The radioactivity in subsoil water outside the Unit 1 turbine building increased about 15 fold between May 27 and May 30, but such increases (up to 166 thousand Becquerels per litre) were only measured near Unit 1. On the same day, the reported level of radioactive water in Unit 1 turbine building dropped 130mm. In that week TEPCO figures show that the water table outside Unit 1 rose 4.1 metres; outside the neighbouring Unit 2, the groundwater level rose 1.9 metres, but at other places round the plant it only went up by about 0.5 metres. However, the water level in the #1 turbine and reactor buildings was reported as several metres below the level of groundwater outside:
- OP 4920 in turbine building basement
- OP 4484 in the reactor basement
- OP 7290 in the subdrain outside
If this leak really happened, very little has been said publicly, nor reported by the IAEA or other countries. However, TEPCO and the government are thinking of building a huge underground wall (down to bedrock) around the units to prevent any leaked water reaching the ocean; although under planning since “groundwater shielding” was added to the second version of the roadmap in May, the massive $1.2 billion cost was apparently not mentioned to shareholders at the AGM, and the government is considering helping TEPCO to pay.
Radioactivity in #1 water:
At the end of May, TEPCO estimeated there was 8400 m3 of water in #1 turbine building, with a radiation level of 400,000 Bq/cm3.
“In order to verify any leakages to underground and sea, and safety, we have been implementing the sampling surveys of subsurface water and seawater” says TEPCO, and the company samples the subdrains outside turbine buildings every three days for this purpose. It and the regulator NISA have not noted a leak of radioactivity from the reactor buildings around May 27 (as of June 14) I believe.
The subdrain pits of units 5 and 6 have constantly accumulated low-radioactive water presumably by leakage INTO the buildings from groundwater. This water in #5 and #6 indicates that there are leakage pathways to and from the buildings – some of it was deliberately discharged to the sea on April 4, when a diagram of the places where groundwater radioactivity is measured was published, and they have been pumped out regularly ever since.
The water table rise: TEPCO’s data shows the increase in groundwater around the various units between May 27 and May 30 as below, with #1 rising to be OP7290 (the level inside the turbine building fell a little to OP4920
|Unit 1||Unit 2||Unit 3||Unit 4||Unit 5||Unit 6|
( seven other places around the site were also measured – they showed an average rise of about 400mm).
The radiation increase: TEPCO’s graph (on a logarithmic scale) shows the sudden increase of radiation, and associated datasheets below summarised below give the actual figures: an increase from 11,000 to 166,000 Bq/L over three days
See similar graphs for other units at the end of May:
|Date||Unit 1||Unit 2||Unit 3||Unit 4|
Other groundwater radiation spikes: A quick look at TEPCOs graph of radioactivity in groundwater outside the turbine buildings up to June 26 indicates that groundwater radioactivity outside Units 1 and 2 also rose dramatically around May 15 and June 24, and was consistently much higher than outside Units 3 and 4.