Fukushima No. 4 reactor saved by upgrade mishap

[kristopher]

Yet another instance where blind luck - not planning, not safety design - was what determined the severity of the meltdowns. They made a mistake in sizing a piece of equipment needed for overhauling the reactor, the end result of which was that there was a large quantity of water available which actually should not have been there to cool #4's fuel pool.

Which side will luck be on next time?

Fukushima No. 4 reactor saved by upgrade mishap
March 08, 2012
By TOSHIHIRO OKUYAMA / Staff Writer

Bungled replacement work and a chance opening in a separator gate very likely saved the No. 4 reactor at the Fukushima No. 1 nuclear power plant from descending into a nightmarish situation, it has been learned.

The governments of Japan and the United States were worried that overheating and the decay of spent fuel rods at the No. 4 reactor could trigger catastrophic developments following the disastrous events of last March 11.

It appears now that the coincidental occurrence of the delayed replacement work and the opening in the separator helped avert the potential scenario of a full-blown meltdown.

The core shroud, a large structure in the reactor core, was undergoing...

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201203080066

[bananas]

1. The reactor vessel also had a flaw

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

Fukushima Engineer Says He Helped Cover Up Flaw
at Dai-Ichi Reactor No. 4

By Jason Clenfield
March 22, 2011 8:54 PM EDT

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

[kristopher]

2. The problem is that this isn't even surprising.

It is all part and parcel of failure in complex systems.

[kristopher]

3. Operator and Swiss Govt Hid Huge Crack in Core Shroud of Mühleberg Nuclear Power Plant in 2009

Core Shroud of Mühleberg Nuclear Power Plant Was Found with a Huge Crack in 2009, Operator and Swiss Government Hid the Fact, Says Japan's Mainichi

(UPDATE) According to Switzerland's Beobachter (in German), the cracks are along the horizontal weld of the shroud, not "top to bottom" as Mainichi describes. The core spray system was also found with cracks. (H/T Atomfritz)

===============================




...

Japan's Mainichi Shinbun (3/8/2012; link goes to a message board with full copy of the article) reports that the plant operator BKW Energy and the nuclear regulating agency of the Swiss government hid the discovery in 2009 of a huge crack in the core shroud inside the Reactor Pressure Vessel.

From Mainichi Shinbun article (part):

ところが、福島原発事故後の昨年6月、地元メディアが、ミューレベルク原発の圧力容器内にある炉心シュラウドという高さ9メートルのステンレス製構造物に、上から下まで貫通するひび割れができていると報道。連邦核安全監督局は「ひび割れがあっても安全基準は満たされており、問題ない」と危険性を否定した。

However, the local media reported in June last year in the wake of the Fukushima I Nuclear Power Plant accident that the 9-meter high stainless-steel core shroud inside the Reactor Pressure Vessel at Mühleberg Nuclear Power Plant [there is only one reactor] had a crack from top to bottom. The federal nuclear safety regulation agency denied the risk, saying "Even if there is a crack, [the shroud] meets the safety standard, and there is no problem."

これを、反原発団体などが「炉心シュラウドは燃料棒や制御棒を囲んでいる大事な構造物で、損傷によって燃料棒がずれるなどの危険がある」と批判。ひび割れが09年には見つかっていながら公表していなかったことへの不信感も加わって、行政裁判所に対し、連邦政府が09年に出した運転許可を無効にするよう求め提訴した。この日の判決で裁判所は、反原発団体の訴えをほぼ全面的に認めた。

Anti-nuclear groups criticized the comment, saying "The core shroud is an very important structure that surrounds nuclear fuel rods and control rods. The damage may cause the fuel rods to shift." The crack had been discovered in 2009 but it was not disclosed. The anti-nuclear group(s?) filed a suit in the Federal Administrative Court demanding the withdrawal of the operation license issued by the federal government in 2009. With the ruling [on March 7], the Federal Administrative Court upheld the complaint from the group.

The crack in the...

http://ex-skf.blogspot.com/2012/03/core-shroud-of-muhleberg-nuclear-power.html