The safer, saltier nu­clear al­ter­na­tive

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pro­duce heat as they de­cay. Nu­clear plants draw power from this process, and typ­i­cally sta­bi­lize the tem­per­a­ture with wa­ter. But dur­ing a power out-age, H2O- which needs pumps to flow can t al­ways pre­vent melt­downs. Molten salt re­ac­tors, which in­stead con­trol heat with melted lithium and potas­sium flu­o­rides, have a fail-safe: If the elec­tric­ity dies, a plug will melt, caus­ing the salts to seep down a safety drain and so­lid­ify around the ura­nium, pre­vent­ing over­heat­ing. Af­ter a decades-long lull in de­vel­op­ment, coun­tries from China to Denmark are build­ing new molten salt re­ac­tors. Here’s how they work.

Re­ac­tor ves­sel

Ura­nium floats in a sta­bi­liz­ing bath of melted flu­o­ride salts in­side this con­tainer. As the ra­dioac­tive atoms split apart, their fis­sion steadily heats the ves­sel to 1,300 de­grees Fahren­heit, the ap­prox­i­mate tem­per­a­ture of magma.

Pri­mary heat ex­chang­ers

Tubes on ei­ther side of the re­ac­tor ves­sel trans­fer the heat to in­ter­me­di­ate pipes, which are filled with clean molten salts. The un­con­tam­i­nated sub­stance can carry en­ergy with­out pro­duc­ing any ad­di­tional ra­dioac­tive waste.

Coolant salt pumps

These pumps move the clean salts in the heat ex­chang­ers away from the ra­dioac­tive re­ac­tor ves­sel and to­ward a steam gen­er­a­tor housed in a sep­a­rate build­ing. This lim­its the haz­ardous ma­te­rial to a sin­gle, iso­lated lo­ca­tion.

Steam gen­er­a­tor

The sear­ing salts heat wa­ter into steam, which spins a tur­bine to pro­duce elec­tric­ity. In one hour, a molten salt re­ac­tor may be able to crank out 500,000 kilo­watts, enough to power 45 U.S. house­holds for an en­tire year.

Drain tank

Con­tam­i­nated re­ac­tor salts and ra­dioac­tive gases fil­ter into a waste-dis­posal sys­tem. These ma­te­ri­als re­main haz­ardous for only hun­dreds of years—com­pared with hun­dreds of thou­sands for tra­di­tional re­ac­tors’ byprod­ucts.

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