The reactors in Japan are GE BWR (boiling water reactor) with MK I containment systems.

[Statistical]

The MK I containment system was a designed by GE to save money. The system has been criticized even by nuclear proponents and nuclear engineers.

Building strong enough primary containment is a difficult and expensive challenge. GE solution was to use a suppression pool to reduce this cost. If the reactor had a significant pressure spike then excess steam would be vented into a suppression pool also called the torus. The vents open underwater in the suppression pool so steam would be cooled as it passes through the water and pressure would drop.



Here is a shot of a GE MK I being built (in Alabama). The central structure is the reactor pressure vessel. When finally finished primary containment will surround this with reinforced steel and concrete. The "ring" at the bottom of the suppression pool.

By using the suppression pool as a "shock absorber" a smaller, weaker primary containment could be built. This is also why the reactor diagrams look very "crowded". Most containment buildings are expensive but large this allows for a less crowded layout. The GE design used a smaller building so all the equipment is crammed into a smaller space. One of the flaws is that the suppression pool is located outside of primary containment so if the suppression pool breaks or raptures primary containment is compromised. Also if water can't be replaced in suppression pool the "shock absorber" capability is also lost meaning future transients can damage primary containment.

There is no technical advantage to using a system like this. The only advantage is cost. You couldn't build a reactor with this design today .

In the US there are 23 reactors using the MK I containment system that are still operating:

Plant Name					STATE	OL Issued	OL Renewed	OL Expires
Browns Ferry Nuclear Plant, Unit 1		AL	12/20/1973	5/4/2006	12/20/2033
Browns Ferry Nuclear Plant, Unit 2		AL	8/2/1974	5/4/2006	6/28/2034
Browns Ferry Nuclear Plant, Unit 3		AL	8/18/1976	5/4/2006	7/2/2036
Brunswick Steam Electric Plant, Unit 1		NC	9/8/1976	6/26/2006	9/8/2036
Brunswick Steam Electric Plant, Unit 2		NC	12/27/1974	6/26/2006	12/27/2034
Cooper Nuclear Station 				NE	1/18/1974			1/18/2014
Dresden Nuclear Power Station, Unit 2		IL	2/20/1991	10/28/2004	12/22/2029
Dresden Nuclear Power Station, Unit 3		IL	1/12/1971	10/28/2004	1/12/2031
Duane Arnold Energy Center			IA	2/22/1974			2/21/2014
Edwin I. Hatch Nuclear Plant, Unit 1		GA	10/13/1974	1/15/2002	8/6/2034
Edwin I. Hatch Nuclear Plant, Unit 2		GA	6/13/1978	1/15/2002	6/13/2038
Fermi, Unit 2					MI	7/15/1985			3/20/2025
Hope Creek Generating Station, Unit 1		NJ	7/25/1986			4/11/2026
James A. FitzPatrick Nuclear Power Plant	NY	10/17/1974	9/8/2008	10/17/2034
Monticello Nuclear Generating Plant, Unit 1	MN	1/9/1981	11/8/2006	9/8/2030
Nine Mile Point Nuclear Station, Unit 1		MI	12/26/1974	10/31/2006	8/22/2029
Oyster Creek Nuclear Generating Station, Unit 1	NJ	7/2/1991	4/8/2009	4/9/2029
Peach Bottom Atomic Power Station, Unit 2	MI	10/25/1973	5/7/2003	8/8/2033
Peach Bottom Atomic Power Station, Unit 3	MI	7/2/1974	5/7/2003	7/2/2034
Pilgrim Nuclear Power Station			MI	6/8/1972			6/8/2012
Quad Cities Nuclear Power Station, Unit 1	IL	12/14/1972	10/28/2004	12/14/2032
Quad Cities Nuclear Power Station, Unit 2	IL	12/14/1972	10/28/2004	12/14/2032
Vermont Yankee Nuclear Power Plant, Unit 1	VT	3/21/1973			3/21/2012

[Raschel]

1. So what's the news today? Is everything still "stable" over there?

[Thunderstruck]

4. Edano said they can't accurately measure the radioactive material in the

atmosphere so they are basing numbers on simulations instead. So, suddenly after decades of nuclear science it is no longer possible to measure radioactive particles in the air and simulations are considered good enough for the public.

[Aerows]

7. If you don't like the numbers...

...you decide you don't trust them and make new ones up, I guess.

[Raschel]

8. When did he say that? And haven't they been measuring it in the air this whole time?

The reporting from this is totally confusing me still. :banghead:

[Marblehead]

2. GE brings good things

to life:(

[M155Y_A1CH]

3. Quote from your OP

"One of the flaws is that the suppression pool is located outside of primary containment
so if the suppression pool breaks or raptures primary containment is compromised."

Is this related to Tokyo's water problems? :shrug:

:kick: &R

[Statistical]

5. I don't know.

I remember last week when there was an explosion in reactor #2 building but the walls and roof didn't explode outward. The press release indicate the explosion occurred near the suppression pool.

[M155Y_A1CH]

6. Wow, you're right

I seem to remember it was the talk about a particular incident;
sometime in the past few days, I think.

:wow:

[Statistical]

9. Kick. n/t