Increasing Nuclear Safety
Ever since the beginning, a high operational safety standard was maintained at the V1 nuclear power plant. A perfect knowledge of the facility, technical competence and qualified approach reflected on the proposed and the realized changes. These included for example the addition of a continuous piping cleaning system at the condensers, or the sieves for the circulation water going to the condensers, or the reconstruction of the cooling towers, the modification of the guide wheels of the high pressure turbine segments and others. In order to reduce the radiation stress on the reactor pressure vessel welds, 36 shielding cartridges were used surrounding the active zone, gradually, in both units.
In the early nineties of the last century, the V1 NPP V230 type units had reached approximately one third of their originally planned lifetime and started to be thoroughly analyzed for their operational safety and reliability with newer criteria in effect. In order to reach even better safety levels of the power plant, the Czechoslovak Atomic Energy Commission issued Resolution Nr. 5/91, in which it only allowed the further operation of the power plant under the condition that 81 items of the resolution be implemented. The modifications realized within the small reconstruction were predominantly focused at the restoring of material properties of the reactor pressure vessels, improvements in safety systems and reactor protection systems. The V1 NPP was improved in the area of seismic reinforcement and fire prevention systems. By realizing these, for the most part, technological improvements, the safety of this nuclear power plant was significantly raised. The sheer amount of work done can be well assessed by looking at the cost of the small reconstruction, which was, by the standards of its time, the considerable sum of two billion Czechoslovak Crowns. An important and exceptionally successful procedure that was done in course of this was the annealing of the pressure vessels of both, the first and the second unit. The annealing had positively affected the reactor pressure vessels’ properties and has significantly contributed to the lowering of the so-called brittle fracture temperature of these pressure vessels. A testament to the exceptionality of the equipment used and the success of the operation is the fact that subsequently annealing was used to treat reactors of a similar design in the Finnish Loviisa power plant.
In 1994, after the completion of the small reconstruction, the ÚJD issued a resolution, which allowed the V1 NPP to continue operating only if internationally accepted nuclear safety standards are attained. Based on this resolution, the V1 NPP was gradually reconstructed in 1996-2000. The investment was significant — about 7.5 billion Slovak Crowns. The goal of the reconstruction was the implementation of safety measures and the creation of prerequisites for the possible lifetime extension of the plant, which was originally designed to last 30 years. It was a pilot project for reactors of this type and after the completion of the final reconstruction the V1 NPP became the safest power plant with WWER V230 type reactors.
The base documentation for the gradual reconstruction project was the conclusion of the International Atomic Energy Agency — IAEA (OSART, Operational Safety Review Team), the expert analyses and engineering review of areas identified by the “Basic Engineering”. The prime supplier was the REKON consortium, which comprised of the German Siemens and the Slovak VÚJE. The Purpose of the gradual reconstruction was not only the replacement of the aged equipment with new, qualified and modern technology, but also the extensive changes and improvements in the philosophy and automatic functions, to meet the requirements of international standards and regulations. The reconstruction affected two areas in total.
The reconstruction work was partly done, while the plant was in operation, but mostly during extended fuel replacement downtimes. The most work was done during the general overhaul in 2000, in the final stage of the gradual reconstruction. The implementation of the measures represented a balanced, strengthening of safety.
In November 2000, after the completion of the reconstruction work, the IAEA mission judged the results of the gradual reconstruction. In a summary report, it concluded that an overall and satisfactory safety improvement program had been realized, which defines a new project base compliant with the Slovak national requirements, and that in some respects it exceeds the recommendations made by the IAEA. Realized Audits and missions of expert international organizations, such as the IAEA, WANO (The World Association of Nuclear Operators), WENRA (Western European Nuclear Regulators’ Association) and others all came to positive conclusions about the condition of the nuclear power plant, while none of them had recommended the discontinuation of the operation of the V1 NPP.
After the completion of the gradual reconstruction, The Nuclear Regulatory Authority of the Slovak Republic issued resolution ÚJD Nr. 144/2001 for Unit 1 and resolution Nr. 220/2001 for Unit 2 of the V1 NPP, in which it approved the continued operation, unrestricted by time, of the V1 NPP.
The fate of the V1 power plant, however, had already been sealed in 1999, when the government of the Slovak Republic approved resolution 801/1999 as a realistic deadline for the shutdown of the V1 Jaslovské Bohunice nuclear power plant units. Shutting down the V1 units in 2006 and 2008 was a political decision based on the European Union admittance talks between the Slovak Republic and the European Union and had nothing to do with the technical condition of the nuclear power plant facility or any potential risks of operating this plant.