a substance (other than fissionable material) that has a large capacity for absorbing neutrons in the vicinity of the reactor core, an absorber dissolved in solutions of fissile materials or incorporated into plant equipment which holds or processes fissile materials, soluble or fixed poisons, respectively, materjal, mis on neutronneeldur (muu kui lõhustuv materjal) ja on lisatud reaktorisse tahkel või vedelal kujul, kas jahutusvedelikku, tuumkütusesse ja/või kontrollvardasse