10 C.F.R. § 1060.101 – Persons who may be paid.

(a) Payment may not be authorized or approved for transportation, lodging, subsistence, or other travel expenses from DOE funds to, or on behalf of, a person who is not a Government employee unless such payment is made—
1. (1) Pursuant to an invitation received by that person from the Department to confer with a DOE employee on matters essential to the advancement of DOE programs or objectives and (i) in the case of a person invited to confer at the post of duty of the conferring DOE employee, a designated official has approved and stated the reasons for the invitation in writing, or (ii) in the case of a person invited to confer at a place other than the post duty of the conferring DOE employee, a principal departmental official has approved and stated the reasons for the invitation in writing;
2. (2) Pursuant to an invitation for an interview to a prospective employee of the Department who is an applicant for (i) a position in the Department classified at GS-16 or above of the General Schedule or the rate of basic pay for which is fixed, other than under the General Schedule, at a rate equal to or greater than the minimum rate of basic pay fixed for GS-16, (ii) a position for which a determination has been made that there is a manpower shortage pursuant to 5 U.S.C. 5723, or (iii) a DOE position for which the Department has the exclusive duties of recruitment and selection;
3. (3) In accordance with 28 U.S.C. 1821 or other applicable law, to a person who is subpoenaed by the Department to appear and testify or to appear and to produce documents at a designated place;
4. (4) To a person who serves as a travel attendant for a handicapped individual who is authorized to travel at DOE expense and who cannot travel alone because of the handicap; or
5. (5) Pursuant to a written determination of a principal departmental officer that it is in the interest of the Government to provide such payment, where the Counselor has determined in writing that the payment is authorized under 5 U.S.C. ch. 57 or other statutory authority.
(b) The authority of a designated official or a principal departmental officer, as the case may be, to provide approval of an invitation to travel under paragraph (a)(1) and of a principal departmental officer to determine that payment of travel expenses is in the interest of the Government under paragraph (a)(5) of this section may not be delegated.
(c) Within 30 days of providing written approval of an invitation under paragraph (a)(1)(i) of this section, a designated official who is an Administrator of a power administration or the head of a Field Organization shall transmit a copy of the written approval to the principal departmental officer to whom the official or the official's organization reports.
(d) Payment of travel expenses may not be made pursuant to an invitation to travel under paragraphs (a)(1) or (a)(5) unless the written approval and statement of reasons required by paragraph (a)(1), or the written determinations required by paragraph (a)(5) of this section, are made before the travel to be authorized by the invitation takes place.
(e) Nothing in this section shall be interpreted to prohibit payment for travel expenses that are reimbursable or allowable by the Department under the terms of a DOE contract or assistance award.