TEPCO compiled and reported to NISA a record of observed seismic data
collected at Fukushima Daiichi Nuclear Power Station and Fukushima Daini
Nuclear Power Station when the Tohoku-Taiheiyou-Oki Earthquake occurred
at 2:46pm on March 11, 2011.
(Previously announced on April 1 and May 16, 2011)
Subsequently, we received an instruction document* from NISA. Following
the instructions, we were meant to conduct a detailed evaluation of the
impact from the earthquake, implement countermeasures for seismometer
malfunctions, and report the results to NISA. By August 17th, 2011, we
had already compiled the following results of the earthquake response
analysis at Fukushima Daiichi and Daini Nuclear Power Station and
submitted them to NISA.
·Results of the earthquake response analysis of the reactor building,
facilities and pipes important to earthquake safety at Units 1 to 6 at
Fukushima Daiichi Nuclear Power Station
·Results of the earthquake response analysis of the reactor building,
facilities and pipes important to earthquake safety at Units 1 to 4 at
Fukushima Daini Nuclear Power Station
·Results of the earthquake response analysis of all turbine buildings,
facilities and pipes important to earthquake safety at Fukushima Daiichi
and Daini Nuclear Power Station
(Previously announced on June 17, July 28 and August 18, 2011)
Later, we discovered an error in the evaluation results of the main steam
system piping arrangement of Unit 2 at Fukushima Daini Nuclear Power
Station in the reports, and concluded that the error needed to be corrected.
We also reported it to NISA.
We have confirmed that the calculated value is lower than the evaluation
standard value even in the results after making the correction and no other
identical error exists at our other plants.
END
○ Attachment
Partial correction of the report on results of earthquake response analysis
of Unit 2 at Fukushima Daini Nuclear Power Station using observed seismic
data during the Tohoku-Taiheiyou-Oki Earthquake (PDF 67.4KB)
* Actions following the analysis of seismic data collected at Fukushima
Daiichi nuclear power station and Fukushima Daini nuclear power station
during the Tohoku-Taiheiyou-Oki Earthquake (Instruction)
NISA No.6, 2011 May 16
On May 16, NISA received TEPCO's report of analysis of observed seismic
data collected at Fukushima Daiichi nuclear power station and Fukushima
Daini nuclear power station during the Tohoku-Taiheiyou-Oki Earthquake.
According to the report, acceleration response spectra of observed seismic
data observed at free foundation point in the reactor buildings in Fukushima
Daiichi nuclear power station was mostly below the acceleration response
spectra for evaluation of basic earthquake ground motion Ss in most periods,
however, spectra collected in Unit 2, 3, and 5 exceeded spectra for
evaluation by 30% at maximum during 0.2 to 0.3 seconds.
Based on TEPCO's analysis above, NISA considers that it is extremely
important to evaluate the impacts from the earthquake on reactor buildings,
turbine buildings, and major facilities and pipes from earthquake resistance
perspective in Fukushima Daiichi and Daini nuclear power station in order to
confirm the status of safety function of those facilities at the time of
earthquake and following period.
The report also states that data recording was interrupted in several
voluntary located seismometers during 130 to 150 seconds after the initiation
of recoding due to the malfunction of recording devices.
The reason of malfunction was analyzed that 1) the program was coded to
finish the recording once the seismometer detects the shake below threshold
even if it detects the shake above such threshold afterwards, 2) while the
recording device was meant to restart the recording when the shake exceeds
threshold even after the recording was interrupted, program didn!Ct restart
the recording due to the malfunction of recognition of recording material.
NISA accordingly requests TEPCO to report following matters by the following
due date.
1. Fukushima Daiichi and Diani nuclear power station
(1) Result of combining seismic response analysis of the impact from the
shake of the earthquake on reactor building and their important
facilities including PCV and RPV in Unit 2 and 4 of Fukushima Daiichi
nuclear power station.
Due date: June 17, 2011
(2) Result of combining seismic response analysis of the impact from the
shake of the earthquake on reactor building and their important
facilities including PCV and RPV in Unit 1 and 3 of Fukushima Daiichi
nuclear power station.
Due date: July 29, 2011
(3) Result of combining seismic response analysis of the impact from the
shake of the earthquake on reactor building and their important
facilities including PCV and RPV in Unit 5 and 6 of Fukushima Daiichi
nuclear power station and in all units of Fukushima Daini nuclear power
station and result of seismic response analysis of turbine buildings
and major facilities and pipes from earthquake resistance perspective
in both nuclear power station regarding the impact from the shake of
the earthquake.
Due date: August 17, 2011
2. Recording device allocated to collect seismic data
Survey of the malfunction revealed in the report regarding the
recording devices of all kinds of voluntary located seismometers in
TEPCO's all nuclear power station and result of modification made
following the survey.
Due date: June 17, 2011