Nuclear Reactor Development History
Nick Touran, 2020-01-12. Reading time: 85 minutes
“You have to know the past to understand the present” — Carl Sagan
The dream for economical nuclear power was born well before the discovery of nuclear
fission, but the quest for it began in earnest in the late 1940s and involved some 100,000
persons for several decades in the USA alone. This page is a grand tour of reactor
development programs from 1945 to about 1970, also known as the nuclear heyday. As we proceed
with new reactor development programs today, remembering what was done back then may help
us navigate developments of the future.
Our economics page discusses developments and
economics from 1970 to the present.
The starting point
When nuclear fission was discovered in 1938, 235U existed at 0.7% in natural
Uranium (decayed down from over 25% when Earth was formed). Without isotopic enrichment
available (of uranium or hydrogen in water), only a handful of configurations could
sustain a chain reaction. Enrico Fermi and co. figured it out by 1942, and operated the
first nuclear reactor, the Chicago Pile 1 (CP-1), using pieces of natural uranium metal
dispersed carefully in a lattice of high-purity graphite blocks in a Chicago squash court.
Note: This is written largely from the US perspective.
Developments in other countries are not well covered here. Also, the chains
of events are difficult to classify so the time linearity of the following is not perfect.
Nuclear weapons production reactors
Vast wealth and effort was first invested in nuclear reactor development because the
unique characteristics of the atomic chain reaction could provide fundamental and dramatic
military strategic advantages. Accordingly, the first high-power reactors were designed
and built to produce plutonium as fuel for nuclear explosives.
As in CP-1, they had natural uranium fuel dispersed in a graphite moderator.
Unlike CP-1, the Hanford reactors were cooled with ordinary water. Since water is a
neutron absorber, the reactor had to be large, and it required extra-pure graphite with
minimal neutron-absorbing impurities (like boron). It also needed a lot of
metallic natural uranium. Eugene Wigner proposed cooling with low-pressure,
low-temperature water instead of high-temperature, high-pressure helium because he was
worried that the fuel would not survive high temperatures, and that pumping and
maintaining an inventory of helium would be challenging. His calculations showed that a
water-cooled reactor would indeed chain-react, and his unwavering drive to beat the Nazis
bolstered his confidence. Water-cooled reactors were built.
After the plutonium-producing B reactor at Hanford was operational, the scientists who
designed it began imagining a better time, beyond the war, when the newfound power of
the atom could be applied to the peaceful enrichment of humankind. The first documented
reactor innovation sessions occurred around this time. Many reactor concepts were dreamed
up at these New Piles Committee meetings. No one knew whether
nuclear-powered electricity generating stations could be cost-competitive with
conventional power plants.
Putting nuclear heat to work
After the war, the civilian Atomic Energy Commission (AEC) took responsibility for US
nuclear technology, as authorized by the Atomic Energy Act of 1946. Building up new
weapons material production capabilities and weapons technology dominated its efforts,
but power reactor development did legitimately begin at this time.
Truly exotic energy conversion was seriously considered in the 1940s
(thermionics, endothermic chemical reactions, etc.), but converting heat to
electricity in a standard steam cycle was considered the easiest way to reach
economical nuclear power. This conversion requires high-temperature,
long-endurance fuel that can withstand an intense radiation environment. This
was a fundamental technological departure from the plutonium-production
reactors, which generated heat only as a nuisance and were kept at low
temperature. Robert Oppenheimer explained this
In 1947, the AEC proposed and funded four new reactors, all of which made use
of new availability of enriched uranium rather than natural
uranium. All four were completed in the early 1950s:
- Fast reactor — A fast reactor to explore the possibilities of breeding (now known as EBR-1)
- Navy thermal reactor — a prototype for submarine propulsion (now known as STR or S1W)
- Materials Testing Reactor (MTR) — A testing facility to investigate potential materials
to be used in power reactor construction. The resistance of materials to the environment
required for power production was the primary challenge of power reactor development.
- Knolls intermediate reactor — to explore the possibilities of breeding and to develop usable
power (soon repurposed as another submarine prototype, called SIR and/or S1G)
The first three were built in Idaho, thus creating what was then called the National
Reactor Testing Station (NRTS) and is now the Idaho National Lab (INL). The fourth was built
north of Schenectady, NY in a giant sphere at the center of Knolls Atomic Power Lab’s
Kesselring site. During design of the MTR, Oak Ridge National Lab (ORNL) built a
mechanical mockup reactor, which they then converted to a real reactor called LITR: the
first water-cooled, water-moderated reactor.
