Cal. Pub. Util. Code § 8328

The expenses associated with decommissioning of nuclear facilities shall be paid from the funds established pursuant to Section 8325. If the money in the funds is insufficient for payment of all decommissioning costs, the commission or the board shall determine whether the costs incurred in excess of the money in the funds are reasonable in amount and prudently incurred. If the commission or the board determines that the excess costs are reasonable in amount and prudently incurred, the commission or the board shall authorize these costs to be charged to the customers of the electric utility.