. -t. •^ . »i:nL'* ^ :. '•n^.o^ o.;^»'-. ^o^ "^^0^ :< -^^0^ r o ."iq. '^'-''°o y.c:^/^'^. /.^vA o*^\c:^*/v 35<=^^ ^^•^-^ '/ ^^ "^ .f=»5l« -^ '- / .... -. /.'i-:«&-.\ ■- -^^o* f A. <}i, " n - < ' • ^ .•or ^ ^^^o. ^^ ,*• %'«••'/ v^'V 'H.'^*/ v^/ -".'^^y .. V /\Air compressor Portal B I Portal A I I Shop Instrument trailer FIGURE 22. - Plan map of Twilight Mine. Eight ore samples from the Twilight Mine were measured to determine their radon emanation coefficient (1). The results range from 13 to 32 pet and are typical of other ores from the Uravan Mineral Belt, which have a mean emanation coefficient of 19.5 pet. The sandstone is highly fractured with a major fracture pattern that trends northwest-southeast. These fractures have a significant effect on the radon levels in the mine. Declining barometric pressures tend to pump radon from frac- tures, which serve as reservoirs for the gas. 12 FIGURE 23. . Twilight Mine in 1973. Surface Facilities Major surface facilities installed by the Bureau include an instrument trailer, an office building, and a shop for main- tenance, all of which are located at Por- tal A. An air coinpressor and a diesel engine are located at Portal B, Figure 24 shows most of the surface facilities that are located along a rim road. Instrument Trailer The instrument trailer is an 8-ft by 40-ft van (fig. 25) that was modified into a mobile laboratory. It contains a central air conditioner and heating sys- tems operating on propane gas. Labora- tory furniture includes, work benches, cabinets, drawers, and a hood that draws its air supply from outside of the trailer. Figure 26 shows an interior view of the trailer. The trailer serves as a data acquisi- tion and processing center for the mine FIGURE 24. - Surface facilities located along mine rim road. and one of several storage areas for project supplies. Mine Shop Figure 27 shows an exterior view of the mine shop building. This metal building has about 320 ft^ of floor area and serves as a maintenance and storage facility. It has a forced-air heating system and a variety of shop equipment including an air compressor, gas and electric welders, and several types of power tools. Figure 28 is an interior view of the shop. Mine Office The plan map (fig. 22) shows the lo- cation of the mine office building, a 14- by 20-ft structure that serves as an office and a project work site. Figure 29 is an interior view of this facility. 13 FIGURE 25. - Instrument trailer. FIGURE 26. - Interior of instrument trailer. FIGURE 27. - Vehicle entrance to shopbuilding. FIGURE 28. - Interior of shop building, 14 FIGURE 29. - Interior of mine office building. FIGURE 30. - Electric cart. FIGURE 31. - One-ton tramming vehicle. Mine Vehicles Several types of vehicles are in use at the mine: A crawler tractor with a load- ing bucket, two electric carts (fig. 30), a 1-ton rock-tramming unit (fig. 31), and a small front end loader (fig. 32). Compressed Air A 300-ft2/min air compressor is located in a metal building near Portal B, The compressor is driven by an electic motor and the main compressed air line runs from the compressor through B FIGURE 32. - Small front-end loader. haulageway to a point near test site 1R5 (fig. 25). Diesel Engine A diesel engine located near the build- ing that houses the air compressor is used to generate diesel smoke. The ex- haust from this unit is carried by pipes to the vicinity of bulkhead B (fig. 33) for injection into the mine atmosphere. 15 FIGURE 33. - Bulkhead B. FIGURE 34. - Main exhaust fan at Portal B. Underground Facilities Ventilation System The primary ventilation system for the mine is located at Portal B. Two 20-hp vane-axial fans are installed back- to-back. The innermost fan (fig. 34) is the exhaust fan, which is operated most of the time. Occasionally, the ventila- tion is reversed for special tests and the outermost fan is operated. These fans are equipped with an automatic re- start system. In the event of a power failure, the operating fan will restart as soon as all three phases of power are available. Smaller fans are used at various sites to control radon-daughter levels. Figure 35 shows a 1/2-hp fan installed near test site 1R7. Air from this fan is directed to the instrument room located at test site 1L8. A similar fan provides venti- lation air for the instrument room lo- cated at test site 1L7. This fan draws air from the surface through a borehole that has been cased. Not all areas of the mine are venti- lated; unventilated areas are marked with warning signs. Table 1 lists the environmental charac- teristics of the mine atmosphere. A secondary ventilation fan is