B Reactor Museum AssociationB Reactor Museum AssociationAuthor: Michele S. Gerber, Ph.D., Facility Operations Division, Westinghouse Hanford Company, April 22, 1993 (approved for public release May 19, 1993)
The need and justification for the Hanford Site's C Reactor was born in the international tensions of the Cold War. In September 1949, the Soviet Union demonstrated that it had achieved a workable, atomic weapons capability, when it detonated a test bomb over Siberia. In June 1950, the Korean War began, and six months later Chinese communist troops surprised the American troops that comprised nearly 90 percent of the United Nations forces in Korea by entering the conflict against them. Many U.S. leaders then believed that the Soviet Union, which had a mutual assistance pact with China, would enter the war. Throughout late 1949 and 1950, the AEC was busy responding to these developments by selecting the Savannah River Plant site and planning the construction of five heavy water defense reactors there. The Commission also was building an addition to the K-25 gaseous diffusion facilities that separated uranium-235 at the Oak Ridge Plant, and implementing research and development on the hydrogen (or "super") bomb. At the Hanford Works, the AEC had authorized expensive and hurried development of the REDOX (reduction-oxidation) process, the tri-butyl phosphate (TBP) process that would extract uranium from high-level waste in the U-Plant, and the P-10 Project (see Section 3.17). Eighteen more underground waste tanks were under construction, as were two evaporators that would concentrate high-level wastes. Camp Hanford, an Army anti-aircraft defense facility with a main base and 16 forward weapons installations also was authorized and emplaced during 1950.
Still, many prominent national leaders believed that further defense preparations were necessary. On December 29, 1950, a special advisory panel to the Department of Defense, chaired by atomic bomb developer, Dr. Robert Oppenheimer, finished its report entitled, "Military Objectives in the Use of Atomic Energy." This report stated that it was "possible" that within the next five years there might be "limited wars or general war" with the Soviet Union. Impressed by this document and the entrance of People's Republic of China into the Korean War, President Truman declared a state of national emergency in January 1951. Meeting in Washington, D.C., January 4-6, the AEC's General Advisory Committee affirmed its "advocacy of additional graphite reactors" at Hanford Works, despite its full plate of other building programs. On January 12, in response to oral instructions from AEC headquarters, the Hanford Operations Office (HOO) of the Commission submitted a hurried proposal to build a new, 500-MW graphite moderated reactor in the 100-B Area. The AEC headquarters approved this proposal on January 22, and informed President Truman on February 6, stating that such a reactor was "absolutely necessary" to meet mid-1956, national production goals. Design work on the new reactor, 105-C, began in March 1951, and, with dizzying speed, construction began on June 6, 1951.
The design and construction of C Reactor was undertaken on a "no-delay" basis. It was to be located sufficiently near to the 100-B complex to take economic advantage of existing utilities, services, and facilities. In the interests of speed, initial HW planners specified that many features and operations would be similar to those at the 105-H reactor, with deviations focused on those which offered the possibility of enabling power level increases. Lattice spacing and size, the number of process tubes (2,004), the control system and graphite block construction all would be patterned after H-Pile. Additionally, the shutdown and transitional coolant flows would be identical to those used at 105-H. However, C-Pile was sturdier and bigger in many respects. Its nameplate design level was 650 MW, as compared to 400 MW at H-Reactor. Each of the process tubes in C Reactor had a water annulus 25 percent larger than that of any other existing HW reactor, and the initial operating process water flow was planned to deliver 62,000 gpm, but to be capable of expansion to 80,000 gpm. Heavy aggregate concrete was used in the core shielding, and the pile building itself was constructed of reinforced concrete. The two effluent basins were bigger (9-million-gallon capacity each), the charging elevators were constructed so as to provide for easy, future installation of operational "C-D" equipment, and C Reactor was the first to be equipped, at initial construction, with a Ball-3X safety system. Indeed, 105-C was conceived and designed so quickly that not enough boron-steel balls could be procured, and the initial loading of the ball hoppers contained 20 percent ordinary steel balls. Additionally, the 105-C Building was furnished with a metal examination facility, a water tank capable of holding and shielding "stripped" (bare - uncanned), irradiated fuel elements for metallurgical testing. The effluent water from this facility drained to underground storage tanks.
The construction of C Reactor proceeded at a speed nearly as unbelievable as that of B-Reactor in World War II, and initial startup was achieved on November 18, 1952. During the 17 months between groundbreaking and startup, design specifications sometimes changed while fabrication of components actually was underway. As finally completed, the influent-reactor-effluent flow system worked as follows: No 181-C River Pump House was constructed, but the 181-B facility was enlarged eastward to house 12 additional pump bays. Ten of these bays were equipped with 10,000-gpm pumps, and two were left empty to provide for later pump additions. Operation of these pumps was controlled from a remote panel in the 183-C facility. Three parallel, 48-inch raw water lines were laid from the 181-B Building to a new 183-C Treatment and Filter Plant, and one 24-inch emergency raw water pipe was installed from the 182-B Building to the 183-C facility. Existing 100-B fire, sanitary and steam lines were expanded to feed the 100-C Area, and the 184-B Steam Plant received a diesel generator to supply emergency electric power to 105-C.
