TEPCO disclosed the latest result of the analysis of the gas coming from the Containment Vessel of Reactor 2 at Fukushima I Nuclear Power Plant, along with the result of the analysis done on October 28, 2011 when the gas management system started operating in Reactor 2.
There was no xenon or krypton detected on October 28. Then they were there in the analysis on November 1.
From TEPCO's handout for the press (11/2/2011), from November 1 to November 2,
Krypton-85 (half life 10.8 years) went from 3.6 x 10^-3 to 5.3 x 10^-1, 100-fold increase
Xenon-131m (half life 12 days) went from to 5.3 x 10^-4 to 6.1 x 10^-4
Xenon-133 (half life 5 days) went from 6.5 x 10^-6 to below detection limit
Xenon-135 (half life 9 hours) went from 1.3 x 10^-5 to 1.7 x 10^-5.
The unit is Bq/cubic centimeter. According to wiki, "About three atoms of krypton-85 are produced for every 1000 fissions (i.e. it has a fission yield of 0.3%)". It sure looks like a nuclear chain reaction happening, i.e. re-criticality, the possibility of which TEPCO's Matsumoto has already admitted.