Nuclear Resin Quality and Operating Capacity
Ion exchange resins used in nuclear power plants (see table below) are quality rated and must meet nuclear-grade specifications that are established by plant chemical engineers. These quality specifications establish limits on low levels of residual inorganic and organic constituents found in the resin that remains after resin manufacturing.
The operating capacity of nuclear-grade ion exchange resins, whether in bead form or powder form, is a function of:
- Impurities to be removed from the influent
- Amount of ionic leakage tolerated
- Concentration of ions remaining on the resin treating the influent after regeneration
- pH of the influent stream
If exchange conditions are favorable (low velocity), the operating capacity of new nuclear-grade ion exchange resins should be close to the total capacity.
The use of boric acid will convert anion resin to the boron form quickly, and the capacity of an anion exchange resin for boric acid increases with increased boron concentrations.
Resins used to treat the water in the spent fuel pool will reach the end of life sooner than resins in other systems because the cation component of the mixed bed will degrade in the presence of peroxide, thus releasing organo-sulfonic compounds. Energy from fuel will support the radiolysis of water, forming this peroxide and hydrogen. Organo-sulfonic compounds will foul the anion resin and leach into the pool, where it will subsequently degrade to sulfate. Higher cross-linked gel and macroporous cation resins have extended mixed bed resin life with limited success. The concentration of fuel volume and temperature of the pool water is related to cation resin life.
Condensate polishing resins are subjected to high linear flow rates. Resins used to polish BWR condensate streams will operate until the bed reaches the end of life, usually a predetermined date, reactor sulfate exceeds 2 ppb, chloride exceeds .3 ppb, or iron exceeds 8 ppb. Boiling water reactor (BWR) plants will not regenerate their resins so replacement with new resin is required.
Resins used to polish pressurized water reactor (PWR) condensate resins are impacted by multiple chemistries being fed to the steam generator. The presence of different amines at different concentrations will quickly load the resin. Anion fouling by organo-sulfonates reducing anion kinetics will drive resin replacement. Ionic leakage of sodium, sulfate or silica will generally determine resin regeneration.
Regeneration of PWR condensate is challenging because of the low ionic sodium and chloride leakage required. As a result, service companies are often contracted to provide this service offsite.
Resins used to treat steam generator blowdown encounter the same issues as the condensate resin but at a lower flow rate. If the cation resin has sodium < 10 ppm, it is possible to operate these resins for many months past the ammonia break. Additionally, this resin is designed to remove sodium primarily. Resin life can exceed two years for very clean systems when regenerated. If not regenerated, the life expectancy of resins in this service is generally between six weeks and six months.