TEPCO Press Release (Mar 12,2011)
Plant Status of Fukushima Daini Nuclear Power Station as of 1PM March 12th (11:00:00 p.m. Friday March 11 Eastern Time)
 
Unit 1 (shut down at 2:48PM on March 11th)

– At 5:22AM, the temperature of the suppression chamber exceeded 100
degrees. As the reactor pressure suppression function was lost, at 5:22AM,
it was determined that a specific incident stipulated in article 15,
clause 1 has occurred.
– We decided to prepare implementing measures to reduce the pressure of
the reactor containment vessel (partial discharge of air containing
radioactive materials) in order to fully secure safety. This preparation
work started at around 9:43am.

Unit 2 (shut down at 2:48PM on March 11th)

– At 5:22AM, the temperature of the suppression chamber exceeded 100
degrees. As the reactor pressure suppression function was lost, at 5:22AM,
it was determined that a specific incident stipulated in article 15,
clause 1 has occurred.
– We decided to prepare implementing measures to reduce the pressure of
the reactor containment vessel (partial discharge of air containing
radioactive materials) in order to fully secure safety. This preparation
work commenced at around 10:33AM and completed at 10:58AM.

Unit 4 (shut down at 2:48PM on March 11th)

At 6:07AM, the temperature of the suppression chamber exceeded 100
degrees. As the reactor pressure suppression function was lost,
at 6:07AM, it was determined that a specific incident stipulated in
article 15,clause 1 has occurred.
– We decided to prepare implementing measures to reduce the pressure of
the reactor containment vessel (partial discharge of air containing
radioactive materials) in order to fully secure safety. This preparation
work commenced at around 11:44AM and completed at 11:52AM.

Indication from monitoring posts installed at the site boundary did not
show any difference from ordinary level.
No radiation impact to the external environment has been confirmed. We
will continue to monitor in detail the possibility of radioactive material
being discharged from exhaust stack or discharge canal