Passage: In April 2009, reports surfaced that North Korea has become a "fully fledged nuclear power", an opinion shared by International Atomic Energy Agency (IAEA) Director General Mohamed ElBaradei. On May 25, 2009, North Korea conducted a second nuclear test, resulting in an explosion estimated to be between 2 and 7 kilotons. The 2009 test, like the 2006 test, is believed to have occurred at Mantapsan, Kilju County, in the north-eastern part of North Korea. This was found by an earthquake occurring at the test site.In February 2012, North Korea announced that it would suspend uranium enrichment at the Yongbyon Nuclear Scientific Research Center and not conduct any further tests of nuclear weapons while productive negotiations involving the United States continue. This agreement included a moratorium on long-range missile tests. Additionally, North Korea agreed to allow IAEA inspectors to monitor operations at Yongbyon. The United States reaffirmed that it had no hostile intent toward the DPRK and was prepared to improve bilateral relationships, and agreed to ship humanitarian food aid to North Korea. The United States called the move "important, if limited", but said it would proceed cautiously and that talks would resume only after North Korea made steps toward fulfilling its promise. However, after North Korea conducted a long-range missile test in April 2012, the United States decided not to proceed with the food aid.On February 11, 2013, the U.S. Geological Survey detected a magnitude 5.1 seismic disturbance, reported to be a third underground nuclear test. North Korea has officially reported it as a successful nuclear test with a lighter warhead that delivers more force than before, but has not revealed the exact yield. Multiple South Korean sources estimate the yield at 6–9 kilotons, while the German Federal Institute for Geosciences and Natural Resources estimates the yield at 40 kilotons. However, the German estimate has since been revised to a yield equivalent of 14 kt when they published their estimations...

Question: Where did the 2009  North Korea nuclear power test occur?
Mantapsan, Kilju County