Fukushima 1 Nuclear Accident Day 10: Sunday, 20 March 2011

03:00
Restored emergency power to the spent fuel pond cooling systems for units 5 and 6 have brought the unit 5 pond temperature down from 68.8 °C to 43.1 °C and the unit 6 pond temperature down from 67.5 °C to 52 °C as of 03:00 JST.
04:26
"The Nuclear and Industrial Safety Agency said there is some positive progress and engineers at the end may not need to open valves inside the container vessel of the No. 3 reactor to alleviate pressure that is building up", while they were initially planning this action. Such a move, if forced, would release more radioactive steam.
09:00
Spent fuel pond water temperature dropped to 36.1 °C at Unit 5 and 36.6 °C at Unit 6.
16:00
Status of Fukushima I at 16:00 on 20 March

Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6
Power output (MWe) 460 784 784 784 784 1100
Type of reactor BWR-3 BWR-4 BWR-4 BWR-4 BWR-4 BWR-5
Status at earthquake In service -> shutdown In service -> shutdown In service -> shutdown Defueled Outage Outage
Fuel integrity 70% damaged 33% damaged Damaged No fuel rods Not damaged Not damaged
Pressure vessel integrity Unknown Unknown Unknown Not damaged Not damaged Not damaged
Containment integrity Not damaged Damage suspected Unknown Not damaged Not damaged Not damaged
Core cooling system 1 (ECCS/RHR) Not functional Not functional Not functional Not necessary Not necessary Not necessary
Core cooling system 2 (RCIC/MUWC) Not functional Not functional Not functional Not necessary Not necessary Not necessary
Building integrity Severely damaged Slightly damaged Severely damaged Severely damaged Vent hole opened on rooftop to prevent hydrogen explosion Vent hole opened on rooftop to prevent hydrogen explosion
Pressure vessel, water level Fuel exposed Fuel exposed Fuel exposed Safe Safe Safe
Pressure vessel, pressure Stable Unknown Stable Safe Safe Safe
Containment pressure Unknown Low Stable at higher level after increase Safe Safe Safe
Seawater injection into core Continuing Continuing Continuing Not necessary Not necessary Not necessary
Seawater injection into containment building Continuing To be decided Continuing Not necessary Not necessary Not necessary
Containment venting Temporarily stopped Temporarily stopped Temporarily stopped Not necessary Not necessary Not necessary
Integrity of fuel in Spent Fuel Pool (SFP) Water injection to be considered (no data) SFP level low,
Water injection continues		 SFP level low,
Water injection started,
Hydrogen from SFP exploded		 Pool cooling capability was recovered Pool cooling capability was recovered
Environmental effect (NPS border) At 05:40, March 20: 269.5 µSv/hour (West Gate); and 3054 µSv/hour to the North of the Service Building (at 15:00, March 20)
Evacuation radius 20 km from Nuclear Power Station (NPS). People who live between 20 km to 30 km from the Fukushima I Nuclear Power Station are to stay indoors.
INES Units 1-3, Level 5 (estimated by Japanese NISA and accepted by the international IAEA); Level 6 (estimated by the French Nuclear Safety Authority, ASN); Unit 4, Level 3.

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