26.08.2015   ATOMIC ACCIDENTS

CAUGHT IN THE RICKOVER TRAP

"If a man fires at the past from a pistol, the future will fire at him from a cannon.”

—Abutalib

It was summer, 1985. We had successfully conceived, designed, birthed, programmed, built, worried over, installed, documented, and exhaustively tested the Safety Parameter Display System for the two General Electric BWR/4 reactor units at Georgia Power’s E. I. Hatch Nuclear Power Plant down in Appling County, Georgia. It was time to celebrate! Instead, the three of us, I, Jeff Hopper, and Mark Pellegrini, retired to our rat-hole motel in Hazlehurst, over in the adjacent Jeff Davis County, to catch up on our sleep.

There is seldom a great deal of civilization near a nuclear plant, and it was a half-hour to Hazlehurst, which was the closest place with a motel. I found my room, collapsed in bed, and extinguished the light. As soon as the springs stopped groaning, I noticed a periodic chirping noise. Eek… eek… eek… eek. Was it a cricket, or was it a dry bearing in the air conditioner blower? My attention was riveted to the sound, and I could not help but try to analyze it. Having just come down off an extended computer system verification exercise, I found that I had to submit it to a test. I turned on the light. The chirp stopped instantly. Yep. It was a cricket. Problem solved. Lights out. I drifted off to sleep and suffered through an incubus of an enormous squirrel-cage fan with a dry bearing, moving closer and closer.

These computer systems were built to satisfy new control-room instrumentation requirements set forth by the Nuclear Regulatory Commission in NUREG-0696, “Functional Criteria for Emergency Response Facilities,” written in response to inadequacies discovered in the TMI-2 disaster of 1979. Our sparkling new systems, bolted strongly to the control-room floor, each collected 128 analog and 512 digital data in real time from each reactor system and displayed them on demand using color video monitors. The equipment had been shake-tested on an earthquake simulator in California, run continuously for years in our lab back in Atlanta, and endured handling by inexpensive student labor from Georgia Tech. It was as solid and glitch — free as a dedicated team of engineers could possibly make it. I was overflowing with confidence that it would perform perfectly, as I would remind anyone standing near it.

The next day began an adventure that went down in the history of nuclear power as the “Rat Cable Problem.”

We wanted to give the systems ample time to run before we returned to examine the overnight performance logs, so we lingered over breakfast and retired to our rooms to relax.

I’m not sure what the other guys did, but I watched cartoons on the television. That afternoon, we drove to the plant. Pellegrini fretted over the party that the control room operators must be planning for us.

The parking lot at the plant was blazing hot, with the power of the sun reflected back at us, making the air seem to sizzle and boil as we walked the distance. There was some race of enormous beetles living on the plant site—they were huge black things with horns. Pellegrini feared that they were mutants caused by irradiated bug-DNA. I scoffed, but they were big, and they were marching eight deep in a line across the parking lot, toward the river, moving perpendicular to our trajectory as we made a straight line for the guard shack.

They were a determined bunch of insects, keeping a disciplined column at a constant speed on the egg-frying concrete. We were equally determined. Our tracks were about to cross, and I was not about to hesitate as we intersected the beetle path. My eyes locked on an individual. He was not going to hesitate either. Estimating his speed and mine, it looked as if he would be walking either over the top of my right shoe or under it. Crunch. The big insect’s life ended suddenly, right under my foot. It was a bad omen. I wondered silently as we completed the hot trek. Why do silly omens seem to gain importance as we draw nearer to an active fission process?

We reached the electronics bay adjacent to the control room. Hopper turned on the maintenance terminal and started reviewing the system’s performance over the last 18 hours. It was bad. The error log was filled with digital data reception failures, and the size of the log was growing as we watched. It was not every reception. It was just every once in a while, a parity

check would fail.281 It could go a minute or an hour between errors, or a burst of errors could occur, as the digital data set was polled once per second, and, even more unnervingly, the failures appeared to be completely random and did not follow any particular pattern or appear to be connected to any one particular system failure.

The digital data were collected using a wired loop running all over the plant and passed on to the computer systems by a Cutler Hammer Directrol Multiplexer Communications Station, bolted to the back wall of the electronics bay. A fat, multi-conductor cable (no. 5769) ran between the Directrol and the ROLM 2150 I/O expansion box. Both the Directrol and the expansion box had been exercised continuously back at our shop in Atlanta for years without a single error. Had something broken at the plant? We decided to let it keep running to see if the system self-regulated, and also so we could collect more data and try and figure out what the problem was.

The errors would not stop coming. The next day, the error log was in crisis mode, and it was eating up all the reserve space on the disc. Another week of this, and the working space on the disc would be gone. The operating system would lock up. The log was now larger than the 30- minute sliding record of everything in the plant that was held on the disc as a “black box”

recording.282 Why? It had to be the only one difference between the development setup in our shop and the operational installation in the power plant.

