 reactor facility in the mode with the shutdown of one of the four MCPS during the operation at nominal power

3/25/2019 2019 - #01 Nuclear power plants

Nikulin I.A. Belozerov V.I. Sobolev A.V.

https://doi.org/10.26583/npe.2019.1.02

The article considers results of the computational analysis of the process with the disturbance in operation of the VVER-1000 reactor facility, caused by the shutdown of one of the four Main Circulation Pumps (MCP-195). The calculations were made with the help of the CORSAR/GP software package developed by the Federal State Unitary Enterprise «Alexandrov RESE». This software package is the contour code which permits to calculate emergency situations taking into account the operation of various systems, including safety systems. The CORSAR/GP is certified and verified for the facilities with the water-cooled reactors including the VVER-1000.

The special computational scheme that takes into account the layout of main circulation circuit and its four-loop design was devised to calculate the process. The computational (also known as nodalization) scheme includes the pressuriser in one of the loops, boundary conditions simulating the second circuit, and nuclear reactor with its dynamics, feedbacks, and automation systems. Devised nodalization scheme of the first circuit of the VVER-1000 permits to add or exclude the operation of the protective safety systems and can also be used for the computational analysis of other disturbances. This nodalization scheme takes into account the reactor feedbacks on the fuel temperature and coolant temperature, as well as the void reactivity effect.

The calculations used the principle of moderate conservatism of estimates. In this case it is ensured by the choice of such core parameters that provide conservative results in terms of the process parameters values that determine the safe operation mode of the reactor facility (fuel temperature, boiling margin, etc.).

The calculations results include the estimates of the changes dynamics of the coolant heating in the core, changes of the nuclear peaking factor, the average temperature of the coolant at the outlet from the core, temperature of the fuel, and the change of the reactor power. The analysis of the results shows that the criteria describing the facility safety in the mode with the shutdown of one of the four MCPs during the operation at nominal power are fulfilled. The main contribution to the reactor facility safe operation is made by simulation of the automatic control system operation. The considerable, but less significant in the absolute value, contribution to the «keeping» of the facility within the safe operation limits is made by internal feedbacks (reactivity effects).

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shutdown of the MCP safety VVER-1000 contour code off-nominal situation

Link for citing the article: Nikulin I.A., Belozerov V.I., Sobolev A.V. Calculated safety justification of the VVER-1000 reactor facility in the mode with the shutdown of one of the four MCPS during the operation at nominal power. Izvestiya vuzov. Yadernaya Energetika. 2019, no. 1, pp. 19-29; DOI: https://doi.org/10.26583/npe.2019.1.02 (in Russian).