Sixty years ago, the former Soviet Union started conducting nuclear tests in a remote area of Eastern Kazakhstan. Much of the plutonium residue never disappeared. When the Soviets pulled out it was left behind and went unprotected for years. Only in recent years has there been an effort to secure it. Last October, scientists marked the completion of a 17-year operation. They had reduced one of the largest nuclear security threats since the collapse of the Soviet Union. Eben Harrell, Associate at the Project on Managing the Atom at Harvard's Kennedy School, has reported on what's now called "Plutonium Mountain."