Back at Georgia Tech, we had built a special room in the high-bay of the Electronics Research Building, complete with enhanced air conditioning and a raised computer-room floor. The room was a good replica of the Plant Hatch electronics bay, except for one detail. There was an open pipe through the wall, leading to the outside. It had been added to the building so that power lines from a gasoline-powered 400-hertz generator could be connected. The pipe was not in use, except as an access walkway for vermin. Somehow, a brown rat, rattus norvegicus, had found our lab, and he visited often. By the time we discovered him, he had chewed up the insulating sheath on our very expensive cable no. 5769, connecting the ROLM I/O box to the Directrol. Why he so enjoyed the taste of plastic insulation on that particular

cable, I could not comprehend. It had zero food value, but he made a meal of it.283

Damage to the cable was strictly cosmetic, and we wrapped some electrical tape over the wound. It still worked perfectly, but we were too embarrassed to deliver it to the plant in that condition, so we called ROLM Military Computers in Cupertino, California, and ordered a new unit. They sent it promptly, and this was an improved example of the cable. The Army had apparently given them grief about the weight of their parallel-digital cables, so ROLM had built new ones using a smaller gauge of wires. It was slender and svelte, not as clumsy and bulky — looking as the original cable, and each individual wire was tested for continuity and lack of cross-talk. Once the new cable passed all the tests, we installed it in to the power plant.

However, not everything was perfect. The problem we soon found with the new cable was that, thanks to the slimmer design, there was a reduced cross-sectional area of the wires used. A digital computer signal is sent over an electrical circuit, and as such it needs a transmission wire and a return wire, or ground. In a wired digital circuit of many parallel paths, such as a data-bus or an interconnection cable as we were using, a common ground connection is used by all signals. In our original cables, the wire gauge was overkill, with more copper than was necessary for the low-current digital signals, and a single ground wire was big enough to carry all the signals firing at once. With the wire size reduced to a gauge that was still good for the signal current, the smaller ground wire was incapable of returning more than a few signals at the same time. If, by pure chance, most of the sent bits at a particular instance happened to be ones, then the signal voltage would drop below the logic threshold, and at the receiving end they would be interpreted as zeros. The reduced-diameter cable would test perfect if every wire and return was actuated individually, but under certain, seemingly rare conditions of data

structure, it could fail.284

We sent home an emergency request for the rat-bitten cable to be returned to us, re-installed it, and experienced no further data drop-outs. The electricians at the E. I. Hatch Nuclear Power Plant found our predicament amusing. The celebration party never happened, but the laughter we generated still rings in my ears.

The lesson of the Rat Cable Problem gave me a sense of sympathy for the engineers at General Electric as they watched their dreams of robust reactor systems, designed to work under the worst conditions imaginable, crumble to pieces at Fukushima I when the unimaginable happened. Trying to build something that will work perfectly for all time is a noble goal, but it is simply impossible. The issue that causes failure can be as grand as an earthquake and tsunami or as mundane as a brown rat.

Admiral Rickover’s nuclear submarine power plant was such a design. It was radical in every detail, and a great number of innovations were necessary to make it work. It started with the idea of using water as both the coolant and the neutron moderator. That would work, but it would mean that the fuel had to be enriched with an unnatural concentration of uranium-235. Some material would have to be devised that would hold the fuel in place with water running among small, cylindrical rods of uranium, and it could not parasitically absorb neutrons. Every neutron was precious. It also had to be able to withstand high temperature and be strong enough to hold the reactor core together without dominating the space. Zirconium fit the list of requirements, but there were no zirconium mines, refineries, or fabrication techniques. Rickover had to invent it all from scratch. He came up with the idea of control rods made of hafnium, which was another material that was not available at the hardware store. His exotic machine was entirely successful, driving his submarines, catapulting the United States Navy further into world domination, and it did not harm a single sailor. Rickover’s system test program was, without question, as rigorous and complete as could be accomplished.

The civilian nuclear-power industry, also starting from scratch in a very small, experimental step-off, was not the sort of enterprise that could develop new metals and radical designs of things that had never been built before. The utilities that were bold enough to try nuclear power were pleased when the naval reactor technology was declassified and turned into a stationary power plant at Shippingport, Pennsylvania, in 1957. It was a small plant, generating only 60 megawatts of electricity, but it never had a problem in 25 years of service. Seeing this as a good sign, the United States and eventually the world eventually stopped experimenting with different reactor concepts and settled on Rickover’s submarine unit as a standard for how nuclear power should be applied to the need for reliable, clean power.

Was this a good idea, or did the world’s utilities fall into a trap? The other radical idea for nuclear power, such as the liquid-metal-cooled fast breeder, had also been tried many times with consistently unfavorable results, just as Rickover had predicted long ago, when the Navy wanted to try it in submarines. The liquid-metal technology, as he pointed out, was expensive, prone to disasters, and extremely difficult to repair when something broke. Having a coolant that would catch fire when exposed to air did not seem right. Rickover was correct on that observation. Why would he be wrong about the pressurized-water reactor?