Specialized military reactors after WWII
As nuclear weapons have orders of magnitude more destructive force over conventional
explosives, nuclear engines for submarines, ships, rockets, and aircraft offer orders of
magnitude more range than conventional fuels. Accordingly, the next major application of
the chain reactor was in specialized military contexts.
The nuclear-propelled Navy was developed by Captain Hyman G. Rickover. Rickover’s role in
the development of naval propulsion goes without saying, but his influence on the
commercial industry simply cannot be overstated. He was born in 1900 in a Polish ghetto,
moved to New York at the age of 6, and then to Chicago’s West Side. He entered the Naval
Academy in 1918 and requested submarine service in 1929. He translated Das Unterseeboot
from the Imperial German Navy as a labor of personal interest. In 1937, he became a
Engineering Duty Only (EDO) officer, focused on the design, construction, and maintenance
of ships. After WWII ended, he was sent to Oak Ridge to learn about nuclear technology as
part of a team to investigate nuclear ship propulsion. He established himself as the
leader of the team and fought hard to secure funds and authority to kick off the naval
He kicked off two reactor development programs in parallel for naval propulsion: the
sodium-cooled beryllium-reflected/moderated reactor (Project Genie) and the pressurized
water reactor (Project Wizard).
The PWR and the Nautilus
Alvin Weinberg and the Oak Ridge team suggested using pressurized water as a submarine
reactor coolant and moderator for two reasons: (1) the distance neutrons in water travel
is one-fifth the distance they travel in graphite, so the water reactor could be very
compact (good for small enclosed spaces), and (2) water systems are simple, familiar, and
reliable in a naval context. The ORNL team made preliminary sketches of such a reactor.
The preliminary work of ORNL was transferred to Argonne along with a team of engineers who
were coming off the just-cancelled Daniels Pile project, which had attempted to
develop a high-temperature pebble-bed gas-cooled power reactor using highly-enriched uranium.
Against the prevailing wisdom (e.g. of Weinberg), Rickover boldly decided to build the
full-scale Nautilus prototype reactor (STR) in Idaho without first building a much-cheaper
pilot model. Simultaneously, construction of the Nautilus submarine itself began in
Connecticut. Rickover’s ruthless and aggressive schedule was driven by a conviction that
whoever developed nuclear engines first would rule the seas.
Rickover strictly required that the two projects fit together. At one inspection, he
forced the Idaho team to move a coffee maker outside the hull since it would not be in the
During STR development, the effect of radiation on components and equipment was tested in
the MTR. Vast programs successfully developed the hermetically sealed pumps with
appropriate bearings, thin stainless steel or Inconel liners, motor winding cooling, and
high-pressure electrical terminal seals. A complete line of hermetically sealed,
hydraulically operated stainless steel primary system valves was developed.
Welding of heavy wall stainless piping was developed. Weldability and weld
cracking as functions of material composition was found and understood. Design criteria
for auxiliary systems supporting waste disposal, coolant purification, emergency cooling,
fuel handling, ventilation, as well as feasible engineering techniques to satisfy the
requirements were developed.
STR went critical on March 31, 1953 and reached full power by May 31.
After a massive reactor technology development program and the operation of a land-based
prototype reactor in Idaho, the second major application of nuclear reactors became the
propulsion system of naval submarines, marked by the message
from the USS Nautilus on Jan 17, 1955:
UNDERWAY ON NUCLEAR POWER
The astoundingly high energy density of nuclear fuel allowed the submariners to gallivant on wild new
adventures, such as reaching the North Pole under
for the first time and circumnavigating the
world in one non-stop submerged
session for the first time. Such high adventures are remembered by people who were young
at the time (like Gwyneth Cravens) as deeply inspiring.
The SIR and the Seawolf
The sodium-cooled intermediate-spectrum power breeder that GE was working on for the AEC
at KAPL got swooped into the Naval Reactors development program, and its first reactor
became the land-based prototype for the USS Seawolf. At first, Rickover preferred the
sodium-cooled approach with a beryllium reflector/moderator because it used silent
electro-magnetic pumps and offered very high thermal efficiency. The prototype (S1G)
experienced leaks in the superheaters due to an incompatibility between the liquid metal
sodium and the particular steel used. Because of Rickover’s insistence in building
prototype concurrently with the real thing, the real Seawolf also experienced
superheater leaks. They plugged tubes, performed difficult repairs (sodium has high
induced radioactivity and high chemical reactivity), and eventually bypassed the
superheater. Seawolf worked at reduced efficiency, logged some tens of thousands of
hours, but eventually had its propulsion system swapped out for a PWR.