A filtered water line and a 20-inch export water line was laid from the 100-B loop to serve the 183-C and 105-C Buildings. The 183-C was equipped as an independent, rapid filtration plant with initial capacity of 72,000-gpm and the capability to be expanded to 90,000-gpm of filtration. A complete chemical storage and handling facility, flocculation and sedimentation basins, mixers, sampling and analyses facilities, flow control devices, and steel clearwell tanks with the capacity for 3-million gallons of storage also were provided as part of the 183-C facility. Dry ferric sulfate storage facilities for 90 days worth of dry alum, as well as complete activated silica storage facilities were included. Two 19,000-gallon horizontal, steel tanks also were emplaced for storage of the sulfuric acid needed for pH adjustment and for the preparation of the activated silica. Such large activated silica equipment capacity was needed because the 100-C facilities supplied both 100-B Area (on an ongoing basis) and 100-D Area during the initial activated silica test period in 1953.
Two, 300,000-gallon, elevated process water storage tanks (187-C structures) were provided for the last-ditch coolant system, and a new 190-C Process Pump House was constructed. The 190-C facility had a steel frame with a transite (asbestos and steel) exterior. It contained ten pumping units with 8,000-gpm capacity each, that supplied process water to the reactor via six, 24-inch lines. These pipes connected to four, 30-inch, carbon steel risers, two at each side of the front face of C Reactor, designed to allow 525 psig at the top of each riser. (Again, these features provided more coolant capacity than the two, 36-inch front face risers at 105-H.) Forty-six, four-inch crossheaders (double the number at H-Reactor) were spaced one to every row of process tubes at the front face, more extensive crossheader piping than at any other HW reactor built before that time.
The front pigtails, and front and rear nozzles on C Reactor's process tubes were the same as those at 105-H, but the rear face pigtails were enlarged to provide a flow area at least equal to a one-inch I.D. tube. This latter feature was meant to allow future power level increases by eliminating the "boiling disease" power level limitation. From the rear pigtails, the effluent flowed through 46, four-inch crossheaders, through two, 36-inch risers, down double downcomers and out two steel pipes (of 80,000-gpm capacity each) to the retention basins. Before leaving the pile building, C Reactor's effluent was monitored to detect the high gamma activity that would indicate slug ruptures. Ninety-four sample points, one at each end of each rear crossheader and one at each rear riser, were monitored. After arriving at the 107-C basins, effluent was discharged into the Columbia River through two, 54-inch steel outfall pipes, each 450-feet long. A 670-foot coffer dam jetty was built into the river in order to emplace the outfall lines. A crane working along the jetty excavated an underwater pipe trench on the downstream side. The two 1904 pipes then were placed on the jetty, welded, and connected by one-half-inch steel plates. After 22 sets of timber skids were placed on the downstream slope of the jetty, three cranes then lowered the outfall assembly into the pipe trench. The cranes then worked toward the shore, using jetty material to fill and cover the pipe trench. The upstream side of this gravel fill cover then was rip-rapped to anchor it.
The 100-C Reactor itself was designed to meet Zone II earthquake requirements of the Uniform Building Code. However, the motive for such a level of protection actually was directed toward sheltering the plant from missiles and enemy attack rather than from natural disasters. The control room walls and ceiling consisted of increased thicknesses of reinforced concrete, the exterior walls of rooms frequented by personnel were made of poured concrete, and a heavy aggregate concrete wall was constructed to provide greater shielding between the inner and outer rod rooms. The top of the reactor was isolated by a sheet metal barrier to prevent the flow of contaminated air from the top of the unit to the work area. The top biological shield was increased to seven feet thick, and made of both heavy aggregate and ordinary concrete supported by 36-inch transverse beams and vertical columns at each side corner. For the first time in a Hanford reactor, the side biological shields had built-in U-loop cooling facilities. Additionally, a 36-inch "shield test facility," consisting of a removable, stepped section of the biological shield, was located on the right side of the reactor. Pre-formed shield sections of various materials could be positioned in the step compartments for testing purposes. The cast iron thermal shields of C-Pile were of the same design and thickness as those at the previous HW reactors (eight inches on the sides and top, and ten inches on the front and back), but their segments were arranged differently to accommodate additional experimental facilities and the Ball-3X exit tubing. The top and bottom cast iron shields each contained 68 cooling tubes with a capacity of 1,500-gpm instead of the 400-gpm at H-Reactor. The top concrete shield of 105-C encompassed 33 cooling tubes.
