TEPCO is facing difficulty as it prepares to inject nitrogen gas into the containment vessel of the No. 3 reactor at its Fukushima No. 1 nuclear power plant to prevent another hydrogen explosion.
TEPCO is facing difficulty as it prepares to inject nitrogen gas into the containment vessel of the No. 3 reactor at its Fukushima No. 1 nuclear power plant to prevent another hydrogen explosion.
Tokyo Electric Power Co. used a robot to inspect the connection port for the injection pipes, but could not photograph the location. Also, the radiation level remains high in the reactor building. TEPCO said in a July 7 news conference that work on the piping, originally scheduled to start on July 8, was likely to be delayed.
The injection of nitrogen is intended to drive out hydrogen gas accumulated in the containment vessel. TEPCO's road map toward bringing the hobbled plant under control has defined nitrogen injection as one of the pillars of "Step 1" that should be completed by around July 17, and accordingly, as a precondition for the return of evacuated residents.
Nitrogen injection has started at the No. 1 and No. 2 reactors, but has yet to be done at the No. 3 reactor, where pipes that could be used for injection were lost. On July 6, TEPCO sent a robot inside mounted on top of a vehicle for tasks at high places and tried to inspect a pipe connection port at an altitude of 5 meters above the ground, but failed to photograph the location because of the placement of other equipment nearby. The radiation level was found to be as high as 50 millisieverts per hour near the pipes. This indicated that work on connecting the pipes, expected to last up to an hour, would require shielding the radiation with lead mats, and employees working in shifts.
The injection requires approval by the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry. The procedure is expected to take about a week, preparatory work included. Possible injection from a different piping system may be considered if the task turns out to be difficult, but the radiation level is also high near this other location.
TEPCO has so far not revised the policy to realize nitrogen injection during Step 1.
"It is an indispensable task, and we want to accomplish it by all means," said Junichi Matsumoto, deputy chief of TEPCO's Nuclear Power and Plant Siting Division.