Aircraft Nuclear Propulsion
Alongside the naval propulsion project, the Aircraft Nuclear Propulsion (ANP) program was
launched. Long-range bombers that could stay in the air for months or years at a time
with unlimited range were thought to be militarily important. In addition, significant R&D
on nuclear-powered cruise missiles and scramjets was performed.
The ANP was a massive program spanning more than 10 years and a billion (1955) dollars.
JFK ended the program early in his presidency at the recommendation of Alvin Weinberg.
Progress in ICBMs effectively eliminated the need for nuclear-powered bombers. The molten
salt reactor technology still actively discussed today is a direct descendent from this
massive development program.
The Army Nuclear Power Program
With the Navy and Air Force reactor programs in full swing, the Army was not to be left
out. The Army Nuclear Power Program (ANPP) focused on the deployment of very small
reactors to remote locations. It got going in the late 1950s and early 1960s, well after
the Navy and Air Force programs. Small nuclear reactors were built and tested at factories
and then transported to, re-assembled, and operated in a military ice base in Greenland
(Camp Century), McMurdo Station in
Antarctica, the Panama canal on a mobile barge, Sundance Air Force Station in Wyoming, and
Fort Greely, Alaska. An exotic nitrogen-cooled truck-mounted model was developed and
tested in Idaho but not deployed.
After the STG and Nautilus, the third PWR to operate was the first plant built under the ANPP: the
APPR-1 (later designated SM-1). It was built by Alco and Stone & Webster, and
came to power in April, 1957. While the Shippingport design effort predates APPR-1 effort
(discussed below), the APPR-1 team pioneered some ideas, such as the vertical vapor
container, as opposed to Shippingport’s horizontal ones. They innovated a lot while
considering internal missile protection, but ended up with a rather expensive reinforcing
Before fabricating the fuel, Alco Products built a critical testing facility to perform
zero-power experiments with their proposed fuel and control design. The mock-up core
was built in a 2500 sq. ft. facility, and by 1957 they were soliciting other companies to
perform related experiments in it.
The PM-3A and PM-2A remote military reactors in Antarctica and Greenland were also PWRs.
The development of civilian reactors
AEC Civilian Reactor Programs
The AEC executed several programs specifically dedicated to the quest for economical
nuclear power. In this period, its prospects were highly tentative, and the magnitude of
work needed to achieve it was regularly estimated somewhat accurately (3-5 years to make a
little power, 20-30 years before contributing significant power). Nonetheless, everyone
was eager to see if it could be done.
The 5-year plan
In 1954, the AEC announced the government-funded Five-Year Plan to explore reactor
concepts from a commercial point of view. They included:
- Shippingport Pressurized Water Reactor
- Experimental Boiling Water Reactor (EBWR)
- Sodium Reactor Experiment (SRE)
- Homogeneous Reactor Experiment-2 (HRE-2)
- Experimental Breeder Reactor-2 (EBR-2)
Atoms for Peace
Eisenhower (the first Republican president in 20 years) vastly increased the AEC’s focus
on private participation in nuclear technology with his famous December 1953 Atoms for
The first international conference on peaceful uses of atomic energy was held in Geneva
in 1955. It was an incredible event filled with optimism and excitement.
Private funding, ownership, and operation was on its way.
Volume 2 of the delegation report (June 24, 1955), recorded AEC Chairman Strauss giving a
rousing speech about how American industry was willing to cover 90% of the Power
Development Reactor Program plant costs. He also hinted at the political situation,
justifying the stockpiling of weapons as protection against “menaces from those who have
destroyed freedom in the expansion of their own ruthless philosophy”. While investments
in conventional weapons could only be recovered as scrap in times of peace, the nuclear
material being stockpiled could be used later for peaceful purposes:
But when the day comes that our atomic armament is no longer required to deter
aggression, the nuclear material which it contains can be easily converted into
energy sources to provide very great amounts of power to turn the wheels of industry,
furnish us with light, heat, transportation, and the many other conveniences
and blessing of peace. We who work in the Atomic Energy Commission work with
the vision of that day before use.
Sidenote: this vision really did come true when between 2003 and 2013, fully 10% of the
USA’s electric power was derived from dismantled ex-Soviet nuclear bombs.
Certainly Atoms for Peace contained an element of propaganda. All involved wanted to
realize a peaceful application for horrifying weapons. By this time, thermonuclear fusion
“H-bombs” had been developed, which were literally 1000x more powerful than the atomic
bombs dropped on Japan. Their horrible implications almost defy comprehension.
