FNR

FNR is an acronym that can refer to several distinct concepts in science and engineering. The two most common meanings are in plant biochemistry and nuclear engineering.

Ferredoxin-NADP+ reductase is an enzyme involved in photosynthesis. It is a soluble flavoenzyme located in the stroma of chloroplasts and, in some organisms, in bacterial cytosol. Its primary role is to transfer electrons from ferredoxin, reduced by photosystem I, to NADP+, producing NADPH. This NADPH is a reducing power used in the Calvin cycle and other biosynthetic pathways. FNR contains a flavin adenine dinucleotide (FAD) cofactor and operates on the stromal side of the thylakoid membrane, linking light-driven electron transport to carbon fixation and metabolic synthesis.

Fast neutron reactor is a class of nuclear reactor that uses fast neutrons to sustain fission, with little or no moderated neutron slowing. Compared with conventional thermal reactors, fast reactors typically require higher fuel enrichment and use coolants such as liquid metals or lead alloys. They are studied for their potential to achieve better fuel utilization and to transmute long-lived radioactive waste. Fast reactors pose engineering and safety challenges, including materials performance under high neutron flux and the need for robust containment and cooling systems.

The acronym FNR also appears in other, less common contexts across different fields. When encountering FNR, context usually clarifies whether it refers to the chloroplast enzyme, a fast neutron reactor, or another specialized term.