Only three releases of contaminated water are currently (June 9) acknowledged, although the IAEA has pointed to another.
1. April 4 to April 10. (10,400 tons 0.15 terabecquerels) Deliberate release of low-contaminated water from the Central Radioactive Waste Disposal Facility (9070 tons) subdrain of unit 5 (950 tons) and of Unit 6 (373 tons) [i] This was because … of the April 2 leak mentioned below. But TEPCO says there is limited risk of such water again leaking into the sea or the ground as it has taken measures to prevent further leaks (footnote [ii]).
2. April 2 Unit #2 500 tons (4,700 terabecquerels) In early April, 500 tons of highly radioactive water leaked into the sea from a work pit near the reactor’s water intake (footnote [iii]), and it took TEPCO several days to stop the obvious spout of water entering the sea from the famous ‘cracked pit’. Afterwards, TEPCO took various measures like silt fences and zeolite bags and extra monitoring, but the other intake channels were not monitored. Water levels in the trenches were monitored, however, and TEPCO started pumping the trench of Unit 2 to the Central Waste facility. Meanwhile, it was clear the level in #3 trench next door was rising and rising….
3. May 10 – Unit #3 started leaking to the sea. (250 tons, 20 terabecquerels), TEPCO thinks the trench of #3 started to fall about 0200 on May 10, and the leak lasted for 41 hours until 1900 on May 11, during which time the trench fell by about 20mm. Note that if the trench level fell, then it must have been some sort of new leakage pathway opening, not just the trench filling to an overflow level. In previous days its water level had been rising by between 10mm and 30mm a day, according to the TEPCO[iv] , but TEPCO did not start pumping it. The leak was discovered when workers removing rubble from a a pit near the sea discovered water was flowing into and out of it. TEPCO said even if there is leak to the sea, the silt screens would prevent a great leak to the outer ocean.footnote [v] TEPCO calculates the rate of this leak at about 100l/m (or 6 t/h). (footnote [vi])
I-131: 3400 Bq/L
Cs-134 : 37000 Bq/L
Cs-137: 39000 Bq/L
4. May 16-17 – Unit #3 the radiation level in the intake canal of #3 rose considerably again, but this is not yet acknowledged by TEPCO as a leak, I believe. In fact, on Monday May 16, TEPCO reportedly said “the changes in readings are within a margin of day-to-day volatility” (see footnote [vii]) On May 21 TEPCO submitted a detailed report on the first known #3 leak on May 11; it said the leak was sealed on May 11 and mentioned no further leaks from #3. (footnote [viii])
[i] http://www.tepco.co.jp/en/press/corp-com/release/11041507-e.html also has a nuclide analysis
[ii] The utility says the levels of the remaining contaminated water at the 2 reactors remain almost unchanged and that there is no immediate risk that the radioactive water will leak into the ground or the sea. TEPCO says it is monitoring operations closely to prevent any leaks.
TEPCO reported that it had discovered contaminated water leaking into the sea in April, and again earlier this month. The utility has since taken measures to prevent further leaks.
Monday, May 23, 2011 19:25 +0900 (JST) http://www3.nhk.or.jp/daily/english/23_25.html
[iv] “from 7:00am on May 4 to 7:am on May 10, the water level was increased by 10 to 30mm per day, wheras from 7:00 am on May 10 to 5:pm on May 11, the water level was decreased by 20 mm per day” TEPCO report http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110521e2.pdf
yomiuri: similar to the leak of #2?
tepco: they see that water is flowing from the opening of the power cable tubes.
water sample was brought to Fukushima 2 for analysis.
no particular change in monitoring points near outlets. even if there is leak to the sea, silt screen would prevent great leak to the outer ocean.
leak to the pit is from one of the multiple power cable tubes.
q: when leak of #2 happened, you said they checked and confirmed no other leaks.
a: it was covered with rubbles before. As rubbles being removed, we could find it. even if there is leak to the sea, silt screen would prevent great leak to the outer ocean.
[vi] The press release with various documents is here http://www.tepco.co.jp/en/press/corp-com/release/11052102-e.html and the one with these numbers is here http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110521e2.pdf
[vii] Radioactivity at intake of No.3 reactor rises
Radioactive materials in the ocean near the Fukushima Daiichi nuclear power plant rose to 3,300 times the legal limit on Sunday.
Tokyo Electric Power Company says it measured 200 becquerels of cesium-134 per cubic centimeter on Sunday morning near the water intake of the No. 3 reactor. The level was higher than on the previous day, when it was 2,300 times the legal limit.
220 becquerels of cesium-137 per cubic centimeter was also detected. At 2,400 times the legal limit, the level exceeded the one found the day before.
On Wednesday, highly radioactive water was found leaking into the ocean from a pit located near the water intake of the No. 3 reactor. 32,000 times the legal limit of cesium-134 was detected there.
TEPCO also reported 2,100 times the legal limit of radioactive iodine was found in seawater near the water intake of the No. 2 reactor. Three points among four research areas along the shoreline also exceeded the legal limit. And 1.7 times the legal limit of Cesium was found close to drainage gates near the No. 5 and No. 6 reactors.
TEPCO says the changes in readings are within a margin of day-to-day volatility. The company will continue to monitor radioactivity levels near the plant.
Monday, May 16, 2011 05:31 +0900 (JST) http://www3.nhk.or.jp/daily/english/16_06.html
[ix] The activity concentrations of I-131, Cs-134 and Cs-137 in seawater close to the Fukushima Daiichi plant at the screen of Unit 2 have been measured every day since 2 April. Concentrations of Cs-134 and Cs-137 decreased from initial values of more than 100 MBq/L to less than 5 kBq/L on 7 May, but increased to levels of around 20 kBq/L on 16 May, and to about 10 kBq/L on 17 May. There was a significant increase in levels of I-131 from about 8 to 80 kBq/L from 10 to 11 May, in parallel with the increase for both radiocaesium isotopes. This indicates that there is still some production of fission products. The I-131 levels decreased to about 20 kBq/L on 17 May.
IAEA Briefing on Fukushima Nuclear Accident (12 – 18 May 2011, 17:00 UTC)
[x] Radiation level at No.3 reactor water intake rises
The operator of the damaged nuclear power plant in Fukushima has reported a sharp rise in the concentration of a radioactive material in samples of seawater near the Number 3 reactor.
Tokyo Electric Power Company says it detected 110 becquerels of radioactive cesium-134 per cubic centimeters in seawater samples taken on Wednesday morning.
The level is 1,800 times the national legal limit, compared to 550 times, which was reported the previous day.
The utility also found 120 becquerels of cesium-137, 1,300 times higher than the limit.
Last Wednesday at the same location near the water intake of the Number 3 reactor, water contaminated with highly radioactive substances was found flowing into the sea from a pit. TEPCO says it detected cesium-134 at 32,000 times the legal limit.
In its latest announcement, TEPCO said the concentration of radioactive iodine in seawater samples from the same location fell from 1,900 times the limit on Monday to 630 times on Tuesday.
The utility also said it detected radioactive materials at levels higher than the national limit at 2 of the 4 survey points along the shoreline near the plant.
It says cesium-134 with a concentration level 1.8 times the limit was found at a point 330 meters south of the water drainage gates of the Number 1 to 4 reactors.
Thursday, May 19, 2011 02:57 +0900 (JST)