More than a month after being shut down, Slovenia's sole nuclear power station was reconnected to the grid late on 17 November after the issue of a tiny pipe leakage in the primary system had been fixed.

"Organizations authorized by the Slovenian Nuclear Safety Administration gave a positive opinion for the start-up after an independent control of the activities," the Krško Nuclear Power Plant (NEK) said in announcing it was back online on 18 November.

It said the plant was running at 28% capacity, which was to be gradually increased.

The plant, which is located in Krško near the border with Croatia and is co-owned by the two countries, was shut down as a precaution on 6 October after a leakage was detected within the containment building.

NEK said the leak posed no threat to nuclear safety and was below limit values but decided for the shutdown in order to determine the source of the leakage and repair it.

Pinhole the size of a needle prick

The leak was discovered at a weld in the safety injection pipeline, about a metre from the reactor, coming through a pinhole the size of a needle prick.

NEK decided to replace the pipeline segment in its entirety - from the connection to the reactor vessel to the first valve. As a long-term precautionary measure, the other system pipeline, which surrounds the central part of the reactor, was fully replaced as well.

Last week 121 fuel elements were moved back from the spent fuel pool to the reactor vessel, where the nuclear reaction takes place.

Repair works were carried out by Westinghouse, the US company that supplied the original technology in the 1970-80s, when the plant was built.

Safety of workers and environment ensured

NEK said that no radionuclides were released into the surrounding area during the event and the repair.

Having received a report from NEK, the Nuclear Safety Administration said the repair of the damaged pipeline had been a challenging task but no worker received a radiation dose above legal limits.

"The measured collective dose of all workers was lower than the dose estimated before the start of the repair work ... all protective measures for the workers were taken, and effective decontamination of the work area and the pipelines was carried out.

"The impact of the unplanned outage on the environment and the population was very low and comparable to the impact during normal operation of the plant," the Nuclear Safety Administration said on 15 November.

"Gaseous discharges to the environment were slightly increased during the unplanned outage, but the levels were still comparable to those during regular outages. All radioactive discharges were well below the legal limits set for NEK," it added.

NEK has sent the dismantled parts of the pipeline abroad for destructive and metallographic examinations of the material and welds in a hot cell laboratory. Based on the results of these analyses, NEK will take additional technical measures if necessary, the administration said.

NEK was launched in 1983. Its lifespan has been extended by 20 years until 2043.