Analysis on pipe rupture of steam condensing line at Hamaoka-1, (I): Accumulation of non-condensable gas in a pipe

• Published in: Journal of nuclear science and technology 2003-12, Vol.40 (12), p.1032-1040
• Main Authors: NAITOH, Masanori, KASAHARA, Fumio, MITSUHAKHI, Toshihani, OHSHIMA, Iwan
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Installations for energy generation and conversion: thermal and electrical energy
• ISSN: 0022-3131; 1881-1248
• DOI: 10.3327/jnst.40.1032

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. The detonation of the hydrogen accumulated in the pipe was considered to be the likeliest cause of the rupture. As the first step of the accident analysis, fluid behavior in the line was analyzed in order to give boundary conditions for hydrogen combustion analysis. From the analysis, it was concluded that: (1) Condensed water filled up the hollowed part at the downstream end of the line within 4 days after the start-up of the cycle operation. (2) The temperature of the accumulated water became almost the ambient temperature at 14 days after the start-up. (3) Hydrogen and oxygen, generated by radiolysis of reactor water, accumulated at the downstream end of the line for a length of 6.9 m from the accumulated water surface, and concentration and temperature were distributed along the accumulated region. (4) At the boundary between the accumulated non-condensable gas and the steam regions, temperature and concentration fluctuated due to operation of the HPCI valve. The fluctuating region was limited within 200-300 mm upstream and downstream across the boundary.