Concession contract between ANP and Newfield for oil exploration and production with an arbitration clause. Supervening impossibility of performance of the contract's subject matter for environmental reasons. Institution of arbitration proceedings to resolve the dispute relating to the rescission of the contract. Enrollment of the amounts that the Union considers owed by Newfield as active debt and filing of the corresponding enforcement action. Granting of Newfield's objection to enforcement without security. Enrollment as active debt does not render the right discussed in arbitration unavailable. An arbitration award declaring the debt nonexistent may only be challenged on the grounds of Article 32 of the Brazilian Arbitration Act, which did not occur: