www.neimagazine.com September 2015
Diversification of the VVER fuel market
Mark Dye, Jan Höglund, and Ulf Benjaminsson give an overview of Westinghouse’s 15-year nuclear fuel development programme at South Ukraine, along with its plans to re-enter the VVER-440 fuel market with a new design. Fuel review | VVER fuel design Diversification of the VVER fuel market Mark Dye, Jan Höglund, and Ulf Benjaminsson give an overview of Westinghouse’s 15-year nuclear fuel development programme at South Ukraine, along with its plans to re-enter the VVER-440 fuel market with a new design.
he supply of electricity in several of Lead test assemblies for Ukraine VVER units in the EU and Ukraine the Eastern European countries is All of the nuclear power plants in Ukraine Name of station highly dependent on the operation of are operated by the government-owned Country Type of unit T and reactor unit their nuclear fleet, which entirely comprises National Nuclear Energy Company (NNEGC) VVER-440 and VVER-1000 units. Following Energoatom, which has headquarters in Bulgaria Kozloduy 5-6 VVER-1000 the political conflicts in Ukraine, including Kiev. Czech Dukovany 1-4 VVER-440 the Russian annexation of Crimea, the The development of the first Republic Temelin 1-2 VVER-1000 governments in these countries have become Westinghouse VVER-1000 fuel design Finland Loviisa 1-2 VVER-440 increasingly concerned about secure supply for delivery to Ukraine started in 2001, of VVER fuel. as a result of a governmental agreement Hungary Paks 1-4 VVER-440 Westinghouse Electric Company LLC is between the Ukraine and the USA on energy Bohunice 3-4 VVER-440 today the only alternative supplier of VVER cooperation and security. The work was Slovakia Mochovce 1-2 VVER-440 fuel, and was recently awarded an extended performed under the Ukraine Nuclear Fuel Khmelnitsky 1-2 VVER-1000 contract to supply VVER-1000 fuel to several Qualification Programme (UNFQP). of the 13 units of this type in Ukraine. In this Westinghouse had earlier designed and Rovno 1-2 VVER-440 article, the journey towards the contract will delivered VVER fuel to the Temelín nuclear Ukraine Rovno 3-4 VVER-1000 be presented, focusing on the performance power station in the Czech Republic, but South Ukraine 1-3 VVER-1000 of the Westinghouse fuel design and the without having to consider mixed core Zaporozhye 1-6 VVER-1000 technical challenges encountered and conditions. Developing VVER-1000 fuel resolved along the way. for mixed cores presented an additional Westinghouse is also actively supporting challenge, especially since compatibility data First deliveries to Ukraine the VVER-440 units in the European Union on the resident fuel was not easily accessible Before following up the LTA programme with (EU). In May 2015, a Westinghouse-led to Westinghouse. fuel delivery of reload (or batch) quantities, consortium with nine partners in different After completing the VVER-1000 fuel Westinghouse took the opportunity to countries was awarded funding from the development project, which was strongly enhance the LTA design, strengthening the European Atomic Energy Community supported by the Pacific Northwest National structural stiffness by adding a second bulge (Euratom) for a programme that will allow Laboratory (PNNL), six lead test assemblies attachment at each grid location (see Figure important steps toward diversification of the (LTAs) were manufactured in Westinghouse’s 1). The fuel design for the reload, referred to VVER-440 fuel market. fuel fabrication facility in Columbia, South as the Westinghouse Fuel Assembly (WFA) There are 33 VVER units operating in the Carolina, USA. Westinghouse shipped the fuel design, also included changes to the material EU and Ukraine, either of VVER-440 or VVER- in 2005 and it was loaded in South Ukraine 3 in 13 of the 16 grids to reduce parasitic 1000 design. Both types use hexagonal fuel, the same year. neutron absorption, thereby reducing the fuel but the VVER-440 fuel design is considerably The LTAs were discharged in 2010 after cycle cost. smaller and contains much fewer fuel rods. completing four cycles of operation as To supply the quantity of fuel assemblies Additionally, while the VVER-1000 design planned. Detailed examinations of the fuel needed for actual reloads in the reactor uses regular rod cluster control assemblies (including visual appearance, corrosion, units, manufacturing was relocated to (RCCAs) to control reactivity, in VVER- straightness, growth, and grid positions) Westinghouse‘s facility in Västerås, Sweden. 440 cores this is achieved by inserting were performed after each cycle and it was In 2009, Westinghouse fabricated 42 or withdrawing control fuel assemblies concluded that the Westinghouse LTA fuel assemblies here that were subsequently (“followers”) in certain positions of the core. performed as anticipated. loaded in South Ukraine 3 in early 2010. This
