On 26 April 1986, Chornobyl's Unit 4 reactor exploded during a test of the plant's turbine-generator system. The reactor core was destroyed. The explosion and subsequent fires dispersed large amounts of radioactive material in the form of gases and dust particles. In an effort to localize radioactivity and temporarily preserve the Unit 4, “Shelter” was constructed over the remains of the reactor. However, the destroyed unit, which contains about 190 tons of irradiated nuclear fuel, is undergoing degradation due to exposure to the environment. This has resulted in the generation of radioactive dust. Ukraine, and the G-7 countries, the G-7 countries include United States, Great Britain, Canada, France, Germany, Japan and Italy, have agreed on a plan to stabilize the Shelter by building a new protective structure and by removing portions of the existing Shelter to ensure its long-term stability. The United States has committed to improve worker safety at the Shelter by reducing radiation doses to workers. As part of the continuing efforts to achieve dose reduction for site personnel at the Shelter, Delphinus Engineering, under contract from Pacific Northwest National Laboratory (PNNL) operated by Battelle, installed and implemented STREAM or System for Tracking Radiation, Engineering, Activities and Materials. STREAM is both a multimedia database system and a decision support system that was developed as a “tool” for management and staff to enhance and/or facilitate productivity, safety, improve communications and training. The STREAM database is utilized to store and manage information relevant for decontamination and decommissioning (D&D) activities. STREAM's decision support system, referred to as the Work Planning System (WPS), allows planning of manned entries into the facility.
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