Details in the press conference at 9:30AM, April 13 in Fukushima (Fukushima I Nuclear Power Plant?), and at 11:00AM at TEPCO's headquarters in Tokyo.
From the tweets by an independent journalist who's on the list to receive TEPCO's emails on the plant situation:
Drop in the amount of nitrogen gas being injected into Reactors 1, 2, 3 was noted by a TEPCO employee at 1AM, April 13 when he was checking the plant parameters.
The nitrogen injection system was inspected at 1:30AM. It turned out that the system alarm had gone off at 1:04AM for "compressor failure", and the system had stopped ("nitrogen gas separation system B").
At 3:10AM, the backup system ("nitrogen gas separation system" on the high ground) was started, and at 3:46AM the nitrogen gas injection restarted.
There has been no discernible change in the plant parameters, hydrogen density, or the monitoring post data.