Analysis on Pipe Rupture of Steam Condensation Line at Hamaoka-1, (II)

Abstract

A pipe rupture occurred in the steam condensing line of the residual heat removal system at the Hamaoka Nuclear Power Station Unit-1 on November 7, 2001. As the accident analysis, the three-dimensional hydrogen combustion behavior was first solved with the one-step irreversible overall reaction model, the Magnussen eddy dissipation model and the SIMPLE method. The ignition point was given at the upstream boundary surface of the non-condensable gas region. The temperature and concentration distributions in the pipe, which were obtained from the analysis of the non-condensable gas accumulation, were given as the initial conditions. The analysis result showed that the detonation pressures in the straight pipes were about 120 MPa and the peak pressures at the elbows were 2.0–2.5 times higher than those in the straight pipes, due to reflection and overlapping of the pressure waves. Then, a three-dimensional dynamic response of pipe deformation was analyzed, with the time transients of the pressure distribution as boundary conditions inside the pipes. The result showed that the strain at the elbow above the surface of the accumulated water exceeded the critical strain and the pipe ruptured there. This was generally consistent with the result of actual pipe deformation observed after the accident.

KEYWORDS:

• hydrogen combustion
• detonation
• pipe rupture
• non-condensable gas accumulation
• steam condensing line
• residual heat removal system
• BWR type reactors
• Hamaoka-1