; or (B) the expiration of the 6-year period beginning upon the Secretary obligating such amounts to the grantee, as such period may be extended pursuant to paragraph (2), the Secretary shall transfer such unexpended amounts to the Secretary of the Treasury for deposit into the Community Development Block Grant Disaster Recovery Reserve Fund established under section 124, except that the Secretary may, by regulation, permit the grantee to retain amounts needed to close out the grant. (2) Extension of period for use of funds The period under paragraph (1)(B) shall be extended by not more than 4 years if, before the expiration of such 6-year period, the Secretary waives this requirement and submits a written justification for such waiver to the Committees on Appropriations of the House of Representatives and the Senate that specifies the period of such extension. (p) Definitions For purposes of this section: (1) Grantee The term grantee means a recipient of funds made available under this section after its enactment. (2) Substantially similar The term substantially similar means, with respect to a plan, a plan previously approved by the Department, administered successfully by the grantee, and relating to disasters of the same type. (3) Other terms Within one year of enactment of this section, the Department shall issue rules to define the following terms: (A) Unmet needs. (B) Most impacted and distressed. (C) Substantial compliance. (D) Full and open competition. (E) Cost plus a percentage of cost. (F) Percentage of construction cost. 124. Community Development Block Grant Disaster Recovery Reserve Fund (a) Establishment There is established in the Treasury of the United States an account to be known as the Community Development Block Grant Disaster Recovery Reserve Fund (in this section referred to as the Fund ). (b) Amounts The Fund shall consist of any amounts appropriated to or deposited into the Fund, including amounts deposited into the Fund pursuant to section 123(o). (c) Use Amounts in the Fund shall be