Fukushima’s two worst-case scenarios explained by Arnie Gunderson
Wednesday, December 04, 2013 by: J. D. Heyes
(NaturalNews) Recently, Japanese Prime Minister Shinzo Abe ordered the Tokyo Electric and Power Co., or TEPCO, to decommission two more reactors at its Fukushima power plant, which was heavily damaged following an earthquake and tsunami in March 2011.
The reactors, 5 and 6, were not in operation at the time of the tsunami and have been in cold storage since then. Reactors 1, 2 and 3 were heavily damaged and suffered meltdowns; there remains concern about the spent fuel rods in reactor 4.
As Japan prepares to take on the expensive and hazardous task of removing more than 400 tons of irradiated spent fuel rods from the entire plant, nuclear expert Arnie Gunderson, chief engineer at Fair Winds Energy Education, was interviewed by WBEZ‘s “Worldview” about the process and described a pair of worst-case scenarios.
Gunderson said that the easiest part of the process would be removing the fuel rods from the 5 and 6 reactors, but that only highlighted how “truly frightening” the entire removal process would be.
The nuclear expert explained that the fuel rods are stored in a water-filled container that is not much different than an ordinary swimming pool, other than the fact that it is “50 feet deep.” At the bottom of the pool, the nuclear fuel is stored on racks, he said.
During the earthquake in 2011, the plant shook so violently, he said, that nearly four feet of water sloshed out of the pool at reactor 4. At the same time, the fuel racks at the bottom of the pool were damaged.
Worse, he continued, shortly after that, the plant suffered some explosions, which caused the roof over the container pool to collapse in on the pool itself.
“Now, I used to build fuel racks, and the tolerances are very, very high precision,” Gunderson said. “If the fuel is in them, and the rack is distorted, it becomes extraordinarily difficult to pull the fuel out. It’s almost like a pack of cigarettes. You can pull the cigarette out easily unless you distort the pack, in which case it becomes really hard.”
So, he continued, the problem facing engineers at Fukushima – particularly with reactor 4 – is major rack distortion.
At this point, the fuel rods which were the easiest to reach and pull out have been removed. But the job gets much more difficult from here on in.
He described a three-pronged problem.
“First off,” he said, “these racks are no longer as designed. They’ve been beat up by sliding side to side in the earthquake. [Secondly,] they have rubble in the rack. The third piece had to do with the building.”
Gunderson said the building housing reactor 4 was “structurally compromised. There was at least two, if not three, explosions in the building,” leaving no “envelope over [the] top of the fuel pool.”
In order to begin the process of removing the rods, Gunderson said TEPCO constructed a containment building and a sort of “esophagus” surrounding a crane system, so that removal can be effected without spreading radiation.
Two worst-case scenarios
He then went on to describe the two worst-case scenarios:
“First off… [the removal of fuel rods from reactor 4] has to be done. The building is structurally compromised. And unit four [is] worse the than others because it has more nuclear fuel in it. So it’s not something that can be delayed by 10 years or something like that, because the threat of [another] earthquake is significant. And in a compromised building, it could really cause a serious radiation release if the building were to collapse…
“The two problems are snapping the fuel [bundle] as they lift it out – and that’s happened here in the states. Periodically, when you go to pull a bundle out, it gets distorted and it breaks. And inside are radioactive gasses… that are released into the atmosphere.
“The other problem though – and this is unique to the Fukushima site – modern fuel racks have boron in the, um… surrounding the nuclear fuel. And the boron at Fukushima… likely leached out over the past two years, for two reasons. Its water was very hot, it was boiling, and this boron was never designed for boiling water. And on top of that, because they ran out of normal cooling water, they had to add salt water. So, the boron wasn’t qualified for salt water, and especially hot salt water…”
Gunderson said Tokyo Electric has had to add boron to the No. 4 reactor fuel pool, because the company cannot be sure that the boron coating the fuel rods is still there.
“If the fuel gets too close to each other, it could cause a chain reaction in the fuel pool,” he said.
If workers trying to remove the fuel rods noticed boiling in the water, they would have to quickly put the fuel rods back in place, which could, of course, prove tricky. “That assumes that the rod can even be pushed back in,” he said.