Rebuilding after successful repair works'Densimet' removalThe rebuilding |
 New ‘day-light’ lighting system in the reactor hall.  The ‘Zero Time Point’ inspection. |
Rebuilding after successful repair worksAfter the successful repair of the High Flux Reactor cooling water pipes, the project team has worked in recent weeks on rebuilding the interior of the reactor vessel, the subpile room (the room directly under the core) and the additional control systems. There have been no safety incidents during the repair period and the radiation dose levels for internal and external employees have remained well below the planned limits. After the positive ‘Zero Time Point’ inspection of the repaired pipework and extensive safety testing, the “densimet” shielding was removed from the bottom of the reactor vessel. The reassembly of the reactor components is now almost completed and the rebuilding of the subpile room facilities is progressing according to plan. This week the control rod drive systems will be put back in place. As the High Flux Reactor is not in operation, some additional improvements and maintenance have also been executed. Providing the reactor hall with a new “day-light” lighting system is one of them. The repair of the High Flux Reactor is proceeding well. Safety and quality remain the paramount concern. The preparation activities required for first start-up should be completed by the end of August and NRG expects to achieve the first HFR Full Power Day (45 MW) on September 9. Update
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 The densimet removal takes place using specially fabricated tools.  The practical skills of the team have significantly increased. |
'Densimet' removalAll of the ‘densimet’ radiation protection material was successfully removed from the reactor pool by Wednesday the 4th of August. The team had acquired a lot of practical experience with this work during the loading process; so the removal of the ‘densimet’ proceeded well and without any difficulties. Shielding Project Managers Johan Best and Chris van Wijk look back on the project. Van Wijk: “The removal took place using tools specially fabricated for this purpose. Despite these tools, a lot of skill and handcraft was required to ensure the controlled removal of the ‘densimet’ components. We used underwater cameras because some parts were not easily accessible. Good lighting during the work was also very important.” The densimet radiation shielding has proven it’s value, the radiation dose levels in both reducers remained well controlled and low enough to enable the repair work. Safety and the precise execution of the procedures had the highest priority during the shielding project. “Furthermore, we paid constant attention to the ergonomics of the work that was performed”, adds Mr. Van Wijk. “This approach has led to a good result, we experienced no safety incidents or technical problems. As a result of this project our practical skills of working underwater with shielding have significantly increased. This is something we will profit from in our future daily work. The combination of solid planning and work preparation, where the theory and the practice go hand in hand, has demonstrated that we are able to cope with very complex tasks. With this work we accomplished a genuine achievement to be proud of.” |
 A birdsview of the reactor hall.  Schematic representation of the reactor and the subpileroom. |
The rebuildingNow that the repair works have been completed, the reactor vessel, the subpile room and coolingwatersystems are being reconstructed. After the removal of the “densimet” shielding a first visual inspection was made in and around the reactor vessel. Following that all the reactor vessel parts were built up, including the all the individual components in the subpile room, the space directly under the reactor vessel. Before the repair started, all the fuel rods, traction systems and reactorvessel internals were carefully removed to make access to the reducers possible. Head Mechanical Service Wilko Wijkenga: “We have encoded all of the parts we removed so that we can replace them precisely. During the repair period of the reducers we have taken the opportunity to overhaul all moving parts. We normally do that with three of the six control rod mechanisms every year. Now we have completed all six at once”. The reconstruction of the reactor parts requires a great deal of precision. Everything needs to be brought into position with millimeter accuracy. “The reassembly of the control mechanisms after a routine maintenance is normal for us”, explains Mr. Wijkenga. “However, it is the first time that we have reinstalled all six drive mechanisms at one time. Everything is proceeding according to plan and we expect to complete the reconstruction and make the final adjustments by the end of this week.” |