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Thompson's Process

by Michele Gerber, Ph.D. and is available to download

4.1.10  The Bismuth-Phosphate Process

          The bismuth phosphate essentially dissolved the jackets off of irradiated U fuel elements, then dissolved the fuel itself, and then carried out a series of precipitations followed by centrifugation and re-dissolving of the precipitate cake.  The valent state of the Pu-239 (known as "product" at this stage) was manipulated so that it would stay with, or separate from, the various solutions and precipitate cakes produced in the operations.  In the +4 (tetravalent) state, the Pu-239 would carry with the bismuth phosphate-based solutions.  In the +6 valent state (hexavalent), the Pu-239 would not carry with the bismuth phosphate, and a by-product precipitation could be achieved.  The plutonium was reduced (taken to the tetravalent state) by adding oxalic acid or ferrous ions, and oxidized (taken to the hexavalent state) by adding sodium bismuthate (when bismuth phosphate was the carrier), or potassium permanganate (when lanthanum fluoride was the carrier).  Actually, lanthanum fluoride was known to be a better carrier of plutonium, in that it could carry with a smaller bulk or volume and could carry away the stronger lanthanides such as Cs, Sr and La.  However, it was/is very corrosive, and for that reason it was rejected for the main phase of the Hanford separations process.

4.1.11  Dissolving

          The first step in the separations process carried out at HEW was dissolving, a process that removed the aluminum fuel jackets from the uranium elements.  It was carried out in the dissolvers and metal solution storage tanks located in Sections 3 and 4 (Cells 5, 6 and 7) of the canyon buildings (T- and B-Plants).  The irradiated, jacketed fuel rods first were placed in boiling sodium hydroxide, to which sodium nitrate slowly was added (reduce the formation of hydrogen).  This step produced "coating removal waste."  Next, three metric tons of declad metal were charged into a dissolver.  Nitric acid was added in three increments, enough to dissolve one ton in each increment.  In order to keep the time cycle as short as possible, "a substantial metal heel" was left [xc] in the dissolver between charges.  New material was charged on top of this heel.

4.1.12  Extraction

          The second step in the process was the extraction step.  This operation separated the product (Pu-239) from most of the uranium.  It also removed about 90% of the fission products into what was called the metal waste solution.  The extraction step reduced the gamma radiation activity level by a factor of 10.  In the first extraction step, plutonium was kept in the +4 (reduced) valent state.  Bismuth nitrate and phosphoric acid were added to the solution that contained the dissolved fuel elements, causing the formation of bismuth phosphate.  A product precipitation (one that carried the Pu with it) then occurred.  The precipitate was centrifuged to separate the solid portion from the liquid.  The liquid portion was jetted away as waste.  The solid portion ("precipitate cake"), which contained the Pu, was placed in another tank and dissolved with nitric acid.  Sodium bismuthate or potassium permanganate were added to the plutonium-bearing solution to oxidize the Pu to the +6 state, and then sodium dichromate was added as a holding agent to keep the Pu steadily fixed in this state.  The BiPO4 then precipitated as a byproduct, leaving the Pu in solution.

4.1.13  Decontamination

     The third step, decontamination, essentially was a repetition of the  extraction process.  The final decontamination cycle reduced the gamma activity level by a factor of 10,000, giving an overall process "decontamination factor" of 100,000 below that of the original uranium solution.  The plutonium-bearing solution from the extraction step was reduced with the addition of ferrous ammonium sulfate.  Then, bismuth nitrate and phosphoric acid again were added, a product precipitation occurred, and the precipitate was centrifuged.  The solid portion, containing the Pu, was liquified with nitric acid, oxidized, and the remaining BiPO4 precipitated away as waste.[xci]

4.1.14  224 Bulk Reduction Process

          Plutonium-bearing solution was transferred from the "tail" ends of the canyon buildings to the 224 Buildings via underground piping.  The starting batch size in the latter facility was 330 gallons.  Here, the Pu solution from the 221 buildings was oxidized with sodium bismuthate.  Phosphoric acid then was added to produce a byproduct precipitation, leaving the Pu in solution.  Centrifuging then separated the solution and precipitate.  Nitric acid was added to dissolve the byproduct cake, and it became waste.  Next, the plutonium-bearing solution was oxidized with potassium permanganate (KMnO4).  Hydrogen fluoride and lanthanum salts were added, in what was known as the "crossover" step.  A lanthanum fluoride precipitate was produced, leaving hexavalent Pu in solution.

          Impurities were precipitated in a byproduct cake, as the fission products were carried with the lanthanum.  This byproduct cake contained all of the lanthanides (cerium, strontium, lanthanum, etc.) that the BiPO4 could not carry out of the stream.  The cake was dissolved in nitric acid, neutralized with sodium hydroxide, and sent to tanks for settling.  The plutonium solution then was reduced to +4 state by adding oxalic acid.  Lanthanum salts and hydrogen fluoride again were added, thus precipitating lanthanum fluoride that contained the Pu.  The precipitate was separated by centrifugation, and potassium hydroxide was added to metathesize the Pu lanthanum fluoride, forming a solid Pu lanthanum oxide.  (Metathesis is a chemical process to convert a solid to another solid.)  Any liquid was removed by centrifugation, and the solid Pu lanthanum oxide was then dissolved in nitric acid to form Pu nitrate.  By this time, the original 330-gallon batch that had entered the 224‑T Building had been concentrated to eight gallons (volume).[xcii]