There were significant changes in the coring pattern of C Reactor's graphite moderator itself. During the manufacturing phase, the coke and pitch were heated to 2500°C in a furnace with a freon atmosphere. The hope and theory was that trace metal impurities would form a fluorine salt, decompose at the high temperature, and be removed in furnace exhaust gas, thereby producing an especially high quality, nuclear grade graphite. Additionally, a systematic variation of process channel block bores was adopted, in order to increase graphite temperatures in regions of low neutron flux. The hope and intent was to increase temperatures in the reactor's fringe zones, thereby annealing any graphite expansion problems. Fringe temperatures were further increased by heat barriers that were provided on all sides of the moderator. Also to accommodate graphite expansion, the graphite tube blocks were undercut by a greater amount than in any other HW reactor (0.122-inch in C Reactor, as compared to 0.120-inch in H-Reactor), and provisions was made for 50°C thermal expansion on the front face and 100°C expansion on the rear face. Furthermore, deliberately breakable trunnion blocks centered the process tubes in the graphite boreholes, in order to minimize tube binding during ruptured slug removal. The top and bottom graphite layers had special insulating layers that provided a dead gas space, and the front and rear graphite faces had aluminum sheets that acted as heat reflectors. Additionally, the graphite sides had an aluminum gas baffle.
Other equipment changes in and around C Reactor were incorporated to allow for higher power levels, hotter operating temperatures, and more throughput. For example, all aluminum thimbles in HCRs, VSRs and test holes were eliminated. Gas seals were provided on C-Pile's 45 VSRs. The VSRs were made of 3-inch diameter, cast boron-stainless steel tubing, chosen to withstand higher temperatures then the chrome-plated, carbon steel rods with boron inserts and polyethylene components used at 105-H. The 15 HCRs in C Reactor were three-inch round, tubular shells filled with rolled cadmium steel canned in aluminum. These HCRs were two and one-half feet longer than those used at 100-H, and were isolated with O-ring and silicon-rubber seals backed with low pressure air. Lubrication of these seals was accomplished with distilled water. Additionally, the "C" elevator capacity at C-Pile was increased from 8,000 to 12,000 pounds, and a monorail system was added to facilitate the movement of four-ton casks. The "D" elevator capacity was increased to ten tons, and the floor loading of both the "C" and "D" areas was increased to accommodate the four-ton casks bearing fuel elements. Furthermore, an irradiated materials storage pit and a waste crib with an absorbing base layer and a 50-gpm capacity for very radioactive process effluents, were located directly adjacent to the 105-C Building. The reactor contained 14 test holes, instead of the 6 at B-Reactor.
Electrical power for the 100-C Area was provided by additional, 750-kVa transformers and secondary switchgear that was installed in the 151-B substation. The small substation serving the 181-B Pump House also was enlarged. Electrical distribution to the 183-C, 190-C, and 105-C structures was through underground ducts, while power to other 100-C structures and to fire and emergency services was via overhead lines. Additionally, the railroad, access roads, walkways and security fences of 100-B Area were extended to include the 100-C Area. Likewise, the 115-B gas purification system was expanded to provide for C-Pile atmosphere. A design change virtually eliminated the gas wing. Instead, a small appendage was built onto the C Reactor building, to house ventilation equipment and machinery serving the process sewage lift station. The two ventilation intake units that served 105-C had a capacity of 80,000 cubic feet per minute (cfm) each. In 1953, just a few months after startup, a gas refrigeration system, housed in the 115-B Building, was installed to serve C-Pile. The equipment, whose purpose was to provide additional water removal capacity from the graphite following a process tube leak, was supposed to be installed at the reactor's original construction. However, it was postponed due to delays in equipment delivery to Hanford.
C Reactor began operations at a power level of 425 MW, equal to the highest level at which any HW reactor had operated previously, except during transient power surges. Enrichment in 30 process tubes was added with J-metal (oralloy) slugs. The initial process water flow was fixed at 72,000 gpm, with the raw water coagulated via the new alum/activated silica method, filtered, and then treated with a two-ppm addition of sodium dichromate to prevent tube and fuel element corrosion. The early operators of C-Pile were plagued with two major worries, both of which concerned slug ruptures. Would the increased water flows (25 percent higher than those then used at other HW reactors) cause the slugs to cock, lift, or "chatter" in the process tubes, thus increasing the slug rupture rate? And, would operations at power levels above 425 MW augment slug corrosion and distortion, again heightening the rupture rate? Because it was designed for power levels at least as high as 650 MW, C Reactor also was equipped with a continuous flow beta activity monitor that sampled each individual water line from each crossheader. This system was more sophisticated and efficient than the cyclically valved ionization chambers that sampled mixed portions of effluent from the older reactors. Despite the new detection system, C-Pile scientists wondered just prior to startup whether the planned, higher power levels might "alter the relationship between the variables now thought to control slug corrosion...it is conceivable that operation at some high power may result in spoiling the metal and perhaps some tubes".
