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.
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 trench and
sub-drain (subsurface water) near the turbine building, together with
accumulated water detected in the Process Main Building of Centralized
Radiation Waste Treatment Facility. The re-valuation was conducted in
accordance with the preventive measures.
The preventive measures are as follows and re-valuation was conducted
based on such 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
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 adequacy.
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).
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. We will announce the results of such re-evaluation
At the site of Fukushima Daiichi Nuclear Power Station, as part of our
investigation for the pathway and the volume of radioactive emissions, we
have been conducting nuclide analysis for air inside the plant, seawater
near the plant and water puddle in the turbine building. We have been
informing you of the results of the nuclide analysis. It is ascertained
that the result of nuclide analysis of tellurium 129 (half life : about 70
minutes) conducted on March 30th, for water puddle collected near the
trench and ground water collected near the turbine building was suspect.
We were verbally severely warned by the Nuclear and Industrial Safety
Agency (NISA) for this matter.
We have seriously taken NISA's severe warning and in order to conduct a
proper assessment for nuclide analysis, we have reported to NISA on the
The causes of the previous mistake in the assessment of nuclide analysis
and improvement plan for the exact nuclide analysis are as follows.
·Even though the main peak of iodine 134 and cobalt 56 were not
detected, we determined those nuclides were detected in the sub peak.
·For the term of assessment, using germanium device of Germanium
semi-conductor type nuclide, since tellurium -129m and tellurium -129
were not registered as parent-daughter nuclide information (library), we
could not conduct calculation considering the creation from parent
○Implementation of analysis work following the opinion from
·We confirm the method of analysis such as detection accuracy
based on the specialty of appliances with experts from manufacturers.
○Reconstruction of back-up system by other electric power companies
·In order to check the data without mistakes, we reconstruct the
back-up system by other electric power companies.
In accordance with the preventive measures, we will review the result of
nuclide analysis in regard to the air at the site of power station,
seawater near the power station, accumulated water in the turbine building,
water in the trench and subsurface water near the turbine building. We
will announce the results of such review accordingly.
(Previously announced on April 4th, 2011)
Attachment-1: Fukushima Daiichi Unit 1 Results of nuclide analysis of
accumulateｄ water in the basement floor of turbine building
Attachment-2: Fukushima Daiichi Unit 1 Results of nuclide analysis of
accumulated water in the trench(PDF 17.9KB)
Attachment-3: Fukushima Daiichi Unit 1 Results of nuclide analysis of
sub-drain (PDF 30.1KB)
Attachment-4: Fukushima Daiichi Results of nuclide analysis of accumulated
water in the Process Main Building of Centralized Radiation
Waste Treatment Facility (PDF 8.24KB)