Steam Rising from Crippled Fukushima Reactor Causes Concern

Officials from Tokyo Electric Power Company (TEPCO) suspect that steam rising out of the top of a destroyed nuclear reactor at the beleaguered Fukushima Daiichi nuclear campus is the result of rainwater somehow making its way into the building, but workers onsite are prepared to douse the reactor with boric acid, should a sustained nuclear reaction begin to occur.

At the beginning of the day Thursday, a TEPCO worker preparing for debris removal work encountered a "steam-like gas" wafting through the air near the central part of the fifth floor of Unit 3, which contains a crippled nuclear reactor. 

Initial checks on temperature, pressure and xenon density did not indicate anything was out of normal conditions inside Unit 3. However, as a precaution, TEPCO officials stood ready to inject boric acid into the reactor, which would stave off sustained nuclear reactions in the reactor's damaged core, The New York Times reported.

TEPCO officials stressed that it was only a remote possibility that they would have to resort to such a measure, citing the unchanged levels of radioactivity around the plant.

"We think it's possible that rain made its way through the reactor building and having fallen on the primary containment vessel, which is hot, evaporated creating steam," said TEPCO spokeswoman Maymi Yoshida, according to Reuters.

The Unit 3 reactor is surrounded by a primary containment vessel made of several inches of reinforced steel. It serves as the first and most critical line of defense against leaking radiation from the reactor. Elevated temperatures around the containment vessel would explain why steam was forming if water were somehow leaking into the unit, TEPCO officials said.

In recent months the Fukushima Daiichi plant has been stricken with a number of problems, including power failures, contaminated water leaks, and groundwater testing for elevated levels of radiation. Water is constantly being pumped into the crippled nuclear reactors -- which were overcome as the result of a powerful earthquake and tsunami in 2011 -- as a means to keep them cool. But in doing so, enough contaminated water to fill an Olympic-sized swimming pool accumulates each week. Storing the contaminated water has proven to be one of the major challenges at the nuclear plant in the wake of the disaster.

After sundown in Japan Thursday, it became too dark to accurately monitor the site for the continued presence of steam, the Times reported, citing a TEPCO official.

TEPCO's latest English-language press release indicates that conditions at the reactor are normal and that the steam situation will continue to be investigated.