12 Dec (NucNet): A gradual rise in radiation readings at a test well at the Fukushima-Daiichi nuclear power station appears to be the result of successful efforts to pump groundwater and divert it from flowing into the ocean, operator Tokyo Electric Power Company (Tepco) said.
Tepco said the level of total beta radioactivity (all-β) at the test wells between units 1 and 2 had been monitored since 26 September and remained at levels between 400,000 and 880,000 becquerels per litre (Bq/ℓ) until 17 October.
On 21 and 24 October, the all-β radioactivity levels dropped to their lowest levels at this location: 390,000 Bq/ℓ and 310,000 Bq/ℓ respectively.
However, from 28 October onwards, beta radioactivity readings of samples from test well number 1-16 between Units 1 and 2 began to increase and reached 1,100,000 Bq/ℓ on 28 November and 1,300,000 Bq/ℓ on 2 December.
Measurements for the same period show that the levels of caesium-134 (Cs-134) and -137 (Cs-137), ruthenium-106 (Ru-106), manganese-54 (Mn-54), cobalt-60 (Co-60), and antimony-125 (Sb-125) did not change significantly. Only the level of tritium (H-3) increased considerably.
Tepco engineers said they believe the increase was associated with the residual highly contaminated water that leaked from Unit 2 into the ground in the first month after the earthquake and tsunami that caused the accident at the plant.
Tepco said the increase in all-β radioactivity in the test wells might be due to efforts begun on 8 July 2013 to control the flow of contaminated groundwater towards the ocean. Those efforts have included ground improvement work and pumping of groundwater from the area in which it was being contaminated.
Tepco said it is “significant” that there has been no change in the radiation density readings of seawater along with the reported increases in the groundwater.
Lake Barrett, a former US department of energy official and currently advisor to Tepco, said the situation has to be monitored carefully, but there is no increased level of risk to workers, the public, or the environment.
“While the rise in radiation readings is an obvious concern that needs to be carefully monitored, in some respects it is an indication of the success of Tepco’s concerted efforts to isolate contaminated water and prevent its flow into the sea,” Mr Barrett said.