Government officials who inspected 22,000 certificates for parts used in 20 working reactors found that 277 or 1.2 per cent of the documents had been forged, the Prime Minister's Office said.
A separate probe of eight other reactors, which are offline or under construction, showed that 0.9 per cent of the certificates had been forged, the office said.
It did not specify whether the defective parts which caused the 128 shutdowns had been given fake certification.
In 2009 it won a USD 20.4 billion contract to build four nuclear plants in the United Arab Emirates.
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But the govenment's inspection revealed widespread corruption in the nuclear industry, which is undergoing a crisis of confidence following a series of shutdowns.
Public prosecutors have charged about 100 people over the scandal involving fake safety certificates.
In a separate case of document forgery eight suppliers last year were found to have faked warranties covering thousands of items used in several reactors.
Despite concern over how the nuclear sector is run, the government has vowed to push ahead with plans to build an additional 16 reactors by 2030.