Hazards Summary Report for the PWAR-3 Critical Assembly Experiments

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This document consists of 84 pages. No. 3^ of 42 copies. Series A, HAZARDS SUMMARY REPORT PWAR - 3 CRITICAL, ASSEMBLY EXPERIMENTS restricted data as. to an unauthorized BAT TELL E MEMORIAL, INSTITUTE This document is

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This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

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Copy No. Distribution 1-20 D. Saxe, Chicago Operations Office 21-30 R. Strough, Pratt and Whitney 31-42 Battelle Memorial Institute

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Purpose of the Experiments REACTOR AND ITS OPERATION Site Location and Description Critical Assembly Building office and Laboratories Description of Reactor Assemblies Control of Critical Assembly Control and Research Instrumentation Types of Experiments Critical Mass Studies Power Distribution Measurements Optimization of Design Special Characteristics of the Critical Assembly Plan of Normal Operation General Limitations Affecting Operations Pre critical Operation Check-Out Approach to Critical it y Initial Approach to Critical it y Subsequent Approach to Critical it y Processing and Disposal of Radioactive Materials and Solutions MAKE - UPOF SURROUNDING AREA . 47 Industry Adjacent to Site Geology and Hydrology . HAZARDS DURING NORMAL OPERATION Fission Product Hazard, Direct Radiation Hazard HAZARDS AFTER AN ACCIDENT Radiation Froma Radioactive Cloud Radiation Due to Fail - Outor Rain-Out From the Radioactive Cloud Inhalation of Radioactive Material

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TABLE OF CONTENTS Mciximum Reactivity Possible 63 Maximum Rate of Reactivity Addition Upon Closure 63 Maximum Rate of Reactivity Addition by Simultaneous Safety Rod Operation 64 LETTERS ON EARTHQUAKES 73 CONCLUSIONS OF GEOLOGY AND HYDROLOGY REPORT 75 Figure 1. Topographical Map 11 Figure 2. Battelle Atomic Energy Center. 13 Figure 3. Aerial Photograph of Battelle Atomic Energy Center 15 Figure 4. Floor Plan of Critical Assembly Building 17 Figure 5. Reactor Table 22 Figure 6. Critical Assembly Core Elements 23 Figure 7. Section of Typical Core Configuration 24 Figure 9. Safety Rod Drive Unit 28 Figure 10. Frame to Hold Reactor Control Units 30 Figure 11. Safety Rod Control System 31 Figure 12. Table Drive Control 33 Figure 13. Interlock and Safety System 35 Figure 14. Block Diagram of Reactor Instrumentation 36 Figure 15. Doses Due to Passing Radioactive Cloud 55 Figure 16. Doses Due to Fall-Out From a Passing Radioactive Cloud 57 Figure 17. Inhalation Activities From Radioactive Cloud 58 Figure 18. Inhalation Activities From Radioactive Cloud 59 Figure 19. Beryllium Doses Due to Passing Cloud 62 Figure 20. Fission Energy Associated With Transients Following Instantaneous Reactivity Additions . . 65

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HAZARDS SUMMARY REPORT PWAR - 3 CRITICAL ASSEMBLY EXPERIMENTS Joel W. Chastain, and Sherwood L,. Fawcett Critical experiments are described and the hazards attendant to these experiments are evaluated for a beryllium-moderated, sodiumcooled, solid fuel element aircraft reactor design (PWAR-3). The proposed critical assembly is composed of beryllium blocks, boron carbide simulated control cylinders, and fuel element assemblies. The fuel element assemblies are composed of strips of stainless steel, aluminum, and uranium foil contained in a stainless steel box. The assembly is arranged with the core axis horizontal, with one-half of the core on a fixed table and the other half on a movable table. Control and safety of the assembly is achieved by inserting or withdrawing certain fuel elements from the assembly. The proposed critical assembly is not inherently safe against power surges. Accordingly, the possibility of an accident either from malfunctioning of equipment or from operator error is minimized by limiting the amount of reactivity available in any one operation. This is accomplished by interlocking the system so only one set of rods can be operated at a time and so that the movable table and rods can not be moved simultaneously. Furthermore, the speed at which reactivity can be added has been limited. The maximum normal rate of reactivity addition is estimated to be less than 6 cents/sec for the control rods and 4 cents/sec for table closure. In addition, the scram system can eject all the rods in about 0.2 second. Hazards calculations are made to determine the dosage from direct irradiation, fall-out and inhalation from a radioactive cloud resulting from an accident. The exclusion area is shown to be adequate for even the maximum hypothetical accident. Pratt - Whitney Aircraft is considering a solid fuel reactor system as part of the aircraft nuclear propulsion project of the AEC. This reactor coolant and beryllium oxide or beryllium metal moderator.Because of the high neutron leakage and high fuel loading, the r e a c t o r will operate with an intermediate energy neutron spectrum. Control is accomplished with

