What is the role of boron in PWR chemistry, and how is boric acid managed?

• A. Boron acts as a catalyst for corrosion inhibition in the coolant.
• B. Boron provides neutron absorption for reactivity control; managed by concentration control and boron precipitation avoidance.
• C. Boron is used to adjust the coolant's pH level.
• D. Boron fortifies the structural steel matrix to enhance strength.

Answer: (B)

The role boron plays in a PWR is to provide a soluble neutron absorber that helps control reactor reactivity. Boric acid is dissolved in the primary coolant, and changing its concentration changes how many neutrons are absorbed in the core, allowing smooth reactivity management as fuel burns up or as power levels change.

The way boric acid is managed centers on keeping the right amount in solution and preventing it from forming solids. This is done through the boron concentration control system, which adjusts boron levels by adding borated water or by removing concentrated coolant through the letdown stream for purification. By diluting or concentrating the boron appropriately, operators maintain the desired reactivity setpoints without abrupt changes.

A key aspect is avoiding precipitation of boron compounds, which would remove boron from the dissolved pool and create uneven absorption in the core. Chemistry controls keep boron in solution, typically by maintaining the proper pH and temperature and ensuring the chemistry remains within established limits so boron stays dissolved and uniformly distributed. This combination—precise boron concentration control plus chemistry practices to prevent precipitation—lets boron do its job as a stable, controllable reactivity mechanism.