IRID has made some progress on their research to find ways to seal the containment structures at Fukushima Daiichi. The plan has been to flood the containment structures in order to provide shielding during the fuel removal procedures. Concern has been raised about the ability of these structures to hold the weight and pressure of that much water or how this would impact the structure during an earthquake. The structures are already severely damaged along with the many locations where they leak. The current research effort is looking for ways to try to seal the leaks in each of the areas known to be a leak path for the containment structure. One aspect that has not been discussed is what would happen if these structures did have a failure and leak after flooding. It is known that the reactor containment structures contain some loose fragmented fuel and other highly radioactive debris. A major leak could let loose a considerable radioactive slurry that would need to be quickly contained and remediated.
The diagram above shows the locations within the torus and torus room (suppression chamber) where they plan to plug the structures to make them potentially hold water.
This diagram shows the types of cable (top left) and pipe (top right) penetrations where they will have to seal connecting joints or bellows joints related to the containment structure. The photo included is of a containment hatch door. These will also need to be sealed.
The MSIV (Main Steam Isolation Valve) rooms are another location discovered to be leaking. In Unit 3 they discovered the bellows joints on these pipes were leaking into the MSIV room. This novel approach is being developed by IRID to try to block leaks from pipes in this room. Cement type materials would be dumped around the leaking pipe to seal the leaking section.
Work has also continued in testing various ways to plug the torus downcomer tubes and also the opening in the containment structure where that tube runs through the thick concrete wall. Leaks have been found in this hole in the containment concrete. Only the steel liner and a small pocket of sand reside in this location as a thin wall between the inner containment and the torus room. IRID has decided this also needs to be plugged in order to flood containment. They are now working on ways to fill the downward sloping hole with sealing material. Work is being done in half scale then in full scale. Full scale downcomer sealing tests. Downcomer tube sealing in 1/4 scale Sealing material tests on a downward slope to simulate the conditions of the containment hole for the downcomer tube. Full scale downcomer plug tests.
These materials are tested for their ability to stay in location under pressure. There is currently no specific date mentioned when they might try implementing these technologies in the actual reactors.
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