There have been trillions of problem-free watt-hours generated by scaled-up Rickover plants, but there may be a problem area that was not evident when submarine reactors were tiny, 12- megawatt machines, but that was revealed when the Rickover model was enlarged multiple times over for industrial use. The reactor core, the uranium fuel pellets lined up in zirconium tubes and neatly separated from each other, is terribly sensitive for such an otherwise robust machine. Let the coolant come off the fuel for a few minutes, even with the reactor shut completely down, and the entire, multi-billion-dollar machine is in irreversible jeopardy. The high — temperature zirconium alloys in an overheated reactor core oxidize, losing their metallic strength, generating explosive hydrogen gas, and contributing to high-pressure conditions in the isolated reactor vessel. The delicately structured core collapses, and the soluble fission products are able to mix with the escaping remnants of the coolant. It has happened as recently as 2011. To start the destruction sequence requires a lot of bad luck and human intervention. It is part of the nuclear power plant that does not easily forgive errors or dampen out mistakes. This part of the reactor design, the orderly matrix of thin tubes filled with fuel, is a weakness in an otherwise robust system.

There have been many engineering fixes and modifications to correct these problems, but ironically, these fixes can then present new issues, as they are complex add-ons, cluttering up an otherwise simple design with a maze of pipes and hundreds of additional valves, tanks, electrical cables, pumps, turbines, filters, re-combiners, and compressed-air tubing. Most of the plumbing in a nuclear plant has nothing to do with generating electricity. It is part of the fix that keeps the reactor core from melting down under unusual circumstances. These complex light — water-reactor designs, the boiling-water reactor and the pressurized-water reactor, have been pursued with such enthusiasm over the past sixty years, one could assume that there is no other reasonable way to build a civilian power reactor. Alternate designs, such as the graphite, as was used in Windscale, and the liquid-metal-cooled reactor at Fermi 1, have proven

impractical and have fallen away.285 If only there were a proven reactor design that was in no danger of melting the fuel, collapsing the core structure, and generating hydrogen, it would

solve many problems that bedevil the current crop of world-wide power reactors.286

The concept of this radical design, a reactor that has no metal core structure and no meltable fuel, dates back to World War II, when anything conceived and built at Los Alamos, New Mexico, was top secret and available only to those with a need to know. By the 1950s, the idea was further developed and incorporated into the Aircraft Nuclear Propulsion project, a program that was so far out on the technical limb, anything developed for it was easily dismissed when the project, again secret, folded up in 1961. In the 1960s the usable concepts developed in the defunct atomic airplane quest were built into an experimental power reactor in Oak Ridge. It was the answer to all problems that had to be addressed in the light-water-reactor designs, including the availability of uranium and the expense of enriching it, but it was too late. Westinghouse, General Electric, Babcock and Wilcox, Combustion Engineering, and a host of copying manufacturers in Europe had already thrown their resources into light-water-reactor development. We had fallen too far down into the Rickover trap to escape, and in 1969 the Oak Ridge experimental power reactor was quietly shut down and dismantled. Ten years later, a brand-new B&W power plant at Three Mile Island, Pennsylvania, was a total loss and a clean­up liability because its reactor core had overheated. The bottom-line expense of nuclear power was rightfully called into question.

Reactor designs with liquefied core configurations were started at Los Alamos in 1943. The first was LOPO (LOw POwer), consisting of a stainless steel sphere filled with 14% enriched uranyl sulfate dissolved in water and surrounded by a reflector made of beryllium. The fuel consisted of the world’s entire stock of enriched uranium at the time. The purpose of the reactor was to measure characteristics of uranium fission, but it was also the first reactor using a single fluid for fuel, neutron moderator, and coolant. It became known as Water Boiler, not because the mixture got hot enough to boil, but because the water broke down into hydrogen and oxygen under the heavy gamma-ray bombardment during fission, and gas would bubble to the surface. It was thus the first observation of radiolysis. Subsequently, any reactor using water as a moderator was equipped with a recombiner, a catalyst screen that encouraged the hydrogen and oxygen to re-form into water.

LOPO begat HYPO, and HYPO begat SUPO, research reactors with increasing mechanical sophistication and power. By 1953, the scientists and engineers working at the Los Alamos Lab began to think about a civilian power source based on nuclear fission. In the early fifties, there was barely enough known reserve of uranium to make bombs for the United States, much less to make electrical power for the world for centuries, but there would be enough plutonium produced artificially to at least power the Western Hemisphere far into the future. Almost 100% of the world’s stockpile of plutonium happened to be in Los Alamos, New Mexico, and there was no reason not to use some of it to build a prototype power reactor.

The first plunge into the Liquid Metal Fuel Reactors (LMFR) was LAMPRE, the Los Alamos

Molten Plutonium Research Reactor.287 It was the first reactor ever built that used molten metal, a eutectic alloy of plutonium and iron, as the fuel. There was no fear of the core melting down, because the core was melted. The reactor would run at 1,200° Fahrenheit, a temperature that was impossible for any reactor with solid, structured fuel, but it would make very efficient steam for running a turbo-generator. The plutonium-239 fissioned efficiently using fast neutrons, so there was no need for a moderator, and there were plans to add a uranium — 238 breeding blanket to the reactor so that it would produce extra plutonium as well as power. Any problem of having the reactor melt was taken care of by making it out of tantalum-tungsten alloy, which would melt somewhere above 6,000° Fahrenheit. It would be possible to slowly draw off the molten plutonium fuel through a pipe at the bottom of the reactor core, filter out fission products, add plutonium to replace that which had fissioned, and pump the fuel back into

the reactor.288

By the time LAMPRE first achieved hot criticality on March 27, 1961, the concern for uranium scarcity was over, and Rickover’s PWR had become the darling of the civilian nuclear-power industry. LAMPRE-2 was planned for, but funding for exotic reactor projects was tight, and the ambitious follow-on project was dropped. Rickover was pleased. He despised the frontier experiments at Los Alamos, Oak Ridge, and Idaho as a silly and impractical waste of federal money.

