A new reactor concept, SECURE (Safe and Environmentally Clean Urban REactor), has been developed in a joint Finnish-Swedish design project. This reactor is operating at a low temperature, and it is intended for district heating purposes. The goal has been to design a reactor where the safety is based on built-in properties and to minimize dependence on engineered safety systems or operator action following abnormal occurrences. Choosing a pool reactor concept and placing the reactor in an underground rock cavern result in many safety advantages. Parallel to the design work, a safety review was carried out including the assessment of plant system reliability and identification of potential accident sequences. Environmental consequences due to both normal operation and even unlikely accidents were calculated to be minor. The proposed plant concept is assessed to result in a safety level that should make the siting of the plant near urban centers possible with minimal risks.