located at bulkhead B, this is a two-stage vane axial fan with two 7-1/2-hp motors. One or both motors can be used to provide various air flows through the mine work- ings that begin at test site 1L9 and return to test site 3R1. Entrance A Facilities A tag board (fig. 36) is located at mine site IRl . Everyone entering the mine is required to tag-in at this point. Visitors without personal tags use num- bered tags available at this site. Hard 16 TABLE 1. - Environmental characteristics of the Twilight Mine Underground temperature ...."F.. 52-65 Underground relative humidity.... pet.. 25-95 Radon-222 levels .pCi/L.. to 80,000 Radon-daughter activity^ WL.. to 800 Condensation nuclei per cubic centimeter ~200 to 10^ Average ventilation air volume ft^/min.. 13,000 Volume of mine opening ft 3.. ~300,000 Host rock effective permeability darcys.. 1 x 10** Absolute barometric pressure in Hg.. 24.6 to 25.6 Altitude of portal A.... ft.. 5,000 ^ 1 WL is any combination of radon daughters per liter of air which, in decaying completely through polonium-214, will result in the emission of 1.3 x 10^ MeV of alpha energy. hats, cap-lamp belts, self -rescuers, used only occasionally to supplement the safety glasses, and respiratory masks are regular mine lighting system, also available here for visitors. The cap-lamp -re charging rack (fig. 37) is A major first aid station located at located at site IRl. These lamps are the entrance to mine (site 1L2) also serves as a storeroom for mine supplies. A 1,000-gal water storage tank and ^^^^^^"''^^^^" electric pressure pump are located at mine site 2R1. The water is supplied to the surface facilities during the months when the low temperature remains above freezing. Water for this tank is purchased from a local water service frf^^^^^^^ that hauls it from Nucla, CO, 30 miles away. Electrical Power One of the primary reasons for select- ing the Twilight Mine was the availabil- ity of commercial electrical power. When FIGURE 36, = Tag board statiotio FIGURE 37. = Cap=lamp=charging racko 17 the mine was leased, the existing power line was extended to a point above en- trance A. Three-phase, 440-Vac service was brought into the mine at this en- trance, and the main disconnect switch was established at the IRl mine site. From this point, the 460-Vac line is con- verted to 230-Vac and 115-Vac service, as required at various sites in the mine and at the surface. Electric power interruptions are not uncommon at the mine. Usually they are momentary, but of sufficient duration to require automatic starting of data- acquisition systems and, the mine venti- lation fans. Test Sites Three major test sites in the mine are monitored for various physical parameters on a continuous basis. These sites, shown in figure 25, are called dosimeter test area, air-cleaning test area, and B haulage test area. Two of the test sites, dosimeter and air cleaning, have instrumentation rooms that are heated during the colder months of the year. Figure 38 shows some of the instruments for measuring radon daughters by grab sampling in the room at the dosimeter test area. Bulkhead A is located at the en- trance to the dosimeter test area. Bulkheads A and B are used to con- trol air flow for a variety of tests that include dosimeter performance, air- cleaning-filter efficiencies, and the effects of over-pressure on radon levels. Test-Site Monitoring FIGURE 38. " Instrumentation room at dosim- eter test area. Radon and working levels are measured continuously at the three test sites. Figures 39 and 40 show two examples of Bureau-developed continuous working-level detectors. In addition, two of the sites (3R1, 1L8) are measured for relative humidity and temperature. The venti- lation air velocity is continuously measured at the B haulage test site ILIO. Signals from the underground instru- ments are brought to the instrument trailer at the surface by coaxial cables. Figure 41 shows the primary data- acquisition system for the Twilight Mine. The raw data is converted to engineering units by a small desk computer (fig. 42). Unless a specific study is being con- ducted, the data system takes 40-inin sam- ples of each parameter being monitored 12 times in 24 hr. The raw data is pro- cessed once a week at the Denver Research Center. 18 FIGURE 39. - Continuous working-level de- tector at dosimeter test site. FIGURE 40. - Continuous working-level de- tector in exhaust airway. FIGURE 41. - Data-^acquisition system in in= strument trailer. FIGURE 42. - Desk computer system. Facility Utilization Equipment Tests The Twilight Mine serves primarily as a facility for testing the performance of radiation-exposure-measuring instruments and the evaluation of control technol- ogies for airborne radiation in a typical mine envioronment. 