Fukushima Daiichi’s Unit 4 Spent-Fuel Pool Up Close
By Phred Dvorak
Tokyo Electric Power Co. is pulling out the stops to show a skeptical world that the troubled reactors at Fukushima Daiichi — and in particular the “spent-fuel pool” atop reactor Unit 4 — won’t collapse and spill out radioactive fuel during the next big earthquake.
- Reuters
- The Unit 4 reactor building is seen at the Fukushima Daiichi nuclear power plant on May 26.
On Saturday, Tepco let a bunch of journalists, as well as Goshi Hosono, the minister in charge of Fukushima Daiichi cleanup, into the Unit 4 building to take a look for themselves.
What did they see? JRT annotates this account, from a pool report of the tour, made available to the foreign press.
The group — suited in a double layer of protective Tyvek — went into the building and climbed a narrow staircase to get to the pool, an 11-meter deep well that stretches between floors three and four. The staircase — around 150 steps, rising 40 meters — was mostly dark, with fluorescent lights at each landing.
Radiation spiked on the second floor at 500 microsieverts per hour — somewhat less than you’d get from a stomach X-ray, and roughly 220 times higher than the level Japan sets for evacuating communities. By the fourth floor, near the top of the building, where an explosion during the nuclear accident a year earlier had blown off the ceiling and bits of walls, readings were down to 300 microsieverts per hour.
The group paused to look at the concrete ceiling under the pool (“very clean, with no cracks,” Tepco’s guide noted). Then they went to the top of the building to look at the pool itself — though they couldn’t see in, since it was covered with a white tarp, supported by a lattice of blue floats. When workers lifted the tarp, reporters saw water, but not the fuel racks, which were too far below the surface. Outside the building was a crane, for use in erecting a huge cover over the top of the reactor building that will keep radioactive material from scattering when workers start removing the fuel, toward the end of next year.
So, is the Unit 4 pool and its cargo of hazardous nuclear-fuel rods safe from collapse? Mr. Hosono seemed largely satisfied. He endorsed Tepco’s analysis that the building could withstand a quake like last year’s, and said there was no need to cancel plans for a partial return of evacuees to nearby areas.
“A variety of concerns have been raised about the spent-fuel pool at Unit 4, and my goal was to assess the situation directly,” he said at a press briefing at the nearby J-Village soccer stadium that’s been converted into a staging area for workers going to the crippled plant.
Mr. Hosono added he’d instructed Tepco to thoroughly check out a three centimeter bulge in the west wall of the building, which Tepco thinks was likely caused by last year’s explosion. Next week, the government and Tepco are meeting to discuss whether they could get the fuel out of the Unit 4 pool faster, he said.
Fukushima Daiichi’s Unit 4 Spent-Fuel Pool: Safe or Not?
By Phred Dvorak
Questions have been bubbling recently over how safe Japan’s stricken Fukushima Daiichi nuclear plant—in particular the pool atop Unit 4, where some 1,535 fuel assemblies are stored—would be if another big earthquake hit.
- Associated Press
- The Unit 4 reactor building at Fukushima Daiichi in February
Plant operator Tokyo Electric Power Co. has been taking steps recently to address that issue, and last month it invited legislator Ikko Nakatsuka, Japan’s senior vice-minister for reconstruction, to check its work.
The bottom line: The steps Tepco has taken look fine, Mr. Nakatsuka said—as far as they go. Speaking to reporters Monday at the Foreign Correspondents’ Club of Japan, Mr. Nakatsuka stayed determinedly away from making big-picture conclusions. And in the wake of last year’s accident, he said, the government has learned there’s no such thing as absolutely safe.
“When we say ‘safe,’ we have to say at what (risk) level,” Mr. Nakatsuka said.
JRT readers may recall that Fukushima Daiichi’s Unit 4 has been the subject of concern because at the time of the March 11 earthquake and tsunami last year the reactor was undergoing a major refurbishing, and its fuel rods were all in the spent-fuel pool for safekeeping. Some nuclear activists and concerned politicians, like U.S. Senator Ron Wyden, have been warning that if another big earthquake hits, the pool could collapse or leak, potentially releasing dangerous amounts of radiation.
On April 23, Tepco took Mr. Nakatsuka inside the reactor 4 building to look at the concrete-and-steel supports it had built under the spent-fuel pool. Then Mr. Nakatsuka went to the fifth floor to witness a test that showed the building—which suffered an explosion last year that blew off the roof and some of the upper walls—wasn’t listing to one side.
Tepco analysis shows the building could survive forces equivalent to those that shook the site during the March 11 quake, Mr. Nakatsuka said.
But just how big an earthquake could Unit 4 withstand before it collapses? That’s one of many questions from reporters that Mr. Nakatsuka and the head of the Nuclear and Industrial Safety Agency’s seismic safety unit evaded or wouldn’t answer. Some others: What plans does the government have in case the pool does come down? What’s the biggest risk at the plant now?
Asked whether he’s satisfied with the safety checks Tepco has done so far, Mr. Nakatsuka answered, “I trust each one they’ve done.” But he added that more steps might be in order—like picking up the pace of plant cleanup.
Corrections & Amplifications: There are 1,535 fuel assemblies in the Unit 4 pool, each containing some 50 to 70-odd nuclear fuel rods. JRT incorrectly said earlier that there were 1,535 fuel rods.
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