An Outline of Water Treatment for Nuclear Powered Steam Generators

11 AN OUTLINE OF WATER TREATMENT FOR NUCLEAR POWERED STEAM GENERATORS 

Corrosion products include iron oxide (Fe203), ferrosoferric oxide (Fe304), nickel oxide (NiO), cobalt oxide (CoO), and complex Fe, Ni, and Co oxides. Cobalt in particular may present a problem (as cobalt59, a naturally occurring isotope), and when present as a contaminant in nickel alloys (such as Inconel 800), may enhance the development of an outer-core radiation field (see Section 7.4.1). 

Boric acid [B(OH)3] is employed in primary coolant systems as a soluble, core reactivity controlling agent (moderator). It has a high capture cross-section for neutrons and is typically present to the extent of perhaps 300 to 1,000 ppm (down from perhaps 500 to 2,500 ppm 25 years ago), depending on nuclear reactor plant design and the equilibrium concentration reached with lithium hydroxide. However, boric acid may be present to a maximum extent of 1,200 ppm product in hot power nuclear operations. 

Boron is, in fact, present not merely as boric acid, but is also distributed as various hydroxborates, such as B(OH)4, B2(OH)7, and B3(OH)10. 

Where continuous demineralization of reactor coolant is provided, premature degradation of the strong base anion (SBA) resins may occur. To avoid this, oxygen removal by use of anion resin in the sulfite form is employed. 

---