After my last post on Dounreay, a number of my readers reached out to say, “Wait a minute! The Prototype Fast Reactor actually worked. You can’t be so negative about liquid sodium.”

Short answer: Yes, I can.

Long answer: Let’s talk about what “worked” really means.

The Dounreay Prototype Fast Reactor (PFR) was conceived as the UK’s commercial-scale proof that sodium-cooled fast reactors were ready for prime time. Construction began in 1966, first criticality was achieved in 1974, and the plant eventually delivered ~250 MWe to the grid.

On paper, this was supposed to be the fast reactor that crossed the line from experimental to practical.

And yes—credit where it’s due—it did operate. It generated electricity. It demonstrated that a sodium-cooled fast reactor can be made to run.

But that’s where the applause stops.

Throughout its operating life, PFR struggled with the same challenges that have followed liquid-sodium reactors from the beginning:

• 𝙨𝙤𝙙𝙞𝙪𝙢 𝙡𝙚𝙖𝙠𝙨

• 𝙘𝙤𝙢𝙥𝙡𝙚𝙭 𝙛𝙪𝙚𝙡 𝙝𝙖𝙣𝙙𝙡𝙞𝙣𝙜

• 𝙙𝙞𝙛𝙛𝙞𝙘𝙪𝙡𝙩 𝙞𝙣𝙨𝙥𝙚𝙘𝙩𝙞𝙤𝙣s

• 𝙡𝙤𝙣𝙜 𝙤𝙪𝙩𝙖𝙜𝙚𝙨

• 𝙛𝙧𝙖𝙜𝙞𝙡𝙚 𝙨𝙩𝙚𝙖𝙢 𝙜𝙚𝙣𝙚𝙧𝙖𝙩𝙤𝙧𝙨

• 𝙢𝙖𝙞𝙣𝙩𝙚𝙣𝙖𝙣𝙘𝙚 𝙩𝙝𝙖𝙩 𝙧𝙤𝙪𝙩𝙞𝙣𝙚𝙡𝙮 𝙩𝙪𝙧𝙣𝙚𝙙 𝙞𝙣𝙩𝙤 𝙢𝙪𝙡𝙩𝙞-𝙢𝙤𝙣𝙩𝙝 𝙚𝙫𝙚𝙣𝙩𝙨.

These were not startup teething problems; they were structural realities of the technology.