The ORNL X-10 reactor (CC-SA Ɱ)

Hanford B plutonium-production reactor (LOC)

• In 1946, Walter Zinn designed a proof-of-principle for breeding
• It was thought that uranium was very scarce, so breeders would be the only option for economical civilian power.
• EBR-1 was hooked to a generator and made the first significant amount of nuclear electricity
• It also proved that a conversion ratio >1.0 was possible
  • They didn’t consider it a true breeder because it used U-235

The EBR-I (AEC)

The LITR, the 1st water-cooled/moderated reactor (CC-BY-2.0 ORNL)

The MTR (AEC)

Prototype submarine in Idaho

Launch of USS Nautilus (1955)

• Intended to be 1st industrial/commercial power reactor
• Sodium-cooled, beryllium-moderated: intermediate-speed neutrons
• Supposed to breed and make commercial power
• On April 15, 1950, was repurposed as a submarine prototype because:
  • Technical challenges
  • Darkening relationships with the USSR
• Ended up as the S1G, the prototype for the USS Seawolf
• Large dome in NY remains

The Knolls Intermediate Power Breeder (AEC)

APEX-901

An actual test of a nuclear-powered jet engine in Idaho, called HTRE-2 (photo by me)

Aircraft Reactor Experiment

• Intended to power remote areas
• PM-1 in Wyoming
• PM-2A in Camp Century ice base (Greenland)
• ML-1 Truck-mounted mobile
• SL-1 in Idaho
• SM-1A Fort Greely, Alaska
• MH-1A floating barge in Panama
• PM-3A in Antarctica

ML-1 field test in Idaho

PM-1 being sent to Wyoming

• 1 MWe portable PWR
• Manufactured and tested in a factory,
• Disassembled into 16 modules,
• Air-lifted to the closest airfield by C-130
• Trucked to site, re-assembled
• Direct air cooling, (no water supply)
• No field welding was needed for re-assembly.
• Could be operated by a crew of 2.
• Awesome film summarizing it

PM-1 fully assembled in Wyoming

• The reactor was difficult to perform maintenance on because of its compactness. The operators recommend designing the next microreactor with maintenance requirements satisfied first, and then compactness requirements
• The conventional steam plant cause roughly half of the unplanned outages and required a lot of maintenance, leading the authors to suggest that perhaps a non-steam approach is needed at this small scale (e.g. other energy conversion systems).
• The nuclear instrumentation system was oversensitive and overcomplicated for a field plant.
• The HVAC system and building design were wholly inadequate
• It was difficult to maintain qualified staff to operate and maintain the reactor
• The reactor was used as a training reactor for crews headed to Antarctica to operate the sister plant PM-3A, which reduced PM-1’s overall performance.

PM-1 Final Summary Report

• Minimal assemblage of fuel/coolant/moderator/control
• Used to check basic nuclear characteristics against theory
• Room temperature
• Very low power (<10 W)
• Often reconfigurable
• Often used to support final design (e.g. rod worth curves)
• Diminished need due to robust nuclear data and radiation transport codes

• Fluid fuel: uranium sulfate
• Ran at ORNL in 1952
• Expected to be simple and compact
• Kept burning holes in containment
• Holes were repaired, but concept was abandoned
• Incredible 1961 film of how they repaired the hole

• Is it possible to operate a core with boiling water?
• Experiments ran at National Reactor Testing Station, starting in 1953
• BORAX-I exploded at end of life (to test limits)
• After small success with BORAX-1 larger BORAX-2 was built.
• Re-designated BORAX-III with the addition of a turbine
• Powered town of Arco, ID
• Formed basis for BWRs
• Some destructive test film

• Molten salt fluid fuel
• Ran at ORNL in 1954
• Expected to be compact and very high power density
• Intended for nuclear-powered bomber
• Ran for 4 days
• Got leak, they blew fission products into the forest to the south
• I wrote the Wikipedia page on it (inspired by Prof. R. Fleming)

• High temperature reactors coupled to jet engines in 1956
• Developing nuclear-powered flight for long-range bomber
• Ran in Idaho
• Never flew
• Can be seen in parking lot of EBR-1 museum
• See APEX-901

• Sodium metal coolant, graphite moderator
• Started in 1957
• Expected to make economical power
• Low pressure, high temperature, LEU fuel
• Near LA
• Prototype for Hallam reactor
• Suffered core melt
• Very cool construction photos

• Terphenyl coolant/moderator
• Low pressure, high temperature, low corrosion, chemically inert
• Ran at the NRTS in 1957
• Expected to lead to low-cost commercial power
• New film coming soon!

