The SL-1, or Stationary Low-Power Reactor Number One, was a United States Army experimental nuclear power reactor. It was a small test reactor at the Idaho National Engineering Laboratory, Idaho, USA. The National Reactor Testing Station (NRTS) was approximately 40 miles (64 km) west of Idaho Falls, Idaho and was part of the American's Army Nuclear Power Program and was known as the 'Argonne Low Power Reactor' or (ALPR) during its design phase and construction.