Under the nuclear fuel diversification project for Ukrainian NPPs, the Work Program will be gradually changing – from introduction of the Westinghouse fuel at one power unit and then at six power units at the next stage and finally – to complete refusal from the russian fuel and transfer to the Westinghouse fuel at all VVER-1000 power units.

Before the full-scale russian invasion of Ukraine, nuclear fuel produced by Westinghouse (TVS-W and TVS-WR) was exported to six of the thirteen power units with VVER-1000 reactors. Among them were four power units of the Zaporizhzhya NPP and two power units of the South Ukraine NPP. At that time, specialists from the STC “Nuclear Fuel Cycle” of NTC KhIPT performed great work to justify the introduction of TVS-WR at power unit 3 of the Rivne NPP, and as a result, one full reloading batch (42 items) of fuel produced by Westinghouse arrived at the RNPP site. The first batch of fuel was loaded in the summer of 2022. This allowed the power unit to pass the difficult autumn-winter period of 2022-2023 without hindrance.

NNEGC Energoatom, after the full-scale invasion of the russian federation, announced its readiness to completely refuse from the russian nuclear fuel and switch to products manufactured by the Swedish Westinghouse plant. There are quite solid grounds for such statements, given the fact that industry experts and representatives of the State Nuclear Regulatory Authority have repeatedly confirmed that this fuel has exemplary performance characteristics and high economic indicators. The Westinghouse fuel was operated under constant oversight and monitoring of its condition during operation. From the very beginning of implementing the TVS-W (TVS-WR), specialists from the SE NNEGC Energoatom and Westinghouse, with the scientific support of the STC “Nuclear Fuel Cycle” of NTC KhIPT, conducted annual inspections of fuel assemblies. As a result, from 2013 to 2021, 86 Westinghouse fuel assemblies were inspected and the values ​​of nuclear fuel parameters affecting its reliable and failure-free operation at Ukrainian NPPs were obtained.

During the inspections, the obtained values ​​of parameters that determine the technical condition of TVS-W/WR manufactured by Westinghouse did not exceed the boundaries established during the fuel design and safety justification for fuel loading. All fuel assemblies, inspected after 1-3 years of operation, were used in subsequent fuel loads. The values ​​of parameters characterizing the technical condition of the TVS-W/WR after four fuel cycles indicate that the nuclear fuel has not exhausted its resource and has a sufficient margin of controlled parameters to achieve higher burnup depths.

Based on the results of post-reactor inspections of 86 TVS-W/WR, the main conclusion was that the technical condition of Westinghouse fuel assemblies operated in Ukrainian reactors, fully satisfy the safety requirements set out in the design and justification of safe operation. Specialists of the STC NFC together with specialists of Energoatom published a number of scientific articles confirming the statement made about the reliability and safety of TVS-W/WR operation. The main ones (Experience in examining irradiated nuclear fuel..., Corrosion resistance of fuel rod cladding...) were published in the journal “Nuclear and Radiation Safety”, the founder of which is SSTC NRS.

Military actions did not suspend the efforts to diversify supplies of nuclear fuel for Ukrainian nuclear power plants, but gave even more impetus. An intense start-up was taken to justify the use of Westinghouse fuel at other power units of Ukrainian NPPs. As soon as the decision was made to supply fuel to the Rivne NPP – the STC “Nuclear Fuel Cycle” of NTC KhIPT conducted a series of justifications to introduce TVS-WR at Rivne NPP power unit 3 and accept a reloading batch (42 FAs) of Westinghouse fuel at the site. In the near future, the STC NFC specialists will complete the preliminary justification for power unit 4 of the Rivne NPP. There is still work ahead for one power unit of the SUNPP and two power units of the KhNPP.

In the first half of 2023, the next batches of fuel assemblies produced by the Swedish branch of Westinghouse arrived at the site of the Rivne NPP, where specialists carried out acceptance and incoming inspection. All fuel assemblies successfully passed the incoming inspection.

As known, the procedure of acceptance and incoming inspection of fresh fuel assemblies includes unpacking the containers, monitoring the unloading of assemblies, checking the geometric dimensions of assemblies and placement of fuel rods, visual inspection of fuel rods, spacer grids, tail and head of each assembly for the absence of mechanical scratches, damage, defects, and foreign objects with additional control of the cells of spacer grids and measurement of parameters that guarantee the FA safe operation and subsequent control of the FA movement to the fuel storage casks (the sequence is shown in figures). After this, the passing ability of the FA guide channels is checked in the casks.

Due to such a thorough check during the nuclear fuel incoming inspection, specialists of the Rivne NPP and STC NFC did not have any questions about the quality of Westinghouse products. All fuel transported to the RNPP has passed the incoming inspection procedure and is waiting its turn to be loaded into the reactor core.

This year, the STC NFC specialists took part in the reloading (offloading / loading) of the reactor core at Rivne NPP Unit 3. During the refueling process, the second full refueling batch (42 FAs) of TVS-WR produced by Westinghouse was loaded into the core.

The STC NFC specialists step-by-step monitored the reloading operations following the recommended sequences. They noted that the consistent transition to Westinghouse fuel led to a reduction in the grouting forces when moving fuel. The fact is that fuel assemblies, having overall length dimensions of more than 4500 mm and a turnkey size of 235 mm, are loaded into the reactor core with the step, which guarantees a gap of only ~1 mm between the cassettes. Therefore, the forces of their interaction during vertical movement are the key point characterizing the state of the mixed core (TVSA (produced by the russian federation) + TVS-WR) and confirms the correctness of its design when justifying the introduction of TVS-WR at Rivne NPP-3. The core reloading at Rivne NPP Unit 3 was conducted successfully, without any unexpected complications or problems.

This year, the STC NFC specialists also participated during reloading of the reactor core at South Ukraine NPP Units 2&3. The specialists paid special attention to the effort and speed of fuel assembly unloading. In addition, they kept control over the integrity of the fuel assembly structural elements and their design position, as well as abnormal signs of corrosion.

This special attention was given due to the fact that SUNPP-2 and SUNPP-3 finish the usage of the unmodified (unreinforced) TVS-W design together with TVS-WR. TVS-W was designed for mixed loading with TVSM (produced by the russian federation). During 2012-outage, the fuel assemblies of this design were damaged when loading a mixed core with TVSA (manufactured by the russian federation).

TVS-W fuel assemblies were not used for the core, because the russian federation began to supply the modified TVSA instead of TVSM to the Ukrainian nuclear power plants, which had a more rigid design. The opportunity to use TVS-W appeared after a complete transition from russian-manufactured FAs to TVS-WR. The reloading of the reactor core of SUNPP Units 2&3, which included TVS-WR and TVS-W, was carried out successfully, without any unexpected complications or problems. According to experts, this indicates the proper quality of the fuel, correctness of the proposed loading sequence and appropriate professionalism of the responsible personnel at the nuclear power plant.

Summarizing the above, the specialists of the STC “Nuclear Fuel Cycle” have been taking part since 2005 in all works of the “life” cycle of Westinghouse nuclear fuel for Ukrainian VVER-1000 reactors - from receiving fresh fuel at NPP sites to examining its condition after the fourth year of operation.

After the full-scale russian invasion, the amount of work increased. The experience gained by the specialists was useful for a large number of scientific and engineering works carried out by NSC KhIPT NASU for NNEGC Energoatom and its separate divisions. First of all, this work includes design, development and manufacture of control rods produced by Ukrainian enterprises for VVER-1000 reactors and conducting research to justify long-term (up to 50 years) storage of VVER spent fuel in “dry” storage facilities.