Condensation and Hydrogen Risk Calculations in FCVS Pipe with Python

The explosion in Fukushima Nuclear Power Plant accident is due to high pressure, high temperature and high-volume fraction of hydrogen in containment vessel. Therefore, the Filtered Containment Venting System (FCVS) is introduced for preventing over-pressurization by venting the gas from containment to FCVS building. However, the hydrogen risk exists in FCVS pipe because the gas flowing into the FCVS pipe is mixture of air, steam and hydrogen. The supersonic flow of gas mixture can make condensation of steam and the changing of the composition ratio of gas can make hydrogen risk increase when the gas passes through the orifice. In this paper, we will confirm the occurrence and hydrogen risk in FCVS pipe by using Python programming language. Through the results from the calculations, if steam is condensable, the composition of gas can be changed through the line that passing initial point and a point where volume fraction of steam is 1 in Shapiro-diagram. In addition, change of gas composition is not small. However, the amount of gas composition change may depend on the temperature or pressure. Therefore, to clarify the appearance of hydrogen risk in FCVS pipe, further researches that consider various temperature and pressure are needed.