Since the entire water treatment system was stopped in the early hours of June 18 after only 5 hours of full run due to the faster than expected rise in radiation level on the Kurion's oil/technetium separation unit, TEPCO has been using the low contamination water to clean out the system.
Well, while they were doing the cleaning run, they found another leak in the same oil/technetium separation unit.
From Asahi Shinbun (10:27PM JST 6/19/2011):
TEPCO announced on June 19 that it found a new leak in the water treatment system for highly contaminated water at Fukushima I Nuclear Power Plant. The amount of leak was about 30 liters of the low contamination water that the company was using to clean out the system after the trouble [of the oil/technetium unit] was found. The leaked water has already been collected.
１８日午後９時ごろ、点検中の作業員が見つけた。放射性物質や油分の吸着に使うゼオライトを入れた装置の安全弁が壊れ、円筒形の装置を囲う容器とのすき 間に水がたまっていた。安全弁は内部の圧力が高まると破れる仕組み。東電はポンプの動作と停止を繰り返した影響が考えられるという。安全弁は停止中に水素 がたまるのを防ぐ目的で取り付けているため、運転中は安全弁の手前の弁を閉めるなどの対応を検討する。
The leak was found at 9PM on June 18 by the worker conducting the inspection. The safety valve [rupture disk] of the oil/technetium unit was broken, and there was water between the cylinder [vessel] that contains zeolite and the container that holds the cylinder. The safety valve is designed to break when the pressure inside the vessel gets high. TEPCO believes it may be the result of having to repeatedly start and stop the pump. The purpose of the safety valve is to prevent the hydrogen leak during the system halt. TEPCO is considering closing the valve leading to the safety valve during the operation.
It looks like this water treatment system will have to involve carbon-based workers on a regular basis, instead of automatic, remote-controls.
Here's the detailed diagram of the hydrogen venting system that includes the rupture disk, which TEPCO labeled as "rapture disk". I thought that was funny. The difference in pronunciation between "rupture" and "rapture" totally escapes the Japanese.
(From the press conference handout on June 19; cleaner copy at the link)