Palo Verde

Decommissioning. Pursuant to the Arizona Nuclear Power Project ("ANPP") Participation Agreement and federal law, the Company funds its share of the estimated costs to decommission Palo Verde Units 1, 2 and 3, including the Common Facilities, through the term of their respective operating licenses and is required to maintain a minimum accumulation and funding level in its decommissioning account at the end of each annual reporting period during the life of the plant. The Company has established external trusts with an independent trustee, which enables the Company to record a current deduction for federal income tax purposes for most of the amounts funded. At September 30, 2017, the Company’s decommissioning trust fund had a balance of $278.1 million, which is above its minimum funding level. The Company monitors the status of its decommissioning funds and adjusts its deposits, if necessary.

Decommissioning costs are estimated every three years based upon engineering cost studies performed by outside engineers retained by APS. In April 2017, the Palo Verde Participants approved the 2016 Palo Verde decommissioning study (“2016 Study”). The 2016 Study estimated that the Company must fund approximately $432.8 million (stated in 2016 dollars) to cover its share of decommissioning costs which was an increase in decommissioning costs of $52.1 million (stated in 2016 dollars) from the 2013 Palo Verde decommissioning study. The effect of this change increased the ARO by $3.5 million, which was recorded during the second quarter of 2017, and will increase annual expenses starting in April 2017. Although the 2016 Study was based on the latest available information, there can be no assurance that decommissioning cost estimates will not increase in the future or that regulatory requirements will not change. In addition, until a new low-level radioactive waste repository opens and operates for a number of years, estimates of the cost to dispose of low-level radioactive waste are subject to uncertainty. As provided in the ANPP Participation Agreement, the participants are required to conduct a new decommissioning study every three years. While the Company attempts to seek amounts in rates to meet its decommissioning obligations, it is not able to conclude given the evidence available to it now that it is probable these costs will continue to be collected over the period until decommissioning begins in 2044. The Company is ultimately responsible for these costs and its future actions combined with future decisions from regulators will determine how successful the Company is in this effort.

Spent Nuclear Fuel and Waste Disposal. Pursuant to the Nuclear Waste Policy Act of 1982, as amended in 1987 ("NWPA"), the U.S. Department of Energy ("DOE") is legally obligated to accept and dispose of all spent nuclear fuel and other high-level radioactive waste generated by all domestic power reactors by 1998. The DOE's obligations are reflected in a contract for Disposal of Spent Nuclear Fuel and/or High-Level Radioactive Waste ("Standard Contract") with each nuclear power plant. The DOE failed to begin accepting spent nuclear fuel by 1998.

On November 2, 2015, APS, acting on behalf of itself and the Palo Verde Participants, submitted to the government a request for reimbursement of spent nuclear fuel storage costs for $12.0 million for the period July 1, 2014 through June 30, 2015. In February 2016, the DOE notified APS of the approval of the claim. In March 2016, the Company received its share of this claim of approximately $1.9 million, of which $1.6 million was credited to customers through the applicable fuel adjustment clauses.

On October 31, 2016, APS filed an $11.3 million claim for the period July 1, 2015 through June 30, 2016. On February 1, 2017, the DOE notified APS of the approval of the claim. On March 10, 2017, the Company received approximately $1.8 million, representing its share of the award, of which $1.4 million was credited to customers through the applicable fuel adjustment clauses.

On October 31, 2017, APS filed a $9.0 million claim for the period July 1, 2016 through June 30, 2017. The Company's share of this claim is approximately $1.4 million. Any reimbursement is anticipated to be received in the first quarter of 2018, and the majority will be credited to customers through the applicable fuel adjustment clauses.

Palo Verde Operations and Maintenance Expense. Included in other operations and maintenance expenses are expenses associated with Palo Verde as follows (in thousands):



	2017		2016
Three months ended September 30,	$	20,441	$	21,123
Nine months ended September 30,	67,980		67,514
Twelve months ended September 30,	97,380		97,451