In April of 2011, BBC and other news media sources reported that TEPCO was injecting nitrogen into Fukushima Daiichi unit 1 to prevent a hydrogen explosion:
Japan quake: Nitrogen pumped into nuclear reactor. BBC. April 7, 2011, available, http://www.bbc.com/news/world-asia-pacific-12992284
Workers in Japan have begun injecting nitrogen into one of the reactors at the crippled Fukushima Daiichi nuclear plant to prevent more hydrogen blasts.The gas is being pumped into reactor 1 of the six-unit plant which was damaged by last month's quake and tsunami....
Technicians began injecting nitrogen, an inert gas, into the number one reactor at 0131 local time Thursday (1631 GMT Wednesday). "The possibility of a hydrogen explosion in current conditions is not necessarily high," said government spokesman Yukio Edano. "But by injecting nitrogen, we can make the possibility very close to zero. So they decided to inject nitrogen."I believe that TEPCO is STILL injecting nitrogen into unit 1 to prevent a hydrogen explosion, although TEPCO does not mention the injections in its December press releases (here).
I have been reporting that Fukushima had recently looked TERRIBLE and I noted what looked like steam coming out of unit 1 during day time hours, as well as high night-time emissions.
Yesterday, late in the day here in the southwest, I noticed that a TEPCO crane was dropping a strange and very large device into unit 1:
In the screenshot immediately above this text, the device is now located inside the building, rather than behind it. The device has red lights that illuminate on and off (although I haven't watched enough to know the pattern).
Today, emissions at unit 1 are lower than they have been recently, although you can see a plume coming up from the unit 3 area (more screenshots here at drop box):