Non-Destructive Measurements on the Containment

Feasibility Study for Non-Destructive Measurements on the Steel Pressure Shell of the Primary Containment of Nuclear Power Plants: the primary circuit, including the reactor pressure vessel, is enclosed by a steel pressure shell as part of the defence-in-depth safety barriers. Depending on the structural design of the nuclear power plant, this is directly surrounded by a concrete casing in the support area of the foundation from both the inner and outer surfaces.

The unexpected action of boric acid can cause local corrosive attacks on the steel pressure shell, so a periodic review is important in order to determine possible decreases in the wall thicknesses. The ultrasound measurement normally used for this purpose is relatively simple on the freely accessible areas of the steel pressure shell, but this is not the case in the areas surrounded by the foundation. In the past, concrete core drillings were carried out at selected points in this area, and these were sealed again after completion of the measurements.

A feasibility study was launched by ENSI in 2009 in order to assess new types of inspection methods on a covered steel pressure shell. For this purpose, a test object which is intended to simulate the difficult inspection situation was built at the Swiss Federal Laboratories for Materials Science and Technology (EMPA). This object consists of a solid steel plate into which various defects are introduced, and which is partially in direct contact with reinforced concrete, including intermediate layers of mineral wool. Theoretical and experimental verifications of various non-destructive measurement methods are to be carried out on the test object to determine their suitability for inspecting concealed corrosion on a steel pressure shell.