Progress toward decommissioning: Fuel removal from the spent fuel pool (SFP)
Work to help remove spent fuel from the pool is steadily progressing while ensuring seismic capacity and safety. The removal of spent fuel from the Unit 4 pool commenced on November 18, 2013 and was completed on December 22, 2014.
Fuel removal from the Unit 4 spent fuel pool
- In the Mid- and Long-Term Roadmap, the target of Phase 1 involved commencing fuel removal from inside the spent fuel pool (SFP) of the 1st Unit within two years of completion of Step 2 (by December 2013). On November 18, 2013, fuel removal from Unit 4, or the 1st Unit, commenced and Phase 2 of the roadmap started.
- On November 5, 2014, within a year of commencing work to remove the fuel, all 1,331 spent fuel assemblies in the pool had been transferred. The transfer of the remaining non-irradiated fuel assemblies to the Unit 6 SFP was completed on December 22, 2014. (2 of the non-irradiated fuel assemblies were removed in advance in July 2012 for fuel checks)
- This marks the completion of fuel removal from the Unit 4 Reactor Building.
- Based on this experience, fuel assemblies will be removed from Unit 1-3 pools.
* A part of the photo is corrected because it includes sensitive information related to physical protection.
Check of the soundness of the Reactor Building
- Regular inspections have been conducted, which have confirmed that the soundness of the Reactor Building has been maintained.
Inspecting the soundness of fresh fuel (unirradiated fuel) inside the Unit 4 SFP
- In order to inspect the status of fuel corrosion to fresh fuel assemblies were removed from the pool and soundness was evaluated (August 27 through the 29th)
- The inspection revealed no significant information or damage to the fuel rods were fuel structures, and no corrosion was found, and it was therefore concluded that material corrosion will not have a large impact on fuel removal.
Main works to help remove spent fuel at Unit 3
- To facilitate the installation of a cover for fuel removal, measures to reduce dose (decontamination and shielding) and rubble removal from the spent fuel pool are underway.
- (Decontamination and shielding: from October 15, 2013, rubble removal from the pool: from December 17, 2013)
- On August 2, 2015, the fuel-handling machine, the largest rubble which fell in the Unit 3 spent fuel pool (approx. 20t), was removed. To facilitate fuel removal, rubble removal from the spent fuel pool and dose reduction on the top floor of the Reactor Building will continue. In tandem with these works, training of fuel removal by remote control is underway.
Removal of debris from top of Unit 3, Unit 4 reactor buildings and construction of Unit 4 cover for fuel removal
- Debris is currently being removed from the top of the Unit 3 reactor building in preparation for fuel removal from the spent fuel pool ( to be completed around the end of FY2012)
- Unstable pieces of steel girder fell into the fuel pool during debris removal at Unit 3. A report on the cause of this incident and reoccurrence prevention countermeasures was submitted to the Nuclear Regulatory Commission (10/3,19 and 11/15). Debris removal work will continue safely and steadily based on this report.
- At Unit 4 building debris was removed on July 11 and large equipment was removed between July 24 and October 2. debris is currently being gathered (until December). In conjunction, a fuel removal cover continues to be built (to be finished around the middle of FY2013)
Unit 3, Unit 4 SFP debris dispersion survey
- Underwater cameras and remotely operated vehicles (ROV) were used to survey the dispersion of debris within the spent fuel pools.
- An underwater debris removal plan prior to spent fuel removal shall be proposed based on the results of the survey.
Main works to help remove spent fuel at Unit 1
- Regarding fuel removal from Unit 1 spent fuel pool, there is a plan to install a dedicated cover for fuel removal over the operating floor(*1).
- Before starting this plan, the building cover will be dismantled to remove rubble from the top of the operating floor, with anti-scattering measures steadily implemented.
- On July 28, removal of the roof panels started. All these panels will be removed by the middle of this fiscal year. Dismantling of the building cover will proceed with radioactive materials thoroughly monitored.
