Additional information (or stating the obvious) on the leak from one of the ALPS (multi-nuclide removal system) tanks Fukushima I Nuke Plant.
From Jiji Tsushin (6/18/2013):
Pinholes found in the weld on the tank for ALPS at Fukushima I Nuke Plant
TEPCO announced on June 18 that two pinholes were found in the weld at the bottom of the tank used in the multi-nuclide removal system ALPS at Fukushima I Nuke Plant, where a small leak of contaminated water was found. The company thinks the water leaked from these holes, and plans to insert a camera inside the tank to further investigate the cause [of the pinholes].
According to TEPCO, two pinholes were found at the weld, about 30 centimeters apart. They are less than 1 millimeter in diameter and couldn't be found by visual inspection. TEPCO applied colored solvent [on the weld] to find the holes.
Cause of the pinholes? Bad weld, bad inspection, I can't think of anything else.
Looking at the diagram that TEPCO provided the other day, there are total 6 Batch Treatment Tanks in ALPS, two each in the three lines. There are numerous other tanks and vessels to absorb radioactive materials, and they are all welded. I wonder if they are properly inspected - i.e. each and every one of the tanks and vessels inspected by professionals and regulatory officials, instead of copying the data of a good weld.