Cost of sales was reduced during the current periods for revisions to prior accrued amounts related to estimated disposal costs for depleted uranium, property taxes and power prepayments related to enrichment operations. These accrued estimated amounts had been previously included in our production costs and included in SWU inventory. The total reduction to cost of sales recognized in the nine months ended September 30, 2012, was approximately $26.2 million. In addition, prior to the start of 2012, a significant portion of the costs related to pension and postretirement health and life benefit plans were attributed to Portsmouth contract services, based on the employee base performing contract services work. Starting in 2012, ongoing pension costs related to our former Portsmouth employees are charged to the LEU segment rather than the contract services segment based on our continuing enrichment activities that support our active and retired employees. These net benefit costs totaled $9.9 million for the nine months ended September 30, 2012, and are directly charged to cost of sales rather than production. Additionally, $2.8 million of costs previously capitalized as part of construction work in progress were charged to expense in the third quarter of 2012 based on a short expected life once placed in service at the Paducah GDP. Excluding the effects of these items, cost of sales per SWU was approximately 2 percent higher in the nine months ended September 30, 2012, compared to the corresponding period in 2011.
Production costs declined $23.0 million, or 13 percent, in the third quarter reflecting a 6 percent decline in volume and an 8 percent decline in unit production cost. Production in the quarter consisted of depleted uranium enrichment under the one-year multi-party arrangement with Energy Northwest, the Bonneville Power Administration, Tennessee Valley Authority (TVA) and DOE. Effective June 1, 2012, although our purchase costs under our power contract with TVA continue to be subject to a fuel cost adjustment, the fuel cost adjustment is included in the power price component of our sales price billed to Energy Northwest under the depleted uranium enrichment agreement. The average cost per megawatt hour declined 10 percent in the three months ended September 30, 2012, compared to the corresponding period in 2011.