CNN and other sources in Japan have reported this:

“Japan’s Ministry of Health, Labor and Welfare is investigating a report that workers at the damaged Fukushima Daiichi nuclear power plant were told to use lead covers in order to hide unsafe radiation levels, an official said.”

You can read a more complete story at http://www.cnn.com/2012/07/21/world/asia/japan-nuclear/.

In other reports, in Japan TEPCO, while denying they knew they were used, admitted they knew they were created.

I can’t think of a single legal or ethical reason why Build-Up, the sub-contractor, would ever create such lead covers.