i.e. “conditional maintenance that is carried out following extrapolated forecasts
and an assessment of important parameters indicating the degradation of the good”
(extract from the French standard NF EN 13306 X 60-319).
Preventive maintenance relies on data that serves as objective causes of possible
damage. Even at the design stage of the nuclear power plant at Fukushima Daiichi,
both the idea of an earthquake occurring near the coast, and a tsunami were taken
into account. To reduce the risk of the degradation of facilities, construction standards were applied. To reduce the risks created by a tsunami, dykes, able to stop
waves 5.70 m high were erected around the plant.
3 The height was based on data
related to the region’s history of tsunamis, seismological expertise and wave
dynamics.
The construction of the Fukushima Daiichi plant that began in 1967 was based on the
seismological knowledge at that time. As research continued over the years, researchers
repeatedly pointed out the high possibility of tsunami levels reaching beyond the
assumptions made at the time of construction, as well as the possibility of core damage in
the case of such a tsunami. TEPCO
4 overlooked these warnings, and the small margins of
safety that existed were far from adequate for such an emergency situation [7].
In the case of the Fukushima Daiichi disaster, it is not certain that the tsunami
(the cause) is the only source of the breakdowns (the effect) that led to the nuclear
accident. Other causes can be highlighted, such as the earthquake, poor maintenance, or the organization of work in general.
TEPCO’s report says the first wave of the tsunami reached the site at 15:27 and the second
at 15:35. However, these are the times when the wave gauge set 1.5 km offshore detected
the waves, not the times of when the tsunami hit the plant. This suggests that at least the
loss of emergency power supply A at Unit 1 might not have been caused by flooding [7].
Since 2006, the regulatory authorities and TEPCO have shared information on the possibility of a total outage of electricity occurring at Fukushima Daiichi should tsunami levels
reach the site. They also shared an awareness of the risk of potential reactor core damage
from a breakdown of seawater pumps if the magnitude of a tsunami striking the plant turned
out to be greater than the assessment made by the Japan Society of Civil Engineers. There
were at least three background issues concerning the lack of improvements. First, NISA
[the Japanese regulatory authority] did not disclose any information to the public on their
evaluations or their instructions to reconsider the assumptions used in designing the plant’s
tsunami defences (…). The second issue concerned the methodology used by the Japan
Society of Civil Engineers to evaluate the height of the tsunami. Even though the method
was decided through an unclear process, and with the improper involvement of the electric
power companies, NISA accepted it as a standard without examining its validity. A third
issue was the arbitrary interpretation and selection of a probability theory. TEPCO tried to
justify the belief that there was a low probability of tsunami, and used the results of a biased
3
The tidal wave that followed the magnitude 9.0 earthquake occurred on 11 March, 2011 at 2:46 p.
m. local time reached its maximum height of 23.6 m at Ofunato, in the Iwate Prefecture, north of
Fukushima Daiichi (Executive Summary of Urgent Field Survey of Earthquake and Tsunami
Disasters, 25 March, 2011, Port and Import and Research Institute). The height of a tsunami varies
according to many criteria. It was estimated to be about 14 m at Fukushima Daiichi, while the plant
itself lay at 7 m above sea level.
4
Tokyo Electric Power Company.
24
D. Pecaud
and an assessment of important parameters indicating the degradation of the good”
(extract from the French standard NF EN 13306 X 60-319).
Preventive maintenance relies on data that serves as objective causes of possible
damage. Even at the design stage of the nuclear power plant at Fukushima Daiichi,
both the idea of an earthquake occurring near the coast, and a tsunami were taken
into account. To reduce the risk of the degradation of facilities, construction standards were applied. To reduce the risks created by a tsunami, dykes, able to stop
waves 5.70 m high were erected around the plant.
3 The height was based on data
related to the region’s history of tsunamis, seismological expertise and wave
dynamics.
The construction of the Fukushima Daiichi plant that began in 1967 was based on the
seismological knowledge at that time. As research continued over the years, researchers
repeatedly pointed out the high possibility of tsunami levels reaching beyond the
assumptions made at the time of construction, as well as the possibility of core damage in
the case of such a tsunami. TEPCO
4 overlooked these warnings, and the small margins of
safety that existed were far from adequate for such an emergency situation [7].
In the case of the Fukushima Daiichi disaster, it is not certain that the tsunami
(the cause) is the only source of the breakdowns (the effect) that led to the nuclear
accident. Other causes can be highlighted, such as the earthquake, poor maintenance, or the organization of work in general.
TEPCO’s report says the first wave of the tsunami reached the site at 15:27 and the second
at 15:35. However, these are the times when the wave gauge set 1.5 km offshore detected
the waves, not the times of when the tsunami hit the plant. This suggests that at least the
loss of emergency power supply A at Unit 1 might not have been caused by flooding [7].
Since 2006, the regulatory authorities and TEPCO have shared information on the possibility of a total outage of electricity occurring at Fukushima Daiichi should tsunami levels
reach the site. They also shared an awareness of the risk of potential reactor core damage
from a breakdown of seawater pumps if the magnitude of a tsunami striking the plant turned
out to be greater than the assessment made by the Japan Society of Civil Engineers. There
were at least three background issues concerning the lack of improvements. First, NISA
[the Japanese regulatory authority] did not disclose any information to the public on their
evaluations or their instructions to reconsider the assumptions used in designing the plant’s
tsunami defences (…). The second issue concerned the methodology used by the Japan
Society of Civil Engineers to evaluate the height of the tsunami. Even though the method
was decided through an unclear process, and with the improper involvement of the electric
power companies, NISA accepted it as a standard without examining its validity. A third
issue was the arbitrary interpretation and selection of a probability theory. TEPCO tried to
justify the belief that there was a low probability of tsunami, and used the results of a biased
3
The tidal wave that followed the magnitude 9.0 earthquake occurred on 11 March, 2011 at 2:46 p.
m. local time reached its maximum height of 23.6 m at Ofunato, in the Iwate Prefecture, north of
Fukushima Daiichi (Executive Summary of Urgent Field Survey of Earthquake and Tsunami
Disasters, 25 March, 2011, Port and Import and Research Institute). The height of a tsunami varies
according to many criteria. It was estimated to be about 14 m at Fukushima Daiichi, while the plant
itself lay at 7 m above sea level.
4
Tokyo Electric Power Company.
24
D. Pecaud