noun
primary cooling water
Technical term used in nuclear engineering and industrial cooling systems; refers to the water that directly removes heat from a reactor core or primary heat source.
原子炉では、一次冷却水が炉心の熱を運び出す。
In a nuclear reactor, the primary cooling water carries heat away from the core.
Secondary cooling water; in a two-loop system, it receives heat from the primary loop via a heat exchanger and is not directly exposed to the reactor core.
Compound of 一次 (primary, first) + 冷却 (cooling) + 水 (water). A straightforward technical term.