• Helium gas-cooled reactor with UC₂ fuel coated with 3 layers of pyrolitic carbon
• 2400 °F coolant temperature
• Elemental carbon structure
• Run at LANL from 1959-1971
• Spin-off of Project Rover (nuclear rocket)
• Rotating core loader
• Un-clad annular porous carbon extruded fuel elements
• Remote online refueling

• High-pressure uranyl phosphate solution fuel
• Highly-enriched uranium
• Would have made 10-50 MWe compact reactors
• Remote power for military bases
• LAPRE-II started in 1959
• See e.g. LAPRE-II (1960)

• Molten Plutonium-Iron alloy fuel in tantalum tubes
• Developed for fast breeder reactors
• Ran in 1960
• In-situ reprocessing
• See LAMPRE I FINAL DESIGN STATUS REPORT

• Nitrogen-cooled
• Supported the truck-mounted Army reactor
• 1962

• Lifted the ORNL Health Physics Research Reactor
• Went up 1500-foot tower
• 1962
• A small Japanese village was built at the bottom
• Tower provided information on neutron dose from elevated sources on tissue

• Nuclear-powered rocket for space propulsion
• Liquid-hydrogen cooled
• NRX-A2 ran in 1964 for 6 minutes, and then 20 minutes

• Follow-up from the ARE
• Focused on commercial power potential
• Ran at ORNL in 1965
• Formed basis for Molten Salt Reactors

• Congress was concerned about falling behind UK and USSR in power reactors
• Rickover was put in charge b/c he could get stuff done
• Dev program tried various fuels, settled on UO₂ with zirconium clad
• Nuclear design by Bettis: HEU seed with NU driver
• Fierce opposition b/c LWRs are inefficient with uranium resources
• Had 2 B&W U-tube SGs and 2 Foster Wheeler straight-pipe SGs
• Critical on December 2, 1957, cost $72.5M
• Open design: all details published at Geneva 1958
• Operated reliably
• 10x more expensive than an equivalent fossil plant

Construction of a boiler chamber in the Shippingport PWR (from Library of Congress)

• Major AEC program started in 1955
• Focus on advanced reactors most likely to achieve economic parity with coal
• Government benefits:
  • waive fuel usage fees
  • perform pre-construction R&D
  • subsidize post-construction R&D
• Intended to inspire private investment in nuclear
• Three main rounds
• Round 1: applicant would fully fund, construct, and operate nuclear and turbine island
• Round 2: focusing on rural utilities, applicant built turbine island; AEC built nuclear island and offered option to purchase

• Consortium of New England utilities came together to propose
• AEC selected under round 1 PDRP
• Constructed by same team as Shippingport
• On time, on budget
• Operated beautifully

Film: Operating Experience Yankee Rowe (1964)

• Consortium of 23 utilities came together to propose
• AEC selected under round 1 PDRP
• More expensive than expected
• Many operational challenges
• Core melt and recovery
• Shut down early due to poor economic performance

• Small utility in Nebraska
• SGR concept appeared highly likely to be economical (low pressure, high temperature, low enriched fuel)
• Literally shared a turbine with a coal plant
• Leaking moderator cans caused operational outages
• Utility declined to purchase
• Coal plant is still there today
• Cool historical films online

Film: The Hallam Reactor (1964)

• Proposal from Rural Cooperative Power Association with newcomer constructor
• Many arguments with contracting
• Municipal reactor in tiny town
• Natural circulation
• Entire control system replaced (single channel -> multi)
• Reactor vessel reworked
• Plant ran for 4 years, but was leaking primary coolant
• When shut down to find problem, repairs deemed too expensive
• Plant was decommissioned, converted to fossil in 1968
• Building torn down around 2021

Film: Nuclear Energy Goes Rural (1963)

• Municipal reactor in tiny town
• Town initially hyped about it: dubbed itself the Atomic City
• Another promising concept: low pressure, high temperature
• Lots of operational and reliability challenges
• Town declined option to purchase
• Shut down early

• Built near Sioux Falls, SD
• Consortium of investor-owned utilities
• Goal was to get practical experience operating a nuclear plant
• Longest run was 30 minutes
• Ran for about a year, had accident in 1967, decided to abandon
• Now a 327 MWe gas plant runs on the site

• Third-round PDRP reactor, proposed by group of 4 utilities
• First US power reactor with heavy water
• 1.5-2% enriched uranium, 65 MWe
• Produced saturated steam, which was fed into an oil-fired superheater
• Operated from 1963-1967 with 78.14% availability
• Co-located with coal AND hydro plants!
• AEC paid $11.3M, industry paid $32.1M
• Power was uprated, but 3 of 4 test assemblies failed
• See Willoughby 1967 or Nath 1967 (neutronics benchmark anyone?)

