Respondent failed to immediately notify the NRC of the release of 67 pounds of chlorine emitted into the ambient air on February 11, 2013 at or about 7:30 a.m. Central Time. Respondent had knowledge of the release on February 11, 2013 at approximately 8:30 a.m. Central Time, and notified the NRC of the release on February 11, 2013 at 12:57 p.m. Central Time.