All provisions of section 52-118, with reference to contractors’ bonds, shall be applicable and effective as to any contract let pursuant to the provisions of sections 70-637 to 70-640, except that with respect to any electric generating facility, the penal sum of any contractor’s bond shall be the lesser of the contract amount or two hundred million dollars. The bond required by section 52-118 may be satisfied by a corporate surety or letter of credit, or combination thereof, approved by the district.