Figure 1. Westinghouse added a second bulge attachment at each grid location of the LTA design (left) to increase the structural stiffness of the WFA design (right) for the reload delivery
Grid sleeve Top of gridGuide thimble Grid sleeve Top of grid Guide thimble
Bulge joint Bulge joint
Reprinted from: NUCLEAR ENGINEERING INTERNATIONAL | September 2015 VVER fuel design | Fuel review
Empty positon where a fuel assembly is to be loaded
Figure 3. Additional grid-stiffening inner straps were added for RWFA (right)
Figure 2. Distorted fuel assemblies were surrounded by co-resident competitor loading, such as smooth-sided dummies present major loading challenges as the fuel assemblies with a significant amount and top nozzle loading guides, were also geometry of the open positions are no of distortion and a high level of structural developed to help open up the target core longer hexagonal stiffness. If a fuel assembly is pushed locations. into (or pulled out of) position under such The measures taken have proven to be effort was performed under the UNFQP. circumstances, it could cause mechanical very effective, and since the 2012 outages, The following year, 2011, another full batch interference with increased risk of damage the lateral forces during the reloading of the (42 WFAs) for reload was inserted in South to the grids. It should be noted, however, cores have been limited and there has been Ukraine 3 and the same number of fresh that none of the fuel rods’ integrity was no case of mechanical damage of the fuel assemblies were also inserted in the plant’s affected. assembly grids. The optimised sequence second unit. As a consequence, several assemblies also saves considerable time in loading the In addition to the fuel hardware, with potential damage were unloaded to assemblies. Westinghouse has received the go-ahead the spent fuel pool; after further inspection, from Energoatom to deliver its core it was concluded that most of these Fuel design enhancements supervision system, Beacon®, which also is could be used as-is, while some had to Several enhancements to the WFA design in operation at Temelín. The system has been be repaired. However, the State Nuclear were made to increase the lateral grid used at South Ukraine 3 to ensure accurate Regulatory Inspectorate of Ukraine (SNRIU) strength and to minimise the risk of harmful modelling of mixed core conditions, and to did not approve loading of any more fresh mechanical interaction between assemblies. enhance the level of support to the reactor Westinghouse fuel assemblies of this design. The outer strap of the spacer grids was operator during transients. To resolve the issue, Westinghouse made thicker and completely from Alloy 718, initiated two programmes: an optimisation of inner straps were added and the profile was Reloading challenges the core loading sequence and modifications modified to reduce the risk of interference In 2012, several Westinghouse assemblies in to the fuel design to reduce the risk of with adjacent resident fuel. Chamfers and both South Ukraine units showed mechanical damage due to mechanical interference. radii were added on the bottom nozzle, scratches and rub marks, and even damage and side plates on the top nozzle, to better of the grids during the reload shuffling. The Optimising the loading sequence facilitate the fuel assembly loading. (See grids had been damaged by mechanical Westinghouse developed the new core Figures 3–6). interference with the reference fuel and by loading sequence based on core loading The new design, referred to as the Robust high lateral loads that exceeded the strength experience and some fundamental principles. Westinghouse Fuel Assembly (RWFA), was limits. The different types of fuel assembly- verified by extensive mechanical and thermal- In contrast to other pressurised water to-fuel assembly loading scenarios were hydraulic testing; the first reload batch of this reactor fuel geometry, which uses a square ranked based on risk of interference, and robust design was inserted in South Ukraine lattice, the hexagonal-lattice VVER-1000 the ranking was then used to optimise the 3 in March 2015. This was the first reload of core is more exposed to mechanical loading sequence. Westinghouse also used Westinghouse fresh fuel that had been loaded contact between the fuel assemblies, a core loading sequence beginning from the since the 2012 outages. The new assemblies particularly if the surrounding assemblies centre of the core and stabilised the loading were loaded with no instances of damage. are distorted (see Figure 2). In the actual with a three-legged bridge from the core The 66 WFAs already in the core continued in cores, the Westinghouse fuel assemblies centre out to the shroud. Devices to aid the operation as planned.
