Thirteen Japanese nuclear reactors were constructed with steel made by the same domestic company that produced material used in a French power plant that has come under scrutiny after anomalies were found in the structure of its reactor vessel.

Six utilities used steel from Japan Casting & Forging Corp. (JCFC), they all said in separate statements Friday. The company was identified by Japanese authorities last month as having supplied steel to the Flamanville nuclear plant, developed by Electricite de France SA and Areva SA, where the French safety authority last year found weaker-than-expected steel.

The Nuclear Regulation Authority asked utilities last month to examine reactor parts made by the same companies that supplied the Flamanville facility. Utilities must now evaluate whether their reactor pressure vessels meet national standards and report the results to the regulator by Oct. 31.