Co-located coal, hydro, and nuclear, thought to be unique worldwide.

• Advanced BWR: Increased thermal efficiency
• Allowed use of off-the-shelf turbine
• Increased corrosion and fuel failures
• Costly repairs and modifications
• Technical difficulties led to shut down in 1968
• Digitized film on Youtube

• Unsolicited proposal by Philadelphia Electric Co. and other utilities
• Ran from 1967 - 1974
• First HTGR in USA
• 37.2% thermal efficiency
• 538 °C superheated steam at 10 MPa
• Capacity factor 74%
• Uneconomical to operate alongside GW-scale neighboring units because it was too small
• Major retrofit was required to meet revised safety criteria

• Joint proposal from Consumers Power and GE in 1959
• Fun promotional film ft. Ronald Reagan
• World's first direct cycle, forced circulation, high power density BWR
• Constructed in 29 months for $27M
• Ran beautifully, shut down in 1997
• 9 miles from my mom's house
• Film: Head Start on Tomorrow (1962) ft. Ronald Reagan

• Co-located with coal-fired Genoa Station #3
• Forced-circulation, direct-cycle BWR
• Constructor, Allis-Chalmers, struggled to deliver it due to various problems; was initially 4 years late
• Contracted under 2nd round terms, though far past deadline (1961)
• Expected to give useful technical info about medium-sized BWRs
• Ran until 1987, when it was deemed too small to compete economically and decommissioned

NRC photo

• Southern California Edison-Westinghouse joint proposal
• More than 2x the size of Yankee
• Forced-circulation, direct-cycle BWR
• An extra containment was built around the dome later
• Ran well until 1987, when it was deemed too small to compete economically and decommissioned

San Onofre 1 (DOE photo)

• 500 Watt nuclear fission reactor in space
• Uranium Zirconium Hydride fuel
• Electromagnetcally pumped NaK
• Rotating control drums
• Thermoelectric power conversion
• Ejected reflector after 43 days of operation
• Still up there!
• There were also 31 USSR RORSATs in space

Print showing SNAP-10A

• 5x more power than ML-1, still on a truck (2.2 kWe)
• HEU fast reactor
• Enriched lithium primary coolant
• Enriched potassium reflector coolant
• Sodium secondary coolant
• Three EM pumps
• FT-12 jet engine power conversion
• Control drums
• Weirdly written into 10 CFR 3 Part 725
• Competed with potassium metal turbine systems like SNAP-50/SPUR

The LCRE system, from CNLM-5170

3000 lbs. reactor with a 78,000 lbs. DU/LiH shield

• Natural safety without backup systems
• More practical to finance (smaller)
• Decarbonize hard-to-decarbonize sectors
• Industry
• Shipping
• World-scale million-year+ sustainability (breeding)
• Waste processing/reduction

But...

• There are lessons to be learned in initial construction and scaling
• New reactor development is hard and slow

A small reactor (ANL)

• Advanced large LWRs
• Modular construction
• Simplified systems
• 72 hours without backup power
• Digital instrumentation and control
• ABWR, AP-600, AP-1000, APR-1400, Hualong 1, VVER
• Small water-cooled reactors
• Modular delivery and/or construction
• Depends on economies of mass production exceeding economies of scale

An AP1000 advanced reactor (Westinghouse)

Pros

• World-scale sustainability
• Waste processing/reduction
• Natural safety
• High thermal efficiency
• Industrial heat

Cons

• Higher fissile concentration
• Chemically reactive coolants
• Extra costs from extra coolant loops
• Plutonium scares people

Fast reactor history (adapted from Walter, Fast Breeder Reactors)

• Plentiful in India and China
• Used in Indian Point initial core
• Works well with fluid-fuel reactors
• China about to turn on a new experimental Thorium Molten Salt Reactor called TMSR-LF1
• Does not completely eliminate proliferation or waste issues

A fluid fueled reactor (ARE)

• Much less radioactive waste
• No afterglow heat to cool
• Many highly-funded startups catching headlines
• Extremely challenging physics
• Unknown power conversion
• Often necessitates tritium breeding
• Often a powerful neutron source
• Worth investigating, but lets not rely on it

Popular Mechanics article about floating nuclear