Sealing of concrete confining structures of French nuclear reactors

Abstract

France has a total of 58 nuclear reactors, which produce 75% of its electricity. The second-generation reactors are protected by two concentric concrete envelopes, which are separated by an annular space. Every ten years, leakage tests are performed, by inflating the confinement structure with pressurized dry air. The confining structures of several second-generation reactors are now close to their allowed leakage limit. As a consequence, several different approaches are currently being studied in order to improve their airtightness. A dedicated wall has been especially designed, by our laboratory, to simulate the leakage tests as they occur in the real in-situ confining structures. The main goal of this “apparatus” was to test different possibilities to recover a large part of the envelope tightness: application of coatings or water re-saturation of the concrete with spraying. The measured airtightness and bond strength (between the wall and coating) of two concrete prototypes revealed these to be unsatisfactory. In parallel, the spraying method allowed a high proportion of the concrete's gas tightness to be recovered. The present study provides a detailed description of the design of the prototype test wall and the results of preliminary tests, including those obtained with the “water spraying technique”.