4.1.15  231 Isolation Process

     Lastly, the plutonium nitrate from the 224 facilities was sent to the 231-Z Building for the final processing that could be done at the Hanford Engineer Works.  Hydrogen peroxide, sulfates, and ammonium nitrate were added to the plutonium-bearing solution.  The hexavalent Pu precipitated as plutonium peroxide.  Nitric acid then was added to dissolve this precipitate.  The Pu nitrate then was placed in small shipping cans and boiled right in these cans, using hot air.  It was reduced to a wet nitrate paste.  In this form, the Pu was stored in the 213-J and K vaults in the southeast end of Gable Mountain, and then shipped to the secret Los Alamos Site.  Each shipping can held about one kilogram (kg) of Pu.[xciii]

4.1.16  Earliest Operations

          Operating experiences during the initial months of canyon operations were described by DuPont as unusually satisfactory."[xciv]  No serious mechanical problems developed, except that the bowl of the centrifuge in Section 16 of T-Plant jammed against some dip tubes when it was run backwards on January 5, 1945.  The centrifuge was replaced via remote operations, partially decontaminated in a spare cell, and then buried in 1954 when it was determined that it could not be repaired.  This and other miscellaneous remote tasks gave operators confidence that "the Canyon Buildings can be operated remotely as planned and with somewhat less loss of fabricated equipment than originally anticipated."[xcv]

          During the next six months of canyon operations, procedures were standardized.  Technical efforts were directed towards reduced time cycles, as production sped for the special nuclear materials needed to win the war.  By mid-1945, emphasis had shifted to "a review of process technology and operating technique in an effort to improve efficiency and reduce waste losses."[xcvi]  Free nitric acid concentration was reduced to obtain an increase in the specific gravity of dissolver solutions.  The most significant improvement, however, came in the late summer, with the installation of piping to allow for intermediate solution transfer from storage to the precipitators in Section 6 (Cells 11 and 12).  This was a safety measure, as metal solution slightly in excess of charge requirements then could be taken from storage, agitated, and sampled so that the correct amount, based on critical mass limitations, could be transferred to the extraction sections of the plant.  Further safety improvements included more rigorous efforts to empty and decontaminate the precipitators used in the extraction and decontamination cycles.  These measures assured the prevention of Pu-239 buildup on equipment.

4.1.17  Early Process Changes

          The original HEW separations canyons were designed on the basis that one plant would have the capacity to process the output from one pile (reactor).  With each HEW reactor originally planned to produce one metric ton of metal (containing approximately 250 grams of product - Pu-239) per day, the earliest standard procedure for T-Plant involved starting a one metric-ton charge of metal into the dissolvers about every 26 hours.  However, by the summer of 1945, production tests had shown that charge size could safely be increased to 1.5 metric-tons of metal, "without noticeable effect of yield or equipment performance."[xcvii]  By September 1, process modifications enabled the plant to complete the processing of a charge in just 20 hours, with only a 10% allowance added onto the average process cycle for equipment repairs.

          Other very early changes included the elimination of potassium carbonate from the separations process in February 1945, and one month later, due to the unavailability of potassium hydroxide containing only 0.0005% iron impurity, the relaxation of process specifications for this chemical to allow for 0.005% iron impurity.  Overall, the first full-scale separations experiences at T-Plant and at the 224-T Bulk Reduction Building and the 231-Z Isolation Building, led to large reductions in many essential materials, per unit of production.  For example, the strength of the key dissolving agent nitric acid was decreased from an average of 95% to an average of 69% (a 33% reduction).  By September 1, 1945, other chemical requirements were reduced by an average of 41%, and potassium carbonate had been eliminated from the process altogether.

            Additional and ongoing process improvement studies carried out during the 1945-46 period were directed at:  simplification of operations to achieve reductions in process time, modification of the process to increase canyon capacity per batch, reduction in waste volumes, recovery of additional product from wastes, the establishment of better understandings of process safety and safety limits,

 [lxxxv].  DuPont, IN-6263.

 [lxxxvi].  DuPont, Construction, HAN-10970, Vol. III, pp. 861-919.

 [lxxxvii]. DuPont, Construction, HAN-10970, Vol. III, pp. 905-908; Gerber, WHC‑MR‑0452.

 [lxxxviii].          DuPont, Construction, HAN-10970, Vol. III, pp. 913-915; Gerber, WHC‑MR‑0452.

 [lxxxix].  DuPont, Construction, HAN-10970, Vol. III, pp. 917-919; Gerber, WHC‑MR‑0452.

 [xci].     Hanford Engineer Works, HW-10475-C; Stoller and Richards, Reactor Handbook, 2nd ed. pp. 227-234.

 [xcii].     Hanford Engineer Works, HW-10475-C.

 [xciii].    Hanford Engineer Works, HW-10475, Section C; Swartout, HW-3-2801.

 [xciv].    DuPont, Operation, HAN-73214, Book 12, p. 75.

 [xcv].     DuPont, Operation, HAN-73214, Book 12, p. 76; G.E. Hanford Co., "Property Disposal Report," #54-217, May 23, 1954.

 [xcvi].    DuPont, Operation, HAN-73214, Book 12, p. 145.

 [xcvii].   DuPont, Operation, HAN-73214, Book 12, p. 49.



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