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.

“It’s just to be sure,” said an NRA official.

JCFC said it has thrown away steel parts that lead to weaker products, adding that its steels have cleared the safety criteria.

The Japanese facilities affected include Kyushu Electric Power Co.’s Sendai No. 1 and 2 reactors in Kagoshima Prefecture, the company said Friday. The plant was restarted last year and is facing opposition from a new governor who has demanded they be temporarily shut for inspections.

Reactors now in operation don’t need to be shut down, Yoko Kobayashi, an official with the NRA’s planning division, said Friday. The affected utilities are now required to submit manufacturing reports and past evaluation results, she said.

The steel scrutiny is the latest hurdle for the nuclear power industry since the 2011 Fukushima disaster and could hamper the government’s goal of having it account for as much as 22 percent of its energy mix by 2030.

Local court challenges have threatened reactor operations, and even those restarted under new post-Fukushima safety rules have faced a rocky road. Only three of the nation’s 42 operable reactors are online.

Parts made by JCFC met rigorous standards requested by the utilities, and the company will provide support going forward, JCFC official Seigo Otsubo said Friday.

EDF and Areva are conducting additional tests to determine whether the anomalies present a safety issue. The two companies said in April that the submission of their report to French regulators about the Flamanville reactor has been delayed until year-end.

EDF has also determined that steam generator channel heads at 18 French reactors contain anomalies similar to those at Flamanville, Autorite de Surete Nucleaire, the safety regulator, said in June.

According to statements from the utilities, the domestic reactors made with steel from JCFC include: units 2 and 4 at the Fukushima No. 2 power plant run by Tokyo Electric Power Co. Holdings Inc.; unit 2 at the Takahama power plant and units 1 and 2 at the Oi power plant, both run by Kansai Electric Power Co.; reactors 2, 3 and 4 at the Genkai plant and reactors 1 and 2 at the Sendai plant run by Kyushu Electric Power Co.; reactor 2 at the Ikata plant run by Shikoku Electric Power Co.; reactor 1 at the Shika plant managed by Hokuriku Electric Power Co.; and reactor 2 at the aging Tsuruga plant run by the Japan Atomic Energy Agency.