Nonetheless, applying the newfound force of nature to the betterment of civilization by
making useful power was a noble goal.
Pressure from abroad
Competing with other countries was a top concern voiced frequently in Congressional
hearings from the early 1950s. The UK got the first full-scale commercial production of
electric power from a dual-purpose plant (Calder Hall) in 1956. The Soviet Union, via Dr.
they would have 2,500 MWe of nuclear capacity by 1960, with developments ongoing in the
following reactor types:
- Water-moderated and cooled thermal and epithermal 200 MW reactors
- Graphite-moderated steam and water-cooled reactors of the type used at the existing 5 MW
- A heterogeneous heavy water-moderated, gas-cooled reactor
- A unit with water-moderated thermal reactor and a turbine operated by slightly
radioactive stream fed directly from the reactor
- A homogeneous heavy-water moderated thermal breeder with thorium fuel
- A thermal graphite-moderated sodium-cooled reactor
- A fast sodium-cooled breeder on the U-Pu fuel cycle
(Recall that heavy water, also called D2O, is water with the
hydrogen atoms replaced with isotopically-enriched deuterium. It has very low
neutron absorption and is a best-in-class moderator.)
The Power Demonstration Reactor Program
The AEC’s Power Demonstration Reactor Program (PDRP) kicked off after the Atomic Energy
Act of 1954 allowed private ownership and operation of reactors. It involved 3 separate
requests for proposals from private industry wherein the AEC would provide nuclear fuel and
perform research and development work necessary to bring forward commercial nuclear power
The three invitations between 1955 and 1960 are visible in the figure below, with some
straggling proposals trickling in around 1960. Utility consortiums sent in significant
and bold proposals covering a diverse range of reactor types and sizes including pressurized
and boiling water reactors, an organic cooled/moderated reactor, two nuclear superheat
BWRs, a sodium-cooled fast reactor, and a sodium/graphite intermediate reactor.
The commercialization of the pressurized water reactor
The positive experiences with the STR and the APPR-1, plus a strong desire to stay ahead
of the Russians and to catch up with the UK resulted in strong support for a large-scale
water-cooled demonstration reactor. At the same time, a troubled aircraft carrier
prototype reactor program was just defunded by Eisenhower. The project was converted to a
commercial power prototype called Shippingport. It would become the USA’s first
commercial nuclear power plant.
The initial Shippingport core used highly enriched uranium. High temperature, high-burnup
fuels in water conditions were developed. Metallic uranium fuel in water failed rapidly.
They found promising results when they alloyed uranium with molybdenum, niobium, and both.
Alloys with 3.8% Silicon with intermetallic U3Si silicides were also promising
(more recently revived under the name Accident Tolerant
Fuels), but a suitable clad
fabrication process with this fuel was elusive. A high-temperature in-pile loop had to be
developed to carry out this alloy development program (at both MTR in Idaho and NRX in
Canada). Troubles with Uranium-Molybdenum cladding were encountered, and high medium-speed
neutron absorption was discovered. Along the way, it was discovered that the ceramic
uranium oxide was surprisingly good as a reactor fuel.
Many lessons were learned in early Shippingport operation. Valves sometimes bounced
between open and closed during the operation of other valves, and valves drifted from
closed to open in certain situations. Pressurizer steam relief valves leaked due to
thermal distortions. Leaks in four steam generators were found, caused by stress
corrosion. Pieces of the turbine moisture separator ended up breaking off and lodging in
the turbine low-pressure blades due to vibrations. Excessive fission products appeared in
the coolant, likely due to defective UO2 blanket rods.
Despite the trouble, Shippingport was a successfully-operated plant, but its capital cost
was about 10x more than an equivalent fossil-fueled plant. Economical nuclear power was
Given the realities of Shippingport, utilities continued in their hesitation. The PWR was
urged toward commercialization by the AEC’s public/private PDRP. The Yankee reactor at
Rowe was proposed in the first round of the PDRP by a consortium of 10 New England
utilities, who funded the entire capital cost. It reached full power of 110 MWe in Jan
1961. Yankee Core I was the first to use UO2 fuel with stainless steel
cladding. The Yankee experience was very positive from R&D to construction to operation.
They completed the plant 23% below projected capital costs. Now things were looking up.
