Presentation Information
[2F06]Study on release pathway of FPs into environment in early stage of Fukushima Daiichi accident in Unit 1
*Akihide Hidaka1, Hidetoshi Okada2 (1. Niigata University, 2. Institute of Energy Safety Technology, Ltd.)
Keywords:
Fukushima Daiichi Nuclear Power Plant Unit 1 Accident,TIP Guide Tube,Radioactive Materials Release Pathway,Hypothetical Amount Emission-Regression Estimation Method,Nitrogen Purge Tube
In the Fukushima Daiichi Unit 1 reactor pressure vessel (RPV), a Traversing In-core Probing Monitor TIP guide tube buckled due to rising temperatures just before 19:00 on March 11, and radioactive materials leaked into the containment vessel (PCV). However, contamination of the TIP room in the downstream reactor building (R/B) was limited, and the release of radioactive materials outside the PCV was considered negligible. On the other hand, the hypothetical release regression estimation method combining the final soil contamination distribution and the meteorological model predicted the release of Te around 19:00 on March 11, which the WSPEEDI reverse-calculation for I, Cs release did not predict. Therefore, we examined the structure of the TIP guide tube from published drawings and noted that the nitrogen purge tube for drying is connected to the TIP indexing mechanism in the PCV and is connected to the R/B outdoor nitrogen supply system via only a PCV pressure-resistant check valve. The possibility emerged that this check valve failed due to reactor pressure after the TIP guide tube buckled, and radioactive materials were released via the nitrogen purge tube.