The Government of the United States reserves the right, in case of war or national emergency declared by Congress, to take possession of all or any part of the property described or referred to in this chapter for the purpose of manufacturing explosives or for other war purposes; but, if this right is exercised by the Government, it shall pay the reasonable and fair damages that may be suffered by any party whose contract for the purchase of electric power or fixed nitrogen or fertilizer ingredients is violated, after the amount of the damages has been fixed by the United States Court of Federal Claims in proceedings instituted and conducted for that purpose under rules prescribed by the court.