Fukushima Daiichi NPS Prompt Report 2014

MONITORING AT ALL UNITS CONTINUED 24/7 AT FUKUSHIMA DAIICHI,STEAM CONTINUES TO BE CONFIRMED AT THE TOP OF UNIT 3 REACTOR BUILDING INTERMITTENTLY SINCE SUMMER WHEN DEBRIS REMOVAL WAS CONDUCTED ON THE TOP FLOOR ACCUMULATED RAINWATER ASSUMED AS THE CAUSE OF STEAM NO SAFETY CONCERNS INDICATED

FUKUSHIMA, January 3, 2014 -Unit 3 Reactor Building at Fukushima Daiichi Nuclear Power Station, where steam continues to be confirmed at the top, is monitored 24/7 as well as other reactors, and indicates no abnormality, Tokyo Electric Power Co. (TEPCO) announced today.

Since July 18, 2013, steam has been intermittently observed at the top of the Unit 3 Reactor Building. It was observed on days with comparatively low temperature and high humidity and, upon almost all occasions, when rain had fallen before.

The steam has been observed around the edge of the shield plug of the Primary Containment Vessel (PCV), which is the upper structure of the reactor. No significant changes were found in either the main parameters related to the plant (temperature, pressure and xenon density of PCV/RPV) nor the monitoring post readings, which indicates no abnormality of the cooling of the reactor, nor dangers to human health, the company explained.

The company assumes rain which accumulates inside the edge of the PCV as the main cause. The following is the mechanism.
1. Generally, steam is generated when warm, moist air meets low-temperature, high-humidity air and falls below the dew-point temperature.
2. Water particles generated by saturation become visible as a steam.
3. The source of the aforementioned steam is considered to be evaporated water from rainfall etc. around the relatively hot PCV, emerging from the shield plug and becoming steam.

There has been no significant change in the radiation dose and nuclide analysis results (dust sampling data) compared to those from before the steam was observed.

With regard to the top of the Unit 3 Reactor Building, as the radiation dose is still high, the company says it will continue to decontaminate the area.

The current situation of Fukushima Daiichi may be seen via Fukuichi Live Camera at
http://www.tepco.co.jp/en/nu/f1-np/camera/index-e.html

Latest radiation dose monitoring results are posted at
http://www.tepco.co.jp/en/nu/fukushima-np/f1/index-e.html
http://www.tepco.co.jp/en/nu/fukushima-np/f1/surveymap/index-e.html

Explanation materials are available at below page (Please see from PDF page 19. We apologize it is only in Japanese.)
http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/d131031_04-j.pdf

TEPCO, Inc. is a provider of electricity to the Kanto region, which includes Tokyo and Yokohama. The company is headquartered in Tokyo. The Fukushima Daiichi Nuclear Power Station was struck by a tsunami after an earthquake that occurred in March 2011. For more information, please go to http://www.TEPCO.co.jp/en/index-e.html.