Fuel removal of Fukushima Reactor 4 commences: decommissioning of the crippled nuclear power plant enters a new stage
核燃料取り出し開始 廃炉作業、新段階 福島４号機
November 19, 2013
Originally posted by Kahoku Shimpo
Originally posted by Kahoku Shimpo
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| Reactor 4 SFP (Spent Fuel Pool) slated for removal operation Source: TEPCO (8 Nov 2013) *Japanese *Click the image to enlarge |
According to Kahoku Shimpo, as part of a cleanup process of the crippled Fukushima Daiichi Nuclear Power Plant, its operator Tokyo Electric Power Co. (TEPCO) has commenced its operation of removing the nuclear fuels from Reactor No. 4 this Monday. The removal of spent fuels from the crippled reactors "will mark the beginning of a new stage of the plant's decommissioning process that is estimated to take at least four decades," Miyagi Prefecture's local newspaper reported.
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| Underwater fuel removal process Source: Fukushima Daiichi Nuclear Power Station Fuel Removal from Reactor 4 Spent Fuel Pool (Nov 2013) |
According to the report, the removal of the first fuel assembly started at 3:18 p.m. of the same day. The operators manipulated the "fuel handling machine" and lifted the 4.5-meter-long "fuel assembly", in a pace of one centimeter per second, and then transferred it onto a 5.5-meter cask--a steel-made transfer chamber that weighs 90 tons if willed to maximum capacity--in the the water. The operation was repeated for 40 minutes per unit, completing the loading of four units by 6:45 p.m. to end the operation for the day.
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Kahoku reports that the task of loading the cask with 22 fuel assemblies is to be completed by Tuesday afternoon (November 19). The loaded cask itself will then be lifted by a large crane and transported to a common storage pool about 100 meters away.
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| Source: Fukushima Daiichi Nuclear Power Station Fuel Removal from Reactor 4 Spent Fuel Pool (Nov 2013) |
The spent fuel pool or SPF still contains the remains of small debris from the blast that destroyed the main reactor building. The assemblies may contact these debris upon their removal. But according to Kahoku, TEPCO says, "We will put safety at the top while proceeding with our operations."
The SPF stores 1,533 units of fuel assemblies, of which 202 are new fuels that are relatively easy to remove. TEPCO plans to remove them first. The remaining 1,331 units that contain highly irradiated spent fuel will all be removed and transferred to the common storage pool by the end of 2014.
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| Source: Fukushima Daiichi Nuclear Power Station Fuel Removal from Reactor 4 Spent Fuel Pool (Nov 2013) |
The SPF of Reactor 4 contains three units of damaged fuel assemblies that are deemed difficult to remove. TEPCO is considering to build a new transport chamber to address this problem.
At the time of the earthquake that crippled the plant two-and-a-half years ago, Reactor 4 was going through a regular inspection and all of its fuels within the reactor core were transferred to the neighboring spent fuel pool, thus managing to avoid core melt down. However, if the water in the SPF is depleted, a massive amount of highly irradiated substances could leak out. The international community has been imploring TEPCO to address the problem and secure a safe storage of the spent fuels.
The removal of the fuels from Reactors 1-3 is to commence after 2015, but the recent revelation of the fact that 70 out of 292 units of fuel assemblies stored in Reactor 1 are damaged is raising concerns of its impact to the entire removal schedule. (related story)
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| Source: Safety Measures etc. concerning Fuel Removal from Unit 4 in Fukushima Daiichi NPS (5 Nov 2013) |
Kahoku's Editorial Comment:
The excuse of "unexpected events" is no longer acceptable
As the operation of removing the spent fuel from Reactor 4 commences, TEPCO is seeing this as a rare opportunity to demonstrate that everything is proceeding as planned in the decommissioning process of the crippled Fukushima Daiichi Power Plant, as they have been under a strong criticism in the way it has dealt with problems like contaminated radioactive water leakage and 'unexpected' blackouts, having the tendency to "approach issues with an optimistic outlook." Hence, TEPCO has placed the removal operation as one of its chief goals for the time being.
One of the major concerns over the removal operation is the possibility that the fuel cask may fall. If it falls from five stories above the reactor building, it could damage the fuel assemblies. If the cast breaks, a highly irradiated substances may be dispersed into the air, causing a severe problem.
TEPCO claims that they have prepared for everything that they can expect. They say they have prepared not only for the falling of the cask but for each cases, for example on emergency cooling of the SPF, leakage of the water in the SPF, earthquakes, fires, and even accidents caused by the transport trailers. So they have prepared a case-by-base scenario, but what if they happen simultaneously all at once in multiple instances? TEPCO assumes, "Such a thing will never happen."
In normal operation, the cranes transferring the fuel assemblies operate automatically. However, in this operation, it is done manually by the operator. The operator will wear a full-sized mask that may narrow the field of vision. There is no guarantee that there will be no human error caused due to difference in the operational environment.
The disaster that crippled the site two years and eight months ago occurred in multitude of instances. TEPCO must be vigilant on their plans that extend to the end of next year to ensure that their plans are fool-proof. We can no longer afford to accept the excuses of "unexpected events" any more.
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