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rotatable cylinders in the reflector region. These cylinders are loaded over a 120° sector with B4C rods. The rest of the cylinder contains reflector The physics and engineering analysis carried out by Pratt - Whitney has shown this type of reactor to have considerable promise. Owing to the i m - portance of this project and the magnitude of effort which will be r e q u i r e d to complete the development of a power reactor of this type, it is necessary that the physics characteristics of this reactor be verified by experiment at this time. Battelle has the facilities ajid the technical manpower to under - take these investigations and has been requested by Pratt - Whitney to perform the necessary experiments.A critical assembly is being constructed and will be operated in the Critical Assembly Laboratory at the Battelle West Jefferson Atoinic Energy Center. A Hazards Summary Report was submitted and a presentation made to ACRS in October 1954, which evaluated the Battelle site and the facility. This report presents the hazards considerations pertinent to the critical experi ment s for the PWAR - 3 . Purpose of the Experiments The purposes of the experiments are the following: (1) Determination of critical mass. The calculation of the critical mass for an epi thermal type of reactor requires elaborate multigroup methods. There has been only limited experience and little ex peri - mental verification of these calculations. The uncertainty associated with such computations makes a critical experi ment mandatory before finalizing the design. (2) Investigation of control effectiveness. The reactor control must give a safe margin of subcritical it y at room temperature at the start of core life and must permit the overriding of peak xenon at the end of life. Consideration will also be given to the effect of malfunctioning of some control elements. (3) Determination of the power distribution. A peak to average power ratio of not more than 1. 2 is desired both throughout the core and averaged over

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any one fuel element. The power distribution should meet these requirements at all times during the r e - actor lifetime and under various control conditions. (4) Optimization of the reactor design if necessary. The number, loading, and location of fuel elements, and the number,size, composition, and location of contro l elements, may be varied to optimize the three items The critical assembly used to perform these investigations will be operated at room temperature. Although the core, control cylinders, and fuel elements in the proposed power reactor have circular cross - sections, the critical assembly will be constructed of small elements of rectangular cross - sections stacked to simulate the shapes of the proposed reactor. This method of stacking the elements to simulate the given reactor shape will per - mit variations in loading, composition, and geonnetry. Control of the criti - cal assembly will be accomplished by withdrawing fuel from the core and by separating the reactor into two equal halves. This critical assembly will be the first reactor constructed and operated for this solid fuel reactor program. However, there have been several reactors built and operated for other programs from which experi en ce can be drawn for aid in the design and safe operation of this criti - cal assembly. In particular, the PPA at Knolls Atomic Power Laboratory, and the reflector - moderated reactor critical assemblies operated at Oak Ridge National Laboratory have been reviewed in formulating the mechanical designs and experimental procedures for this critical assembly program. REACTOR AND ITS OPERATION Site Location and Description The site of the Critical Assembly Facility is in Madison County, Ohio, fifteen miles west from downtown Columbus. The property faces on the Georges ville - Plain City Road, an improved county highway which is not heavily travelled. The Battelle-owned land is bounded on the south by the Pennsylvania Railroad and on the east by Big Darby C r e e k which is the boundary between Franklin and Madison Counties. The tract contains a total of 400 acres and extends about 5000 ft. north-from the railroad tracks. F i g u r e 1 is a topographic map showing the site in relation to Columbus and the surrounding area.

