"To separate 100 grams (3.5 ounces - author's note)... of U235 per day..., 2,000 4-foot... calutrons could enrich material enough for one bomb core every 300 days." [clvi]
Richard Rhodes, author
The Making of the Atomic Bomb
The mad scramble that marked the beginning of the Manhattan Project under General Groves' administration must have seemed like a carnival to the outside viewer. The inertia that marked Colonel Marshall's administration was quickly replaced by frenetic activity, but very little of it seemingly tied to a master plan. Much of the Manhattan Project would be operated this way throughout the war. Often parallel programs were being developed and implemented that depended on one another for success, even though none of the interdependent, and very sophisticated, highly technical and extremely demanding, parts had been proven successful before the next component was begun.
The demands of time, from the very beginning, did not allow for this. Huge investments were made, sometimes speciously, of time, money and effort, justified only on a tremulous belief that technologies could and would be created, the need for which had not yet been conceived much less the technologies themselves envisaged. Groves had faith that requisite answers would be found before they were needed, and that all risks were justified by the global imperatives reflected in the war itself, even if it were all lost in the end.
In Germany in April 1942, Baron Manfred von Ardenne already had completed an operational magnetic isotope separator in his laboratory in Berlin Lichterfelde, his associate Fritz Houtermans having correctly calculated the critical mass of U235 the previous year. Manhattan Project scientists, too, had tried to calculate the critical mass of enriched uranium but came up with a surprising range of values that varied widely. The MAUD Committee, the British group that liaised with the Manhattan Project providing technical support and personnel, calculated the critical mass of U235 to be 25 pounds.
Physicists Frisch and Peierls had at different times predicted the baneful number to be either eight kilograms (17.6 pounds) or five kilograms (11 pounds).clvii Robert Oppenheimer himself, before joining the project, had estimated critical mass at about 100 kilograms (220 pounds). His theoretical group at Berkeley quickly upped that by three times to 300 kilograms (660 pounds).clviii As late as August 1943, when theorists at Los Alamos provided a critical mass estimate of 40 kilograms (88 pounds), the United States' target number for enriched uranium production was still unknown.
And while Ardenne was already proving the effectiveness of his isotope separator, the United States program at the end of April 1942 was still trying to complete development of its calutrons.clix Despite this and other setbacks, in the United States electro-magnetic separation was unrealistically anticipated to begin enriching uranium by the summer of 1943.clx Suffering from choking fits and starts, the program would not actually begin any kind of serious production, and even then production would be in such small quantities as to be valuable only for experimentation,clxi until over a full year later, in the summer of 1944. Arthur Compton, in a report he wrote for the Uranium Committee in 1941, had already stated "atomic bombs can hardly be anticipated before 1945."clxii Now it appeared bombs would not be available until November or December of that year, possibly not until 1946.
The challenges and uncertainty being clear, Groves supported other forms of uranium enrichment - as had the Germans - along with electro-magnetic separation, including gaseous diffusion, a method of separating the lighter isotope of uranium from the heavier ones by vaporizing the uranium and forcing its atoms through a series of "filter" barriers. The Lewis Committee, the select scientific/political review board responsible for oversight of nuclear development at the time, during the winter of 1942 had approved gaseous diffusion as the most likely method to achieve success.clxiii
The committee made this prediction despite the fact gaseous diffusion was calculated to require one hundred thousand barriers and the vessels in which to contain them, and several months of processing, to enrich enough uranium for a bomb,clxiv and despite the fact that, as of yet, the technology was totally unproved. Groves also had supported an effort initiated at the University of Virginia to study isotope separation by centrifuge.clxv Outside of the Manhattan Project, the United States Navy was developing a liquid thermal diffusion process for producing enriched uranium to power its warships.
Roosevelt had given strict instructions to the Manhattan Project not to co-mingle with the Navy program,clxvi the technology of which pumped liquid uranium through concentric tubes of differing temperatures to separate the lighter and heavier isotopes. Liquid diffusion allowed one more avenue of success for making the bomb, and allegedly was eventually utilized despite the President's orders.
In addition to building up these technologies, Groves had to establish a laboratory to study the fundamentals of making and detonating a bomb itself, as well as maintaining a center for studying and implementing the metallurgical processing of uranium that would be required.
The atomic bomb development plan - what meaningful plan there was - depended on the programs moving along and, as the laboratories hopefully started providing accurate answers and technologies began yielding usable results, General Groves would then try to cobble together what he could of the disparate successes to produce a viable program from this eclectic assemblage of science.
