Advances in Decision Analysis: Balancing Environmental and Operational Objectives in Nuclear Refueling Strategies

The New York Power Authority (NYPA) wanted to develop a 10-year schedule for refueling its Indian Point 3 Nuclear Power Plant (IP3) that balanced fish protection, which occurs when IP3 is shutdown for nuclear refueling, and the costs of buying and loading fuel. We developed a decision analysis model to compare alternative strategies for refueling. It explicitly considered key uncertainties associated with future operation: how well IP3 operates, how long it takes to refuel, and when New York State is likely to deregulate the electric utility industry. The NYPA decision-makers used the model to reinforce their choice of a refueling strategy. They were not surprised that more fish protection occurred with strategies that restricted the starting date for refueling to the last full week in May, rather than allowing the starting date to float throughout the period from May through August. However, the NYPA decision-makers were surprised that the more restrictive strategies also resulted in lower costs. Advances: Nuclear Refueling Page 2 of 32 Ch 27 060520 V06 CONTENTS Problem Structuring – Designing the Project for Success Mission Statement Decision Pyramid Objectives Hierarchy Objective—Minimize Total Cost Objective—Maximize Fish Protection Strategies Uncertainties Modeling – Linking Choices to Outcomes Data Collection – Developing Reliable Inputs Evaluation – Performing Analyses to Generate New Insights Stakeholder Reaction Reflections Advances: Nuclear Refueling Page 3 of 32 Ch 27 060520 V06 The New York Power Authority (NYPA) is the nation’s largest nonfederal public power organization, providing about one-fourth of the electricity used in New York State. The NYPA owns 12 power projects. The Indian Point 3 Nuclear Power Plant (IP3), located on the Hudson River, generates approximately one-fifth of its electrical power. Since 1975, IP3 has saved electric power users in Westchester County and New York City more than $1 billion. IP3 withdraws 840,000 gallons of water per minute from the Hudson River for cooling steam and then returns it to the river. When water is withdrawn from the river between February and September so are fish eggs and small fish. Some of the fish do not survive as they pass through the cooling water system of IP3 (entrainment) because of temperature increases, pressure changes, and sheer forces. The effect of entrainment on fish populations in the Hudson River has been the subject of both extensive litigation and scientific research (Barnthouse et al, 1988). The NYPA can reduce the effect of entrainment by scheduling plant shutdowns to refuel IP3 when fish eggs and small fish are most abundant in the Hudson River and taking those outages as scheduled. In the past, the NYPA prepared its nuclear refueling outage schedules for IP3 using a 10-year planning horizon, assuming the operation and refueling of IP3 went exactly as planned. However, unforeseen events often altered operation and refueling, causing refueling outage schedules to deviate from what was planned. In the future, there is uncertainty about when New York State will deregulate the electric utility industry and the effect on the cost of replacement power that the NYPA will have to buy during refueling outages. NYPA must systematically consider these uncertainties to ensure that it can continue to provide low cost power and can reduce the environmental effects of operating IP3. For these reasons, the NYPA decided to use Advances: Nuclear Refueling Page 4 of 32 Ch 27 060520 V06 decision analysis rather than other approaches, such as mixed-integer programming (Fourcade et al., 1997), to help it to schedule nuclear refueling outages at IP3. In this chapter, we describe the decision analysis tools and processes that we brought to the environmental and operational dilemma faced by the NYPA. We will describe the model structure and highlight the key inputs and how we collected those inputs from experts within the NYPA. We conclude with insights and results and comment on our own challenges as well as the reactions from the stakeholders. Problem Structuring – Designing the Project for Success The decision analysis project started on October 23, 1997, and the NYPA required that it be finished by December 4, 1997. Our decision analysis approach consisted of four phases: framing, modeling, data collection, and evaluation. During the framing phase, we determined who would be involved in the project, the scope of the analysis, and the important factors (alternatives, uncertainties, and objectives) of the refueling outage plan. The project team consisted of a core group (NYPA senior managers and decision analysts—the authors), subject-matter experts, and decision-makers. Our role was to conduct a decision analysis that was responsive to the needs of decision-makers. We used various decision analysis tools to organize and record the results of the framing phase. These included a decision-quality spider diagram, a decision pyramid, an objectives hierarchy, a strategy table, a decision tree, and an influence diagram. Advances: Nuclear Refueling Page 5 of 32 Ch 27 060520 V06 Mission Statement We determined the scope of the project by (1) developing a mission statement and (2) clearly defining the decisions and their boundaries. We constructed the mission statement by considering four questions: what are we going to do, why are we doing this, how will we know we are successful, and how can we fail? The resulting mission statement was as follows: 1) Identify strategies for scheduling refueling outages at IP3 over the period 1999 through 2008 that range from unrestricted operation, in which outages can begin at any time and protection of fish eggs and small fish is not a concern, to restricted operation, in which outages must begin during a specified week and the primary concern is maximizing protection of fish eggs and small fish, 2) Develop a decision analysis model for comparing the cost and amount of fish protection associated with the refueling strategies based on information provided by the experts at the NYPA and the level of confidence they have in that information, 3) Compare the refueling strategies in terms of cost and fish protection, and 4) Provide, by December 4, 1997, the results of the decision analysis model to the NYPA decision-makers. Decision Pyramid During the first week of the project, we listed decisions that could affect the mission. We then categorized each decision as policy, strategic, or tactical to help bound the NYPA’s problem and focus our attention at the right level. A decision pyramid (Matheson and Matheson, 1998) helped us to organize the three categories of decisions (Figure 27.1). This decision pyramid defines the Advances: Nuclear Refueling Page 6 of 32 Ch 27 060520 V06 scope of the analysis for the NYPA by focusing attention on the key strategic choices. We assume that policy decisions are given. Tactical decisions are to be made in the future.