To minimize these unknown risks and fears, a policy of intermittent power level raises, along with frequent metal inspections and production tests, was adopted. However top HW management was anxious to pursue the maximum possible power level increases at C-Pile, because, just two months after startup, the reactor's main mission was declared to be to serve as a pilot test facility for two huge new reactors being constructed just a few miles downstream along the Hanford shoreline (KE and KW reactors). By February 1953, C Reactor was operating at 525 MW, well below its nameplate design level but still 17 percent above any other Hanford pile. Wanting to gather as much experimental data as possible, HW management decided on a policy of infrequent, large-step power increases at C-Pile. Each large power augmentation, followed by a period of stable operations of several months, they reasoned, would enable them to see and judge the effects of various power levels more readily than a small series of step changes. Long-term effects of certain power levels might be blurred amid such smaller changes. Furthermore, they decided to use enriched material to run a few selected tubes within 105-C at about 175 percent of the power level of the rest of the reactor for extended periods of time, to observe the effects. Although they knew that such selected enrichment would create "hot spots" within the pile, and "although the technique for controlling the size and relative activity" of such spots had "not yet been developed," they endorsed the plan "wholeheartedly."
Quickly, C Reactor became the chief test facility at the Hanford Works, conducting experiments in the various effects of power level increases for both the new, planned reactors and for the older piles. In May 1953, nine small annulus process tubes of the size used in B, D, DR, F, and H reactors were installed in an experimental area in 105-C, in order to observe the results of allowing bulk exit water temperatures to rise to 105°C. HW operators believed that a six percent production increase per reactor could be obtained with each five-degree rise in exit water temperature. However, they also worried about the effects of higher temperatures on the effluent delivery systems of the older piles. After six months of testing, some bulk exit temperatures had reached 109°C, and much information was being gathered on the effects of irregular water flow caused by steam formation in the effluent piping. It was as a result of these tests in C-Pile that the downcomer and other effluent system modifications eventually made at the older reactors in Project CG-558 were designed. These experiments also led to the major 1955 revision in sitewide policy on bulk outlet water temperatures.
By December 1953, power levels in 180 experimental tubes at C Reactors had been pushed to 820 MW, nearly 17 percent above the then current "maximum allowable" power limits. A new production test, intended to raise power levels in these selected tubes to 935 MW was designed, requiring that the 0.318 inch orifice on all of the reactor's process tubes be replaced. Approximately 200 of the orifices were replaced by larger diameter, conventional orifices, but 1,800 orifices were supplanted by venturi flow meters. These large openings lowered the front header pressure (from 525 to 430 psig), thus creating easier operation for the 190-C pumps and saving money even though more water was being used at the higher power levels. At that time, the overall pumping rate at C Reactor rose to 82,500 gpm.
The next key production test run at C-Pile began in early 1955, and was intended to measure the graphite burn-out (oxidation or "transport") rate as it related to higher operating temperatures. Graphite oxidation, considered by far the most serious threat to pile life because it weakened the mechanical strength of the core itself, was caused when carbon monoxide formed in the CO2/He gas atmosphere of the reactor, and then escaped as gas leakage. The oxidation rate vastly increased when water vapor from process tube leaks contacted the graphite. A key unanswered question, however, was whether or not graphite temperatures above 500°C also would raise the transport rate to the point where the losses made higher power levels undesirable. In March, process tubes in a diamond cluster at C Reactor were charged with enriched material (J-metal or oralloy) intended to take the temperature of the nearby graphite up to 750°C, with the remainder of the reactor operated to produce graphite temperatures near 600°C. Specially constructed graphite thermocouple stringers (11 thermocouples strung along each length of graphite) were charged into two empty process tubes in the center of the diamond cluster, and inspected frequently for oxidation (measured in terms of sample weight loss). Also, perforated gunbarrels were installed at the front and rear of these two channels, in order to measure gas flow. Additionally, during the eleven-month duration of the test, the entire reactor was operated in an atmosphere that contained 50-100 percent CO2. The final results indicated that graphite temperatures up to 600°C, with a gas atmosphere between 50-85 percent CO2, produced no significant rise in the oxidation rate. However, above 600°C, graphite transport rates increased exponentially. As a result, HW Process Specifications for the older reactors were changed to permit operation at graphite temperatures up to 600°C.
By mid-1954, HW scientists already were producing design studies aimed at increasing the pumping and other equipment capabilities at C Reactor, in order to achieve further power level augmentations. That spring, the reactor went to 1,000 MW. The stainless steel rear pigtails began to fail at a worrisome rate and slug ruptures multiplied. Replacement pigtails, with slip joints capable of withstanding angular displacement and linear expansion between the nozzles and header fittings, caused by augmented coolant volume, were tried in 1954. At the same time, two teflon*, stainless steel coated, flexible hose connectors were installed on the pile's rear face to test the ability of teflon to withstand corrosion under irradiation. However, these connectors failed after eight months when hydrochloric acid formed during the decomposition of a polyvinyl coating used on the stainless steel. Despite this failure, the teflon itself was found to have flexibility and both mechanical and tensile strength.
