7 Apr (NucNet): Nitrogen is being injected into the primary containment vessel (PCV) of unit 1 at the Fukushima-Daiichi nuclear power plant amid concern that hydrogen that has accumulated there could cause an explosion.
Because the containment has already been damaged and pressure inside might drop below atmospheric pressure, there is a risk that outside air containing oxygen could leak into the PCV resulting in the build-up of an explosive hydrogen-oxygen gas mix.
Injecting nitrogen is intended to displace oxygen inside the PCV, thereby reducing the risk of explosion caused by the combustible combination of hydrogen and oxygen.
Plant owner and operator Tokyo Electric Power Company (Tepco) said nitrogen injection started at unit 1 today at 01:31 local time (18:31 on 6 April central European time).
Tepco is preparing to take similar measures at units 2 and 3.
Yesterday Tepco said workers at the plant had used 6,000 litres of coagulant to stop a leak from a trench next to the unit 2 inlet point that had been causing highly contaminated water to flow into the sea since 29 March.
Tepco said they used liquid tracer to find the source of the leak in a concrete utility trench and then used the coagulant to seal it.
Additional measures will now be carried out to prevent the discharge of radioactive material from the trench, which holds electric supply cables. One possible measure is to continue the injection of coagulant, Tepco said.
Iodine-131 and Caesium-137 were both detected in water sampled in trenches and in the sea near the water discharge.
The leak was discovered on 2 April when workers detected water releasing a radiation dose rate of more than 1,000 millisieverts per hour in a trench and found a crack about 20 cm wide on the trench’s concrete wall.
>>Related reports in the NucNet database (available to subscribers)
Tepco Makes Progress In Bid To Restore External Power (News in Brief No. 77, 23 March 2011)
Japan Update: Work Begins To Remove Contaminated Water (News in Brief No. 82, 27 March 2011)
Tepco Prepares Liquid Glass Injection To Stem Leak (News in Brief No. 91, 5 April 2011)
