Since October 28, 2011 we have been operating a gas control system for the nuclear reactor at Unit 2 of Fukushima Daiichi Nuclear Power Station. On November 1, as a result of the nuclide analysis by collecting charcoal filters installed inside a dust radiation monitor, some radioactive Xe135 was detected, a nuclide with a short half-life (around 9 hours).
On November 4, we submitted a report to Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry.

(On November 4, announced)

After that, we confirmed that the evaluation result of the concentration of Xe135 reported to Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry includes incorrect data due to the mistaken setting of the internal constants of the Germanium semiconductor detector^*.(On November 17, announced)
In addition, we confirmed that the evaluation result of the concentration of the gas inside the primary containment vessel of Unit 1 of Fukushima Daiichi Nuclear Power Station announced on September 16 includes similar incorrect data. (On September 21, announced) we were ordered to submit the report on cause and countermeasures of these errors from Nuclear and Industrial Safety Agency.
After that, we finished determination of causes and countermeasures of the sampling result error, and submit the report to Nuclear and Industrial Safety Agency.

<Appendices>
Causes and Countermeasures of the evaluation result error of gas concentration inside the primary containment vessel of Unit 2 of Fukushima Daiichi Nuclear Power Station. (PDF 1.50MB)
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* Germanium semiconductor detector
Detector to measure the concentration of radioactive material by analyzing gamma ray nuclides