LOS ALAMOS, N.M. (AP) — The U.S. government on Monday cleared the way for a new management team to begin taking over one of the nation's top nuclear weapons laboratories as it looks to rebuild its reputation.The National Nuclear Security Administration issued an official notice to proceed to Triad National Security LLC , marking the beginning of a transition at Los Alamos National Laboratory that will take about four months.Made up of Ohio-based Battelle Memorial Institute, Texas A&M University and the University of California, the management team was announced as the winning bidder in June of a coveted $2.5 billion-a-year contract to manage the northern New Mexico lab.The University of California has played a key management role at the lab since it was created as part of a top-secret effort during World War II to build the atomic bomb. The federal government opted to put the contract up for bid following missed goals and a string of safety lapses involving the handling of plutonium and radioactive waste.The new contract also comes as the U.S. has tasked the lab with building at least 30 plutonium cores a year. The cores are used to trigger nuclear weapons, and the work is complex.The University of California on Monday touted the scientific work done at the lab over the decades — from its role in the Human Genome Project to experiments in nuclear medicine and work on renewable energy and climate change."UC and Los Alamos have been at the forefront of solving some of the greatest scientific, technological and engineering challenges of our times," UC President Janet Napolitano said in a statement. "The U.S. Department of Energy's decision is a testament to UC's historic commitment to scientific and technological excellence at Los Alamos."Asked about any changes to address the recent string of safety lapses, university officials said "safe and secure operations" at Los Alamos are the highest priority.Triad is working on a formal transition plan and the new management team is committed to reforms that will boost accountability, said Stephanie Beechem, a spokeswoman for the UC president's office.Triad has named Thomas Mason as the group's president and the lab's director designate. He currently serves as senior vice president for Battelle's global lab operations, and he's a former director of Oak Ridge National Laboratory in California.Other senior leadership appointments include Robert Webster as deputy director of weapons and John Sarrao as deputy director of science, technology and engineering. Webster is a 29-year veteran of Los Alamos' weapons program. He began his career at the lab as a graduate student in 1984. Sarrao also has worked at Los Alamos for years and received his doctorate in physics from UCLA.