Water Technology at
The Shippingport Atomic Power Station S. F. WHIRL and J. A. TASH Duquesne Light Co., Pittsburgh, Pa.
station at Shippingport consists of a single-cylinder 1800-r.p.m. steam turbogenerator having a capacity of over 100,000 kw., and four boilers each having a steaming rate of 329,000 pounds per hour at 600 p.s.i. and 486'F., saturated. High purity water at a pressure of 2000 p.s.i. is used both as core coolant and neutron moderator. Its flow, approximately 58,000 gallons per minute for the 60,000-kw. power level, enters the bottom of the reactor vessel at about 510' F., moves upward through the core, and leaves from the top at about 540' F. Then it flows to the heat exchanger section of the boilers, through single-stage canned motor pumps, and back to the bottom of the reactor. A separate loop, pump, and isolation valves are provided for each boiler. Two internal bypass purification systems, one for each of the two loops, help maintain quality of the primary water which also lubricates the reactor control mechanisms, canned pumps, and valve stems and seats ( 3 ) . For the primary system, the materials of construction selected have proved satisfactory in neutral or alkaline water having a low concentration of dissolved oxygen ( 7 , Z ) . For piping, valves, pumps, and water-wetted surfaces of the reactor vessel, stainless steel is the basic alloy, and only minor quantities of Stellite, graphite, chromium, and Inconel are used to satisfy special structural and operating requirements. Both the plate elements which consist of enriched uranium alloyed with zirconium and the sealed cylindrical rod elements which contain ceramic pellets of natural uranium dioxide are clad in Zircaloy. Like steam-electric power stations, the basic material of construction for the secondary system is carbon steel. However, stainless steel is used in the boiler heat exchangers, valve trim, turbine liners, and turbine buckets; copper alloys are used in the condenser, feedwater heaters, and miscellaneous cold water pumps and valves. T H E ATOMIC P O m R
closed cycle cooling systems are of highest purity. The maximum limit of impurity is specified a t 1.5 micromhos of electrical conductivity. The water, prepared by standard commercial processes, is taken from the Ohio River, clarified, filtered, and softened. Graded anthracite is the filter medium and styrene base resin is used in the cation exchange softeners. The softened water passes through a hydrogen hydroxide mixed bed ion exchanger, deaerated in a mechanical-type unit, and stored in two steam-sealed tanks, each holding 50,000 gallons. The ion exchanger has a nominal capacity of 60 gallons per minute, and the deaerator is rated for 37,500 pounds per hour. The primary water storage tank is of stainless steel Type 304 and the secondary system storage tank is carbon steel painted with Dampney Co.'s Apexior No. I . The piping to the deionizer is copper and thereafter of stainless steel to the deaerator which is carbon steel with stainless steel trays and stainless steel-lined deaerator section. Reactor System Requirements
The coolant must contain a minimum of radioactive fission products and of other material, both suspended and in solution, that may become radioactive. Also, it must be radiation stable, have
favorable nuclear properties, and limit corrosion rates. This imposes limitations on the choice of chemicals usable for treatment. Also, impurities and activity of waste water should permit disposal in a safe and economical manner. Nuclear radiation induces chemical reactions which are normally not spontaneous a t temperatures of 500' to 600' F. -e.g., breakdown of water to hydrogen and oxygen, formation of ammonia, nitric acid, and breakdown of nitric acid to hydrogen, nitrogen, and water. Fortunately, however, these reactions are controllable. Hydrogen in the coolant exceeding 0.4 p.p.m. favors the production of water and ammonia as the end products (4). Normally the coolant will contain 25 to 35 cc. of hydrogen per kilogram of water, which is sufficient to scavenge oxygen and nitrogen from air trapped during filling, and protect the system against these gaseous impurities in the make-up water. Eliminating dissolved oxygen keeps the system in a reduced atmosphere which lowers corrosion rates and crud concentration. Hydrazine removes oxygen from isolated loops and during precritical tests. pH of the reactor coolant is adjusted to 9.5 to 10.5 with lithium hydroxide (1 to 6 p.p.m.). This reduces corrosion rates and the amount of corrosion products released.
