This paper considers a generic thermal energy storage (TES) system as a retrofit to an existing nuclear power plant in the United States (Texas). The authors use a validated PLEXOS model of the Electric Reliability Council of Texas electric grid to simulate electricity market clearing in 2030. They use three scenarios of natural gas price forecasts with a coupled capacity expansion model to simulate the deployment of competing technologies. The power, energy capacity and ramp rate of the TES system are varied parametrically in order to calculate the revenues arising from arbitrage as well as ancillary services. The authors find that increasing the ramp rate and power increases the storage system net revenue in all cases. And increasing energy capacity has a positive effect on net revenue in a small number of cases but has mixed results overall.