; or (ii) the retrofitting of 1 or more existing natural gas pipelines— (I) to transport a blend of hydrogen and natural gas; and (II) in a manner that will significantly increase the capacity of the pipelines to transport hydrogen, as determined by the Secretary. (7) Eligible project cost (A) In general The term eligible project costs means— (i) the costs of carrying out an eligible activity; and (ii) any costs described in subparagraph (B) relating to, or incurred in connection with, an eligible project. (B) Costs described The costs referred to in subparagraph (A)(ii) are— (i) the costs of capitalized interest necessary to meet market requirements, the costs of reasonably required reserve funds, capital issuance expenses, and any other carrying costs during construction of the applicable infrastructure; and (ii) transaction costs associated with financing an eligible project, including the cost of legal counsel and technical consultants. (8) HIFIA pilot program The term HIFIA pilot program means the hydrogen infrastructure finance and innovation pilot program established under subsection (b)(1). (9) Letter of interest The term letter of interest means a letter submitted by a potential applicant prior to an application for a grant or a loan under the HIFIA pilot program that— (A) is in a format prescribed by the Secretary on the website of the HIFIA pilot program; (B) describes the project and the location, purpose, and cost of the project; (C) outlines the proposed financial plan, including— (i) the requested grant or loan assistance; and (ii) the proposed obligor, if applicable; (D) provides a status of environmental review