Safety Management In PNC's Shaft Excavation Effects Project in Japan

Kozo Sugihara

Abstract

The Power Reactor and Nuclear Fuel Development Corporation (PNC) constructed a shaft with a diameter of 6 m and a depth of 150 m in the Tono Mine, where comprehensive geoscientific studies are underway, and carried out the Shaft Excavation Effects (SEE) Project. The shaft excavation was performed using the drill-and-blast method in the Tertiary sedimentary rocks, which consist mainly of tuffaceous sandstone. In the SEE Project, many kinds of in situ experiments were carried out before, during, and after the shaft excavation in order to measure and estimate the mechanical and hydrological influences induced by the shaft excavation.

The SEE Project has been controlled by PNC in cooperation with contractors. The organization for safety management of the Tono Mine has managed the safety issues of the SEE Project according to the Japanese laws and regulations for metal mines and PNC's own regulations.

Excavation and in situ experiments were performed alternately and sometimes concurrently, so many groups of workers from different companies worked together in the shaft. PNC held weekly and monthly meetings attended by the heads of all groups to discuss the time schedule and safety issues of each task.

The most important goals of safety management are to enhance each worker's sense against dangers and to teach each worker to avoid dangerous actions. For this purpose, safety education was conducted for workers who were newly joined to the project, and a meeting of each group was held every morning informing all workers of the schedule and precautions for the day.



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--> Safety Management In PNC's Shaft Excavation Effects Project in Japan Kozo Sugihara Abstract The Power Reactor and Nuclear Fuel Development Corporation (PNC) constructed a shaft with a diameter of 6 m and a depth of 150 m in the Tono Mine, where comprehensive geoscientific studies are underway, and carried out the Shaft Excavation Effects (SEE) Project. The shaft excavation was performed using the drill-and-blast method in the Tertiary sedimentary rocks, which consist mainly of tuffaceous sandstone. In the SEE Project, many kinds of in situ experiments were carried out before, during, and after the shaft excavation in order to measure and estimate the mechanical and hydrological influences induced by the shaft excavation. The SEE Project has been controlled by PNC in cooperation with contractors. The organization for safety management of the Tono Mine has managed the safety issues of the SEE Project according to the Japanese laws and regulations for metal mines and PNC's own regulations. Excavation and in situ experiments were performed alternately and sometimes concurrently, so many groups of workers from different companies worked together in the shaft. PNC held weekly and monthly meetings attended by the heads of all groups to discuss the time schedule and safety issues of each task. The most important goals of safety management are to enhance each worker's sense against dangers and to teach each worker to avoid dangerous actions. For this purpose, safety education was conducted for workers who were newly joined to the project, and a meeting of each group was held every morning informing all workers of the schedule and precautions for the day.

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--> Introduction: A History of the Tono Mine The Tono Mine is located on the main island of Japan, Honshu, approximately 300 km west of Tokyo, as shown in Figure 1. In 1964 a uranium deposit was discovered in this area, and 1972 marked the start of the Tono Mine's operation. The goal of the mine Figure 1 Map showing the location of the Tono Mine in Japan.

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--> was limited to the exploration of the uranium deposit. Exploration revealed that development of the mine for production was economically infeasible. In 1987, geoscientific studies were begun in the mine and were for the most part aimed at gaining a basic understanding to support a waste disposal project. Scientists conducted in situ experiments observing the corrosion of engineered barrier materials, as well as a hydrochemical investigation of ground water, a geochemical investigation of uranium-series radionuclides using the ore body of uranium, and mine-by experiments (see Figure 2). Planning for the SEE Project began in 1988, and pre-excavation experiments started in 1989. Excavation commenced in 1990 and ended in 1991. Overview of the Shaft Excavation Effects Project The geology of the Tono Mine area can be described as a granitic basement overlaid with Tertiary sedimentary rock that consists primarily of tuffaceous sandstone. Unconsolidated sediment covers the sedimentary rock layer. This sedimentary rock is about 150-200 m thick. The new shaft excavated for the SEE Project has a depth of over 150 m; the sedimentary rock was the main object of study during the project. The Tsukiyoshi Fault adjoins the Tono Mine. It runs roughly east-west and dips about 65 degrees. The new shaft crosses the Tsukiyoshi Fault approximately 125 m below the surface. Using the mechanical properties of the sedimentary rock shown in Table 1 as parameters, the standard section of the shaft was designed as shown in Figure 3. The inner diameter is 6 m. The concrete lining has a width of 40 cm except in the first 5 m of the shaft, where the lining has a width of 1.5 m. A cross section of the shaft is shown in Figure 4. The shaft has a depth of 150 m and 4 horizontal drifts. The upper connecting drift is connected to an old mine drift. These drifts were designed to accommodate many kinds of in situ experiments. The lower measurement drift was excavated to study excavation effects around the Tsukiyoshi Fault. The upper part of the shaft, to a depth of approximately 31 m, was excavated with a small backhoe. A crawler crane and a kibble removed the excavated rock from the shaft. After excavating down to 31 m, the team constructed a shaft tower with a height of about 24 m. A double-deck scaffold and the shaft loader were lowered into the shaft using a winch. The drill-and-blast method was used to excavate the rock, and a kibble raised by a second winch removed the excavated rock from the shaft. A third winch raised and lowered a cage used to transport the workers. Segment work made use of a mobile hopper, a concrete kibble, and a round steel frame. Concrete was poured between the frame and the excavated wall. The SEE Project

