Proceedings of the conference

Gusev A.S. Shvetzov U.K. Faljkov A.A.

Analysis of LBLOCA for Introduction of TVSA-12 on «Kozloduy» NPP using codes RELAP/SCDAPSIM/MOD3.4 and KORSAR/BR

State-of-the-art computer codes based on a two-fluid thermal hydraulic model, which are verified by experiments and adequately describe thermal hydraulic processes in a reactor plant, ensure the required quality of safety justification for operating NPPs with VVER/PWR and those under construction.

Large break loss-of-coolant accident (LBLOCA) with break of the main circulating pipe at reactor inlet is a bounding design-basis accident at NPP with WWER-1000 in a class of LOCA for which safety systems are being developed.

The paper presents sensitivity analysis results for LBLOCA at Units №5 and №6 of “Kozlodyi” NPP with core containing TVSA-12 at power level of 104 % using best estimation code RELAP/SCDAPSIM/MOD3.4.

The thermal hydraulic part of the RELAP/SCDAPSIM/MOD3.4 code is based upon the RELAP5 models. The RELAP5 code has a substantial experimental validation and is one of the most widespread best estimate codes for thermal hydraulics of light water reactors. The reflooding analysis is done by the RELAP/SCDAPSIM/MOD3.4 with employing the general thermal hydraulic model.

JSC “Afrikantov OKBM” performed additional validation of RELAP/SCDAPSIM/MOD3.4 code using data from more than 50 LOCA experiments. Certain key parameters of the code models influencing core temperature conditions during a reflood stage of LOCA were defined during PREMIUM benchmark, organized by working group under the analysis and management of accidents (WGAMA) of the Nuclear Energy Agency OECD/NEA.

An alternative analysis has been performed using the Russian best estimation code KORSAR/BR, developed by FSUE “Alexandrov NITI” with participation of JSC “Afrikantov OKBM”. Capabilities of KORSAR/BR code are similar to those of RELAP/SCDAPSIM/MOD3.4. Reflooding analysis in the КОРСАР/BR code is made with use of special model.

Calculations by RELAP/SCDAPSIM/MOD3.4 and KORSAR/BR codes have confirmed that safety criteria for the given accident on the maximum cladding temperature and equivalent degree of cladding oxidation are met.

The paper presents results of the analysis of sensitivity of the maximum cladding temperature during LOCA to change of significant parameters:

- the mixed/homogeneous core

- axial power distribution in core ,

- break discharge coefficient Cd,

- configuration and initial parameters of ECC system,

- the key parameters of a code influencing a reflood process (based on PREMIUM benchmark).

Calculations by RELAP/SCDAPSIM/MOD3.4 code have been performed within the framework of the contract between JSC “Afrikantov OKBM” and JSC “TVEL”.

The full report isn't submitted..