The next big step was the Direct Contact Reactor (DCR) at Oak Ridge, where the Aircraft Reactor Experiment (ARE) was underway. The ARE was a hyper-exotic setup, meant to become a jet engine in a strategic bomber, using a molten fuel made of uranium fluoride, sodium fluoride, and zirconium fluoride, moderated with beryllium oxide, with liquid sodium as a coolant. The metal structure was made of Inconel 600 alloy, and the thing ran for 1,000 hours at a temperature of 1,580° Fahrenheit. In the history of the art, nuclear reactors did not get much fancier than the ARE.

The goal of the DCR was a high-efficiency, fast-neutron power reactor using molten plutonium fuel. The fuel was to be a plutonium-cerium-cobalt alloy, and in this innovation the fuel would also be the primary coolant, pumped around in a loop. Using the principle of “critical shape” that was employed in all the fuel-processing plants, the plutonium would be in a critical configuration, generating power by nuclear fission, only when it happened to be in the reactor core, which was a sphere. In the spherical reactor tank, the surface-area-to-volume ratio was at a minimum, and a large percentage of fission neutrons were able to propagate fission. Going around in the coolant pipes, the plutonium was thinned out, and most of any neutrons were lost out the walls of the pipes. There was no need for a moderator, because plutonium-239 was the fuel, and there was no core structure. This was a major idea.

Instead of there being a heat exchanger to pass off the high temperature created by fission, the fuel mixture was mixed with liquid sodium in the loop outside the core by a jet pump. The heat transfer from the direct contact of the hot fuel and the coolant was 10 to 100 times more efficient than using a metallic heat exchanger. The hot sodium then transferred the heat to water in an external steam generator, so that a standard turbo-generator could be used to make electricity.

A gravity-drop separator then took apart the sodium/plutonium mixture, putting the sodium back into the continuous jet pump loop and the cooled plutonium, still melted, back into the reactor. Another great feature of this plan was that the fission products would stick to the sodium and be scrubbed out of the fuel loop. A blanket of depleted uranium around the core would breed new plutonium fuel. With radioactive products continuously processed out of the fuel, there would be no buildup of radioactivity to escape, and there was no chance of the molten metal being able to blow off like steam and spread anything over the environment. The primary loop could, in fact, run at atmospheric pressure. Each DCR in a power plant would be small, only four feet wide, and generating about 227 megawatts of heat. A power plant would consist of 20 reactors, each encased in a 60-foot-long tube, sunken into the ground. It was almost too good to be true. The Atomic Energy Commission applied for the patent in 1961.

By August 1960, a mockup of the DCR had been built at the Los Alamos Science Laboratory and the new subsystems for the reactor were being tested. In May of 1962, a functioning DCR, code-named the Pint Bottle Experiment (PBX), was ready to be built. The budget for experimental reactors, however, was collapsing as the research projects were growing numerous. The nuclear-reactor market was expanding all by itself, without any DCRs, PBXs, or LAMPREs to help it along. The need for anything better than a Westinghouse PWR or a General Electric BWR was vanishing. Not only was there enough uranium to run the world into the far future, but the cost of it was dropping fast. PBX died on the drawing board. A new report predicted that by the year 2000, half of the electricity used in the United States would be generated by nuclear fission.

While the Los Alamos lab was suffering from a mismatch of funds-to-ambitions, the Oak Ridge National Laboratory was working on a very interesting mutation of the aircraft reactor. The nuclear bomber had been euthanized as soon as John F. Kennedy was sworn in as president, but lessons learned while operating the ARE led to a new, radical design for a civilian power reactor, the Molten Salt Reactor Experiment (MSRE). It was possibly the most important advance in nuclear-reactor design in the 20th century.

At the end of the nuclear airplane era, the ARE was dismantled, and Oak Ridge secured funding to construct the MSRE in the same building. One fluid, a mixture of salts composed of fluorine compounds of fuel plus neutron moderator, was pumped into the round reactor chamber, where the fuel would fission, and out into a salt-to-sodium heat exchanger. The

cooled but molten salt would then re-introduce into the reactor in a loop configuration.289 Operating temperature was 1,300° Fahrenheit. Steam was then made in a liquid-sodium-to — water heat exchanger. Neither the primary fuel loop nor the secondary sodium loop inflicted any

pressure on the reactor structure.290

The innovation of this reactor was the fuel. Instead of using uranium or plutonium, it used thorium-232. It turns out that thorium is four or five times more common than uranium, and there is a large reserve concentration of it in the United States. Mined uranium is over 99% uranium — 238, and less than 1% is the usable isotope, uranium-235. All of the thorium available is thorium-232. There is no unusable thorium in nature. No isotope separation or enrichment is necessary.