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The Critical Assembly Laboratory is one of three buildings at the Battelle Atomic Energy Center which i s located at the northern end of this property. The location of these buildings with respect to each other and the details of the immediate vicinity are shown in Figure 2. Figure3is an aerial photograph of the area and shows all of the Battelle land. The criti - cal assembly laboratory is labelled ZPR. The nearest boundary of the property is over 1200 feet from the building. The surrounding area is a farmiing community and is sparsely populated. The c l o s e s t town is West Jefferson, population 1650, which is about two miles southwest of the laboratory location. The closest building is a barn, 2000 feet northwest of the site and the closest dwelling i s 3100 feet to the southwest. During the summer months,agirl scout camp located across the river is inhabited. The site i s about 2000 feet from the camp. The estimated total number of residents within the mile radius circle is 54. The site is located on a level ground having an average elevation of 900 feet above sea level. The average elevation of downtown Columbus i s approximately 750 feet. The change in elevation from the site to downtown Columbus takes place by a gradual rise over the 15 mile interval.A flat bottom ravine about 40 feet deep c r o s s e s the plot from east to west and is the bed of a small intermittent stream. The Big Darby Creek flows in a broad valley along the eastern boundary of the property and is approximately 50 feet below the elevation of the site. Critical Assembly Building The Critical Assembly Facility is a building having 10, 500 square feet of floor space. The building contains the reactor assembly room,a control roonn, a vault, a counting room, an instrument laboratory,a shop, and rooms which may be used as offices or laboratory space. The first and second floor plans are shown in Figure 4. The building is constructed of concrete block faced with brick, with a structural steel frame except for the storage vault and assembly room. The storage vault is constructed entirely of reinforced poured concrete. The assembly room walls are two feet thick up to 26 feet. The wall above this and the roof a r e Q panel aluminum siding. All of this i s supported by a heavy structural steel frame. The arrangement of the assembly roonn, control room, eind vault, and the associated stairwell, forms an area which can be shut off from the rest of the building. The power provided for the installation i s 300 KVA. Other utilities are compressed air,de mineralized water,natural gas, and a 3-inch water supply main.Battery - powered emergency lights are provided in the assembly and control rooms.

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The building is heated by forced hot - water heat. The temperature is controlled by thermostats in the assembly room and by valves on the individual heaters in other locations. The control room, the instrument laboratory, and the counting room are air - conditioned. The reactor assembly room is approximately 40 foot square and 50 foot high. The three walls facing into the building are of reinforced poured concrete two foot thick. The other wall is 1 foot thick poured concrete. This concrete extends to a height of 26 feet which is enough to shield personnel in the inhabited portion of the building. Above this height the walls are constructed of Q-panel aluminum metal siding on the outside and steel sheets on the inside. The Q-panels have caulking material between them. The steel plates have lead tapes sealing the s e a m s . This type of construction furnishes a tight enclosure so that activity from a possible accident will be contained or will be released very slowly to the atmosphere if the building is not damaged by the accident. The siding above the solid concrete wall is supported by structural steel framework which also supports a ten-ton crane. The roof i s built-up of asphalt and gravel over heavy building paper which is supported by a Q-panel metal deck. A large exhaust fan located in a penthouse above the office area supplies fresh air to the r o o m . The exhaust is through the ceiling. Both the air inlet and the exhaust opening are equipped with louvers and a solenoid-operated sheet m e t a l plate to make the openings tight when the fan is not in operation. The assembly roonn has a single entrance into the remaining part of the building which can be closed off with a steel and concrete door having gamma shielding properties equivalent to the two-foot wall. In addition to this door there is a personnel entrance and a truck entrance to the outside which will be kept closed and locked during reactor operations. There area number of 4 in. conduit openings between the assembly room and control room for the passage of control wiring. These openings are at a 45° angle above head height to prevent radiation streaming ' from reaching personnel. The openings which are not in use will be fitted with shielding plugs. The ones in use will be filled with a material to make them reasonably gas tight.

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Lab Lob 2 Lab 3 Lab 4 Instrument rm. Second Floor Plan Critical assembly area V///A FIGURE4.FLOOR PLAN OF CRITICAL ASSEMBLY BUILDING First Floor Plan

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The control roonn is located on the second …