In some PWRs, corrosion products deposited on the fuel cladding can cause boric acid and LiOH to accumulate in deposits in regions of sub-cooled nucleate boiling, leading to a shift of core power to other regions. This can cause

• A. Power-induced fuel failures
• B. Improved core stability
• C. Decreased corrosion rates
• D. Lower power output

Answer: (A)

Local neutron poisoning from boron-laden crud in regions where sub-cooled nucleate boiling occurs changes how reactivity is distributed in the core. The crud deposits act as sinks for neutrons because boron absorbs them, so those regions lose reactivity and produce less power. To maintain the overall reactivity, the power shifts to neighboring regions with less boron-containing crud. That redistribution creates hot spots in the other regions, and if the shift is significant, fuel rods in those regions can experience excessive local heat flux and cladding temperatures, risking fuel damage. This phenomenon is why the outcome is described as power-induced fuel failures.

The other options don’t fit because the situation doesn’t improve stability, reduce corrosion, or lower the overall power output; instead, it redistributes power and can drive local over-power conditions that threaten fuel integrity.