Realizing it was critical that each step was accomplished at the earliest possible moment, in his very first week Groves signed the approval to purchase 59,000 acres in Tennessee to house uranium enrichment efforts. He also quickly approved a $100 million expenditure to begin construction of the gaseous diffusion plant - the plant was code named K-25 - before the technology had even been proven.clxvii
K-25 would eventually consume half a billion dollarsclxviii of the Manhattan Project's $2 billion war-time outlay but, despite the traditional history if recently declassified records are believed, the program would contribute nothing to the atomic bombs dropped on Hiroshima and Nagasaki. Gaseous diffusion did, however, produce enriched uranium for triggering the post-war nuclear generation of weapons - the hydrogen bombs.
K-25 would stand for many years as the world's largest totally enclosed single building, and was twice the size of the calutrons' electro-magnetic isotope separation facility,clxix which became known as Y-12. But Y-12 would be the one and only United States plant through which every gram of American-made bomb-grade enriched uranium is claimed to have been processed.clxx Despite the Lewis Committee's recommendation for gaseous diffusion, the calutrons was still the only technology that had successfully enriched uranium and it remained the method of choice for the Manhattan Project.clxxi
The original calculations of calutrons requirements were nearly as dizzying as those for K-25. Experiments indicated that 2000 uranium ionization sources and an equal number of collectors to gather the final enriched product were required to yield 100 grams - only three and one-half ounces - of enriched uranium per day.clxxii Such a rate would require 455 days, one and one-quarter years, to produce enough enriched product for the bomb that was eventually dropped (Rhodes calculates 300 days per bomb, based on a smaller bomb estimate than the bomb actually dropped). And the above calculations assumed the calutrons worked reliably. In fact, the calutrons throughout their wartime lives proved to be models of inefficiency and poor operation.
Another humbling fact was that the first production calutrons contained only two,clxxiii not two thousand, sources and collectors. Ground had been broken 18 February, 1943 for the first "track," as it was called - because its oval shape resembled that of a race track - and it went into operation for the first time 1 August, 1943. But the device ran so poorly due to mechanical and technical shortcomings that it still had not been tested by September. Stone and Webster, the engineering contractor hired to run the operation, finished repairs and final installation in October and "powered up" the machine again in Novemberclxxiv - to experience a similar failure.
An engineering flaw caused the apparatus to be completely disassembled and shipped back to its manufacturer in Milwaukee to be cleaned and rebuilt. The entire year passed with so little uranium enriched that it could not be counted as production material but only as experimental stock.clxxv Also, the enrichment rate was nominal, having raised the level of U235 from .7 percent to 10 percent. True, this was over a 1,000 percent improvement, but bomb-grade enrichment needed to be 80 to 90 percent enrichment. A 1,000 percent increase to just 10 percent was disheartening. There was still a long way to go.
Despite the setbacks, Groves not only approved a second track to be built, with more sources and collectors, but he added plans for a third, with a new wrinkle. The newest track would be used to run already-enriched product, the end result being bomb-grade enrichment resulting from using the "seeded" slightly enriched feedstock. The two different types of track were designated "Alpha" tracks, which were those that consumed raw uranium and produced 10 percent-enriched uranium, and "Beta" tracks, which consumed the 10 percent-enriched uranium and produced bomb-grade uranium. At about the same time, the General decided to reduce the number of planned tracks from 2000 to 500, trusting that technology would become more efficient and bridge the wide chasm between political/military requirements and uranium's realities.clxxvi
The second Alpha track was in operation by mid-January 1944clxxvii and the first, dismantled, Alpha track was returned to Oak Ridge, reinstalled and placed back in operation by March.clxxviii But problems persisted. To make matters worse, spare parts were non-existent and operators ruefully inexperienced. There was no track record to guide them; no experience base upon which to rely. And the Beta tracks were suffering much the same setbacks as the Alpha tracks.
In the spring of 1944, with only a year left to achieve success, still no enriched uranium had been produced in anything close to production quantities.clxxix Still, Groves and his gargantuan, though dubious, enterprise carried on. By the end of June, five Alpha tracks and two Beta tracks were operating, but to very poor performance levels. The ionization sources in the calutrons that converted the uranium feedstocks to a "sublimed" gas in order to separate the atoms, only vaporized up to 75 percent of the feedstocks. a condition that remained prevalent even to the end of the war, leaving anywhere from 25 to 40 percent of the material with enrichment potential sitting useless in the "feed can" at the beginning of the process.clxxx All of this had to be cleaned out, reclaimed chemically, and reprocessed before it could be rerun - to the same result.