By 1955, the maximum coolant flow capability of the 100-C influent systems was about 89,000 gpm. Later that year, a detailed study had been completed of the pumping and machinery additions and modifications necessary to supply 105,000 gpm. By the spring of 1957, the reactor power level stood at 1,450 MW; by January 1958 it had climbed to 1,740 MW; and in 1959 it reached 2,100 MW. At the same time, the reactor began to show many of the same signs of equipment stress as did B-Pile during the late 1950's. Water pressure surges and Panellit gauge fluctuations produced 30 spurious reactor scrams in 1958. Front nozzles failed and process tube corrosion increased. In 1959 and 1960, 15 instances of serious water leakage into the graphite occurred as the result of tube corrosion. At that time, a key site study of the limits to reactor power levels concluded that, for C-Pile, the rupture control limit would be reached long before technical operating factors curtailed the reactor. The rear face piping, especially the riser supports, crossheaders, crossover lines, and the downcomers were identified as needing strengthening on an immediate basis. Additional components listed as requiring attention in the near future were the water plant filters, underground raw water lines, high tanks, 190-C tanks, pumps and valves in the 183-C and 190-C buildings, gas seals on the gunbarrels and VSRs, various instruments, and safety circuits, thermocouples, and the prototype operational "C-D" equipment. Concern over these conditions brought intensified planning for Project CG-600, C Reactor's equivalent of Project CG-558 at B-Reactor.
The first fuel element rupture at C-Pile occurred on February 19, 1953, and was a full side-split failure requiring process tube replacement and over 19 hours of downtime. Later that year, the nine small-annulus process tubes that were installed in 105-C to pilot experimental bulk exit water temperature increases, became the sites of many slug ruptures. The higher flux and temperature levels were attained by using C-metal and E-metal (or "Ike" slugs). During September 1953, three "Ike failures" occurred, and, throughout the experimental period, several of small-annulus process tubes failed due to severe internal corrosion. HW scientists observed that the lightweight, low-density C-metal tended to cock and chatter in the slug columns, due to the high velocity of the cooling water stream. Furthermore, these slugs often rotated more than did regular uranium slugs during the charging process, and such rotation produced lateral "rib" scratches over as much as half the diameter.
Reactor operators began coating these slugs at charging with glue containing a dextrine base, sodium silicate, and an inert filler material. This glue, which was applied with a spray gun, dissolved after about 40 minutes of exposure to the cold coolant water in the reactor. Additionally, they "seated" all C-metal columns firmly against the rear end caps before the coolant flow was raised, and they tried to maintain as low a water flow as possible around these slugs, in order to minimize the water turbulence that caused cocking and chattering. Also, elongated Ike slugs were developed, some as long as 13.8-inches.
Other high-heat, experimental conditions in C Reactor throughout the mid-1950's (including the graphite burn-out test and others) produced slug and tube rupture rates that were higher than the averages for other HW reactors. Thirty-six ruptures of regular, eight-inch uranium fuel elements occurred in C-Pile during the 13 months from February 1953 through March 1954, about half of which stuck in the process tubes and required tube removal. Also, many process tubes failed from corrosion "barnacles" and hot spots produced by misaligned and cocked slugs. The total number of slug failures rose throughout 1954 due to experiments with C, J, and E-metal, with thorium (Q) slugs, and because C Reactor that year began the first Hanford experiments with cored fuel elements (see Section 3.4). Between January 1955 and February 1956, C-Pile experienced 46 fuel ruptures, with a one-month high of ten failures in March 1955. The 26 slugs that failed between late February and late July all exhibited heavy corrosion build-up and pits and blisters up to 15 mils thick in spotty areas, presumably caused by uneven temperature distribution.
A special series of high goal exposure (length of exposure time) experiments produced ten ruptures in the two-month period of July-August 1956. HW scientists found that fuel failure rates stayed fairly constant at and below the 440 megawatt day per ton (MWD/T) level, but that the rate doubled in the 440-480 MWD/T range, and that it tripled again in the 480-519 MWD/T range. These high rupture rates cost so much downtime that the plutonium production rate actually dropped, despite the inherent efficiencies of high goal exposures. The situation was made worse by the fact that C Reactor did not carry enough excess reactivity, on a regular basis, to be able to perform "quickie" ruptured slug replacements. Every rupture during this period required about a day of downtime -- enough time so that the buildup of neutron poisons such as xenon could decay sufficiently to enable re-start. Consequently the length of exposure time for fuel charges in C Reactor was lowered, and the general reactivity level was boosted with uniform (non-experimental) enrichments.
