primary circuit and secondary circuit如何理解？

ASME+API

FAC has caused a large number of failures in piping and equipments in all types of fossil, industrial steam, and nuclear power
plants and it is a predominant mode of failure of pipelines in the secondary circuit and has also affected carbon steel
pipelines in the primary circuit of light water reactors.

请问上述这段话中primary circuit and secondary circuit如何翻译和理解？

WASPCN

primary circuit：  一回路
secondary circuit：二回路
反应堆堆芯因核燃料裂变产生巨大的热能，由主泵泵入堆芯的水被加热成327度、155个大气压的高温高压水，高温高压水流经蒸汽发生器内的传热U型管，通过管壁将热能传递给U型管外的二回路冷却水，释放热量后又被主泵送回堆芯重新加热再进入蒸汽发生器。水这样不断地在密闭的回路内循环，被称为一回路。








FAC在各种类型的火力发电厂、工业蒸汽发电厂和核电站的管道和设备中造成了大量的失效，是二回路管道失效的主要形式，也影响了轻水堆一回路的碳钢管道。