Accelerated Corrosion Tests of Nuclear Reactor Pressure Vessel Materials in NaCl–H3BO3 Solutions

Following the 2011 accident at the Fukushima Daiichi nuclear power station, sea water for cooling and boric acid for maintaining a noncritical condition, both corrosive liquids, were injected into nuclear pressure vessels. In order to estimate corrosive characteristics of the pressure vessels an experimental study was undertaken to provide an accelerated corrosion test on SA533B low alloy steel and Inconel 600, materials used in the construction of the pressure vessels. In a typical experiment, samples of these materials were immersed in saturated NaCl and concentrated H3BO3 aqueous solutions at a temperature of 423K. SA533B suffered little or no corrosion in saturated NaCl solution, significant corrosion in concentrated H3BO3 solution and substantial corrosion in the binary saturated NaCl-concentrated H3BO3 solution. Galvanic corrosion of SA533B was accelerated when Inconel 600 was also immersed in the same solution and the two samples were electrically connected either externally by a wire lead or internally by a screw made of SA533B or both. Corrosion rate in the initial stage was 0.07mm per hour. The corrosion product on SA533B was porous and easily detachable, indicating corrosion to be progressive without producing a stable protective corrosion layer. The validity of the extreme experimental condition for accelerated corrosion tests is discussed and experimental programs for further investigation are proposed. [doi:10.2320/matertrans.M2012405]