The Swiss nuclear safety programme has reported one of the highest annual levels of incidents at its power plants in the last ten years.
But Switzerland's nuclear power plants were well protected from the threat of terrorist air attacks, or a plane crash.
In its 2001 report, released at a press conference in Bern on Monday, the Swiss Federal Nuclear Safety Inspectorate (HSK) said 18 incidents had been recorded in the industry during the past year - double the number for 2000.
The most serious incident occurred at the nuclear power reactor in Leibstadt, in northern Switzerland. Investigators found a disparity between what two employees had reported verbally and what appeared in the written records.
The irregularities came to light while the plant was closed for servicing.
But Hans Pfeiffer, deputy director of HSK, said the incident had never threatened the security at the plant; He said inquiries carried out at other nuclear installations across the country had not revealed any similar discrepancies.
The HSK report also stressed that the incident at Leibstadt was graded at level 1 on the international scale of safety within the industry (INES). All 15 of the remaining cases at nuclear power plants, were graded at 0 - the lowest level of danger.
The report also focused on security issues in light of the September 11 attacks. The HSK director, Ulrich Schmocker, said no expense had been spared in ensuring the security of Switzerland's nuclear installations.
HSK underlined that Swiss facilities were among the safest in the world, and every new plant since the 1970s had been designed with specific measures to withstand a plane crash. Plants built before the 1970s had been brought up to the same standards.
The events of September 11 had made the industry question its vulnerability to terrorist attacks. Auguste Zurkinden, a department head at the HSK, said initial results carried out by a group of experts from the fields of aviation, construction and fire safety, rated the more modern plants very highly.
But questions remained about some of the older plants and results from specifically designed tests would not be available until the end of the year.
Zurkinden said the HSK was evaluating conditions for the future transport of Swiss nuclear waste for reprocessing. He stressed that safety measures would remain vigorous. A report is expected at the end of May.
Since August 1999, most of the waste has been sent to France or Britain. The HSK said there had been no cases of contamination from the convoys.
swissinfo with agencies