19 1957 Engineering Test Reactor Five years after MTR came online, the Engineering Test Reactor represented a significant advancement in testing capabilities.The 175-megawatt reactor provided larger, more versatile test spaces and a more intense neutron flux, allowing for evaluation of fuel, coolant and moderator materials in environments similar to those inside power reactors. In 1972, ETR’s core was modified with a Sodium Loop Safety Facility, allowing it to play a role in the breeder reactor safety program. Other modifications included a helium coolant system and sodium-handling system.