core of the Three Mile Island Nuclear Generating Station after the accident in 1979. Also in 1972, Peter Mazur, a biologist at ORNL, froze with liquid nitrogen, thawed and implanted mouse embryos in a surrogate mother. The mouse pups were born healthy. The technique is popular in the livestock industry, as it allows the embryos of valuable cattle to be transported easily and a prize cow can have multiple eggs extracted and thus, through in vitro fertilisation, have many more offspring than would naturally be possible. In 1974 Alvin Weinberg, director of the lab for 19 years, was replaced by Herman Postma, a fusion scientist. In 1977 construction began for 6 metre (20 foot) superconducting electromagnets, intended to control fusion reactions. The project was an international effort: three electromagnets were produced in the US, one in Japan, one in Switzerland and the final by remaining European states. Experimentation continued into the 1980s. The 1980s brought more changes to ORNL: a focus on efficiency became paramount. An accelerated climate simulation chamber was built that applied varying weather conditions to insulation to test its efficacy and durability faster than real time. Materials research into heat resistant ceramics for use in truck and high-tech car engines was performed, building upon the materials research that began in the nuclear reactors of the 1950s. In 1987 the High Temperature Materials Laboratory was established, where ORNL and industry researchers cooperated on ceramic and alloy projects. The materials research budget at ORNL doubled after initial uncertainty regarding Reagan's economic policy of less government expenditure. In 1981, the Holifield Heavy Ion Research Facility, a 25 MV particle accelerator, was opened at ORNL. At the time, Holifield had the widest range of ion species and was twice as powerful as other accelerators, attracting hundreds of guest researchers each year. The Department of Energy was concerned with the pollution surrounding ORNL and it began clean-up efforts. Burial trenches and leaking pipes had contaminated the groundwater beneath the lab, and radiation tanks were sitting idle, full of waste. Estimates of the total cost of clean-up were into the hundreds of millions of US dollars. The five older reactors were subjected to safety reviews in 1987, ordered to be deactivated until the reviews were complete. By 1989 when the High Flux Isotope Reactor was restarted the US supply of certain medical isotopes was depleted. In 1989 the former executive officer of the