Thorium-232 is not a reactor fuel. It will not fission, but upon capture of a neutron, it develops
into uranium-233, which is as fissile as uranium-235. The conversion of thorium into uranium can take place in the reactor core, using surplus neutrons produced in the fission process.

When uranium-233 fissions, it produces 10 times less radioactive fission product than does uranium-235. Moreover, the cumulative fission product that it does produce has a half-life 100 times shorter than that produced by uranium-235. The danger of the radioactive waste is gone after 300 years, whereas the waste from uranium-235 fission remains dangerous for 30,000 years.

There was no fuel cladding, no zirconium egg-crates holding the fuel in a rigid matrix, no steam in the reactor vessel to float away with fission products into the atmosphere, and, of course, there was no danger of the fuel melting. In the power-plant embodiment of the MSRE, the fuel would be continuously reprocessed by running the primary loop through a chemical scrubber to extract fission products and inject fresh thorium. An atomic bomb cannot be made from thorium-232, because it does not fission, and it becomes uranium-233 only in the reactor

core under neutron bombardment.291

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The advantages of this reactor design seem overwhelming, particularly after the turn of the century, when we have seen an entire power plant go down because of melted core structures and broken steam systems spreading fission products. These weaknesses that destroyed light — water reactors would not exist in the molten-salt reactor.

The MSRE ran for four years. The program was shut down in 1970, and by 1976 any trace of the reactor was gone. There was no need for an improved way of making power by fission, and all the eggs by now were in one basket. An entire industry, from fuel-pellet manufacture to steam-generator fabrication, had been built around the water-cooled reactor designs used in Rickover’s nuclear navy, and there would be no turning back. We effectively had to dance with the reactor we came with.

It could have been worse. The water reactors were well designed, and they have given us 40 years of reliable electrical power in the United States. A good thing that you can say about water is that it is not sodium, which is an isolated drawback to any molten-fuel reactor concept. The high operating temperature of sodium, which is over 1,000° Fahrenheit, is an advantage for heat-to-electricity conversion, and it makes sodium or sodium-potassium coolant a necessity for reactors using molten metal or salt fuel. If we grudgingly acknowledge the relative dependability of the water reactors, there is one more flaw in the system: where do we put the fission product wastes?

Our system of waste disposal for water reactors is horrifically wasteful and inefficient. We have decided to simply bury everything that comes out of a nuclear reactor core. This amounts to wasting a lot of unburned fuel, along with valuable medical and industrial isotopes. When the fuel comes out of a power reactor and is stored away, 95.6% of it is uranium, and most of it is harmless U-238. Radioactive nuclides are 0.5%, 0.9% is derived plutonium, and 2.9% is non­radioactive fission products. A tiny fraction of the spent fuel should be buried, but we are set to bury the entire load, without having chemically processed the fuel and separated out what needs to be buried. If we could process the fuel, as nearly every other nation with nuclear power does, it would drastically reduce the volume and weight of the buried material and thus simplify the disposal process.

The problem of waste disposal, while solved, has not been implemented. Although it has been paid for by a coalition of the commercial nuclear power utilities in the United States, the spent fuel repository built under Yucca Mountain in Nevada is currently having trouble accepting fuel deliveries. The state of Nevada has changed its welcoming position to the facility after spending $12 billion of the power companies’ money to study the site and dig the tunnels. Although a federal law designating the Yucca Mountain facility as the nation’s nuclear-waste repository is still in effect, usage of the facility is being blocked. As this controversy continues, nuclear waste builds up in dry storage casks at every light-water reactor in the United States.

The option of processing the waste down into extremely small parcels and easing the burden of burying it was once a goal in the United States. Learning from all previous attempts to process spent reactor fuel as a commercial venture, the Allied Corporation, the Gulf Oil Company, and Royal Dutch Shell combined resources and began construction of a sleek, very sophisticated chemical plant in South Carolina, named the Barnwell Nuclear Fuels Plant. It was fully automated using computer controls and gravity-driven processes through seamless stainless steel pipes and tanks. In 1977 it was nearly completed, and with the permission of the Nuclear Regulatory Commission, it ran a test load of spent fuel through the plant. It performed perfectly, and a license for its operation was assumed to be on the way.

On April 7, 1977, United States President James Earl Carter announced at a special press conference, “We will defer indefinitely the commercial reprocessing and recycling of plutonium produced in the U. S. nuclear power programs. The plant at Barnwell, South Carolina, will receive neither federal encouragement nor funding for its completion as a reprocessing facility.”

This announcement hit the nuclear industry like a two-by-four to the back of the head. There was no way not to process plutonium out of nuclear fuel. It is a byproduct of all commercial power generation using uranium as fuel. The operating license for the plant was denied, on

presidential order.292 It turned out that the reason for this strange action, stopping an industrial plant from operating after a quarter of a billion dollars had been spent building it, was President Carter’s fear of nuclear-weapons proliferation via easy access to plutonium. He was not necessarily afraid that the United States would build weapons using plutonium, as we were running two large, federally owned plants to turn out bomb-grade plutonium by the ton. He was afraid of smaller countries using their own fuel reprocessing for this purpose, and he wanted to symbolically show them that if we did not do it, then they should follow our example and not touch their nuclear waste.