Main works to help remove spent fuel at Unit 2
- Regarding fuel removal for Unit 2 spent fuel pool, two plans are being considered: Plan 1 to share a container for removing fuel assemblies and debris from the pool; and Plan 2 to install a dedicated cover for fuel removal.
- As both plans require work areas of large heavy machines, etc. to install a structure for fuel removal and a fuel handling machine, preparatory work is currently underway to construct a yard around the Reactor Building.
Unit 1, Unit 2 operating floor survey
- A survey of the operating floors was conducted in order to help with the deliberation of fuel removal from spent fuel pools.
- At Unit 1 a camera attached to a balloon was used to take footage and to measure dose levels. A maximum dose of 53.6mSv/h was measured at a 1 m from the operating floor.
- At Unit 2 a remote-controlled robot was used to take footage, and measure radiation levels and temperature/humidity levels. A maximum dose of 880mSv/h was measured at the top of the reactor well.
Desalination of Unit 1～4 spent fuel pools
- Unit 1: Saline levels are low enough since seawater was not injected
- Unit 2: Desalination completed on July 2. Water quality being monitored through periodic sampling.
- Unit 3: Being desalinated with desalination equipment
- Unit 4: Desalination completed on October 12. Water quality being monitored through periodic sampling
- Close range chloride ion concentration: Unit 1 5ppm（7/17), Unit 2 28ppm（10/18）Unit 2 72ppm（10/18）, Unit 49ppm（10/18）(Below technical specification limits of 100ppm)
Replacement of fuel rack for common pool
- An open space will be maintained in the common pool (Transfer to the temporary dry cask storage facility)
Progress to date
- The common pool has been restored to a condition allowing it to re-accommodate fuel to be handled (November 2012)
- Loading of spent fuel stored in the common pool to dry casks commenced (June 2013)
- Fuel removed from the Unit 4 spent fuel pool began to be received (November 2013)
(*2) Cask: Transportation container for samples and equipment, including radioactive materials.
Future issues and the direction of countermeasures
Handling the risks associated with earthquakes and tsunami
- Alternative coolant injection equipment, such as concrete pump trucks, having been deployed so as to enable sufficient time to restore cooling function if the fuel pools become unable to be cooled due to damage to primary/secondary pump pipes, etc., by an earthquake or tsunami.
- In this instance, it has been concluded that a minimum of 16 days (Unit 4 ) would be required to reach a point where fuel pool water level is maintained at a certain level (2m from top of active fuel: water level at which shielding is deemed effective) since water temperatures will rise and water levels will decrease.
- Even if it is difficult to cool the pools using emergency coolant injection equipment, and concrete pump trucks, etc., are used to cool the pools, cooling could be restored in approximately 6 hours even if cooling function is lost
- Furthermore, every effort shall be made to comply with newly gained knowledge, including the handling of changes to the reference ground motion.
Issues that may impact work schedules
- The following issues that may impact work schedules must be resolved in order to carry out fuel removal as planned.
- Debris removal work: the status of falling debris within the pools and radiation levels have yet to be confirmed which may prolong work and add to it.
- Fuel removal cover construction: many uncertainties, such as building damage and radiation levels, exist that may prolong or add to work.
- Pool fuel removal work: if more of the fuel than expected is damaged, or if the extent of damage to the fuel is greater than expected, work may be prolonged or added to.
Unit 1, Unit 2 fuel removal
- Detailed plans shall be proposed based on a survey of debris at Unit 1 while acquiring knowledge and experience through removing debris at Unit 3 and Unit 4, the operability and malfunctions of remote operated equipment and fuel surveys, etc.
- Detailed plans for the inspection, repair, and fuel removal at Unit 2 shall be proposed based on the establishment of remote decontamination technology and upon decontaminating the inside of the building, shielding it and conducting surveys at a point in time when fuel handling equipment can be approached.