On March 14, 2011, Environmental Defense Institute (EDI) filed an Appeal from a determination issued by the Idaho Operations Office (Idaho) of the Department of Energy (DOE) under the Freedom of Information Act. EDI filed a request in which it sought several documents concerning the Advanced Test Reactor, located at the Idaho National Laboratory. In a February 8, 2011, determination, Idaho provided responsive documents, but withheld portions of one responsive document on the basis of Exemption 3. EDI raised several challenges to the determination in its Appeal. Except for the challenge regarding Idaho’s application of Exemption 3, EDI’s challenges were addressed in a separate Decision and Order issued in Case No. TFA-0465. Because Exemption 3 protects from disclosure information that is properly identified as Unclassified Controlled Nuclear Information (UCNI) pursuant to the Atomic Energy Act of 1954, we referred this Appeal to the Office of Health, Safety and Security, which is responsible for reviewing such information. That Office determined that some of the information previously withheld under Exemption 3 was properly identified as UCNI, and therefore should continue to be withheld from public disclosure under Exemption 3 of the FOIA. It also determined that some of the information initially withheld did not qualify for protection under Exemption 3. Consequently, we remanded the matter to Idaho for a new determination as to whether the information previously withheld but not currently withholdable should be released to EDI or withheld pursuant to any other provision of the FOIA. Accordingly, EDI =s Appeal was granted in part and denied in part.