Fukushima Reactor No.2, THE most Vulnerable Design

general-electric-boiling-water-reactor-mark-I (Fukushima Daiichi No. 2)

The nuclear power reactor of Unit No. 2 at the Fukushima I (Daiichi) power plant, is a General Electric Boiling Water Reactor (BWR) completed during 1974.

The containment designs are referred to by the names Mark I (oldest), Mark II, and Mark III (newest).

The No. 2 reactor at Fukushima Daiichi is a Mark I (oldest).

The No. 2 reactor at Fukushima Daiichi currently has a ‘stuck’ vent valve.

The No. 2 reactor at Fukushima Daiichi is currently suffering a meltdown.

In 1986, Harold Denton, then the NRC’s top safety official, told an industry trade group that the “Mark I containment, especially being smaller with lower design pressure, in spite of the
suppression pool, if you look at the WASH 1400 safety study, you’ll find something like a 90% probability of that containment failing.”

The GE Mark I reactor design is called a “pressure suppression” design. Rather than be built to withstand large pressure increases, General Electric sought with this design to attempt to reduce such increases in an accident scenario. The design has been criticized by independent nuclear experts and even Nuclear Regulatory Commission staff for many years.

In a General Electric Mark I reactor, the containment building is fairly weak and is considered the secondary containment. The primary containment is a steel liner that surrounds the reactor core.

Apparently the GE Mark I pressure suppression containment was conceived as a cost-saving alternative to the larger reinforced concrete containment’s.

From NIRS,
A report by NRC published in 1993 confirmed that age-related degradation in BWRs (Boiling Water Reactors) will damage or destroy many vital safety-related components inside the reactor vessel before the forty year license expires. The NRC report states “Failure of internals could create conditions that may challenge the integrity the reactor primary containment systems.”

The study looked at major components in the reactor vessel and found that safety-related parts were vulnerable to failure as the result of the deterioration of susceptible materials (Type 304 stainless steel ) due to chronic radiation exposure, heat, fatigue, and corrosive chemistry. One such safety-related component is the core shroud and it is also an indicator of cracking in other vital components through the reactor made of the same material.

Update, 14-Mar, 2300 UTC
The No. 2 reactor at Fukushima Daiichi has just reportedly exploded

(Updates on the Fukushima situation here)

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  1. You sure about the MOX in #2? Everything I’ve seen indicates 32 fuel bundles of MOX in #3, not #2

    1. @Puff, thanks for the heads-up. I believe that there is no MOX in No. 2 (It’s No. 3 – which I had reported in an earlier post… too many numbers to keep track of ;) My mistake. Will correct the post…

  2. Now there is a fire at #4, probably the spent fuel. If that gets out of hand its going to be hard to bleed n’ feed the three crippled reactors with out killing a bunch of workers.

    1. @odk, They are GE designed, but I do not know if the components were built in Japan or the U.S., I do know that approximately 25 percent of the U.S. nuclear reactors are of the same design, according to an interview with one of the engineers during that era.

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