Fukushima in recriticality ? A Fukushima Diary blogger thinks so : “At four different places in Japan, Iodine 131 was detected between 15th-25th August. The half life time of Iodine 131 is about 8 days. It’s natural to think Fukushima got into the recriticality state.” Read the full post on Fukushima Diary. A comment to this blog entry mentions that the source could be medical, i.e. hospitals… A week after writing this post, some new elements published on Fukushima Diary, reproduced hereafter, seem to confirm the thesis of a recriticality over that of a medical waste :
“On August 25th, 2,300 Bq/kg of radioactive Iodine 131 was detected in the sewage sludge at Maesawa Sewage Treatment Center in Oushu City. This was followed by testings on September 2nd and on 6th with the results 590 Bq/kg, 480 Bq/kg respectively, according to media.
Some commented that these were caused by medical treatment or testing uses, trying to explain the discharge point as such, which I thought suspicious and tried to investigate for facts directly with the local [medical facilities].
There are only two facilities, *Tanzawa [please check the name before uploading] Hospital and Mizusawa Hospital, that currently practice nuclear medicine in Oushu City.
So I called each on September 14th and confirmed directly with the staff.
The results: Mizusawa Hospital did not use Iodine 131 but Iodine 123, and its protocol followed that the waste was stored first and then discharged out of the hospital after the radioactivity was confirmed to be below a lawful disposal standard.
On the other hand, *Tanzawa Hospital did use Iodine 131; however, its protocol was the same [as Mizusawa Hospital], storing the waste first in the tank within the Hospital and then testing done to confirm that the waste contained radioactivity below a lawful discharge standard before discharging out of the Hospital.
Dr. “Sugawara”, the radiation tech who answered the phone commented it would be extremely unlikely that the detection of Iodine 131 [at the Treatment Center] was caused by the Hospital’s discharge due to its adherence to the protocol. Moreover, he went on to check the past data as there was a slight chance that a patient of Graves’ disease, etc. could be prescribed I-131 and discharged it after s/he left the Hospital, but the result was the last such prescription was issued to a patient in September of the last year, 2010. Therefore, the explanation that this [recent] detection of Iodine 131 (half-life of 8 days) in the sewage sludge being connected to the medical I-131 from Tanzawa Hospital, including the possibility that a patient carrying it out in the body and discharging it later in Oushu City, turned out to be extremely difficult one and was unlikely.”