Indian Point was a 163 MWe PWR that went critical in August 1962 with homogeneously mixed
oxides of highly enriched uranium and thorium. Its purpose was to develop the thorium fuel
cycle for power breeding in order to extend the resources available to PWRs in the event
of a global-scale fleet ramp-up. The benefits of thorium fuel proved elusive, and so the
second core was low-enriched UO2 with no thorium.
Also in 1962, the small 20 MWt Saxton PWR “hook-on” reactor became critical in
Pennsylvania. It added nuclear-generated steam to an existing fossil-powered turbine.
San Onofre and Connecticut Yankee came online in 1968, and then somewhat of
a deluge of orders became the majority of today’s nuclear fleet.
A land-based prototype for the NS Savannah merchant ship’s core was built and operated
in Lynchburg, VA in February, 1960. This reactor had full-length fuel assemblies and
provided information needed before finishing the NS Savannah plant.
Nuclear-powered merchant ships could help decarbonize and clean up
international shipping. However, the one such operating
vessel is basically forbidden from most
international ports. So either hearts and minds would have to be wholesale changed, or
some kind of nuclear-powered deep-sea tugboat/barge system is needed to progress in this
On the military side, dozens of land-based prototypes of new naval PWRs have been
built, along with hundreds of their deployed at-sea counterparts (mostly
in subs and aircraft carriers, but also in a few Destroyers).
Many variations on the PWR, like the thorium-fueled spectral shift control PWR
were studied but didn’t break through.
The N-reactor at the Hanford site was a dual-purpose water and graphite
moderated variation on a PWR used to make power for the area as well as weapons materials.
This was a somewhat significant deviation from the low-temperature earlier production
As cost dynamics pressured PWRs in the 1970s, simpler and more economical
designs were developed. France chose a standard PWR and built them in bulk.
South Korea also developed highly-optimized PWRs based on CE designs. This will
be covered in a follow-up article.
The development of the boiling water reactor
With the PWR developed for naval propulsion, the Argonne National Lab (ANL) set forth to
develop a simpler and cheaper water-cooled reactor intended specifically for power
production. The Boiling Water Reactor (BWR) avoided the 2000 psi pressure, reduced the
required pumping power, and eliminated the costs and complications of intermediate heat
exchangers (i.e. the steam generators). For the most part, it was able to leverage the
materials and fuel work already done for PWRs.
Boiling water in a reactor was mentioned on the front page of the New York Times in 1939.
Early concerns about whether a reactor with boiling in the core would be stable were
investigated in lab tests of heat transfer in boiling water at the ANL. After
calculations suggested stability was possible, Argonne performed a series of BOiling water
ReActor eXperiments (BORAX) with real chain reactions at the NRTS in Idaho to prove it.
BORAX-1 was built by the AEC in a hole in the ground. It proved that BWRs could be
self-regulating, though it indicated oscillatory “chugging” with 1 second frequencies
given certain large reactivity insertions. A larger experiment, BORAX-2, was built to
ensure stability at higher powers. It was re-designated BORAX-III with the addition of a
turbine, which subsequently powered the entire town of Arco, ID for one hour.
Positive indications in these small experiments motivated the creation of a small but
prototypic reactor called the Experimental Boiling Water Reactor (EBWR) rated at 5 MWe.
R&D plus construction were estimated to cost $17 million.
The EBWR was built at ANL. It was a direct-cycle BWR making saturated steam at 600 psig
(489 °F). A complete, integrated power plant was necessary to answer questions associated
with direct coupling between the reactor and the power generating equipment: uncertainties
in induced radioactivity, reactivity feedback, corrosion, erosion, leakage, and water
quality control. The EBWR was unusually flexible because it was an experimental plant
intent on providing as much information about future BWR operation as possible. It
accommodated future conversion from light water moderator with natural circulation cooling
to forced circulation and heavy water moderation.
General Electric rallied hard for the 1954 changes to the Atomic Energy Act allowing
private ownership and operation of nuclear facilities. Before it passed, they had
three nuclear departments: operating the Hanford production reactors, doing submarine
testing at KAPL, and working on the aircraft nuclear propulsion project. They also
contributed significantly during the Manhattan Project. After the 1954 act, they added a
fourth nuclear division: an atomic power equipment department.
At this time, General Electric (GE) boldly took on a contract to build what became the
large-scale Dresden BWR. They started performing vast amounts of commercial nuclear R&D on
their own dime because they were convinced at this time that commercial nuclear was going
to be big business. Regarding the proposed large-scale Dresden BWR, GE’s VP McCune said
in 1956 that:
I have already testified that the developmental work required to produce this plant,
particularly fuel element development, will be very expensive. Unless we obtain
substantial future business, we will lose considerable sums on the Dresden station. At
the time we contracted to build this plant for Commonwealth, we were well aware of this.
