Sunday, March 13, 2011

Fukushima update: Unit 3

From TEPCO:
Unit 3: High Pressure Coolant Injection System automatically stopped. We endeavored to restart the Reactor Core Isolation Cooling System but failed. Also, we could not confirm the water inflow of Emergency Core Cooling System. As such, we decided at 5.10AM, Mar 12, and we reported and/or noticed the government agencies concerned to apply the clause 1 of the Article 15 of the Radiation Disaster Measure at 5:58AM, Mar 13. In order to fully secure safety, we operated the vent valve to reduce the pressure of the reactor containment vessels (partial release of air containing radioactive materials) and completed the procedure at 8:41AM, Mar 13 (successfully completed at 09:20AM, Mar 13). After that, we began injecting water containing boric acid that absorbs neutron into the reactor by the fire pump from 09:25AM, Mar 13.
(Note: TEPCO access has been sporradic due to high traffic volume)

Basically, until recently an emergency system for injecting water into the core called a High Pressure Coolant Injection System (HPCE, or "hip-see") was working, until it shut down. Because engineers were unable to restart it, they have moved to the next plan, which involves the direct flooding of the reactor containment building with seawater, similar to Unit 1. While this is unfortunate for the reactor itself (like Unit 1, it likely means Unit 3 is a total loss), it means that the cooling situation will likely be under control and little further danger of fuel failure or subsequent radioactive release exists.

Additionally, they have vented steam from the primary containment of Unit 3. This is similar to Unit 1; without the ability to circulate coolant, it will begin to boil and form steam. This steam then builds up pressure and must be "bled off" in order to prevent damage to the containment itself. (The containment itself is designed to withstand high pressures - much higher than ambient atmosphere - however, this is done as a preventative measure). In this case, there does not appear to have been the same risk that the core became "uncovered" as in Unit 1, and thus the risk of any further radiological release by venting boiled coolant appears to be very small - i.e., much of what is released will be of very low half-life (such as Nitrogen-16, which has a half-life on the order of 7 seconds), or very weakly radioactive and in low concentrations (such as tritium).

However, NEI reports some fuel damage may be suspected at both Units 1 and 3. Currently, off-site and backup electrical power is unavailable at both Units 1 and 3.

The full TEPCO update below the fold.


[Nuclear Power Station] Fukushima Daiichi Nuclear Power Station:
Units 1 to 3: shutdown due to earthquake
Units 4 to 6: outage due to regular inspection
* The national government has instructed evacuation for those local residents within 20km radius of the site periphery.
* The value of radioactive material (iodine, etc) is increasing according to the monitoring car at the site (outside).
* Since the amount of radiation at the boundary of the site exceeds the limits, we decide at 4:17PM, Mar 12 and we have reported and/or noticed the government agencies concerned to apply the clause 1 of the Article 15 of the Radiation Disaster Measure at 5PM, Mar 12. After that, the radiation dose at the monitoring post decreased once. Today, the measured value revamped and the radiation dose measured at site boundary exceeded the limiting value again. As such, at 8:56AM, today, it was determined that a specific incident stipulated in article 15, clause 1 occurred and at 09:10AM, today, notified accordingly.
* In addition, a vertical earthquake hit the site and big explosion has happened near the Unit 1 and smoke breaks out around 3:36PM, Mar 12th.
* Unit 1: We started injection of sea water into the reactor core at 8:20PM, Mar 12 and then boric acid subsequently.
* Unit 2: Reactor has been shut down and Reactor Core Isolation Cooling System has been injecting water to the reactor. Current reactor water level is lower than normal level, but the water level is steady. After fully securing safety, we are preparing to implement a measure to reduce the pressure of the reactor containment vessels under the instruction of the national government.
* Unit 3: High Pressure Coolant Injection System automatically stopped. We endeavored to restart the Reactor Core Isolation Cooling System but failed. Also, we could not confirm the water inflow of Emergency Core Cooling System. As such, we decided at 5.10AM, Mar 12, and we reported and/or noticed the government agencies concerned to apply the clause 1 of the Article 15 of the Radiation Disaster Measure at 5:58AM, Mar 13. In order to fully secure safety, we operated the vent valve to reduce the pressure of the reactor containment vessels (partial release of air containing radioactive materials) and completed the procedure at 8:41AM, Mar 13 (successfully completed at 09:20AM, Mar 13). After that, we began injecting water containing boric acid that absorbs neutron into the reactor by the fire pump from 09:25AM, Mar 13.
* We continue endeavoring to secure the safety that all we can do and monitoring the periphery. Fukushima Daini Nuclear Power Station: Units 1 to 4: shutdown due to earthquake
* The national government has instructed evacuation for those local residents within 10km radius of the periphery.
* At present, we have 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. These measures are considered to be implemented in Units 1, 2 and 3 and accordingly, we have reported and/or noticed the government agencies concerned.
* Unit 3 has been stopped and being "nuclear reactor cooling hot stop" at 12:15PM.
* The operator trapped in the crane operating console of the exhaust stack was transferred to the ground at 5:13PM and confirmed the death at 5:17PM.