Progress toward decommissioning: Fuel removal from the spent fuel pool (SFP)
Immediate targets
Commence fuel removal from the Unit 1-3 Spent Fuel Pools
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.
Unit 4
Fuel removal status
- 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.
Unit 3
- Prior to the installation of a cover for fuel removal, removal of large rubble from the spent fuel pool was completed in November 2015.
- To ensure safe and steady fuel removal, training of remote control was conducted at the factory using the actual fuel-handling machine which will be installed on site (February . December 2015).
- Measures to reduce dose on the Reactor Building top floor (decontamination, shields) were completed in December 2016.
- Installation of a cover for fuel removal and a fuel-handling machine is underway from January 2017.
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.
Unit 1
Dismantling of wall panels
- 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 was dismantled to remove rubble from the top of the operating floor, with anti-scattering measures steadily implemented.
- All roof panels and wall panels of the building cover were dismantled by November 10, 2016.
- Following the investigation into the status of rubble on the operating floor, pillars and beams of the building cover will be modified and windbreak sheets installed. Thorough monitoring of radioactive materials will continue.
(*1) Operating floor: During regular inspection, the roof over the reactor is opened while on the operating
floor, fuel inside the core is replaced and the core internals are inspected.
Flow of building cover dismanting
Unit 2
- To facilitate removal of fuel assemblies and debris in the Unit 2 spent fuel pool, the scope of dismantling and modification of the existing Reactor Building rooftop was examined. From the perspective of ensuring safety during the work, controlling impacts on the outside of the power station, and removing fuel rapidly to reduce risks, we decided to dismantle the whole rooftop above the highest floor of the Reactor Building.
- Examination of the following two plans continues: 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 from the pool.
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)
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.