Understanding Flow Fouling Deposition and Solute Hideout-Return Behavior at the Phase Change Interface

Area of Science:

• Nuclear Engineering
• Materials Science
• Chemistry

Background:

• Corrosion deposition and boron hideout on nuclear fuel cladding pose significant safety and economic risks in pressurized water reactors.
• Understanding these phenomena is critical for preventing localized corrosion and power shifts.

Purpose of the Study:

• To investigate corrosion product deposition under subcooled boiling conditions.
• To elucidate the mechanism of boron hideout and return, explaining power shift failures during power reduction.

Main Methods:

• Simulated accelerated deposition in a controlled environment mimicking reactor conditions.
• High-resolution characterization of corrosion deposits.
• Analysis of boron concentration changes in coolant after power reduction.

Main Results:

• Subcooled boiling intensity influences corrosion product supersaturation, crystal size, and deposition layer characteristics (looser, thicker, smaller particles).
• Boron is primarily hidden within deposits as H3BO3 and Li2B4O7.
• A significant increase (307.9 ppm) in boron coolant concentration post-power reduction confirms boron return from deposits.

Conclusions:

• Subcooled boiling, solute concentration, and water chemistry are key factors in corrosion deposition.
• The study confirms porous boron hideout and return mechanisms, highlighting challenges for operational safety.
• Findings provide a foundation for developing strategies to mitigate corrosion and boron-related issues in nuclear reactors.