On April 4th, 2011, we reported on the preventive measures to be taken
after receiving severe verbal warning from Nuclear and Industrial Safety
Agency (NISA) on April 1st in regard to the results on nuclide analysis at
Fukushima Daiichi Nuclear Power Station.
(announced on April 4th, 2011)
Accordingly, we would like to inform the results of re-evaluation on
nuclide analysis in regard to samples collected before March 30th from
accumulated water in the turbine building, water in the sub-drain
(subsurface water) near the turbine building and accumulated water detected
in the Process Main Building of Centralized Radiation Waste Treatment
Facility.
The preventive measures are as follows and re-valuation was conducted based
on such measures.
<Preventive measures>
1.Evaluation of nuclide analysis based on experts' opinion
Experts from third-party institution verified the concept of nuclide
identification and evaluation was conducted after reflecting such experts'
opinions.
2.Deliberation on the method of cross-check
Experts from manufacturer confirmed the adequacy of nuclide library in the
analytical equipment. In addition, experts from third-party institution
confirmed the adequacy of concept in regard to program used for nuclide
analysis evaluation.
3.Improvement of accuracy achieved by support from other institutions, such
as electric utilities
We attempted to improve the accuracy of nuclide analysis evaluation by
asking other electric utilities and third-party institutions for support
on reviewing data and reasonableness.
4.Preparation of preliminary report and definite report
In order to achieve good balance between accuracy and promptness, we made
announcement in 2 stages. Firstly, we released a preliminary report
(determination of radioactivity density regarding the 3 major nuclides,
while providing them as reference data in the results of nuclide analysis)
and thereafter a definite report (determination and announcement of
radioactivity density regarding major nuclides as well as other nuclides).
(announced on April 20th, 2011)
We re-evaluated the results on nuclide analysis of air collected within the
site boundary, seawater close to the power station, seawater at the bar
screen of Unit 1 to Unit 4, sub-drain water around the turbine building,
sub-drain water at the Centralized Radiation Waste Treatment Facility which
were collected during May 21st to June 3rd, sea water of offshore of
Ibaraki Prefecture those collected on May 25th, and sea-bottom soil those
collected on June 2nd respectively and report as a final figure.
We will re-evaluate the results on nuclide analysis in regard to samples
collected from the air at the site of power station and seawater near the
power station after June 4th. We will announce the results of such
re-evaluation accordingly.
Appendix: [Definite Report]Result of Nuclide Analysis of Radioactive
Materials at the Site of Fukushima Nuclear Power Stations
(PDF 388KB)