Despite the continuation of fuel element failures, C Reactor remained an efficient production machine. It averaged 8,660 hours of operating time per year, a nearly 85 percent efficiency rate, during its first two full years of performance. It yielded 277,680 MWD of production in 1953, and, due to higher power levels, 334,957 MWD in 1954. By 1957, its throughput stood at 720 tons of uranium per year. The constant experimentation caused C-Pile to experience more startups and scrams than other HW reactors, with 119 startups and 78 scrams in 1954 alone. Scientists responsible for C Reactor undertook a number of steps to try to minimize, detect, understand, and mitigate slug ruptures, uneven temperatures distributions, and other undesirable consequences of experimentation. In 1956, pilot tests in 105-C proved that the gamma spectrometer (scintillator) rupture detection equipment was more sensitive than the beta ionization chambers used at Hanford since World War II. The success of these tests led to the installation of the gamma detectors at the outlet crossheaders of every HW reactor during Projects CG-558 and CG-600.
Still, the fuel ruptures and other equipment failures associated with operating on the edge of the technical frontier continued. In March 1956 and again in July, the brass fitting (actually 62 percent Cu, 35 percent Zn, and 3 percent Pb) on a front pigtail at C Reactor failed, spilling irradiated coolant into the front face area. Radiometallurgical examination of the failed part showed that operating stress, caused by continual high velocity water flow, had brought about the malfunction. In September, a ruptured fuel element hung up on a broken piece of process tube as both were being removed from the reactor, ignited, and burned for about six minutes. The incident contaminated the reactor's "D" area, the exhaust system, and ground areas south of the 105-C Building, both inside and outside of the exclusion area. In early 1957, the first pilot loading of I&E fuel elements took place at C-Pile, and immediately effected a rise in the fuel failure rate. The I&E elements because they were larger and rested in a somewhat eccentric balance on the bottom tube ribs, produced disproportionately high temperatures in the top of the process tubes. As a result, hot spot corrosion attacked both the elements and the tubes. Soon, a "mixer charge" (sometimes just called a "mixer") was invented at HW. It was a six-inch I&E fuel element, onto which was welded a two-inch extension perforated with eight holes. The attachment, made of "63-S" aluminum alloy (containing .04% silicon and .07% magnesium), spread the cooling water in an "in-and-out" fashion, first through the inner hole of the I&E element and then out the sides of the perforated extension. Such "mixing" of the coolant water achieved sufficient distribution to overcome hot spots and other problematic areas within the reactor.
At the same time, C Reactor's new attempts to use the "quickie" restart method after fuel ruptures proved awkward, as operators often exceeded the HW Process Specifications rate of rise limit of 150 MW/min. In some of the early "quickie" attempts, at this reactor, the rate of rise approached 300 MW/min. As a result a "slug rupture outbreak" took place at 105-C in the spring of 1957. Eleven ruptures occurred in March alone, all of them serious "split-types," and ten out of 20 additional blistered charges that were examined showed evidence of near-rupture deterioration. Two of these ruptures produced gaseous fission product emissions from the 105-C effluent line vent stacks that contaminated the entire 100-B/C Area. By 1959, C Reactor's TOE rating stood just above 65 percent, or 6,841.5 hours of operating time, and in 1960 slug ruptures, usually resulting from experimental conditions, increased the shutdown time by 15 percent.
A number of salient process improvements at C-Pile during the late 1950's helped to solve the fuel rupture problems and other difficulties associated with the constant push to higher power levels and technical changes. The introduction of poison splines at 105-C in 1957 proved especially helpful in eliminating the hot spots that accompanied so many experiments and off-standard fuel elements and designs. Additionally, an undersized C-metal I&E fuel element (14 mils less in O.D. than the standard 1.460-inch C-metal I&E slug) was developed especially for use in C-Pile. The smaller size of the element allowed for additional cooling. Full-pile loading of regular I&E elements was authorized in late 1957. By 1958, ribbed, zircalloy-2 process tubes were being used to replace aluminum process tubes on an as-needed basis at C Reactor. These tubes had greater mechanical strength, so their walls could be thinner and provide a larger cooling annulus, and they had greater corrosion resistance and a lower neutron absorption cross-section. Additionally, the higher melting temperature of zirconium was thought to be a safety factor in reactor incidents that involved high heat caused by loss of coolant. The zircalloy-2 tubes were considered safe and reliable enough that a proposal was made to fill a few of them with lithium-aluminum (Li-Al) slugs at C Reactor and make tritium (H3). However, this key component in hydrogen thermonuclear explosions was never produced at C-Pile. The full I&E loading, with its inherent cooling capacity improvements, along with the increasing use of zircalloy-2 tubes, allowed a further upward revision of the bulk exit coolant temperature limits at C Reactor. In late 1957, the "trip-before-instability" limit was replaced by the "trip-after-instability" (TAI) limit. In other words, the Panellit gauges at 105-C were set to trip only after nucleate boiling had begun in the coolant exiting the process tubes. Another crucial process improvement first tested at 105-C in 1955 and then installed on a large scale in the late 1950's was operational "C-D" equipment. This machinery improved the reactor's TOE rating and also provided for quick detection and flush-discharge of ruptured slugs.
