Scheduling the maintenances of nuclear power plants is a complex optimization problem, formulated in 2-stage stochastic programming for the EURO ROADEF 2010 challenge. The first level optimizes the maintenance dates and refueling decisions. The second level optimizes the production to fulfill the power demands and to ensure feasibility and costs of the first stage decisions. This paper solves a deterministic version of the problem, studying Mixed Integer Programming (MIP) formulations and matheuristics. Relaxing only two sets of constraints of the ROADEF challenge, a MIP formulation can be written using only binary variables for the maintenance dates. The MIP formulations are used to design constructive matheuristics and a Variable Neighborhood Descent (VND) local search. These matheuristics produce very high quality solutions. Some intermediate results explains results of the Challenge: the relaxation of constraints CT6 are justified and neighborhood analyses with MIP-VND justifies the choice of neighborhoods to implement for the problem. Lastly, an extension with stability costs for monthly reoptimization is considered, with efficient bi-objective matheuristics.
The demand for electrical energy is globally growing very quickly. For this reason, the optimization of power plant productions and power plant maintenance scheduling have become important research topics. A Large Scale Energy Management (LSEM) problem is studied in this paper. Two types of power plants are considered: power plants of type 1 can be refueled while still operating. Power plants of type 2 need to be shut down from time to time, for refueling and ordinary maintenance (these are typically nuclear plants). Considering these two types of power plants, LSEM is the problem of optimizing production plans and scheduling of maintenances of type 2 plants, with the objective of keeping the production cost as low as possible, while fulfilling the customers demand. Uncertainty about the customers demand is taken into account in the model considered. In this article, a matheuristic optimization approach based on problem decomposition is proposed. The approach involves mixed integer linear programming and simulated annealing optimization methods. Computational results on some realistic instances are presented. We address the problem of planning outages of nuclear power plants submitted by EDF (Electricite De France) as the challenge EURO ROADEF 2010. As our team won the first prize of the contest in the senior category, our approach may be of interest: it is conceptually simple, easy to program and computationally relatively fast. We present both our method and some ideas to improve it.  This paper presents a heuristic approach combining constraint satisfaction, local search and a constructive optimization algorithm for a large-scale energy management and maintenance scheduling problem. The methodology shows how to successfully combine and orchestrate different types of algorithms and to produce competitive results. We also propose an efficient way to scale the method for huge instances. A large part of the presented work was done to compete in the ROADEF EURO Challenge 2010, organized jointly by the ROADEF, EURO and Electricite de France. The numerical results obtained on official competition instances testify about the quality of the approach. The method achieves 3 out of 15 possible best results. This paper addresses a large-scale power plant maintenance scheduling and production planning problem, which has been proposed by the ROADEF EURO Challenge 2010. We develop two lower bounds for the problem: a greedy heuristic and a flow network for which a minimum cost flow problem has to be solved. Furthermore, we present a solution approach that combines a constraint programming formulation of the problem with several heuristics. The problem is decomposed into an outage scheduling and a production planning phase. The first phase is solved by a constraint program, which additionally ensures the feasibility of the remaining problem. In the second phase we utilize a greedy heuristic--developed from our greedy lower bound--to assign production levels and refueling amounts for a given outage schedule. All proposed strategies are shown to be competitive in an experimental evaluation. 