Though Tepco stated they could not measure neutron ray in November, Tepco turned out to have no equipment to know if recriticality is going on by measuring neutron ray.
It became clear by the question of Japanese journalist, Iwakami Yasumi on the press conference of 2/13/2012.
Having reactor 2 heated, it became important to know if there is recriticality going on.
For the question of Mr. Iwakami to ask if they didn’t measure neutron ray, Tepco answered it is impossible to measure neutron ray out of reactor because it’s protected by perfectly designed facility.
However, when they measured Xe133 and 135 on 11/1/2011, Tepco denied the possibility of recriticality to state they couldn’t detect neutron ray in the plant area.
The statement of 2/13/2012 contradicts this explanation.
Japanese government declared cold shutdown without measuring neutron ray.
Their way of measuring Xe135 is suspicious too.
On 2/12/2012, they announced the Xe135 was not detectable (less than 9.5×10-2Bq/cm3)
However, the detectable limit was 1.0×10-5Bq/cm3 when they measured it in November.
They raised the limit by 10,000 times.
(9.5×10-2Bq/cm3 is almost 1.0×10-1Bq/cm3. They might have wanted to write 10-2, instead of 10-1.)
When it fissions, Xe135 is produced 10,000 times much as usual.