In addition, losses of sublimed material accumulated throughout the mechanical system of the calutrons,clxxxi leaving partially-enriched uranium embedded in equipment surfaces and linings within the device. The enriched material, even in microgram quantities, was so valuable that following each run the tracks were disassembled and thoroughly cleaned using geiger-counters (to locate each small particle), appropriate chemicals and special technologies, in order to reclaim every scintilla of enriched uranium.
Calutrons operators' clothing was specially laundered each day as well, to ensure every microgram that may have been captured in their clothing was recovered. The sum total of all of these efforts, on all of these machines that were operated and supported by literally thousands of people, was still an enriched uranium average daily yield of 11.5 grams per day throughout the month of Julyclxxxii - not even half an ounce.
More calutrons were installed to increase production levels. By November, nine Alpha tracks and three Beta tracks - most of them with a full contingent of 96 sources and collectors each - were operating to only slightly better efficiency performance than their predecessors, but the additional machines put production on the rise. Daily output in the first week of November averaged 45 grams (1.6 ounces).
In the second week it was 57 grams (2 ounces). The third week production dropped slightly to 50 grams, but in the fourth week of November, production climbed to 81 grams (2.84 ounces) per day.clxxxiii A significant increase but a rate that would still require 620 days, a full one and two-thirds years, to accumulate enough enriched uranium to fuel the bomb that must be used against a belligerent enemy - either Germany or Japan - within eight short months or the United States would forever lose the politico/military nuclear initiative it stood on the cusp of grasping.
Despite the fact that output had not yet reached required levels, the enriched material that had been produced was many times more valuable than any other commodity present on earth at the time - if a price could be set on it at all. The potential this material held to change the world made it, in many ways, valuable beyond the mere computation of cost-to-produce versus volume-of-grams. To protect his enormous investment from what could be an immeasurable loss, Groves prepared a secure location for its storage before transit. Inconspicuous among the indigenous households of east Tennessee, a lone farm house stood at the end of a dusty dirt road.
Lumbering farmhands in the peaceful pastures were actually a patrol of security guards. The innocuous silo next to the barn hid a machine-gun nest. The embankment that framed the picturesque homestead harbored a submerged bunker made of reinforced concrete buried under the escarpment's leafy foliage. Inside the invincible bunker a vault stood, surrounded on all sides by yet another cadre of watchful guards.clxxxiv Inside the vault was a few ounces of enriched uranium waiting for the weekly courier to whisk it away to a mountaintop in New Mexico.
Gaseous diffusion at K-25 was just beginning to receive working barriers for filtering the atoms, but only a few at a time.clxxxv As they arrived, the barriers were installed in the headmost possible stage and tested for integrity, the plan being to allow the first-stage of "converter" vessels to begin the long diffusion process before the numerous ensuing stages had even been completed. In other words, K-25 was making excruciatingly slow headway and had still not produced an atom of enriched uranium.
To crank overall production to a higher level, General Groves either ignored, circumvented or had otherwise persuaded President Roosevelt to belay his presidential order refusing Navy involvement in the atomic bomb project, and Groves adopted the liquid thermal diffusion technology the Navy had been devising as his own. Within K-25, besides the massive gaseous diffusion apparatus, stood a 100-column liquid thermal diffusion pilot plant that Groves had ordered constructed in January 1944 and that had been completed in July of the same year.clxxxvi The plant was soon expanded and began production, according to Groves, at the end of October, and, he claims, it reached peak production in June 1945.clxxxvii
Herbert Childs, author of An American Genius, differs from Groves in his account of events, stating that liquid thermal diffusion production output actually began on 1 March, 1945 three months earlier than Grove's assertion. Careful review of charts based on daily Beta calutrons production output, however, shows no hint whatsoever of an increase of production in March or any other time between the beginning of the year and the middle of June. In fact, charted average daily output is so consistent throughout the first six months of the year as to form an almost straight line, with the lone exception being a small dip in production during the third week of January.
This fact not only draws into question Mr. Childs' statement regarding when the thermal diffusion plant began operating, but General Groves' implication, as well, that liquid thermal diffusion continuously rose in productivity until it peaked in June. The record shows a significant upward production curve from mid-November 1944 to the end of the year, corroborating Groves' version of when thermal diffusion production began, but by the beginning of the new year daily production had reached a plateau, consistently producing about 240 grams (8.4 ounces) per day, with no further increase in daily productivity.clxxxviii
Production did take a significant upward turn the fourth week of June 1945, but this advance certainly is related more to other influences than to continuously improving liquid thermal diffusion processes. Groves tries, nonetheless, to account for the significant, immediate, and otherwise anomalous increase of Beta production in mid-June by crediting the increase to the thermal diffusion process. Later, he credited the gaseous diffusion process with the same production expansion,clxxxix although gaseous diffusion is reported to have first gone into operation less than two months after thermal diffusion did, on 20 January, 1945.cxc
While the process would not have born an immediate impact on output since it is a cumulative process that requires several weeks for end-product to be available, it would have undoubtedly begun producing enriched material long before the six-month time period reflected between the January start-up and the June upward surge.