In early 1960, C Reactor was fitted with a 100-unit installation of ribless zircalloy-2 process tubes. Self-supported or "projection" fuel elements, made in Hanford's 300 Area and having eight longitudinal protrusions, were used in these tubes. The new slugs offered advantages in terms of overcoming the seating, cocking, and misalignment problems that had produced coolant flow irregularities, hot spots and slug and tube failures at 105-C for so many years. The new ribless tubes and projection elements worked so well that 200 more such tubes were installed in July. By that time, these tubes had helped to bring overall slug rupture rate down to the point where it accounted for only a five percent production loss (including outage time) in C Reactor. The only safety disadvantage lay in the fact that the older nozzles used for the existing process tubes had to be overbored (hence weakened) to fit with the larger zircalloy-2 tubes (1.681-inch I.D. as compared to 1.640-inch I.D. for the older aluminum tubes). When a study estimated that most of the old C Reactor tubes were corroded to the extent that they would need replacement by late 1961, HW operators incorporated a full ribless, zircalloy-2 tube loading and new process tube nozzles into their specifications for Project CG-600. A rash of fuel ruptures in the pile in the spring of 1960 further enlarged the scope of Project CG-600. The ruptures were caused by neutron flux surges in various parts of the reactor where enrichment loadings were being used to compensate for the neutron-absorbing effects of stuck and embedded boron-steel 3X balls.
As the 1950's progressed, C Reactor underwent few repairs other than process tube replacements. In 1954, a pilot-scale facility for the decontamination of dummy slugs, using nitric acid, was installed in the rear area of the 105-C Building. The new system soon proved that it could ready 95 percent of the non-expendable dummies (nearly three-fourths of the total dummies used in the reactor) for quick re-use, without waiting through a lengthy decay period. Despite the success of this system, full-scale dummy decontamination facilities were not installed until 1960. In 1955, C-Pile was fitted with prototype gamma monitoring equipment, located so as to test small water samples from the rear crossheaders. The instrumentation quickly proved so sensitive in detecting slug ruptures that it was incorporated in the Project CG-558 designs and installed in all of the HW reactors. During the same period, tests were undertaken to find seals for C Reactor's HCR channels that would be effective when used with unlubricated rods. The water miscible lubricant used on C-Pile HCRs during the first two years of operation exhibited unacceptable contamination levels. A built-up rubber washer seal was tried in 1954 but found to be inadequate. Finally in 1955, a molded silicon sphincter seal, capable of sustained use without lubrication, was tested successfully at C-Pile.
The 107-C retention basins were renovated in March 1954, and a cathodic protective coating against corrosion was applied. However, the coating failed and the basins again needed repair in April 1957 and in December 1957. Each of the three repairs produced serious particulate contamination spreads from the dried-out residues of the basins. Other radiation incidents in the 100-C Area occurred on an occasional basis when particulates and other materials from waste loads and washes were dropped along the route to the burial trenches, spread from the contaminated dirt of the burial grounds themselves, or scattered from wash pads used to decontaminate irradiated equipment. On one occasion in 1958, contamination was blown out of the vent line from the 105-C Metal Examination Facility, and was distributed on the manhole covers and surrounding outside area. One serious radiation event occurred in March 1960, when the C-Pile was operated with a VSR still in the reactor.
The 105-C modifications undertaken in Project CG-600 were less extensive than those of Project CG-558 at 105-B, primarily because so many experimental modifications already were underway at C Reactor and because C-Pile originally had been built with larger pumping and piping systems and other oversized and heavy-duty components. As a part of Project CG-600, carried out between late 1958 and mid-1960, the 100-C influent pumping systems attained the capacity to deliver 105,000-gpm of process water to the reactor itself, 4,000-gpm of non-process water to 105-C, and 1,500-gpm of water for miscellaneous purposes. The "C side" of the 181-B pump house received an additional 10,000-gpm pump with a 450-HP motor. As on the "B side," a 48-inch line was installed between the 181-B facility and the 183-B head house, bypassing the 182-B reservoir. The filtration system within the 183-C Building required almost no changes, but an additional 21,000-gpm pump with a 450-HP motor was installed. In the 190-C Building, the original two-stage pumps were replaced with ten, single-stage, 10,700-gpm pumps that utilized the existing motors, flywheels, and other equipment. Larger diameter drives were planned for the pump motors. However, improvements in motor cooling capacity achieved a gain from 3,500-HP to 3,660-HP in these units. The solids feed and process water piping from the 190-C Building to the 105-C Building received no modifications.
