Integral Fast Reactor/Debate Guide

Nuclear power is a controversial topic, and some of the controversies remain unsettled, even after the facts in the article are agreed on. This Debate Guide will provide a concise summary from each side of these unsettled issues. Much of this discussion is collected from Internet forums and other unreliable sources. We welcome updates with better sourcing.

Disadvantages of sodium cooled fast reactors

What is a nuclear reactor? By Dr. Nick Touran, Ph.D., P.E., accessed 9-May-2023:

• Sodium coolant is reactive with air and water. Thus, leaks in the pipes result in sodium fires. These can be engineered around but are a major setback for these reactors.
• To fully burn waste, these require reprocessing facilities which can also be used for nuclear proliferation.
• The excess neutrons used to give the reactor its resource-utilization capabilities could clandestinely be used to make plutonium for weapons.
• Positive void coefficients are inherent to most fast reactors, especially large ones. This is a safety concern.
• Not as much operating experience has been accumulated. We have only about 300 reactor-years of experience with sodium cooled reactors.

Response from Captain Roger Blomquist, United States Navy (retired) email 8 May 2023:
There is considerable experience with molten sodium in fast reactors and other industrial applications. Japan suffered a small sodium-air fire at Monju involving a leaking thermocouple well. EBR-II was engineered to prevent sodium fires in air and water -- usually involving a second layer of steel between sodium and water or air. These included double-walled steam generator tubes, guard pipes surrounding intermediate sodium piping outside of the reactor vessel, and a double reactor vessel. There were no consequential sodium leaks in the 30 years of operation.

It is not clear that SFRs should be prohibited in all countries because some countries might use them for weapons plutonium production. In principle, any uranium-fueled reactor can be used to produce plutonium for weapons, but the simplest, fastest, cheapest, most effective way is using a dedicated production reactor. Safeguards are definitely in order for SFRs, as for other reactors.

Positive void coefficients are definitely to be avoided -- a more challenging task for large cores, as pointed out. But strong negative power coefficients can protect SFRs from boiling sodium, even in unprotected accidents. Here, the IFR fuel temperature being lower than an oxide-fueled SFR makes a robust negative power coefficient easier to design in. This was comprehensively demonstrated by the EBR-II Shutdown Heat Removal Tests in 1986 in which outlet sodium temperature was never within a few hundreds of degrees of sodium boiling. To be sure, core size and configuration need to prevent temperatures far from sodium boiling.

The 300 reactor-years of SFR operation are indeed far shorter than LWR history, but far longer than the competing advanced reactor concepts (except possibly lead-cooled fast reactors). Additional experience will yield further advances in efficiency, safety, and economics.

Sodium Fires

Comment from Robert Steinhaus in a discussion on FaceBook accessed 27 June 2023:
The amount of molten sodium coolant used in commercial SFRs is HUGE, on the order of 5000 metric tons per GWe of designed reactor power. The stored chemical explosive potential of this much sodium is enormous. Once again, designers and advocates of SFRs never mention the facts using quantitative numbers relating to the potential explosive energy of hydrogen that could be rapidly generated from contact of 5000 tons of reactive, neutron activated Sodium coolant with water or the cement floors and walls of the reactor, which contain from 6% to 10% water.
...
There are circumstances where large releases of neutron activated sodium coolant are possible.
Examples
Floods - SFRs are typically built near large bodies of water to provide cooling water for the outlet leg of the turbine generator. Rivers overflow from time to time. Many SFRs, like the GE PRISM, are designed such that the reactor vessel is below ground level and flood waters could enter the reactor and reach the sodium coolant, causing the rapid generation of hydrogen and a very powerful and energetic hydrogen detonation.
Tsunami - also possible and historically has happened
Earthquake - also has historically happened
Operator error - also has happened
Response:
see section 7.12, Sodium Reaction with Air and Water in Till & Chang, 2011 for a thorough discussion of the safety of sodium in nuclear reactors.
"In properly designed sodiumcooled fast reactors, there are sufficient preventive and mitigation features to deal with sodium leakages, sodium/water reactions, and sodium fires so that the reactor safety should never be in jeopardy. The nonradioactive secondary sodium poses no more risk than is typical in common industrial safety."

Readiness of this design

The National Academy of Sciences has a report Laying the Foundation for New and Advanced Nuclear Reactors in the United States, 2023. They have concluded that this design needs a lot more work.
From the Summary:
P.1) demonstrations of advanced nuclear designs are not expected until the late 2020s or early 2030s,
P.2) SFRs and HTGRs will need to address supply chain and high-assay low-enrichment uranium (HALEU) issues and operational reliability, which have impacted those designs in the past.
... for example, reactor core materials and cladding.
From Chapter 2, Finding 2-5: ... More mature concepts, such as ... small modular sodium fast reactors, and ... might be technically ready for demonstration by the end of this decade.

Response from Captain Roger Blomquist, United States Navy (retired) email 8 May 2023:
The EBR-II fuel design was upgraded during the reactor's 30-year operating life. The metal fuel in the reactor was subjected to prototypical and off-normal conditions, and thoroughly evaluated and documented. The latest DOE-approved driver fuel was Mark III, but Mark V fuel (U-19Pu-9Zr) was tested extensively, including burnups exceeding 18% and run-beyond-cladding-breach. Thorough post-irradiation examinations were completed and and evaluated. The safety case is an Argonne report because the Clinton administration cancelled the entire IFR project in 1994 for political reasons. There are, however numerous open literature publications reporting this work.

EBR-II operated reliably for 30 years. While a the first-of-a-kind larger version might have its teething problems, there is enough experience in hand to take the next step in commercialization: licensing.