Make-up Water
About a dozen easily identifiable grades of water are used at Shippingport; however, that used for reactor coolant, boilers, fuel handling canal, and
High purity water at a pressure of 2000 p.s.i. is used as both core coolant and neutron moderator VOL. 50, NO. 7
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pump. T o sustain the boiler free of oxygen during the starting period, the air ejector and condensate pump must be kept operating. Sampling and In-stream Analysis of Water
Make-up and sanitary water, prepared b y standard commercial methods, is taken from the Ohio River, clarified, filtered through graded anthracife, and softened using styrene base resin
T o eliminate activity build-up of the high specific-ionization, long-lived impurities, part of the mainstream (80 gallons per minute) is withdrawn at the discharge side of the main coolant pumps, cooled, and passed through lithium hydroxide mixed-bed ion exchangers and returned to the system on the suction side of the same pumps. All cations are replaced by lithium ions and the anions by hydroxide ions; the insoluble matter is filtered out by the resin bed and the soluble impurities are replaced by lithium hydroxide. Lithium is not displaced and tritium is unaffected because it is in chemical combination in the water molecule. When exhausted, the resin is slurried to buried storage tanks in the waste disposal plant. Neither free nor combined hydrogen contributes to undesirable side reactions, and lithium reacts with neutrons to yield radioactive tritium which is not removed by the purification system. This reaction depends on lithium concentration, reactor power level, and time of irradiation. The estimated concentration of tritium, reached near the end of core life is below 5 mc. per ml. This is readily reduced to below drinking water tolerance by dilution with the condenser cooling water effluent stream. Because tritium is chemically bound with water, its concentration is unaffected by either purification processes or the waste disposal system. Secondary System
Make-up water for the secondary system is of the same high purity as for the primary plant, but it is taken from a separate carbon steel tank. The boiler water is treated with sodium chemicals, and the coordinated phosphate-pH method of alkalinity control is supplemented by sulfite for oxygen scavenging. Hydrazine may also be added after the hot well pumps to provide protection throughout the condensate system. Chloride stress corrosion cracking of austenitic stainless steel is the most serious
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problem anticipated in boiler operation on the secondary side. The identified factors involved in stress cracking of stainless steel are chloride and oxygen concentration, and wetting and drying; also temperature, time, and stress, but these are established by the design. Keeping the tube bundle submerged should not be too difficult when the boilers are drained; their water may be diluted with deaerated condensate to reduce chloride concentration on susceptible surfaces. During 8 months of normal operation with the boiler blowdown less than O.lyo and the condensers tested periodically for leakage with fluorescin dye and black light, the maximum chloride concentration in the boiler water was 0.4 p.p.m. Chloride concentrations are determined by a modified Clarke method using diphenylcarbazone and mercuric nitrate. This method is sensitive to concentrations as low as 0.05 p.p.m. and variations of this magnitude in concentrations up to 1 p.p.m. are readily discernible. A special trough with conductivity cells a t both ends is provided at the bottom of each tube sheet to catch drippings from tube-roll leaks (5). This should increase the sensitivity of the conductivity method for detecting in leakage of cooling (river) water a t the tube rolls. During normal operation the condenser provides deaeration but during start-up a special setup is necessary. All turbine shaft glands are steam-sealed using the house-heating boiler and full condenser vacuum is established with the turbine idle. With a condensate pump operating and the steam air ejector in service, condensate recirculation through flash nozzles in the condenser provides the required deaeration. Boiler piping drains and vents are arranged so that before filling, each boiler can be subjected to a condenser vacuum in excess of 28 inches of mercury, and then be filled with deaerated water through the bottom drain system from the condensate
INDUSTRIAL AND ENGINEERING CHEMISTRY
The primary water is sampled at each inlet and outlet of the two purification ion exchangers. I t is piped to one of three sampling trains which contain a series of instruments for continuously measuring and recording the soluble activity, activity of insoluble crud collected on a filter, pH, electrical conductivity, dissolved oxygen, and dissolved hydrogen. A pilot ion exchanger located in the train collects an integrated sample of ionizable solids from which samples are taken for laboratory testing. A 3/4-inch sample line located approximately 3 feet into the end of each steam drum and 16 inches below the horizontal center line (10 inches below the normal water level) terminates at a sampling and monitoring station in the turbine plant. Each sample is continuously monitored to detect leakage from the primary (2000 p.s.i.) to the secondary side (600 p.s.i.). An alarm sounds when a predetermined level of activity is reached; both the sample and the boiler drainage can be diverted to the radioactive waste disposal plant. Cahal Water
The canal water provides a neutron shield over the reactor vessel, permits refueling and fuel transfer without waiting for complete decay heat loss, and provides storage for spent fuel prior to shipment to the reprocessing plant. Deionized deaerated make-up water from the primary storage tank is used to fill and maintain the water level. During service, the water is purified by recirculation through hydrogen hydroxide mixedbed ion exchangers, which act as filters as well as ion exchangers, and through coolers, using river water on the tube side. Aluminum piping, valves, and equipment are used in this system where feasible because water becomes aerated in service. Literature Cited (1) Shaw, Milton, Donworth, R. B., Lyman, W. J., Westinghouse Engr. 52, 388 (November 1955). (2) Thomas, D. E., Proc. Intern. Conf. Peaceful Uses Atomic Energy, vol. 9, p. 407, United Nations, New York, 1956. (3) Welinsky, I. H., Cohen, P., Seamon, J., Chem. Ener. Prow. - 52.. 388 (Septem. ber 1956y. (4) Whirl, S. F., Buchanan, R. M., Proc. Ensr. 16th Ann. Water Conf. (1955). . SOC. of Western Pa. (5) Wroughton, D. M., Depaul, D. J., Am, Inst. Mining and Metallurgical Engrs., IMD Rept. Ser. 2, 1956. RECEIVED for review November 2, 1957 ACCEPTEDJanuary 15, 1958 I
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