This paper presents an integrated maintenance and lot-sizing problems under energy constraints with risk assessment in the case of unforeseeable circumstance. The considered production system is composed of identical parallel machines that must meet a random demand with a required service level. The lot-sizing optimization consists in determining the number of operating machines and produced quantity to meet demand and/or replenish the stock. Then, an analytical model is developed to determine a common maintenance plan for all machines while minimizing the total maintenance cost. The failure rate, of each machine, assumed that increases according to both manufactured size and the cumulative failure rate. In the second part of this paper, a novel risk assessment is presented in order to overcome the unforeseeable circumstance making some machines unavailable. The conducted experiments on generated instances show that the proposed approach is efficient and provide good solutions for maintenance plan, lot-sizing plan and risk assessment.