my.firedoglake.com
These spent fuel pools are more vulnerable to disaster than the core – the containment may well remain intact but those fuel pools are more vulnerable. It’s hard to imagine they haven’t been compromised in these explosions.
Robert Alverez has a blog at the Instititute for Policy Studies – he’s a Senior Scholar and former DOE official:
ips-dc.org
Along with the struggle to cool the reactors is the potential danger from an inability to cool Fukushima’s spent nuclear fuel pools. They contain very large concentrations of radioactivity, can catch fire, and are in much more vulnerable buildings. The ponds, typically rectangular basins about 40 feet deep, are made of reinforced concrete walls four to five feet thick lined with stainless steel.
The boiling-water reactors at Fukushima — 40 years old and designed by General Electric — have spent fuel pools several stories above ground adjacent to the top of the reactor. The hydrogen explosion may have blown off the roof covering the pool, as it’s not under containment. The pool requires water circulation to remove decay heat. If this doesn’t happen, the water will evaporate and possibly boil off. If a pool wall or support is compromised, then drainage is a concern. Once the water drops to around 5-6 feet above the assemblies, dose rates could be life-threatening near the reactor building. If significant drainage occurs, after several hours the zirconium cladding around the irradiated uranium could ignite.
Then all bets are off.
On average, spent fuel ponds hold five-to-ten times more long-lived radioactivity than a reactor core. Particularly worrisome is the large amount of cesium-137 in fuel ponds, which contain anywhere from 20 to 50 million curies of this dangerous radioactive isotope. With a half-life of 30 years, cesium-137 gives off highly penetrating radiation and is absorbed in the food chain as if it were potassium.
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This is an interview of David Lochbaum, nuclear safety engineer of the Union of Concerned Scientists and a consultant to both industry and the Nuclear Regulatory Commission by Roger Witherspoon – this was after the Unit 1 explosion:
spoonsenergymatters.wordpress.com
The acid could also be used to help prevent a far more serious melt down in the spent fuel pool. The explosion, said Lochbaum, as dramatic as it was, was not likely to have been strong enough to destroy the walls of the spent fuel pools, which usually consist of about five feet of reinforced concrete. These reactors have 6 spent fuel pools above the reactors.
But water containing boric acid has to continually circulate in the pool to keep the bundles cool. When the power was lost at the site, the cooling system for the pools stopped. And the batteries used to try and restore cooling to the reactor vessel itself are not strong enough to also operate cooling systems for pool. On average, the water in these pools would heat up and evaporate to the point where the tops of the fuel bundles were exposed about 24 hours after the cooling system shut down.
In addition, if the explosion knocked debris from the roof into the pool, it could interfere with natural convection cooling of some of the fuel bundles, or even break some of them, sending the irradiated fuel chunks to the bottom of the pool where they could reach critical mass. Boric acid could be added to the pools to help prevent that development.
Witherspoon’s followup:
spoonsenergymatters.wordpress.com
And then, there is the unspoken issue: the spent fuel pool.The most extensive assessment of the damage to be wrought by an exothermic fire in a spent fuel pool was developed by the Nuclear Regulatory Commission in October, 2000, and removed from public view following the September 11, 2001 terrorist attacks. The report is available here: bit.ly.
According to Paul Gunter of the non-profit Beyond Nuclear, information is crucial at this time — but it is just not available. The reactors at Fukushima have six separate spent fuel pools, each located above the reactors. If the reactors are overheating, is the spent fuel above them being slowly grilled?
The situation, particularly in light of the second explosion at Fukushima Daiichi Unit 3, raises these questions:
1. Why hasn’t the government mentioned the disposition of the stored fuel in these pools?
2. Has the water level dropped to the point where these fuel rods are exposed.
3. Have any of them begun burning?
4. What steps, if any, can they take to prevent an exothermic fire in the spent fuel pools.
The link is to a PDF titled Technical Study of Spent Fuel Accident Risk at Decommissioning Nuclear Plants |