We are aware also of the difficult technical problems ahead of us and of the large
investments in developmental facilities, these very expensive tools of the trade, which
would be required.
Moreover, when we signed the Commonwealth contract, we faced serious problems in
addition to the technical ones. The regulatory and licensing situation was still
unsettled. The Commission was just beginning to break down the information barriers.
Above all, the liability problem had not been resolved.
Nevertheless, we took on the Dresden station because we were convinced that by doing so
we would serve the long-run interests of our share owners, our responsibilities to the
system of private enterprise, and the national interest. Out decision to go forward was
also based on the belief that Congress expected this kind of a job to be done by private
industry. We had faith that Congress, and particularly this committee, as well as the
Commission, wanted to encourage private development and would take all reasonable steps
to promote that development.
Soon, GE enlisted services of their steam turbine-generator department for the plant
design, their induction motor department for special motors, their carboloy department for
fuel development, their general engineering lab for instrumentation, and their R&D
capabilities, also for fuel development. They created the 1,600-acre Vallecitos Atomic
Laboratory in California to be their component testing grounds, with a hot lab and an
experimental physics building containing a critical experiment facility. They went so far as to
build the Vallecitos BWR (VBWR) on the site with 100% private capital to help GE staff
gain the knowledge and experience necessary to deliver on the large-scale Dresden BWR
project. It was about the same size as the AEC’s EBWR (Senator Anderson even prodded
McCune about what they’d learn at VBWR that wasn’t learned at EBWR), but featured a dual
cycle, where steam could be generated from the stream drum or from a lower-pressure steam
generator. This was expected to improve load-following capabilities. It was also higher
pressure: 1000 psia instead of 600.
As Dresden was being designed, GE had 2,250 scientists and engineers in their four nuclear
Given their experience operating the Hanford production reactors, GE spent a lot of their
own money exploring the design of a graphite-moderated electricity-producing plant. They also
looked hard into homogeneous reactors. But, when the time came, they decided that the BWR
design was the most promising, and they leapt in full-force with the Dresden contract.
Specifically, Dr. Walter Zinn’s confidence in the ANL-designed BWR is what convinced GE to
go for it rather than the homogeneous reactor.
Dresden featured a dual-cycle steam system, and produced power in April, 1960. The
plant operated well. After Dresden came Humboldt Bay with natural circulation.
There was one tragedy along the BWR development pathway. The Army’s SL-1 in Idaho was part
of the Army Package Power Program, previously called the Argonne Low Power Reactor, ALPR.
It was designed to be built on the tundra above the DEW
line to power radar stations.
It suffered an explosion on January 3, 1961 that resulted in 3 casualties. SL-1 was a
small, natural circulation, direct cycle BWR designed and built by ANL. ANL directed the
project, and Pioneer Service & Engineering Company was the A/E. Operation was turned over
to Combustion Engineering after the plant was operational.
Before the accident, the reactor had been shutdown and the night-shift workers were
preparing for a power ascent. The procedure required them to lift the inserted central
control rod about 4 inches to hook it back to the drive mechanisms. For a reason that will
forever be unknown, the worker lifted the rod quickly by 20 inches. A prompt-supercritical
(e.g. very fast) chain reaction ensued, vaporizing and expanding fuel before the water had
time to boil and add its negative feedback component. After the core was at very high
power (around 20 gigawatts), the vaporizing fuel elements vaporized and rapidly boiled the
water. The steam accelerated the seven-foot column of water above the core, slamming it
into the lid of the pressure vessel at 160 feet per second, forming a massive water
hammer. The shield plugs ejected at up to 50 feet per second, along with much of the
shielding. The three military personnel who were on
top of the reactor head at the time suffered fatal and gruesome injuries (one was pinned
to the roof through the groin by an ejected moderator assembly). The creation of 10,000
psi pressure from the water hammer within the sealed pressure vessel had not been expected.
Had the vessel featured an open top, for example, the most destructive effects would not have
occurred. It became an important lesson to never put reactors into such a configuration.
Analysis showed that the control rod was pulled with less than full force. Some have gone
so far as to hypothesize that a love triangle was involved, and that this accident was a
murder-suicide by nuclear chain reaction. (This seems very unlikely). In any case, a
cleanup ensued and the site is now barely noticeable as you drive through the Idaho
Big Rock Point in Charlevoix, MI (critical on September 27, 1962) first conducted a 4.5
years AEC research program demonstrating high power density
cores that had
been tested in VBWR. Obtaining more power out of a volume would possibly allow smaller
pressure vessels and uprates at existing plants. After the tests, the plant switched over
to producing commercial power for the region, which coincidentally is where I spent my
childhood. I grew up about 10 miles from Big Rock, which operated well until my teens.
