Containment Vessel Plate Evaluation

摘要

As part of the license renewal process, FirstEnergy committed to the NRC that it would verify that the containment vessel had not degraded in interior regions of the containment due to refueling canal leakage at its Davis-Besse plant. Confirmation of the material condition of the interior of the containment vessel plate would require excavation of nearly five feet of reinforced concrete to expose the plate at a critical low elevation where water could accumulate for examination and ultrasonic thickness testing. Further complicating the interior effort was that the area to be investigated was in a hallway adjacent to the area under the reactor vessel, which made it a high radiological dose rate region and a congested location. Due to the poten-tial for irreversible damage to occur to the containment ves-sel plate during the concrete excavation phase, and the need to perform work efficiently in a high dose area, the process to expose the containment vessel plate at the interior would be treated as a Special Process per 10CFR50 Appendix B, " Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants" Criterion Ⅸ. Therefore, procedures were developed off site to efficiently access the containment vessel plate at the interior of the containment without damage to the plate.