The rest of the world went on about their business, and there is no record of anyone giving a thought to the President’s symbolic gesture. The Barnwell plant suffered drastically from the lack of an operating license, and although the next president, Ronald Reagan, lifted the ban on commercial fuel reprocessing, the concept of the federal government being able to shut it down at its discretion discouraged any further idea of operating it as a business, and its major customer, the Clinch River Breeder Reactor, had also been cancelled by President Carter. If there could be no civilian fuel reprocessing, then there was no sense in building a civilian breeder reactor. A fast breeder reactor runs on plutonium, and it must be extracted from the breeding blanket. The Barnwell plant was decommissioned in 2000. It had been a fine, constructive idea, a large investment, and 300 workers’ jobs, all gone down the drain.

The premise of the Carter administration’s decision to shut down civilian fuel reprocessing was incorrect, and it shows that a little knowledge is dangerous. Yes, spent uranium fuel from a commercial power reactor does contain plutonium, but it is not “bomb-grade” plutonium. In a plutonium-production reactor, specifically built to make plutonium for nuclear weapons, the fuel is natural uranium, containing very little fissile uranium-235. It burns up quickly, in weeks of running at full power, and it is changed for fresh fuel on a regular basis. The plutonium is separated chemically from the spent fuel. The plutonium is primarily the nuclide Pu-239, with a small amount of Pu-240. Pu-240 is made when a neutron is captured by Pu-239, presumably after it has been made by neutron capture by U-238. U-238 becomes U-239, and it does two quick beta-minus decays into Pu-239, using neptunium-239 as the bridge nuclide.

It is important to minimize the Pu-240 contamination, which is why the fuel is not allowed to linger in the neutron-rich environment of an operating reactor core. Pu-240 fissions spontaneously, not waiting for a neutron trigger, and in a bomb it would cause the device to engage in runaway fission and melt before it ever had a chance to explode. The presence of a Pu-240 contaminant, which cannot be separated from the desired Pu-239, is what forced the original design of the complex, difficult implosion method of setting off an atomic bomb in World War II. Minimizing the Pu-240 content is the reason for quick turnaround in the refueling of a plutonium production reactor.

A civilian power reactor does not turn around fuel quickly. It is usually changed out on a three — year schedule. Refueling requires the reactor to be taken offline, cooled down, and dismantled.

You are not making electricity and the money from selling it when the reactor is down, so the time between refuelings is drawn out as long as is practical. Because it stays in the neutron

environment for so long, the plutonium-239 is heavily invested with plutonium-240.293 Its only

application is for reactor fuel.294 Nobody has ever built a nuclear explosive device using

plutonium taken from a civilian power reactor.295

So, the current status of commercial nuclear power in the United States sums up bleakly as this:

1. America’s 100 operating nuclear power reactors are bloated examples of Rickover’s celebrated submarine power plants, increased in size to the point where the core structures are the weak point.

2. There is not a single reactor fuel reprocessing plant in the United States, making us unique in the nuclear-powered world, causing our reactor waste to be mostly inert filler, and discarding unused fuel.

3. That does not matter, because we presently have no place to bury the waste, even if to do so would be grotesquely inefficient. The waste is being stored in dry casks on the property of every nuclear power plant in the United States, waiting to be hauled away.

But all is not lost, and nuclear engineers and scientists, or what is left of them, are not sitting idle. There are currently in design or test at least five new power reactors, and they are all small, modular units, as was carefully planned for the Direct Connection Reactor back in 1960. It was a brilliant concept, to install from two to twenty tiny reactors at a power plant instead of four huge ones. Small reactors have small problems, small explosions, small coolant drips, and small investments. An entire reactor can be built in a production-line factory, loaded onto a truck, and taken to a pre-made hole in the ground. The difference in efficiency of building a small reactor out of standardized parts in a factory instead of welding together a unique mountain of plumbing in the field is mind-boggling.

This important concept, of minimally sized simple power units had been exploited by the U. S.

Army in its Engineer Reactors Group beginning in 1954.296 Its reactors provided reliable power for Army installations from the Panama Canal Zone to McMurdo Station in Antarctica. After a stunning list of accomplishments, including a nuclear power plant that could fit on the back of a truck, the program was laid to rest in 1977, due to budget cuts.

The companies that are planning to make modular reactors available in the competitive market are all private companies, and not any government or military organization. Three of them are in the United States. The NuScale Power Company in Corvallis, Oregon, is working on a 45- megawatt power reactor enclosed in a steel tube. Gen4 Energy, Inc. in Santa Fe, New Mexico, has designed a 25-megawatt modular reactor. Generation mPower LLC in Bedford County, Virginia, is planning to put six very small reactors in the ground in Tennessee where the Clinch River Breeder Reactor was supposed to have been.

