(a) If any portion of an electric generating facility is determined to be excess capacity and if the facility is a nuclear fission power plant, the state corporation commission shall determine whether there has been approved by the United States government through its authorized agency, a proven technology or means for the disposal of high-level nuclear waste which is available for use at or by the plant. If the commission finds that no such technology for disposal exists, it shall be presumed that the costs of acquisition, construction or operation of the facility were incurred due to a lack of prudence and the commission shall not include such costs in the reasonable value of the public utility property.