BWR Control Rod CR 99

Categories: General Topics

Flawless Operability. Market-Leading Service Lifetime

The CR 99 control rod incorporates an optimized design with two separate high-density boron carbide pins in each hole. During control rod operation, neutron irradiation causes boron carbide to swell as B-10 atoms are transformed to Li-7 and He-4. With reduced diameter and tapered ends, the hot isostatic-pressed two-pin design minimizes swelling-induced mechanical strain on the blade wings and improves the ability to control mechanical behavior.
The CR 99 incorporates the same basic, robust blade wing design as former evolutions, but includes important refinements that have resulted in a sophisticated product that yields superior mechanical and nuclear performance. Many customers must agree: While Westinghouse has always had a large market share of BWR control rods – about 50 percent of the global market with presence in every country in the world with operating BWRs – this share is growing even more thanks to the outstanding performance of the CR 99, which has been extensively demonstrated during the last few years.

A Design Advantage Found Only in the Westinghouse CR 99

The most important design feature of Westinghouse’s high-performance CR 99 control rod is the introduction of hot isostatic-pressed boron carbide pins. These pins are approximately 40 percent denser than the standard boron carbide powder currently used in all other BWR control rod designs – offering the following distinct advantages:

  • High density – allows for free expansion gaps and more boron carbide, yielding a longer mechanical and nuclear lifetime
  • Flexible geometric pin design – enables tailor-made pin designs that can accommodate local depletion and swelling peaks, avoiding mechanical degradation such as irradiation-assisted stress corrosion cracking (IASCC)
  • Improved material integrity – provides resistance to boron leakage
  • Controlled swelling behavior – enables reliable characterization and prediction of mechanical behavior

Defense-in-depth: Four Inherent Safety Barriers

The most important propertyof a control rod is that it maintains its safety functions during the licensed operating range, which is defined by its nuclear lifetime limit. To achieve this objective, CR 99 design development has been founded on a system of inherent safety barriers to protect the control rod from mechanical degradation up to very high depletion levels – well beyond the nuclear lifetime:

  • Controlled absorber pin swelling with free pin swelling phase
  • Blade construction proven resistant to irradiation-assisted stress corrosion cracks
  • Blade and pin design proven fully resistant to boron leakage
  • Basic design with small but numerous horizontal absorber units

For additional information, please contact Björn Rebensdorff, product manager, BWR Control Rods at +46 21.347528 or