Romatom: Any similarity of Cernavoda's Units 1,2 unplanned stops, Chernobyl accident causes impossible to sustain

Any similarity between the unplanned stops or power rebates of the CNE Cernavoda Units 1 and 2 and the Chernobyl accident causes is impossible to sustain through technical, operational arguments, the Romanian Atomic Forum - Romatom says, recommending caution and a rigorous research in addressing such topics in the public space.

"Nuclearelectrica acts in strict conformity with the nuclear security procedures and I'm certain that these stops, although with no major nuclear security impact, are analysed so to ensure that such events won't repeat. The nuclear industry is a place of ceaseless learning from experience, and once the causes investigated all the measures are taken to avoiding them to appear again. One must understand that these halts are not a risk to the nuclear security, are not incidents or accidents, they are simply technical events that need the reactor's stop," the Romatom honorary Chairman Teodor Chirica says.

Unit 2 of the Cernavoda nuclear power plant has automatically disconnected from the national power grid on Thursday morning as a result of a malfunction of an electrical system, Nuclearelectrica, the operator of the plant, has announced.

The company states that it is the classic part of the plant, not the nuclear one.

"The specialists are investigating the cause and will perform the necessary repair work in accordance with the specific nuclear industry procedures in such situations." There is no causal link between Unit 2 power reduction on March 25, 2018 and the automatic disconnection of the reactor on March 29, 2018. The automatic disconnection of the reactor is provided for and achieved through the protection systems in certain situations, so it is conservative procedure, without impact on nuclear safety," the energy producer's officials explained.

"Romatom is certain that Nuclearelectrica, through its experts, is implementing all the necessary measures to reduce the frequency of such events, the company being among the nuclear power producers the most safe at global level," the release adds.

In addition, says Romatom, the unplanned halts cannot be ranked on the INES with the International Agency for Atomic Energy in Vienna, where the level 0 (the lowest) exclusively refers to deviations, the Cernavoda stops never being part of these categories.

"Unfortunately, the recent stops of the CNE Cernavoda power plant were associated erroneously with the precursory conditions that have led to the Chernobyl accident. This association is technically impossible, because: the differences between the CANDU reactors (the Cernavoda technology) and the RBMK (the Chernobyl's) are fundamental. The in-depth defence specific to the CANDU reactors means in fact a fundamental approach of the nuclear security from the outlook of the project, of the construction, of the operation. When it comes to CANDU reactors, 4 special security systems exist: 2 independent fast stop systems, redundant and different as regards their construction, the emergency cooling system of the active area of the reactor and the envelope's gear. (...) The basic cause of the Chernobyl accident was a designing imperfection of the stop system which in the circumstances of having an ill-fated experiment, which is not the case of CNE Cernvoda, has introduced an uncontrolled increase of the reactivity followed by the melting of the active area and the kick off of the well-mediatised accident," Romatom explains.

Moreover, as regards the RBMK reactor, the stop and control gears were not independent, therefore existing the possibility for key security systems be ignored and operated through manual adjustments of the control gear. When it comes to the CANDU reactors, the two systems are totally independent, the two acting automatically at exit from the normal operation parameters.

Another difference is the fact that the Chernobyl reactor had no protection envelope, and the key factor in the major radioactivity discharge in the environment was the power resulted from the graphite burning, a moderator specific to the RBMK reactor. The CANDU reactors have an envelope and preservation gears of the radioactive products, being designed to face a severe accident, with the heavy water as moderator, Romatom concludes.AGERPRES(RO - editor: Oana Tilica; EN - author: Maria Voican, editor: Bogdan Gabaroi)