THE NUSCALE POWER PLANT

image037is simplified down to the point where the steam generator is built into the reactor vessel, and the power level of a single unit is such that it cannot build up enough delayed fission to melt the mechanism. The modular reactor may be an idea whose time has

come.

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Toshiba of Tokyo, Japan, is planning to install one of their tiny 4S reactors in Alberta, Canada, in 2020, and in France a consortium consisting mainly of AREVA is working on an interesting plan to use a nuclear submarine without a propeller as an off-shore, underwater mini-reactor power plant, the Flexblue. It will be controlled remotely by a person having a laptop computer, and if it should melt down they will simply unplug it. Being sealed up in a submarine hull

underwater, it could be abandoned in place without causing environmental harm.297

An even better development is the Generation IV International Forum, a coalition of nine countries, including the United States, which was brought together by the Department of Energy in January 2000. The purpose of this group of scientists and engineers is to identify realistic targets for research and development of a new generation of nuclear power plants, using all that we learned in 50 years of experimentation and experience. The goal is to develop and build these new power plants by the year 2030, without discouraging the building of Generation III reactors, such as the Westinghouse AP1000s now under construction in Georgia.

The list of exotic reactors being studied by the Forum includes sodium-cooled, gas-cooled, and lead-cooled fast reactors, supercritical water reactors, and very high temperature reactors, but right at the top of the pile is the molten-salt thorium-fueled reactor. The old, nearly forgotten concept of constantly melted fuel may find a new, productive life in the 21st century. It and the other revived reactor designs could help save us from packing more carbon dioxide into the
atmosphere than nature can handle. The dangers of atomic bomb fabrication, flying nuclear weapons around in airplanes, Soviet engineering and bureaucracy, and ingesting radium will be in history books, along with the curious recreation of crashing train locomotives into each other. As the nuclear engineering community lifts its graying head and looks to the future, remember one thing. If the person sitting next to you seems concerned with the radioactive fish from Japan, the air over the Tokyo Olympics heavy with fallout, or the contaminated junk that washes ashore in Oregon, then caution him or her not to eat a banana. It is crawling with potassium-40, a naturally occurring radioactive nuclide that spits out an impressive 1.46 MeV gamma ray. Neither radiation dose, from eating a banana or a bluefin tuna contaminated with cesium-137 (0.662 MeV gamma), is considered to be the slightest bit dangerous. In fact, tuna fish have been contaminated with radioactive cesium for the past 60 years or so, ever since the oceanic nuclear weapons tests from long ago, and it is used as a radioactive tag to trace migratory routes. The destruction of the Fukushima I nuclear plant may have added to the countdown period when all the detectable cesium-137 will have decayed away, but the danger remains indetectably slight.

The real danger is that any engineering discipline can fall into its own Rickover Trap. We do not, for example, necessarily burn gasoline at the rate of 134 billion gallons per year in the United States because it is the best way to power an automobile: we do so because we have been doing it a long time, and the infrastructure is in place. As is the case of pressurized water reactors, it has worked well for us for a long time, but there could be a better way to do it.

The dangers of continuing to expand nuclear power will always be there, and there could be another unexpected reactor meltdown tomorrow, but the spectacular events that make a compelling narrative may be behind us by now. We have learned from each incident. As long as nuclear engineering can strive for new innovations and learn from its history of accidents and mistakes, the benefits that nuclear power can yield for our economy, society, and yes, environment, will come.

281Digital data consisted of the open/closed status of valves and the on/off status of electrical motors and solenoids, collected at nodes all over the plant. Each datum was a 16-bit digital “word” with an extra parity bit. If the binary bits in the 16-bit word added to an even number, the parity bit was set to a one. If the addition was an odd number, the parity bit was zero. Upon reception back at the computer, the binary bits were added up, and the odd/even character of the resulting number was compared to the parity bit. If the results did not agree, then the datum had been corrupted somewhere, having either dropped or gained an odd number of spurious bits. This condition was logged as an error, and a repeat transmission was requested.

282 We started the project specifying a 32-megabyte hard disc. Remember, this was the early 1980s, and 32 megabytes was considered to be a large data-storage capacity It was housed in a box that fit in a 19-inch rack. Casey Lang, head of the software development group, came to me requesting a 50-megabyte upgrade to the specification. That was huge! It was hard to see how we could ever fill a monstrous 50-megabyte bucket, but I changed the order. It is amazing how data capacities have drifted up in the decades since then.

283 Having had 30 years to think about it, I now believe that the rat’s interest in the plastic cable insulation was caused by salt left on the surface by people having handled the cable. Human sweat contains a lot of salt, and when the water evaporates, the salt is left on the surface. Both ends of the cable had been handled many times, both at the factory in Cupertino and at the application point in Atlanta.

284 We were not the only ones bitten by the ground-return problem. The S-100 “Altair” data bus (IEEE696-1983), introduced in 1974, was an extremely popular design feature used in many micro-computer applications in the late seventies through the eighties, but it suffered from too few grounds.

285 Another alternate design, the Canadian CANDU reactor, continues on. Although its coolant/moderator, heavy water, is extremely expensive, the concept of a power reactor that runs on natural uranium with constant refueling has been attractive to countries such as India and China. A byproduct of CANDU power generation is bomb-grade plutonium-239.

