A company charged with decontaminating the devastated Fukushima Nuclear Power Plant encouraged its workers to falsely lower their radiation dosimeter readings by covering the devices with lead, according to a leaked tape of an internal meeting.

Nuclear plant workers are not allowed to be exposed to more than 50 millisieverts of radiation a year. But managers at Build-up, a company that provided insulation on the pipes that would pump irradiated water out of the plant, believed that doses experienced inside the plant, which suffered a meltdown, meant workers would quickly reach their limit.

A senior executive gave the team at the site lead boxes that they were told to make into shields.

The workers were then told to place these over the dosimeters. Lead effectively blocks radiation, and produces a significantly lower reading.

When some of them refused, the executive called a meeting.