TOKYO (Kyodo) -- Japan's nuclear watchdog said Thursday another faulty antiterrorism measure had been found at the Kashiwazaki-Kariwa nuclear complex, operated by Tokyo Electric Power Company Holdings Inc.

The Nuclear Regulation Authority convened an emergency meeting to discuss responses to the latest discovery that a TEPCO employee had made an unauthorized copy of a confidential document in June and stored it in his desk at the complex in Niigata Prefecture, northwest of Tokyo.

TEPCO is preparing to restart a reactor at the site for the first time since the 2011 crisis at its Fukushima plant.

The NRA said it will review the company's measures to prevent a recurrence of the document mishandling.

The latest flaw comes on top of a series of security defects at the Kashiwazaki-Kariwa plant in April 2021 that led the NRA to ban TEPCO from moving nuclear fuel at the complex, effectively prohibiting its restart. The ban was lifted in December 2023.

The incident came to light ahead of the proposed reboot of No. 6 reactor at the seven-unit Kashiwazaki-Kariwa complex that Niigata Gov. Hideyo Hanazumi is expected to soon approve.

Restarting a nuclear reactor is virtually impossible without local consent after multiple meltdowns at the Fukushima Daiichi nuclear power complex in the aftermath of 2011 major earthquake and tsunami heightened public anxieties and concerns about nuclear safety. Many of the country's reactors are still offline.

TEPCO'S own investigation of the document mishandling saw other security flaws come to light, including a document containing emergency response measures erroneously being sent to a partner company, and a tool brought into the complex without the required authorization.

No leakage of confidential information outside the company has been confirmed, the NRA said.

Nos. 6 and 7 reactors at the Kashiwazaki-Kariwa plant cleared safety reviews by the NRA under stricter post-Fukushima safety regulations in December 2017.

Preparations ahead of a restart were completed last month at No. 6 unit, TEPCO has said.

The central government is keen to see the reboot of the Kashiwazaki-Kariwa plant to ensure a stable electricity supply to Tokyo and surrounding areas and increase revenue at TEPCO, which needs to secure funds to compensate people affected by the Fukushima nuclear accident.

NRA also said Thursday that officials of Tohoku Electric Power Co. were found to have doctored records of performance tests for equipment, including sensors that detect intruders, since 2018 at its Higashidori nuclear power plant in Aomori Prefecture in northeastern Japan.