Figure 4. Outer strap profile was modified for RWFA (right) Fuel review | VVER fuel design
fuel operations, when BNFL acquired Figure 5. Chamfers and radii were added to bottom nozzle for RWFA (right) Westinghouse. Westinghouse decided that the reload fuel would be assembled by ENUSA in Spain instead of at Springfields. Following some unsuccessful fuel tenders in 2006 and 2007, Westinghouse decided to exit the VVER-440 business. Lately, the increased importance of diversification of fuel supply has resulted in discussions with different utilities about re-entering the market with an upgraded Westinghouse fuel design, including more advanced materials, as well as improved mechanical features.
Euratom programme Euratom has allocated funding to support Chamfers on all six faces Chamfers and radii at sharp edges diversification of the nuclear fuel supply for the VVER units operating within the EU. Earlier this year, a consortium of Post-irradiation examinations ■ grid growth was consistent with the Westinghouse and eight European partners The reload batches of WFAs for South database for zirconium grids; and was awarded more than €2 million ($2.2 Ukraine 2 and 3 have been carefully inspected ■ peripheral fuel rod oxide thickness was million as of 14 July 2015) by the Euratom for and examined. Of these, 26 WFAs under significantly below the limits. a programme to qualify a second supplier. the UNFQP have completed their planned Based on the performance of the The programme will mainly focus on four cycles and 36 are currently operating Westinghouse fuel and the company’s ability establishing the methods and methodology their fourth and last cycle in unit 3. Post- to effectively resolve the challenges that required to license a VVER-440 fuel design. The irradiation examinations of the assemblies arose during the reloading of the cores in consortium includes partners with expertise were completed after each cycle of operation. 2012, Energoatom awarded Westinghouse and knowledge from different technical The results were all within the Westinghouse an extended fuel contract at the end of disciplines and the countries operating VVER- database for healthy fuel and in line with 2014. The contract will not only include 440 within the EU are represented (see box). expectations. An overall summary of the assemblies for South Ukraine plant, but also As part of the programme, steps will be taken results is: the Zaporozhye plant. to update the design previously delivered to ■ rod-to-top-nozzle gap measurements Loviisa, and to create a state-of-the-art design. showed sufficient margins, confirming a VVER-440 fuel development fuel rod growth that is consistent with the Countries operating VVER-440 units in the EU Summary Westinghouse ZIRLO® database; and Ukraine have also announced a growing A significant effort has been invested to ■ channel closure (fuel rod bow) results were interest in qualifying a second supplier. develop and qualify reliable fuel designs all lower than the maximum limit; Back in 1998, BNFL (British Fuel Nuclear for the VVER plants in Eastern Europe ■ fuel assembly axial growth measurements Limited) delivered lead test assemblies to unit and Ukraine. Fundamentally, the technical were as expected; 2 at Finland’s Loviisa plant. The assemblies challenges are similar to those encountered ■ RCCA drag force was well within the limits were manufactured in the fuel facility in in Western-designed light water reactors, and consistent with the Westinghouse Springfields, UK, and the purpose of the but sometimes more difficult to foresee and database for ZIRLO guide thimbles; programme was to qualify a second supplier overcome due to the difficulty of accessing ■ fuel assembly bow and twist were for Loviisa, as well as for Paks in Hungary. required technical data and information. measured and confirmed to be within After successful completion of the operation With the increased knowledge and experience for fuel assemblies with ZIRLO of the LTAs, in December 1999 BNFL was experience gained, Westinghouse has been guide thimbles; awarded a contract to supply reload deliveries able to establish a stable foundation for to Loviisa and a total of seven reload batches developing, manufacturing, and delivering Westinghouse’s partners in European were delivered between 2001 and 2007. competitive products to VVER utilities, which Supply of Safe Nuclear Fuel programme Shortly before the contract award, Springfields will foster diversification and thereby achieve ■ VUJE (Slovakia) was incorporated into Westinghouse the goal of enhanced security of fuel supply. ■ ■ ÚJV Rˇ ež (Czech Republic) Figure 6. Side plates were added to the top nozzle for RWFA (right) ■ Lappeenranta University of Technology (Finland) ■ National Nuclear Laboratory (UK) ■ NucleoCon (Slovakia) ■ National Science Center Kharkov Institute of Physics and Technology (Ukraine) ■ Institute for Transuranium Elements of the Joint Research Centre of the European Commission (EU) ■ Enusa Industrias Avanzadas (Spain)