Via NHK News :
" The operator of the crippled Fukushima Daiichi nuclear power plant says it continues to inject nitrogen gas into the containment vessel of the No.1 reactor without problems. The nitrogen gas is being used to prevent a hydrogen blast at the reactor.
The Tokyo Electric Power Company, or TEPCO, says that as of 6 AM Thursday pressure inside the containment vessel of the No.1 reactor had risen only slightly and that this indicates the operation is going well. The gas injection began at 1:30 AM Thursday.
Fuel rods inside the No.1 reactor are nearly half exposed because coolant water levels remain low. It is thought that the overheated fuel rods have caused a buildup of the volatile mix of hydrogen and oxygen. It is hoped the chemically stable nitrogen will counteract this buildup.
TEPCO says it plans to continue the injection for about 6 days and will also consider taking similar measures at the No. 2 and No. 3 reactors."