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--> Figure 2 Geoscientific studies in the Tono Mine.

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--> TABLE 1 Rock Mechanical Properties of the Sedimentary Rocks  

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--> Figure 3 Standard section of the shaft. team excavated 1.2 m at a time and then installed the concrete lining, an approach they call the Short Step Mining Method.

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--> Figure 4 Cross section of the shaft.

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--> Objective and Approach The objective of the SEE Project was to develop methodologies to measure and simulate the mechanical and hydrological effects induced by shaft excavation. To accomplish this, the SEE Project team designed many sections and boreholes for measurements. These are illustrated in Figure 5. For example, in sections A, B, and C, rock properties such as permeability and deformability were measured. In other sections the project team measured displacement, support stress, and inclination and applied seismic tomography. These in situ experiments were performed in very confined settings. The team sometimes interrupted excavation to conduct experiments in the shaft. At other times, excavation and experiments were carried out concurrently. This combination of activities required people from several different organizations to work together. Project Management and Organization The PNC project management and organization is illustrated in Figure 6, which shows relevant portions of the overall PNC organization, and Figure 7, which shows the organization of PNC's Chubu Works. A Board of Executive Directors heads the PNC organization. The Public Relations Office conducts public affairs; they also compiled the visual record of the SEE Project, which includes photographs and video recordings. The Finance Division and the Contract Division controlled the finances and contracts of the project for both excavation work and in situ experiments. The Radioactive Waste Management Project was the group responsible for the SEE Project in PNC's head office. Three sections managed the shaft construction. The Construction and Maintenance Management Office (see Figure 6) assisted in managing the excavation work and gave advice to the other two sections, the Mine Group of the Exploration and Mining Technology Development section and the Shaft Group of the Waste Isolation Research section; both of these fall within the PNC Chubu Works (see Figure 7). The Mine Group, under the Exploration and Mining Technology Development section, is responsible for the management of the Tono Mine. Since the new shaft was constructed in the Tono Mine area, the Mine Group managed the shaft's construction and was responsible for safety management. The Shaft Group, under the Waste Isolation Research Section, planned and conducted the entire SEE Project, including the research activities as well as the construction. The Hydrogeology, Geochemistry, and Natural Phenomena Groups also joined the Project to conduct their respective experiments, and the Drill and Survey Group drilled the boreholes and carried out borehole surveys.

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--> Figure 5 Location of sections and boreholes for measurements in the SEE project.

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--> Figure 6 Relevant organization chart of PNC.

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--> Figure 7 Organization chart of PNC's Chubu Works.

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--> Because there were many experiments carried out in the SEE Project, there were many kinds of contracts and several contractors, and some of these had subcontractors. For the excavation of the shaft, however, there was a single contractor, which had several subcontractors. PNC controlled all of the contractors but had no direct relationship with the subcontractors. The Science and Technology Agency of Japan ultimately controlled the plan and budget of the project. Under the laws and regulations for rock labor safety and health, the Local Labor Standards Inspection Office controlled PNC, and under the laws and regulations for mine safety, the Regional Mine Safety Inspection Bureau controlled the SEE Project. These two organizations can be compared to the Occupational Safety and Health Administration and the Mine Safety and Health Administration, respectively. Shaft Excavation Effects Project Safety Management Safety activities on the SEE Project can be broken down into six parts: (1) a safety plan and rules of safety management, (2) safety documentation, (3) the safety and health management structure, (4) safety inspections, (5) safety meetings, and (6) safety education. Safety Plan and Rules of Safety Management Japan's laws and regulations governing mine safety required the development of an implementation program, annual safety programs, and rules of safety management in the Tono Mine. The plan and rules formed the foundation of safety management at Tono Mine during the SEE Project's tenure. Safety Documentation Documentation of project safety activities consisted of a monthly report to the Mine Safety Committee of the Chubu Works. The Mine Safety Committee then submitted an activity report to the Regional Mine Safety Inspection Bureau.