Elk River was another small “hook-on” reactor that added steam to an
existing conventional plant. It was a BWR though, and a part of the PDRP. Its criticality
was 2 years behind schedule. Steel strikes and other strikes delayed the project, as well
as hairline cracks discovered in the cladding inside the pressure vessel. Repairs were
made and authorization to operate was given. It was coupled to a coal-fired superheater.
In 1964, GE sold the Oyster Creek reactor to Jersey Central Light at a guaranteed fixed
capital cost that was competitive with fossil fuels. Widespread euphoria spread throughout the
nuclear developers. At a State of the Lab speech, Alvin Weinberg shouted:
Economic nuclear power is here!
Between 1963 and 1966, 10 utilities purchase 12 PWRs and BWRs from GE and Westinghouse
under these turnkey contracts.
Alas, the turnkey era was short lived. The reactor vendors struggled to make money on
these sales. Coal executives claimed that GE had priced Oyster Creek below cost. GE denied this,
saying they’d make a small profit unless unforeseen difficulties were encountered. The plants
were still large, complex, and expensive. Increasing public scrutiny and the associated
regulatory instability caused various cost escalations.
Today, multiple PWRs have had to shut down prematurely due to intractable steam generator
problems. This at least partially validates the major BWR advantage of having a direct
primary cooling loop.
Advanced-model BWRs were developed in more recent years, focusing on simplicity and economics.
The Hallam sodium-graphite reactor in Nebraska
Ok, you may have been aware of the developments so far, but let’s now dip into some of the
more exotic developments of the days gone by.
Liquid metal is an excellent coolant fluid, enabling low-pressure operation, phenomenal
heat transfer, and thrillingly little corrosion. It was used in the EBR-I fast-neutron
reactor in 1951. Since fast-neutron reactors require far more fissile material to start
up, a sodium-cooled, graphite-moderated reactor was envisioned as a potential candidate
for producing low-cost nuclear electricity. This would allow low-pressure operation
without all the expensive and thick pressure containment systems and backup cooling while
also allowing the reactor to run on natural or very-slightly enriched fuel.
On the downside, many liquid metals are chemically reactive with water, air, and concrete,
and the complications related to inerting the environment and dealing with leaks and fires
would have to be weighed against the aforementioned benefits. Additionally, sodium becomes
highly radioactive as it passed through a nuclear core. The combination of radioactivity
with chemical reactivity necessitates an additional intermediate heat transfer loop,
especially when a metal-water steam generator is used. The extra loop comes expensive
additional equipment: pumps, valves, instrumentation, controls, heaters, and piping.
North American Aviation contributed $2.5M to the $10M cost of research, development,
and construction of the 20 MWt Sodium Reactor Experiment (SRE) at Santa Susana, CA.
Heavily informed by the AEC’s S1G submarine prototype reactor in New York and the Sodium
Reactor Experiment north of LA,
the Hallam Nuclear Power
Facility was a 75 MWe
attempt to approach commercial viability of a sodium-graphite reactor. It was proposed in
the first round of the PDRP.
The component testing and R&D in advance of Hallam operation was astounding. In spite of
experience acquired at from the smaller SRE, Atomics International still knew they
needed to build much of the equipment at the larger scale in order to shake down the
scaled-up designs. For example, they built an entire mockup fuel handling facility and a
full-scale fuel handling
operated it at temperature, in sodium! This allowed them to fix scaling design issues as
well as to practice the various fuel handling activities that would be required in the
operation of the plant.
The Hallam facility was built relatively quickly but struggled with reactor problems
during the shakedown period. After many repairs and lessons, the issue of rupturing
moderator cladding and subsequent over-expansion and closing-off of coolant channels was
the final straw. Consumers Public Power District chose to not purchase the facility from
the AEC, and it was grouted in place by 1969.
