Recent years have witnessed a continuous rise in the performance requirements for nuclear fuel assemblies: nuclear plant operators today want the highest possible reliability with optimum fuel utilization and flexible operation. Framatome ANP has successfully achieved these goals with the development of its HTP X5 fuel assembly for PWRs.

Our HTP X5 fuel assembly: Leader in fuel economy and reliability

Designed for Enrichments up to 5 wt.% U-235

Optimum fuel utilization and maximum fuel assembly reliability are key factors for reducing nuclear fuel cycle costs and thus enhancing the competitiveness of nuclear power. The employment of higher-enriched fuel and high operational reliability of fuel assemblies in reactors with demanding power histories were two of the main objectives in fuel assembly development. Framatome ANP's new fuel assembly, HTP X5 (High Thermal Performance eXtended up to 5 wt. %) for PWRs is designed for enrichments of up to 5 wt. % U-235 and permits fuel assembly burnups of around 70 MWd/kgU and fuel rod burnups of up to 75 MWd/kgU.

Comprehensive Experience in the Use and Management of HTP Fuel Assemblies

By the end of 2001, 3,400 HTP fuel assemblies were installed in 22 PWR plants built by various vendors in Europe, Asia and the US, predominantly in reactors using 17x17 lattice fuel assemblies. A maximum fuel burnup of 56 MWd/kgU was achieved with these assemblies. Despite the ever- increasing rate of achieved burnup, the operating performance of these fuel assemblies has been exceptional.

High Reliability Despite Continuously Increasing Discharge Burnups

The continual increase in discharge burnup is clear testimony to high reliability. In the last 20 years, the average discharge burnup of peak reload batches of PWR fuel assemblies has risen by more than half to over 50 MWd/kgU. With the advanced HTP fuel assemblies now already in use, discharge burnups of 55 MWd/kgU will be achieved in the near future. The materials and design of the HTP fuel assembly have been optimized such that within two annual cycles, burnups of some 35 to 40 MWd/kgU are possible without any operational limitations.

Over a number of operating cycles, the superiority of the HTP line contact fuel rod support has been proven, even at positions in the reactor core in which failed rods were frequently encountered in assemblies equipped with traditional spring-and-dimple spacers. No rod failures have occurred since the HTP fuel assemblies were installed at these locations.

HTP X5 Characteristics

The term, "HTP," refers to both a spacer type and the entire fuel assembly design, equipped with this spacer as a main component.

Spacers:
The unique, innovative design of Zirconium HTP spacers combines fuel rod support and coolant flow mixing in a single component. The curved flow channels increase coolant mixing and improve thermal-hydraulic behavior. The line-contact fuel rod support across four double lines ensures a large contact area and thus optimum resistance to grid-to-rod fretting: No fuel rod damage due to fretting has been observed over a period of 15 years. In the HTP X5 fuel assembly, the innovative Inconel spacer derived from the HTP spacer design is used at the bottom spacer position where high loads are incurred.

Bottom end fitting:
To contain debris and thus prevent fretting damage to the fuel rods, the fuel assembly bottom end fittings are optionally fitted with an integrated debris filter or with FUELGARD™.

Cladding tubes:
Increased requirements placed on advanced reactor operation require cladding tube materials with excellent corrosion resistance, low hydrogen uptake and assured mechanical properties. Our advanced M5™ cladding is designed to fulfill all PWR operational requirements even under the most demanding plant conditions (temperature, void, power history etc.) up to the maximum burnup one can achieve with 5 wt. % U-235.

"New Generation Fuel Assembly"

Framatome ANP conducted extensive testing and lead design programs working closely with its customers, to enable continuous improvements in fuel economy and reliability. Working with customer needs, Framatome ANP will develop, through the "New Generation PWR Fuel Assembly" project, a new PWR fuel assembly design based on previous design experience and operational feedback in the coming years.