Underground final disposal facilities achieve readiness for Trial Run of Final Disposal
Posiva’s preparations for the final disposal of spent nuclear fuel again made significant progress when the building services engineering works in the underground final disposal facilities were completed to readiness for the Trial Run of Final Disposal (TRFD). This means that the underground ventilation and piping systems have been completed and commissioned in the extent required for the TRFD.
- In practice, we have now tested with acceptable results the trouble-free operation of ventilation in the underground repository in both normal operating conditions and special conditions, such as fires – and this covers all the fire compartments of the repository, says Programme Manager Kimmo Kemppainen from Posiva.
According to Kemppainen, the tests related to ventilation during the normal operation of the final disposal facilities were relatively easy to verify. The complexity factor increased with tests pertaining to fires and other special conditions.
- The underground facilities of ONKALO® are divided into several fire compartments. The repository-level tests cover a fire in each of them, with the fire detectors activated to issue an alarm and the automatic system to move fans and smoke control dampers into appropriate positions. All in all, the air systems of the final disposal repository include dozens of chambers and hundreds of control dampers. The recent tests were designed to verify that they all operate as planned.
The piping systems are not very simple either in the underground facilities. For example, there are separate systems for service water, drilling water, and drainage water, as well as fire extinguishing water.
- The three big main pumps are installed under the sedimentation basin. In addition to the main pumps, there are four further smaller pumping systems through which drainage water is directed to the sedimentation basin. The pumped water must travel about half a kilometre upward, Kemppainen says.
Long days and working through weekends
For the past three weeks, Posiva’s commissioning organisation has worked long days as well as through the weekends. The personnel involved has included, for example, the persons in charge of the implementation of the automation system, an expert in the fire alarm system, the future operator of the systems, representatives from installation contractors, as well as the plant fire brigade. The reason for the long hours was the desire to complete the tests on schedule.
Kemppainen also gives praise to the subcontractors.
- Some three kilometres of ventilation ducts have been installed underground with Ilmastointi Salminen Oy in charge of the work. The piping systems, on the other hand, have been implemented by Vesi-Vasa Oy. The contractors also took part in commissioning processes, on both system and repository level.
Nuclear systems have their own processes
The finishing works in Posiva’s underground facilities continue without interruptions in May. The recently completed building services engineering systems have been tested to verify that none of them will cause a hindrance to the execution of the Trial Run for Final Disposal which will start in August. The entire final disposal process of spent nuclear fuel is tested in the TRFD using simulated fuel elements: the test covers not only the seamless operation of the equipment but also the readiness of the organisation for the production stage.
The nuclear systems operating underground were not part of the building services engineering works that were now completed. These nuclear systems include the systems installed in the encapsulation plant that extend into the underground facilities, such as the canister lift and the canister truck.
Text: Pasi Tuohimaa