Evidence of a small leak has been found in the ALPS contaminated water treatment system. A trace of discoloured water near the weld line was found on the outside of the A line batch treatment tank on 15 June.
Only a few drops of discoloured water have been found, but the water had a radioactivity almost 50 times background radiation (in terms of counts per minute), and had a total gamma and beta dose measurement of 0.18 mSv/hr. That the discoloured area has a higher activity level than the non-discoloured area suggests that contaminated concentrated salt water could be leaking out of the tank. Water vapour condenses on the tanks (dew), and is contaminated by the leak; workers collected 370 mL in 16 hours.
As a result, TEPCO informed the regulator and stopped line A processing on 16 June. It is investigating the cause of the incident.
In other news, underground reservoirs 1, 2, 3 and 6, which were expected to be leaking, were all completely emptied by 8 June, into aboveground tanks. Tanks 1 and 2 were emptied by the beginning of May, but tanks 3 and 6 took longer.
One aboveground tank in a farm of 20 was found to be leaking (one drop every three seconds) in early June. After the bolted flange was tightened, the leak did not stop, so the capacity of the tank was lowered to beneath the point of the leak.