Cyber-physical systems consist of interconnected physical processes and computational re- sources. Because the cyber and physical worlds are integrated, vulnerabilities in both the cyber and physical domains can result in damage to the physical system. As cyber-physical systems, nuclear power plants must be secure in both domains in order to maintain operational safety. Nuclear power plants may be targeted by a variety of threat actors such as state actors, hack- tivists, and disgruntled employees|each with a unique motivation and set of resources. This work predicts the outcome of a cyber-physical attack on a nuclear power plant by examining the interaction between a threat actor and a plant defender. A game-theoretic approach is presented to analyze attacks on cyber-physical systems. The cyber-physical attack is analyzed as a two-player strategic-form game. The two players are an attacker and a defender: the defender attempts to maintain plant operation while the attacker attempts to disrupt it. The attacker's strategy set consists of a cyber attack, physical attack, cyber-physical attack, and abstaining from an attack. The defender's strategy set consists of a cyber reinforcement, physical reinforcement, cyber-physical reinforcement, and abstaining from reinforcement. Each player incurs a cost from either attacking or defending. If an attack is successful, the attacker incurs a gain and the defender incurs a loss. A mixed strategy Nash equilibrium is identi ed. Under the mixed Nash equilibrium conditions, the expected utility of the attacker is zero, and the expected utility of the defender is the cost of cyber-physical reinforcement.