Session: 14-17 Student Paper Competition

Paper Number: 65756

Start Time: August 6, 2021, 04:45 PM

65756 - Dynamic Model of the VVER-1000 Reactor for Seismic and LB LOCA Evaluation 

The assessment of seismic and dynamic strength for the VVER-1000 reactor with emphasis on fuel assemblies interaction will be carried out based on experience for Ukrainian NPPs. Evaluation of fuel assembly structural response to externally applied forces will be performed according to NUREG-800 “Standard Review Plan”, item 4.2 “Design of fuel systems” and to НП-094-15 "Basic requirements for justification of strength and thermo-mechanical behavior of fuel assemblies and fuel elements in the nuclear core of pressurized water reactors". The analysis consider a combination of Safety Shutdown Earthquake (SSE)  and Large break Loss Of Coolant Accident (LB LOCA). As LB LOCA for the VVER-1000 – “Maximum design accident” Recirculation Line Break is considered. For the analysis of the initial dynamics, the CFD model of the VVER-1000 was adapted to account for the two-phase flow. To take into account the transience of the phase transition during depressurization, a special model of interphase exchange is proposed, which takes into account not only the nonequilibrium temperature, but also the features of the pressure change by analogy with cavitation. For full dynamic analysis, it is necessary to develop an analytical and/or FEM model of the reactor, which will include reactor elements, their masses stiffness and inertia characteristics. The seismic analysis consider the available response spectra for NPP site with 3-component seismic impact of SSE level. Another important issue is to analyze reactor elements interaction and in case of need, to account for the non-linear behavior of the model. The seismic impact at the location of fixation of the fuel assemblies (lower and upper support plates) is calculated by taking into account the dynamic response of the reactor system as a whole. The developed model is validated against available experimental commissioning data found in literature.

Seismic analysis of pressure vessel internals (PVI) in accordance with NUREG-0800 is performed for two criteria:

Fuel assemblies fragmentation must not occur as a direct result of the blowdown loads.

Control rods insertability must be assured.

For grid components the P(crit) - the crushing load, margin is decisive in assessing strength. For all other components strength calculations should be performed accordingly to ASME BPVC Code or НП-094-15 requirements.

 The seismic stability of the reactor internals, the resident fuel assemblies and their components is demonstrated for the conditions of a mixed core loading. The seismic stability of the reactor internals, the fuel assemblies and their components is demonstrated for the conditions of a homogeneous core loading.

After demonstrating the seismic stability of the fuel assemblies and the reactor internals, a justified conclusion is provided on preserving the seismic stability of the reactor installation as a whole.

Presenting Author: Oleksii Ishchenko National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”

Authors:

Oleksii Ishchenko National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”
Vladislav Filonov National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”
Yaroslav Dubyk IPP-CENTRE