19 Instrumentation for measuring radon and radon daughters has been frequently tested in the mine to determine accuracy and reliability. Figure 43 shows a rapid radon monitor undergoing tests for per- formance after receiving it from a con- tractor. Figure 44 shows several commer- cial radon dosimeters (lower right, below suspended filter holder) being monitored by a continuous radon detector at test site ILIO. Figure 45 shows a hard hat with a face shield undergoing tests for effectiveness in removing radon daughters from the wearer's breathing zone. The hard hat contains an air system with a filter for removal of dust and airborne radioactivity. A continuous working- level monitor in the mouth region of the simulated head measures the radon- daughter activity. Studies of radiation hazard control in the facility have included overpressure using the portion of the mine north of FIGURE 43. - Rapidradondetector undergoing test. FIGURE 44. - Passive radon dosimeter under- going test (lower right). i' 1 ^■'^'^^^i!:^m.^- '■ sk- - ' 1 ' » ■'■'*■% ^'■' '^^^^^^^^S^^K wmf^-- FIGURE 45. - Air-cleaning hard hat undergoing test. FIGURE 46. - Air-cleaning test site. 20 FIGURE 47. - Filter=media test site. FIGURE 48. = Cartridge filter tests. FIGURE 49. = Prototype air cleaner undergoing tests. bulkheads A and B; wall sealants at test sites 1R5, 1R6, and 1R7 bulkheads to seal old workings at 1R5, 1R6, and 1R7 ; and air cleaning at test site 1L8. Figures 46-48 show an air-cleaning sys- tem installed to evaluate filter media for effectiveness in removing airborne radioactivity and life expectancy under typical mine conditions. Figure 49 shows a prototype air cleaner developed under contract undergoing performance evalua- tion tests at the air-cleaning site in the mine. High levels of dust, diesel smoke, and airborne radioactivity are generated in the portion of the mine north of bulkheads A and B. Air contain- ing these materials is ducted to the air- cleaning systems under test. 21 FIGURE 50. • Demonstration of condensation nuclei counter. Training Training sessions related to the mea- surement and control of radiation hazards in mining are conducted several times a year in this facility. Personnel receiv- ing the training represent industry, and FIGURE 51. • Trainee using rapid working-level monitor. both State and Federal Governments. The training is conducted jointly by the Mine Safety and Health Administration (U.S. Department of Labor) and the Bureau of Mines. Figure 50 shows a demonstration of a condensation nuclei counter, and figure 51 shows a trainee using a rapid working-level monitor. These training sessions provide hands-on experience for the participants in the use of several types of instruments. CONCLUSIONS The test facilities described in this report are considered essential to the Bureau's radiation hazards research pro- gram. The radon test chamber provided the controlled environment needed for instrumentation and methods evaluation. The Twilight Mine provided a typical uranium mine environment for evaluating methods of radon-radon daughter control. Both of the facilities serve as training centers for government and industry personnel. REFERENCES 1. Austin, S, R. , and R. F, Droullard. Radon Emanation From Domestic Uranium Ores by Modification of the Closed-Can Gamma-Only Assay Method. BuMines RI 8264, 1978, 74 pp. 2, Craig, L. C, C. N. Holmes, and R. A. Cadigan. Stratigraphy of the Mor- rison and Related Formations, Colorado Plateau Region. U.S. Geol. Surv. Bull. 1009E, 1955, pp. 125-168. 3. Droullard, R. F., and R. F. Holub. Continuous Working Level Measurements Using Alpha or Beta Detectors. BuMines RI 8237, 1977, 14 pp. 4. Droullard, R. F., and R. F. Holub (assigned to U.S. Dep. Interior). Meth- od of Continuously Determining Radia- tion Working Level Exposure. U.S. Pat. 4,185,199, Jan. 22, 1980. 22 5. Fischer, R. P., and L. S. Hilpert. Geology of the Uravan Mineral Belt. U.S. Geol. Surv. Bull. 988-A, 1952, 13 pp. 6. Kaufman, E, L,, and R. E. Din- widdle. Project Dakota — A Uranium Mine Atmosphere Research Laboratory. NM Health and Social Services Dep., 1969, 21 pp. 7. Leong, K. H, , H. C. Wang, S, J. Stukel, and P. K. Hopke. An Improved Constant Output Atomizer. AIHA J. , v. 43, No. 2, Feb. 1982, pp. 135-136. 8. Thomas, J. W. Measurement of Radon Daughters in Air. Health Phys., v. 23, 1972, pp. 783-789. INT.-BU.OF MINES, PGH., PA. 27 303 H 21^ 8^ c""" .^T*\A ^' .. V^\^^' %^^'^/ \*^V' %,'^\^ \'^\/ -c o > «V "