The Beta output records themselves show that neither gaseous diffusion nor thermal diffusion caused a late-spring dynamic production upturn, as the traditional history assert. In fact, liquid thermal diffusion was shut down for good just a few weeks after the material for the bomb was accumulated in June,cxci suggesting its ineffectiveness. The mid-June 1945 timing of the increase in enrichment fits perfectly with events of the offloading of the enriched uranium captured from U-234.
With or without the June 1945 spike in enriched uranium output it appeared at the time that the combined isotope separation technologies were going to be successful. Output was finally on track to produce 50 kilograms of enriched uranium by early August - the Manhattan Project's goal for the uranium bomb project.cxcii And, even better, the critical mass for U235 finally had been determined to be only 15 kilograms, only one-third the amount of enriched uranium that would be available when it came time to start fabricating bombs. If desired, at the present rate of production, the United States would be able to assemble as many as three uranium bombs in early August. Success appeared to be just around the corner.
clvi Richard Rhodes, The Making of the Atomic Bomb, p. 488
clvii David Irving, The German Atomic Bomb, p. 69, 95
clviii Herbert Childs, An American Genius, pp. 321, 344
clix Robert Serber, The Los Alamos Primer, p. xxix
clx Richard Rhodes, The Making of the Atomic Bomb, p. 406
clxi Leslie Groves, Now It Can Be Told, p. 96
clxii Richard Rhodes, The Making of the Atomic Bomb, p. 365
clxiii Richard Rhodes, The Making of the Atomic Bomb, p. 489
clxiv Leona Libby, The Uranium People, p.53
clxv Richard Rhodes, The Making of the Atomic Bomb, p. 550
clxvi Leslie Groves, Now It Can Be Told, p. 22; Herbert Childs, An American Genius, p. 350
clxvii Richard Rhodes, The Making of the Atomic Bomb, p. 493
clxviii Richard Rhodes, The Making of the Atomic Bomb, p. 496
clxix Richard Rhodes, The Making of the Atomic Bomb, pp. 494, 495
clxx Richard Rhodes, The Making of the Atomic Bomb, p. 601
clxxi Herbert Childs, An American Genius, p. 333
clxxii Herbert Childs, An American Genius, p. 341; Richard Rhodes, The Making of the Atomic Bomb, p. 488
clxxiii Herbert Childs, An American Genius, p. 341
clxxiv Herbert Childs, An American Genius, p. 346; Richard Rhodes, The Making of the Atomic Bomb, p. 491
clxxv Leslie Groves, Now It Can Be Told, p. 110
clxxvi Richard Rhodes, The Making of the Atomic Bomb, p. 489
clxxvii Richard Rhodes, The Making of the Atomic Bomb, p. 492
clxxviii Herbert Childs, An American Genius, p. 349
clxxix Stephen Groueff, The Manhattan Project, p. 312
clxxx Jerry Rice, Y-12 Beta shift supervisor, interview via telephone with the author (date not recorded)
clxxxi Herbert Childs, An American Genius, p. 350
clxxxii P.B.O. Report (daily Beta output report), National Archives,
Southeast Region, East Point, Georgia
clxxxiii P.B.O. Report (daily Beta output report), National Archives, Southeast Region, East Point, Georgia; also compare to; Richard Rhodes, The Making of the Atomic Bomb, pp. 600, 601
clxxxiv Richard Rhodes, The Making of the Atomic Bomb, p. 602
clxxxv Richard Rhodes, The Making of the Atomic Bomb, p. 602
clxxxvi Richard Rhodes, The Making of the Atomic Bomb, p. 551
clxxxvii Leslie Groves, Now It Can Be Told, p. 122
clxxxviii compare to Richard Rhodes, The Making of the Atomic Bomb, p. 601
clxxxix Leslie Groves, Now It Can Be Told, p. 69
cxc Richard Rhodes, The Making of the Atomic Bomb, p. 602
cxci Leslie Groves, Now It Can Be Told, p. 379
cxcii Beta Oxide Transfer Report, National Archives, Southeast Region, East Point, Georgia; also compare to Richard Rhodes, The Making of the Atomic Bomb, p. 601
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