(UPDATE 6/19/2013) TEPCO found two pinholes in the weld, says it will investigate why these pinholes are there.
TEPCO released the photographs of the weld that leaked highly radioactive water that was going to the Line A of ALPS multi-radionuclide removal system at Fukushima I Nuclear Power Plant.
The photographs are not big enough to see the details of the weld clearly, but it looks like a poor weld. Another rush job, I suppose.
From TEPCO's Photos and Videos page, 6/17/2013:
Overview of ALPS by TEPCO, here.
ALPS stands for "Advanced Liquid Processing System", developed by Energy Solutions in Salt Lake City, Utah.
I wonder which subcontractors of Toshiba did the welding of these tanks being used in the ALPS system. The weld in the photos above sure doesn't look like a "nuclear power plant" grade.