Today, the fossil side of the plant still operates, and if you look at a satellite
you can see the perfect outline of the nuclear part partially entombed in beautifully cut
grass, which is actually part of the containment. You can also see a big coal train right
Since Hallam operated, vast amounts of experience have been gained in sodium-cooled
fast-neutron reactors. It’s curious to wonder if a sodium-graphite reactor with that
expanded knowledge-base wouldn’t perform significantly better than Hallam did. Then again,
some of the world’s newfound sodium experience (e.g. Monju, SuperPhénix) has not been
Organic cooled/moderated reactors: Piqua in Ohio
The second solicitation for the PDRP specifically sought small reactors. The Piqua
proposal fit the bill, at just 11.4 MWe. It featured organic coolant and moderator made of
terphenyl isomers (hydrocarbons). It was supposed that organic coolant
would lead to low capital costs. The low vapor pressure of the coolant allowed
low-pressure operation at high temperatures, reducing the weight and bulk of the pressure
vessel while increasing the thermal efficiency. Organic coolant also has low corrosion,
allowing conventional materials like carbon and low-alloy steel to be used rather than
stainless steel in the pressure vessel, pumps, pipes, etc. Lastly, induced radioactivity
in pure organic liquids is very low, unlike in the liquid metals.
The price to pay for the benefits of organic coolant comes in the form of decomposition
cleanup and purification systems. Radiation and heat both cause the fluid to break down
into water vapor, hydrogen, methane, and other hydrocarbons. Also, the heat transfer
characteristics are generally worse than for water, requiring high surface area
fuel element design.
The AEC contracted Atomics International (AI) to do research and development at the
Organic Moderated Reactor
Experiment (OMRE) in
Idaho. This established the basic feasibility of organic-cooled reactors, and allowed AI
to build experience in the system. They measured coolant properties, fabricated fuel,
built and operated the reactor, measured heat transfer, operated purification systems,
built control rod test towers, built a hot cell to examine irradiated fuel, and performed
dozens of other R&D tasks.
As a follow-up to OMRE, the AEC contracted AI to build the Experimental Organic Cooled
Reactor (EOCR), also at the NRTS. This facility was built to 99% completion by the
contractor, but ended up never operating.
The OMRE established the organic-cooled concept sufficiently to motivate the Piqua team to
submit a proposal for a commercial plant.
The business plan for Piqua was that the AEC would own and operate the plant for 5 years,
selling steam to the city for the same price of conventional fossil-fueled steam. After 5
years, the city would have an option to purchase the plant from the AEC. Given their
experience from the OMRE, Atomics International was again contracted to design and build
the Piqua plant.
Piqua was brought to criticality on June, 1963, and reached full power in January 1964.
The plant produced 20% of Piqua’s power in 1965, and the city proudly referred to itself
as The Atomic City.
In 1966, two control rods were found to not move freely in their guide tubes, and four fuel
elements required abnormally high forces to unseat and would not reseat. The obstruction
was found to be a carbonaceous deposit. Fuel was shipped to Atomics International for hot
cell examination, where a hard continuous film was found on the surface, patches of film
were found on the tips of the cladding film, and the inner moderator space was found to be
full of carbonaceous material. A three-phase core disassembly/rehab program was developed.
As the rehab was ongoing, it became clear that Milton Shaw, the director of Reactor
Development at the AEC, had given up on the organic concept:
There is an expression used around our office about reactor projects. It is not
those that have the slow death that worries us; it is those that have a life after
He concluded that the AEC would support the Piqua facility but would otherwise discontinue
all work on the organic cooled concept. The writing was on the wall. In the FY1969
authorization hearings of the
announcement to terminate the Piqua contract was made:
The Commission is in the process of terminating the operating contract for the Piqua
reactor project. Several factors entered into this decision including: an increasing need
for available resources (manpower and funding) by higher priority programs; little
programmatic interest since support for organic cooled and moderated reactors and the
HWOCR concept has been phased out; the technical problems which continue to delay
reoperation of the plant and the unlikelihood of the City to purchase the plant.
Today the small dome still stands, and it looks
it’s used as a warehouse. The City had to change its nickname to “The City of
A 23-minute video explains Piqua in some detail.
Fate of molten salt
Notably, Milton Shaw is much derided for focusing all reactor development efforts on the
fast breeder program around this time. In particular, Oak Ridge’s Alvin Weinberg and Shaw
fought at this time over the fate of the molten salt reactor program.
Apparently, the organic reactors and molten salt reactors are brethren in this.
Atomics International: reactor development badasses extraordinaire
Take note that the AEC contractor, Atomics International designed and built those last
two wildly innovative reactors. They had a process:
- Explore feasibility in the Santa Susana lab
- Build and operate a small reactor experiment to shake it down at power
- Perform large-scale component development, building and operating them in mock-up
- Build a medium-sized municipal reactor in a rural town to produce power
Their component development and testing facility at Santa Susana was incredible.