At the reactor itself, larger influent risers were not needed, and the front face nozzles and flexible (pigtail) connectors were not replaced as C-Pile was scheduled to receive operational "C-D" equipment for all of its process tubes in the near future. The 105-C effluent system was modified to handle a process flow of 100,000-gpm. The reactor's two downcomers, which had been used in alternating fashion, began to be used together, to handle the huge new flows. Knock-out walls between the main and outlet chambers in the effluent diversion box were removed, and new, motor-operated sluice gates were installed. The two pipe connections at the diversion box were linked with a 66-inch pipe to the existing 66-inch connections at the 107-C Basins, and a splash guard was installed at the basin inlets to prevent splashing over the basin walls. Reactor instrumentation was re-set to accommodate greater water flows, higher temperatures, and closer operating tolerances in the Panellit gauges. Additionally, badly corroded components of the Ball-3X system, including the ball exit valves and actuators, the ball return system, the carbon-steel ball elevator, and the ball hopper and drop mechanism, were replaced. These mechanical parts all had accumulated so much graphite dust, moisture, and other foreign material that operation of the system was unreliable.
During the same time period that the major upgrades of Project CG-600 were underway at C Reactor, other modification endeavors were taking place. One such undertaking was Project CG-815, the installation of a 30-inch cross-tie line from the 183-C filtered water plant to the 183-B clearwells in 1959-1960, in an effort to share some of the surplus water pumping and filtration capacity of the 100-C systems with B-Reactor (see Section 4.9). Another major effort was Project CGI-791, the "reactor confinement" program that was being installed at B-Reactor at nearly the same time (see Section 4.7). It's purpose was to secure or contain most of the airborne particulates, and more than half of the halogens, released on a regular basis as reactor exhaust, and to provide a measure of local protection against minor airborne fission product release events. The project was initiated at C Reactor in late 1959, with the installation of a rear ("D") area fog spray system. Excavation for the filter building began in January 1960, and final tie-ins between the filter building piping and the 100-C exhaust stack were completed a year later. Additionally, Project CGI-889, the re-routing of normal B-Reactor effluent to the 107-CW retention basin in late 1960 and 1961, had obvious effects on the operation and piping systems of 105-C and the 100-C Area. A new inlet box and expansion joint was emplaced at the 107-CW basin, along with new piping from B-Reactor and switching equipment to divert normal effluent from C Reactor only to 107-CE. The result was a shortening of average effluent retention time for both B-Pile and C-Pile (see Section 4.6).
Many of the same instrumentation upgrades that took place at B-Reactor during the late 1950's and in 1960 also occurred at C Reactor. Although they sometimes are grouped under Project CG-600, they actually had separate project authorizations and funding. Among such modifications was the installation of stop-gap, octant-type, rate-of-rise instrumentation designed to monitor rapidly changing power levels during reactor start-ups. In March 1958, C-Pile became the first HW reactor to receive this equipment. It consisted of eight ionization chambers (flux detectors) located in the reactor shielding, and it proved more accurate in measuring shifting power levels than resistance-type temperature detectors tested at other reactors. It recorded and displayed real-time power level changes on a chart in the C-Pile control room, and helped to reduce the large numbers of reactor scrams being produced by localized power surges and flux variations. Additional instrumentation designed to reduce spurious reactor scrams caused by minor and localized flux shifts was installed in C Reactor in January 1959. Part of Project CG-786 that also affected B-Reactor, this equipment was the "dual trip" flux monitor system that required two concurrent signals that flux levels were above or below pre-set limits, in order to produce a scram (see Section 4.10).
Later that year, installation of crossheader differential pressure indicators was completed at C-Pile. Its purpose, like that of similar instrumentation at B-Pile, was to avoid overpressurization of process tubes caused by steam generation from residual heat during low flow conditions (especially during "D" operations) (see Section 4.4). In December 1957, such pressure had caused the ejection of irradiated fuel onto the "D" platform at C Reactor during tube end-cap removal. The new instrumentation installed in 1959 was connected to the crossheaders, and signaled low pressure flow levels during "D" operations. That same year, additional sub-critical neutron flux monitors were installed in the G and H test holes of C Reactor. Similar to the instrumentation emplaced in the A and D test holes of B-Reactor in 1959, this equipment consisted of neutron detectors, log counting rate meters, recorders, amplifiers, and an alarm relay system (see Section 4.10). In early 1960, automatic gas make-up equipment, designed to prevent gas composition and flow fluctuations and to mix and maintain constant, pre-set levels, was installed in the 115-B Building to serve B and C Reactors. Subsequent malfunctions in the system required replacement of the portions serving C-Pile in March 1962, and of the portions serving B-Pile soon after that (see Section 4.10).
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