Shippingport Light Water Breeder Reactor
Overview
[edit | edit source]The Shippingport Light Water Breeder Reactor (LWBR) was a demonstration of thorium-based nuclear power at commercial scale, operated within the Shippingport Atomic Power Station in Shippingport, Pennsylvania. It remains one of the two most significant large-scale demonstrations of the thorium fuel cycle in history (alongside the Molten Salt Reactor Experiment), and the only demonstration that a light water reactor could breed fuel using a thorium-uranium cycle.
Background
[edit | edit source]The Shippingport Atomic Power Station was the first full-scale commercial nuclear power plant in the United States, entering operation in 1957. It was originally fuelled with conventional enriched uranium and operated as a pressurised water reactor (PWR) under the direction of Admiral Hyman Rickover's Naval Reactors programme.
In 1965, Rickover initiated the LWBR project — a plan to convert the Shippingport reactor to demonstrate thorium-based breeding using a light water reactor design. Rickover was motivated by a genuine interest in thorium as a fuel and by the challenge of demonstrating breeding in a thermal neutron spectrum, which conventional nuclear theory regarded as difficult or impossible.
Design and Operation
[edit | edit source]The LWBR core used seed-and-blanket fuel assemblies:
- Seed assemblies: Contained uranium-233 and thorium-232. Fission of U-233 generated both power and neutrons.
- Blanket assemblies: Contained thorium-232. Neutrons from the seed bred additional U-233 from the thorium.
- Coolant and moderator: Ordinary light water, as in a standard PWR.
The LWBR first reached criticality on August 26, 1977. It operated at a power level of approximately 60 MWth for approximately five years.
Results and Significance
[edit | edit source]When the LWBR was shut down and its fuel discharged and analysed:
- Measurements confirmed that the reactor had produced more U-233 than it consumed — it had bred fuel, achieving a breeding ratio greater than 1.0.
- This made it one of very few reactors ever to achieve fuel breeding in a thermal neutron spectrum.
- It demonstrated conclusively that the thorium-uranium cycle could sustain itself in a practical reactor design.
The LWBR demonstration was publicly announced and the results published, but received relatively little public attention. The US government was at this point committed to the uranium-plutonium cycle, and the LWBR results were not leveraged into a follow-on programme.
The Fort St. Vrain and Other Thorium-Fuelled Reactors
[edit | edit source]Other US commercial reactors also used thorium-containing fuel:
- Indian Point 1 (New York): Operated with thorium-uranium mixed oxide fuel.
- Peach Bottom 1 (Pennsylvania): A high-temperature gas-cooled reactor that used thorium-uranium fuel from 1966 to 1974.
- Fort St. Vrain (Colorado): A 330 MWe high-temperature gas-cooled reactor that used thorium-uranium fuel from 1979 to 1989.
These reactors demonstrated the practical feasibility of thorium fuel fabrication and use in commercial reactor conditions, though none were designed specifically to breed fuel.
Legacy
[edit | edit source]The Shippingport LWBR is frequently cited as definitive proof that thorium fuel breeding is not merely theoretical but has been achieved in a full-scale commercial power reactor. Critics of the thorium reactor concept who argue that breeding has never been demonstrated outside the laboratory are factually incorrect — the Shippingport demonstration disproves that claim.
The Shippingport station was decommissioned between 1989 and 1989. Decommissioning was completed in 1989, with the reactor vessel transported intact to a DOE burial site in Hanford, Washington.
