It has come to my attention that a tank holding radioactive waste water at Fukushima has been leaking,
The story is that workers found leak from a tank and a puddle of water which was about 9 square meters (1 to 2 cm deep) which had leaked, this was found to be radioactive. This water was contained inside a dyke and had not started to flow into the sea. A second puddle was found outside the dyke (3 square meters and 1 cm deep). This was in the H4 area.
This water was found to be radioactive, it had 46 Bq of Cs-134 per cubic cm, 100 Bq of Cs-137 per cubic cm, 1.2 Bq Co-60 per cubic cm, 1.9 Bq of Mn-54 per cubic cm, 71 Bq of Sb-125 per cubic cm, 80 kBq of total beta activity per cubic cm and it contained 5200 ppm of chloride per litre.
In this area TEPCO workers measured dose rates of 6 mSv per hour in a drainage channel.
TEPCO workers also found a pair of leaks in the H3 area near a tank where the worst dose rate was 100 mSv per hour. Later radioactive water was found in drainage channel B (0.15 Bq of Cs-137 per cubic cm) this is near the H4 area. A set of diagrams of the tank farms and the drainage channels can be seen here.
The cesium level in the water leaking from the tank farms is much lower than the water which is flowing out of the reactor buildings, according to a recent report the water in the central radioactive waste treatment buildings is in the range of 55000 to 28000 Bq of Cs-137 per cubic cm. After the cesium removal plant the water only has 5 or fewer Bq of Cs-137 per cubic cm.
The radioactivity levels suggest one of two things is happening, either the leak is a very new leak which and the radioactivity has not had a chance to percolate out into the drainage channel which flows into the sea. Alternatively the soil is acting as a filter for the radioactivity, this could account for the much lower radioactivity level in the ditch water which is flowing to the sea.
What is needed in the long term are details of how well the soil on the site binds to cesium and also the cesium absorption capacity of the soil. When I know more I will provide you with my thoughts on what is happening. But always bear in mind that when radioactive cesium is a problem clay can often be your best friend.
On of the key parameters needed to understand how well the clay will trap radioactivity is the Kd value, to understand Kd please look at this post about plutonium in spanish soil. Also do bear in mind that not all clays are equally good at catching cesium for details of some different clays please see here.