Friday, 7 September 2012

Beyond Nuclear Fact Sheet Catastrophic Risks of GE BWR Mark I

High-Level Radioactive Waste Storage Pools

High-Level Radioactive Waste Storage Pool Fire at Fukushima Daiichi



The Fukushima Nuclear Catastrophe has clearly shown just how risky General Electric Boiling Water Reactors of the Mark I design are, including their high-level radioactive waste (HLRW) storage pools. Although the U.S. nuclear power establishment is still trying to deny it, evidence has mounted that Fukushima Daiichi Unit 4’s pool boiled dry to the point that highly radioactive irradiated nuclear fuel assemblies were exposed to air overheated, caught fire, and discharged catastrophic amounts of radioactive cesium-137 directly into the environment. This is because GE BWR Mark I pools – as with most pools at nuclear plants – are not locate within a primary radiological containment structure. Also, at Fukushima the reactor meltdowns and explosions damaged or destroyed the secondary containment structures (referred to as reactor buildings), at Units 1, 3 and 4, leaving those pools open to the sky. Unit 1 has since been covered with a tent. Unit 2 did suffer relatively small hole in its reactor building, as well.

As Stohl et al. have reported: “Our results indicate that 137Cs emissions peaked on 14–15 March but were
generally high from 12 until 19 March, when they suddenly dropped by orders of magnitude exactly when
spraying of water on the spent-fuel pool of unit 4 started. This indicates that emissions were not only coming
from the damaged reactor cores, but also from the spent-fuel pool of unit 4 and confirms that the spraying wa an effective countermeasure.”1 Thus, the HLRW fire in the Unit 4 storage pool caused some of the worst
radioactive Cs-137 releases during the catastrophic first week at Fukushima. It was his concern that the Unit 4 pool had boiled dry that prompted U.S. Nuclear Regulatory Commission (NRC) Chairman Gregory Jaczko, in the very first days of the catastrophe, to order an emergency warning to Americans in Japan to evacuate to at least 50 miles away from the Fukushima Daiichi nuclear power plant.

The Reactor No. 4 pool contained 135 tons of irradiated nuclear fuel; Reactor No. 1’s pool had 50 tons, No. 2’ 81 tons, and No. 3’s 88 tons. It took months for Tokyo Electric Power Company (TEPCO) and emergency responders to restore regular cooling water flow to certain of the pools. Some may still lack it. To restore water to the pools, as the thermally hot irradiated nuclear fuel boiled it away, ad hoc cooling efforts have include attempts to drop water by helicopter, as well as water spraying by fire truck, concrete pump truck, and even rio control water cannons. The Unit 4 reactor building is severely listing; its pool floor is supported by steel jacks for fear that it could fall out. A large aftershock could collapse the pool, instantly drain its cooling water, an reignite a radioactive waste fire. Unit 3’s pool appears filled with debris, so the condition of its irradiated fuel i unclear. Given the dangers on-site, including high radiation dose rates, when and how TEPCO and/or th Japanese federal government will be able to remove the HLRW to a safer location is yet to be determined Also, it is unclear when, or even if, a close examination of the four pools will occur, to determine what exactly happened where, why, and how bad the radioactivity releases have been.
What are the risks?

While all nuclear power plant HLRW storage pools are risky, GE BWR Mark I pools are especially vulnerable to accidents or attacks. A boil down or drain down of the cooling water could spark a fire in the irradiated fuel, as seen at Fukushima. GE BWR Mark I pools are elevated four to six stories high, above the reactor as well as outside the primary containment structure. The reactor building is not robust, as shown by the explosions at Fukushima. The design made it easier for the plants to remove irradiated fuel from the reactor core directly into the pool, but puts the pools at increased risk of heavy load drops, attacks by airplanes, etc. Emergency response is complicated by the pools’ high elevation above ground. NRC has not required pools to have emergency backup power connected to cooling systems, nor emergency make up water. Thus, they...(Keep reading http://www.beyondnuclear.org/storage/catastrophic%20risks%20of%20GE%20BWR%20Mark%20I%20HLRW%20storage%20pools.pdf )

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