Related Rule
France
Practice Relating to Rule 42. Works and Installations Containing Dangerous Forces
France’s LOAC Summary Note (1992) provides: “The specific immunity granted to certain persons and objects by the law of war [including works and installations containing dangerous forces] must be strictly observed … They may not be attacked.” 
France, Fiche de Synthèse sur les Règles Applicables dans les Conflits Armés, Note No. 432/DEF/EMA/OL.2/NP, Général de Corps d’Armée Voinot (pour l’Amiral Lanxade, Chef d’Etat-major des Armées), 1992, §§ 2.2–2.3.
The Summary Note further specifies:
The immunity of specifically protected objects may only be lifted under certain conditions and under the personal responsibility of the commander. Military necessity justifies only those measures which are indispensable for the accomplishment of the mission. 
France, Fiche de Synthèse sur les Règles Applicables dans les Conflits Armés, Note No. 432/DEF/EMA/OL.2/NP, Général de Corps d’Armée Voinot (pour l’Amiral Lanxade, Chef d’Etat-major des Armées), 1992, § 2.4.
The Summary Note qualifies “attacks against works and installations containing forces which are dangerous for the civilian population” as a war crime. 
France, Fiche de Synthèse sur les Règles Applicables dans les Conflits Armés, Note No. 432/DEF/EMA/OL.2/NP, Général de Corps d’Armée Voinot (pour l’Amiral Lanxade, Chef d’Etat-major des Armées), 1992, § 3.4.
France’s LOAC Teaching Note (2000) states that “the law of armed conflict grants specific protection to certain specially marked installations and zones”, including certain works and installations containing dangerous forces. 
France, Fiche didactique relative au droit des conflits armés, Directive of the Ministry of Defence, 4 January 2000, annexed to the Directive No. 147 of the Ministry of Defence of 4 January 2000, p. 5.
The Teaching Note further states: “Dams, dykes and nuclear electrical generating stations are considered to be installations containing dangerous forces and must not be attacked in any circumstances.” 
France, Fiche didactique relative au droit des conflits armés, Directive of the Ministry of Defence, 4 January 2000, annexed to the Directive No. 147 of the Ministry of Defence of 4 January 2000, p. 6.
France’s LOAC Manual (2001), with reference to Article 56 of the 1977 Additional Protocol I and Article 15 of the 1977 Additional Protocol II, includes works and installations containing dangerous forces among objects which are specifically protected by the law of armed conflict. 
France, Manuel de droit des conflits armés, Ministère de la Défense, Direction des Affaires Juridiques, Sous-Direction du droit international humanitaire et du droit européen, Bureau du droit des conflits armés, 2001, p. 31.
The manual further restates the prohibition on attacking dams, dykes and nuclear power plants, and the exceptions thereto, as found in Article 56 of the 1977 Additional Protocol I and stresses: “A decision to attack such works and installations belongs to the commander whose criminal responsibility is engaged in case the action undertaken is illegal.” 
France, Manuel de droit des conflits armés, Ministère de la Défense, Direction des Affaires Juridiques, Sous-Direction du droit international humanitaire et du droit européen, Bureau du droit des conflits armés, 2001, p. 69.
Upon ratification of the 1977 Additional Protocol I, France declared:
The Government of the French Republic cannot guarantee absolute protection to works and installations containing dangerous forces, which may contribute to the opposing Party’s war effort, or to the defenders of such installations, but will take all necessary precautions, pursuant to Articles 56, 57(2)(a)(iii) and 85(3)(c) [of the 1977 Additional Protocol I], to avoid severe collateral losses among the civilian population, including during possible direct attacks against such works and installations. 
France, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 11 April 2001, § 15.