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DEVELOPMENT OF THE RBMK-1500 MODELS USING STATE-OF-ART CODES

Eugenijus Uspuras
Laboratory of Nuclear Installation Safety, Lithuanian Energy Institute, Breslaujos str. 3, LT-44403 Kaunas, Lithuania

ABSTRACT

The Ignalina nuclear power plant is a twin-unit with two RBMK-1500, graphite moderated, boiling water, multichannel reactors. Several important design futures of RBMK-1500 are unique and extremely complex with respect to western reactors. The design full thermal power level for each reactor was 4800 MW, however, actual full thermal power level is 4200 MW. A safety assessment of RBMK-1500 reactors was performed by Russian design institute using their own home-made codes only for 4800 MW power level. A safety reassessment of the Ignalina NPP using state-of-art techniques to determine priorities for safety enhancement is necessary. A program of data verification and analysis is presently being conducted by Ignalina Safety Analysis Group. The state-of art codes, such as RELAP5/MOD3 (USA) and ATHLET (Germany), were originally designed for Pressurized Water Reactors. Because of unique RBMK designs, the application of these codes to RBMK-1500 encountered several problems. The paper deals with the development of suitable RELAP5 and ATHLET nodalization schemes for Ignalina nuclear power plant and investigation of loss-of-coolant accidents as well as safety-related operational transients. A successful best estimate RELAP5 and ATHLET models of the Ignalina NPP has been developed. These models include the reactor main circulation circuit, reactor control systems and plant safety systems required for transient and accident analysis. Calculations performed with those models compare favorable with plant data.