The Nuclear and Industrial Safety Agency (NISA) has now concurred (Yomiuri Shinbun 11/7/2011) with TEPCO's conclusion that it was just ordinary spontaneous fission, not re-criticality, which generated xenon gas in Reactor 2 of Fukushima I Nuclear Power Plant.
Here's a view from the supposed insider, the worker who tweets from Fukushima I Nuclear Power Plant who seems to work for one of the top-tier subcontractors.
He wonders why TEPCO announced the xenon detection when it did and strongly hinted that it was from re-criticality. I wonder the same thing, particularly when krypton-85 and xenon-131m were detected in even greater amounts in Reactor 2 Containment Vessel back in August.
From the worker's tweets on the subject:
Xenon from spontaneous fission is routinely detected in the regular maintenance. TEPCO normally make announcements after exhausting all possibilities.
They provide information to the government and the NISA in a timely manner. But when it comes to announcing to the public in the press conference, they would always investigate thoroughly before announcing. But yesterday, they shocked the public with the word "re-criticality" which TEPCO would never want to use. And today they are saying don't worry it is just spontaneous fission?
In the yesterday's press conference [when they hinted re-criticality] it seemed like it would take long time to investigate, increasing the sampling. As they would do in normal circumstance. By the way, Minister Hosono [in charge of nuclear accident] was at the Fuku-1 plant yesterday but it was not reported in the media.
What event happened yesterday which they wanted to cover up with even more sensational news [like "re-criticality" at Fukushima I Nuke Plant]? What did they want to manipulate?
His answer to his own question is also shared by many people in Japan:
Could it be the restart of Genkai Nuclear Power Plant?
Reactor 4 of Genkai Nuclear Power Plant in Saga Prefecture, which is operated by the scandal-ridden Kyushu Electric, restarted on November 2 despite strong protests and opposition in the neighboring municipalities and from all over the country. The company just did it with the approval from the pro-nuke governor of Saga Prefecture (whose father worked for Kyushu Electric) and the NISA, saying there is no need for consent from the community (Mainichi Shinbun 11/2/2011) at all.
The same vein of thinking as the petty bureaucrats in the Tokyo Metropolitan government.
But back to the xenon/krypton detection in Reactor 2 of Fuku-I Nuke Plant, not all nuclear experts are convinced of spontaneous fission, particularly those not so intimately connected with the government. I am reading what they have to say, and will report back if I can digest.
Maybe the news they wanted to cover up with a hasty declaration of re-criticality possibility and dismissal the very next day was the real re-criticality. Next time when xenon-135 is detected, no one will pay attention. "Oh it's just routine spontaneous fission, happens all the time."