286 The nuclear-power industry is acutely aware of these weak points and has not been sitting idle. The newer Generation 3 reactors, such as the Westinghouse AP1000, address the issues pointed out here with several innovations. The emphasis is on passive systems, not requiring electricity, to keep water covering the fuel and preventing core damage. Two of these reactors are currently being built at the Vbgel Nuclear Power Plant near Augusta, Georgia. The nuclear division of Westinghouse is now a Japanese-owned company.

287 A bridge between LOPO and LAMPRE was the Los Alamos Power Reactor Experiment (LAPRE) in 1955. Its liquid fuel was uranium oxide dissolved in phosphoric acid. The fuel was so corrosive, the entire inside of the primary loop, including the reactor vessel, had to be pure gold. The experimental budget of the Los Alamos Scientific Laboratory in the 1950s could cause heart palpitations.

288 That was the plan, but there was a lot to learn about molten fuel, and in reality LAMPRE-1 started out smaller and less complicated than was laid out in the proposal. The power was dialed back from 60 megawatts to 1 megawatt, and the core structure was reduced to tantalum tubes containing the molten fuel. Unforeseen problems turned up, as are expected in a leading-edge experimental program, but much was learned in two fuel loadings and three years of experience. The project was terminated in 1964, before the third fuel loading could be tested, and LAMPRE-2 was changed to the Fast Reactor Core Test Facility (FRCTF). The FRCTF project was abandoned, 70% completed, as was the Molten Plutonium Burnup Experiment (MPBE). The light-water reactors from Westinghouse and GE were succeeding beyond the Atomic Energy Commission’s wildest dreams, and everything else fell by the wayside.

289 In the Oak Ridge MSRE, criticality was established in the reactor vessel by sending the fuel through a perforated moderating core made of pyrolytic graphite. A cleaner design would make use of the good moderating qualities of the lithium in the salt and do away with any core structure, but this was the first attempt to build a molten salt reactor, and all advantages could not be accomplished in the initial experiment.

290 The plumbing and reactor vessel did require a special, high-performance nickel alloy to withstand the molten salt. Haynes International developed Hastelloy-N for the MSRE project, and it has found use in other nuclear power applications worldwide.

291 The problem with using U-233 in a bomb is that the bridge nuclide between Th-232 and U-233 is protactinium-233. The Pa-233 is very active, with a half-life of 27 days, and it beta-minus decays into U-233. Unfortunately, its decay also involves a 317 kev gamma ray and while the half-life is days, all of the protactinium never really goes away The energetic gamma activity makes it very dangerous to work with, and a lot of shielding is necessary Inside the reactor primary loop, there is nothing to worry about. The fuel is processed by machinery with no human interaction; but to make a bomb, a lot of fabrication and machining is necessary. Plutonium, for all its faults, is easier to work with than U-233.

292 Not exactly a presidential order. Barnwell and the Clinch River Breeder Reactor were shut down by presidential veto of S. 1811, the ERDA Authorization Act of 1978, preventing the legislative authorization necessary for constructing a breeder reactor and a reprocessing facility.

293 “Bomb-grade” plutonium is defined as 92% Pu-239. Commercial reactor-derived plutonium is 60% Pu-239. The United States, just to show off, once tested a plutonium-based bomb made of 85% Pu-239 having an explosive yield of less than 20 kilotons.

294 Uranium fuel mixed with recovered plutonium is called “MOX.” MOX fuel was being used in reactor units 3, 5, and 6 at Fukushima I when it was hit by the Tohoku earthquake and tsunami, and this caused a great concern of several milligrams of plutonium dust possibly escaping into the atmosphere. (With 550 plutonium-based bombs having been tested above ground or underwater, there were probably already several tons of plutonium in the atmosphere.) MOX is commonly used in European power reactors.

295 The President’s heart was in the right place, but his nuclear waste isotope was wrong. What he should have been worried about was not plutonium, but neptunium. Neptunium-237 shows up in spent fuel, and it can be extracted using published chemical processes. No tedious isotope extraction is necessary because it is all Np-137, which is just as fissile as Pu-239, U-235, or U-233. Np-137 makes a very low neutron background, so it can be used in a simple assembly bomb, just like U-235. There is evidence of an Np-137 atomic bomb test in the U. S., but it is, of course, classified SECRET. The neptunium bomb is something to worry about.

296 Right in the middle of the development program, the Army’s SL-1 reactor exploded in Idaho. The Army took this accident to mean that their reactor was too simple, and they dialed back the requirement of using as few moving parts as possible.

297 I applaud them for their various efforts and I wish these companies well, but, realistically, Toshiba and probably mPower have a chance of success. The Toshiba 4S design raised some licensing concern at the USNRC. It uses one central control rod, the part of the oversimplified SL-1 reactor that caused its destruction in a fatal steam explosion. We had pledged to never do that again. Toshiba will prove that its 4S reactor will not suffer from the single-control problem, but the other small companies are somewhat underfunded, and all are competing for what may be an initially limited market.