Tremors exceeded design limits for 3 reactors

[FBaggins]

The operator of the Fukushima Daiichi nuclear power station says 3 of the plant's 6 reactors were shaken on March 11th by tremors exceeding forces they were designed to withstand. The Tokyo Electric Power Company, known as TEPCO, says reactor No.2 suffered the largest horizontal ground acceleration of 550 gals, which is 26 percent stronger than the reactor's design limit.

TEPCO says the readings were 548 gals at the No.5 reactor, about 21 percent higher than its design limit; and 507 gals at the No.3 reactor, topping the capacity by about 15 percent. The power company says the strength of ground motions were close to or within the design parameters at the remaining 3 reactors, and at all 4 reactors of the nearby Fukushima Daini nuclear plant.

The utility says it was planning to reinforce the reactors so they could withstand horizontal shaking of 600 gals, after the government reviewed their quake-resistance standards 5 years ago. But the work was not finished.

http://www3.nhk.or.jp/daily/english/01_39.html

In 2008, they updated the design basis expectations for the location to 600 Galileo, but hadn't modified the plants yet.

Interestingly, the design basis for the Kashiwazaki Kariwa plant was moved to 1,000 gal at roughly the same point (after the 2007 quake). That's pretty incredible. 1,000 gal is essentially 1G of lateral acceleration.

[OKIsItJustMe]

1. TEPCO Press Release (Apr 01,2011) The record of the earthquake intensity observed at Fukushima Daii…

http://www.tepco.co.jp/en/press/corp-com/release/11040103-e.html

Press Release (Apr 01,2011)
The record of the earthquake intensity observed at Fukushima Daiichi Nuclear Power Station and Fukushima Daini Nuclear Power Station (Interim Report)

---

This is the record of the earthquake intensity observed at the lowest 
basement of the reactor buildings of Fukushima Daiichi Nuclear Power 
Station and Fukushima Daini Nuclear Power Station when the 
Tohoku-Taiheiyou-Oki Earthquake occurred approximately at 2:46pm on March 
11th, 2011.

This report also contains Maximum Response Acceleration based on 
"Regulatory Guide for Reviewing Seismic Design of Nuclear Power Reactor 
Facilities (Revised in 2006)".
We will endeavor to keep collecting as much data as possible and examine 
it in more detail.

【Table】
The comparison between Basic Earthquake Ground Motion and the record of 
the earthquake intensity observed at the lowest basement of the reactor 
buildings of Fukushima Daiichi Nuclear Power Station and Fukushima Daini 
Nuclear Power Station when the Tohoku-Taiheiyou-Oki Earthquake occurred. 


【Reference】
Threshold for reactor scram at each unit(The reactor automatically stops 
if the intensity of the quake exceeds the threshold.)


Glossary
· Observed Record of Earthquake Intensity
    Record that indicates the intensity of an earthquake (Unit: gal)

· Regulatory Guide for Reviewing Seismic Design of Nuclear Power Reactor 
  Facilities
    Revised in September 2006 based on the newly accumulated knowledge on 
    seismology and earthquake engineering and advanced technologies of 
    seismic design, this is a regulatory guide in reviewing the validity 
    of the seismic design of nuclear power reactor facilities.

· Basic Earthquake Ground Motion Ss
    A basic earthquake ground motion in seismic design of facility, 
    stipulated in Regulatory Guide for Reviewing Seismic Design of Nuclear 
    Power Reactor Facilities


· Maximum Response Acceleration against Basic Earthquake Ground Motion Ss
    Assuming Basic Earthquake Ground Motion Ss in the evaluation of the 
    earthquake-proof safety, this is the Maximum value of the quake of a 
    building, which is expressed in acceleration.

[Fledermaus]

2. nuclear energy = FAIL!

[bananas]

3. reactor #4 had a manufacturing flaw - good thing it was off at the time

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=102x4783516

Fukushima Engineer Says He Covered Up Flaw at Shut Reactor

Source: Bloomberg

One of the reactors in the crippled Fukushima nuclear plant may have been relying on flawed steel to hold the radiation in its core, according to an engineer who helped build its containment vessel four decades ago.

Mitsuhiko Tanaka says he helped conceal a manufacturing defect in the $250 million steel vessel installed at the Fukushima Dai-Ichi No. 4 reactor while working for a unit of Hitachi Ltd. (6501) in 1974. The reactor, which Tanaka has called a “time bomb,” was shut for maintenance when the March 11 earthquake triggered a 7-meter (23-foot) tsunami that disabled cooling systems at the plant, leading to explosions and radiation leaks.

“Who knows what would have happened if that reactor had been running?” Tanaka, who turned his back on the nuclear industry after the Chernobyl disaster, said in an interview last week. “I have no idea if it could withstand an earthquake like this. It’s got a faulty reactor inside.”

Tanaka’s allegations, which he says he brought to the attention of Japan’s Trade Ministry in 1988 and chronicled in a book two years later called “Why Nuclear Power is Dangerous,” have resurfaced after Japan’s worst nuclear accident on record. The No. 4 reactor was hit by explosions and a fire that spread from adjacent units as the crisis deepened.

<snip>

Read more: http://www.bloomberg.com/news/2011-03-23/fukushima-engineer-says-he-covered-up-flaw-at-shut-reactor.html