Japan’s nuclear power programme has suffered a public confidence setback so profound it can hardly be exaggerated, arising from a series of disclosures concerning falsified inspection documentation over a number of years and a cover-up that implicates its major nuclear utility and even public officials all the way into the ministry of Economy, Trade and Industry (METI).

The irregularities, at first disclosed as a series of systematically concealed or falsified reports of cracking in Tepco (Tokyo Electric Power Co) BWR reactors in the late 1980s and early 1990s, are now revealed as going far deeper – because a whistleblower employed by Tepco’s consultant reported the irregularities to METI as long ago as mid 2000. It appears that METI has been co-operating with Tepco ever since, by not formally (and therefore publicly) ordering new inspections, or taking any other public action, in an exercise designed to resolve discrepancies between what Tepco had reported to regulators and the actual conditions of core internals.

The falsifications involve 29 cases of suspect repair records at eight reactors in three plants. Most of the cases involve cracks in the stainless steel shroud enveloping the reactor core. Of the 29 instances, in 18 the equipment concerned has since been replaced or modified.

Several senior executives have tendered their resignations from the utility as investigations continue into Tepco and its maintenance contractor GE International (GEI). Nobuya Minami, the president of Tepco, is among them.

Following these disclosures METI leaked the news, known for two years only to Tepco executives and the regulators, that the utility had failed to properly report the results of core shroud inspections since the late 1980s. The inspections, covering BWR core internals, were requested by regulators after defects began showing up at GE-design units elsewhere.

The government’s Nuclear and Industrial Safety Agency, part of METI, has said that these cases “have no serious impact on the safety of the reactors in operation.” METI has denied charges of covering up the incident, saying that it could not go public prior to investigating the claims, but it is now under suspicion itself. 16 months went by before METI and Tepco began seriously addressing the charges raised by a GE employee in his first letter to regulators in July 2000. It now appears that Tepco tried to suggest that they along with their consultant GE had discovered the discrepancies themselves, and voluntarily reported them to METI.

More damaging in the long term may be the revelation that in at least one case Tepco repaired the flaw without informing regulators. Making such an engineering change would render void the operating licence, and in some countries that would lead to criminal prosecution.

These revelations come at a time when Tepco is already having to cope with the impact of the recent discovery of cracks in 316L low carbon steel components at its Fukushima I-3 plant and in the coolant shrouds inside the pressure vessel of Kashiwazaki-Kariwa 3. Five reactors have been temporarily shut down and Tepco has delayed indefinitely its plans to load MOX fuel into its plants.

Cracks had been discovered on the surface of sleeves of control rod drive hydraulic system piping at Fukushima I-3, and on the shroud inside the pressure vessel of Kashiwazaki-Kariwa 3. Tepco said that it discovered the cracks at Fukushima after it had temporarily removed and reinstalled the control rod drive hydraulic system piping, which supplies driver coolant in normal operations and high pressure coolant in scrams from a condensate system to the control rod drive mechanism. After reinstallation, NDT to detect cracks and other defects were carried out, revealing the faults.

Following the discovery, Tepco carried out investigations of other piping in the control rod drive hydraulic system near areas of penetration of the reactor containment. Additional cracks were found on some surfaces and Tepco decided to investigate further to determine the cause.

There has been a long history of stress corrosion cracking in BWRs. But it is only in the past year, when a deep crack due to SSC was discovered at Fukushima I-3, that cracks have been found in the advanced material 316L steel, previously claimed by Tepco to be highly resistant to this kind of fault.