A set of critical valves designed to release pressure inside the No. 2 reactor at the Fukushima No. 1 nuclear power plant likely failed due to surging temperatures and extreme stresses that built up in the early stage of the 2011 disaster, the plant’s operator said Dec. 17.
A set of critical valves designed to release pressure inside the No. 2 reactor at the Fukushima No. 1 nuclear power plant likely failed due to surging temperatures and extreme stresses that built up in the early stage of the 2011 disaster, the plant’s operator said Dec. 17.
In its report on this specific aspect of the catastrophe, Tokyo Electric Power Co. concluded that the failure of the valves to reduce pressure likely prevented water from being injected into the reactor.
The accident was triggered by the magnitude-9.0 Great East Japan Earthquake that struck March 11, 2011, and spawned towering tsunami that inundated the site.
Workers at the plant attempted to open eight “pressure-releasing safety valves” early on the morning of March 15, but failed to release pressure inside the No. 2 reactor's containment vessel, TEPCO said. The pressure level was reduced around 1 a.m. only after one of the valves finally opened.
TEPCO, until now, has tried to confirm whether the valves, a key safety feature, functioned properly.
After a thorough analysis, the utility concluded that the valves did not function as pressure inside the No. 2 reactor was too high.
The valves are designed to open under the pressure of nitrogen gas piped in from tanks and other sources.
TEPCO concluded that the valves initially functioned properly after the earthquake and tsunami hit.
But after the meltdown of nuclear fuel inside the reactor, heat and pressure levels rose significantly in the late hours of March 14, preventing the valves from opening.
The rising heat inside the reactor likely caused sealing materials and other bits of equipment to disintegrate, apparently leading to nitrogen gas leakage.