While Stellite remains the material of choice for certain internal parts in industrial process valves (valve seat hardfacing), its use has been discouraged in nuclear power plants. In piping that can communicate with the reactor, tiny amounts of Stellite would be released into the process fluid and eventually enter the reactor. There the cobalt would be activated by the neutron flux in the reactor and become cobalt-60, a radioisotope with a five year half life that releases very energetic gamma rays. This phenomenon is more problematic in boiling water reactor (BWR) plants, since the steam is in direct contact with both the reactor and the steam turbine. Pressurized water reactor (PWR) designs are less susceptible. While not a hazard to the general public, about a third to a half of nuclear worker exposures could be traced to the use of Stellite and to trace amounts of cobalt in stainless steels. Replacements for Stellite have been developed by the industry, such as the Electric Power Research Institute's "NOREM", that provide acceptable performance without cobalt. Since the United States nuclear power industry has begun to replace the Stellite valve seat hardfacing in the late 1970s and to tighten specifications of cobalt in stainless steels, worker exposures due to cobalt-60 have dropped significantly.