Japan's nuclear regulators plan to look into work management at the crippled Fukushima Daiichi nuclear plant, which is being decommissioned following the 2011 accident.
The move follows a series of mistakes and violations. In June this year, smoke came out when workers misconnected power lines at the No.5 and No.6 reactors.
It has also come to light that water servers were placed for the past four years in restricted areas where radioactive materials are stored.
The commissioners at the Nuclear Regulation Authority on Wednesday certified both incidents as safety violations.
In addition, work to remove nuclear fuel from the No.3 reactor's storage pool has been delayed due to repeated mechanical problems.
The commissioners also decided to request a report from their inspectors stationed in Fukushima Prefecture on whether the plant's operator, Tokyo Electric Power Company, is conducting its work properly. The regulators also plan to directly question TEPCO officials.
Authority chairman Toyoshi Fuketa told reporters that simple procedural errors raise concern as to whether TEPCO has enough electricians and quality managers at the site.
He said the regulating body will make sure that small mistakes don't lead to big ones.