[2] The 2010 U.S. population within 10 miles (16 km) of LaSalle was 17,643, an increase of 7.1 percent in a decade, according to an analysis of U.S. Census data for msnbc.com.Workers were shutting down Unit 1 for refueling when the plant's turbine control system malfunctioned, SCRAMing the reactor.Plant instruments indicated three of 185 control rods used to shut down the reactor were not fully inserted triggering the emergency declaration.Post trip evaluations have confirmed that all control rods were fully inserted within four minutes of the reactor SCRAM.[4] The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at LaSalle was 1 in 357,143, according to an NRC study published in August 2010.