Posted on 04/13/2011 10:00:10 PM PDT by ransomnote
The No. 1 reactor of the Onagawa nuclear power plant in Miyagi Prefecture on April 7 sustained a jolt greater than what it was designed to withstand during a strong aftershock from the powerful March 11 earthquake, according to nuclear safety officials.
The finding raises further doubts about the viability of the assumed quake resistance at the Tohoku Electric Power Co. complex, even though it had been shut down safely after the deadly quake last month.
The Nuclear and Industrial Safety Agency has instructed the regional utility serving northeastern Japan to analyze the impact of such a jolt on key facilities at the three-reactor plant, the officials said.
During the aftershock, the biggest after March 11, measuring upper 6 in Miyagi on the Japanese seismic scale of 7, a seismometer at the building housing the No. 1 reactor registered a quake acceleration of 476.3 gal vertically, against the 451 gal assumed for the facility.
The assumed level of the jolt ''shouldn't be exceeded in principle,'' said agency spokesman Hidehiko Nishiyama. ''While I intuitively think that if it is this much, it shouldn't be a cause for concern, but we still have to evaluate its safety.''
None of the reactors at the plant was operating when the aftershock struck. But as a result of the temblor, the plant lost part of its external power supply and saw a cooling system for pools storing spent nuclear fuel briefly lose power.
Both the troubled Fukushima Daiichi nuclear power plant in Fukushima Prefecture and the Onagawa plant were hit by the March 11 quake and tsunami, but the latter has been largely under control with its key cooling functions kept alive.
(Excerpt) Read more at english.kyodonews.jp ...
Also, given TEPCO's unfortunate habit of dribbling bad news out late...I am looking at that last sentence in the article once or twice and wondering what it might eventually be revealed to mean. (crosses fingers - please let it not be another 'oh we forgot to tell you but....")
A gal is a derived unit used physics and gravimetry. It is 1 cm/s^2.
Sorry, forgot to add:
So from the use of a unit of acceleration, what they’re talking about is the vertical design parameters for acceleration of the plant (or some aspect of the plant) in an upward direction. The plant will have design parameters for acceleration in horizontal and vertical directions that the structure(s) are supposed to withstand without breaking or failing.
What this amounts to is that the quakes they’re experiencing are exceeding the design parameters of their nuclear plants. This is sort of an obvious factoid by now, but the addition of numbers and units is interesting.
Thanks.I should have been more specific in my mooching. Can you tell me if the article is saying, according to gals, there was more acceleration vertically than anticipated? The ground rose abruptly more swiftly than anticipated? I hadn’t heard of this consideration before - interesting. I would have thought Richter scale would be the calculation and then I imagined horizontal movement as a building breaker.
OK I posted my last at the same time you posted your last. Thanks for the info.
And WRT to the Onagawa plant’s status:
http://www.nisa.meti.go.jp/english/files/en20110414-1.pdf
It appears that they had a couple of the blowout panels on the upper part of the reactor building deformed and they lost some of their off-site power. The power feed is now redundant again, it was down to one off-site feed being left after last Friday’s quake.
Thanks again.
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