Highly radioactive deteriorating exhaust pipe may not be priority

October 10, 2015

TEPCO begins examination of Fukushima reactor containment vessel exhaust pipe

http://mainichi.jp/english/english/newsselect/news/20151010p2a00m0na007000c.html

Tokyo Electric Power Co. (TEPCO) are examining an exhaust pipe used to release pressure inside containment vessels at the Fukushima No. 1 nuclear plant shortly after the March 2011 nuclear meltdowns there, company officials said.

Poles supporting the pipe have begun to deteriorate in the 4 1/2 years since the outbreak of the nuclear crisis, which was triggered by the March 2011 Great East Japan Earthquake and tsunami. Although TEPCO said there is no danger that the pipe will collapse, the company decided to examine the assembly to see if it needs to be dismantled or reinforced.

The pipe is about 120 meters high from the ground level and was used for the plant's No. 1 and 2 reactors.

Radiation levels at the base of poles supporting the pipe were extremely high because it was used to vent radioactive steam from the containment vessels of these two reactors shortly after the outbreak of the nuclear crisis, preventing TEPCO from examining the pipe's condition. 

A measurement conducted by TEPCO using a gamma camera in summer 2011 showed that radiation levels exceeded 10 sieverts per hour. Another measurement conducted in 2013 using a dosimeter mounted on a remotely controlled vehicle suggested that the figure was actually about 25 sieverts per hour -- a level guaranteed to be fatal.

In the ongoing examination, radiation levels at the base of the support poles will be measured again to see how they have changed. TEPCO will also check if fractures and deformations found at eight places on the support poles have worsened.

Based on the results of computer analysis of the support poles, TEPCO has concluded that they would not collapse even if hit by a Great East Japan Earthquake-scale temblor, or an upper-6 on the 7-point Japanese intensity scale.

Therefore, the company intends to prioritize efforts to decommission the plant, including work to collect spent nuclear fuel from storage pools in the reactor buildings.

However, a TEPCO official said, "We may need to either reinforce or dismantle the pipe depending on the results of the ongoing examination."