Evaluation of loads on the main joint of reactor pressure vessel under hypothetical severe accident at VVER-1200 NPP

•Prototypical tests do not reveal detonation of steam explosions at in-vessel stage of SA.•Conversion ratios obtained in tests with steam explosion lie within 0,003–0,04.•Design features of VVER imply several factors which are limiting the likelihood of steam explosion.•In case of in-vessel steam explosions, the calculated peak pressure on VVER upper head is 6 MPa. This paper presents the results of calculations of the loadings that reactor main joint may experience after energetic fuel-coolant interaction in a hypothetical severe accident at VVER-1200 reactor. Estimates of the loadings are performed using a semi-empirical procedure with conservative assumptions. The initial data for estimates are deduced from the modeling of representative severe accident with an integral code SOCRAT/V1. The loadings can be used for further thermomechanical calculations of the integrity of elements that are fixing the upper head of VVER-1200 RPV.