|The decommissioned Boiling Nuclear Superheater(BONUS) reactor, located northwest of Rincón, Puerto Rico, was developed as a prototype nuclear power plant to investigate the technical and economic feasibility of the integral boiling-superheating concept. This small-scale nuclear reactor produced saturated steam in the central portion of the reactor core, superheated it in four surrounding “superheater” sections of the same core, and then used the superheated steam in a direct loop to drive a turbine generator.|
It was one of only two boiling-water superheater reactors ever developed in the United States. The reactor was designed to be large enough to evaluate the major features of the integral boiling-superheating concept realistically without the high construction and operating costs associated with a large plant.
Construction of the began in 1960 through a combined effort of the U.S. Atomic Energy Commission and Puerto Rico Water Resources Authority. The reactor first achieved a controlled nuclear chain reaction on April 13, 1964. It underwent a series of criticality tests and then was operated experimentally at various power levels, first as a boiler and later as an integral boiler-superheater.
Operation at full power (50 megawatts of thermal energy) and full temperature (900 F [482 °C] steam) was achieved in September 1965, and tests demonstrated satisfactory operation at 10 percent over power in November 1965.
Operation of the BONUS reactor was terminated in June 1968 because of technical difficulties and the ensuing need for high-cost modifications. The Puerto Rico Water Resources Authority decommissioned the reactor between 1969 and 1970. During decommissioning,all special nuclear materials (fuel) and certain highly activated components (e.g., control rods and shims) were removed to the mainland, all piping
systems were flushed, the reactor vessel and associated
internal components within the biological shield were entombed in concrete and grout, and systems external to the entombment were decontaminated.
Many contaminated and activated materials were placed in the main circulation pump room beneath the pressure vessel and entombed in concrete.