MSR Benefits

Molten Salt Reactor Advantages

  • Molten Fuel - Fuel circulates through the reactor, fission products get removed, for over 99% fuel use (vs. LWR ~3%). No long-term radioactive waste.
  • Salt Cooled - Coolant far below boiling point, reactor operates at atmospheric pressure. Fuel dissolved in stable salt (no water), no loss of coolant accident possible. No need for high-pressure safety systems.
  • High Inherent Safety - No water, no high pressure, nothing that could propel radioactive materials into the environment. Thermal expansion/contraction of molten fuel salt strongly regulates fission rate; MSR is a very stable reactor. Simple safety systems work even if no electricity or operators.
  • Easy Construction and Siting - Low pressure operation, so no high-pressure safety systems. No water, so no steam containment building. Reactor factory assembled, with modern quality control, sensors and communication.
  • Lower Cost - Even with exotic materials, construction costs will be dramatically lower than LWR — factory construction, minimal manual on-site preparation. No long-term radioactive waste, so no long-term storage.
  • High Temperature Operation - Heat to generate electricity, desalinate water, produce CO2-neutral vehicle fuel, etc.
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One of the reactors India is working on is the AHWR, a solid thorium fueled, water cooled reactor. “AHWR is a 300 MWe, vertical, pressure tube type, boiling light water cooled, and heavy water moderated reactor. AHWR is being set up as a technology demonstration reactor keeping in mind the long term deployment of Thorium based reactors in the third phase. It will provide a platform for demonstration of technologies required for thorium utilisation. The reactor will use (Th-Pu) MOX and (Th-233U) MOX types of fuel. The fissile 233U for this reactor will be obtained by reprocessing its spent fuel, while plutonium will be provided from reprocessing of the spent fuel of PHWRs.  The adoption of closed fuel cycle in AHWR helps in generating a large fraction of energy from thorium. A co-located fuel cycle facility (FCF) is planned along with the reactor and it will have facilities for fuel fabrication, fuel reprocessing and waste management. Some of the technologically challenging issues in this are handling of the highly radioactive fresh fuel, the requirement of remote fuel fabrication and carrying three-stream aqueous reprocessing by dissolution of the stable thoria matrix.” Also see the AHWR more info, “On an average, about 39% of the power is obtained from thorium.” The reactor has passive water cooling, with a pool of water above the reactor sufficient for 3 days “Later, cooling of the core is achieved by the injection of cold water from a large Gravity Driven Water Pool (GDWP) located near the top of the reactor building. In AHWR300-LEU, subsequent to energy absorption in GDWP in vapour suppression mode, the Passive Containment Cooling System (PCCS) provides long term containment cooling following a postulated LOCA. GDWP serves as a passive heat sink yielding a grace period of three days.”

The Molten Salt Reactor Experiment was designed and built in 5 years, with engineers using slide rules, with 1960s design tools, materials testing, etc. We have computer aided design, modern sensors, much better materials and materials testing facilities, computer nuclear modeling, flexible robotic assembly. You really think that with comparable number of people and budget to what Oak Ridge National Laboratories had, a better MSR would take more than the same 5 years?

I think in 5 years with proper staffing, we would have a reactor designed and factory designed and built to mass-produce MSR, with even better safety and fuel use than AHWR — MSR is a simpler design, if you include the fuel fabrication (none) and reprocessing (only fission products, no long term nuclear waste to deal with).

Fluorides are easier to chemically process than solid oxides; a required step in PUREX for LWR fuel is getting the fuel out of oxide). A two-fluid MSR such as LFTR wouldn’t have to separate thorium from the rare earth fission products, and simple fluorination returns uranium to the reactor. AHWR would have thorium, fission products, and uranium all in the same pellet.

AHWR is a solid fueled reactor, so there will be low fuel usage, though it will use less uranium and produce less actinides. Fission products trapped in fuel rods will stop fission long before the fuel is used. Most MSR designs would use over 99% of the fuel, and all fission products with long half-lives would remain in the reactor to decay by neutron bombardment; only isotopes with 35-year half lives or shorter as waste. MSR would have no need for “long-term storage of the spent fuel along with monitoring and retrieval” that AHWR will need.

AHWR is a water cooled reactor. Good that the passive safety features are so much better than LWR; but it still needs high-pressure systems for the cooling loop, and needs water after the 3 days the GDWP provides. Molten Salt Reactors are cooled by molten salts far below their boiling point, no high pressure systems needed at all. (Of course, the heat would be transferred outside the reactor to drive high pressure steam or other gas for the electric turbines.)

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