[en] The helium accumulation fluence monitor (HAFM) technique has been used to measure the ¹⁰B(n,He) reaction rate within B₄C pellets in a control rod in ZPPR. Knowledge of this reaction rate is important to control rod design studies because helium production leads to control rod swelling, buildup of gas pressure and a reduction in thermal conductivity which can limit the lifetime of a control rod. We believe these to be the first measurements of boron capture within boron pins in a fast reactor spectrum. Previously reported measurements used ²³⁵U foils to measure fission rates in a control rod, and to infer boron capture rates