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--> Safety and Health Management Structure To clarify and assign safety responsibilities, PNC established several organizations or systems, such as the Safety and Health Management Organization, the Emergency Countermeasure System, the Explosives Management Organization, and the Fire Safety Management and Fire Fighting System. PNC also kept a list of subcontractors and charts of these organizations; the list and organization charts were posted in each office of PNC and the contractor in charge of excavation work. The Safety Manager and Health Manager of the contractor in charge of excavation work were appointed to their positions and notified. The Safety Manager at Tono Mine is the director of PNC's Chubu Works. During the SEE Project, the Mine Safety Committee and the Safety Superintendent reported to him, as did the senior safety staff. Senior safety staff were assigned for each area of safety, including general safety, machinery safety, electrical equipment safety, and environmental pollution safety. Figure 8 illustrates this safety management structure. The safety staff of the contractor in charge of excavation work was considered part of the safety staff of PNC. Safety in Tono Mine has always been the responsibility of PNC, not of any contractor. The accident reporting system, an important part of the safety management structure, is illustrated in Figure 9. When an accident occurred, it was reported up the chain to the head office of PNC and related governmental authorities. Safety Inspections SEE Project safety inspections can be sorted into three categories by frequency of occurrence: monthly, annually, and occasionally. The Mine Safety Committee of the Chubu Works, the Safety and Health Committee of the Chubu Works, and the Safety and Health Committee of Contractors all conducted monthly safety inspections of the project site. The central Safety Committee of PNC inspected the site annually. Finally, the Regional Mine Safety Inspection Bureau conducted occasional safety inspections of the Tono Mine. Safety Meetings Safety meetings were a way of life at the Tono Mine. Each group or section held daily safety meetings attended by all of its members. PNC and its contractors, including

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--> Figure 8 Organization chart of safety management in the Tono Mine.

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--> Figure 9 Accident report system of PNC's Chubu Works.

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--> the contractor in charge of excavation work and the contractors running in situ experiments, held safety meetings on a weekly basis. The Mine Safety Committee of Chubu Works, the Safety and Health Committee of Chubu Works, and the Safety and Health Committee of Contractors met once a month. Weekly safety meeting subjects included particular issues of concern at the time of the meeting, operations progress and planning, a review and reconfirmation of safety issues, and any findings of recent safety inspections. In the weekly meetings, team members informed the group of any upcoming excavation work or research activities. Based on these reports, the group coordinated the impending activities, and the safety staff delivered a safety report and appropriate safety instructions. The weekly safety meeting effectively kept safety uppermost in the minds of team members. Education Safety laws and regulations required safety education for both the new worker and the licensed worker. In addition to this required safety education, the SEE Project also conducted KY activities, which were exercises to identify potential risks and to propose countermeasures to address the risks. The KY stands for Kiken Yochi; in Japanese Kiken means potential risk and Yochi means to find them. Figure 10 shows an example of a picture used in KY activities. A sheet such as this one, designed by project workers, was distributed to all those attending the meeting. Attendees identified potential risks in the scene depicted and then proposed and discussed possible countermeasures to reduce or, better yet, eliminate the risks. The Result Only one serious accident occurred on the SEE Project, during the drilling of a horizontal borehole in the shaft. The injured worker was a member of the drilling team. His right hand became stuck between the water delivery hose and the rotating rod, and the injury kept him out of work for two months. After this accident the project team covered the gap with wire mesh. Excavation and research work were stopped by the Regional Mine Safety Bureau for one week following the accident.

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--> Figure 10 A sample KY sheet. Conclusion As will the Exploratory Studies Facility at Yucca Mountain, the SEE Project combined excavation and experiments, sometimes alternating between these and sometimes conducting them concurrently. This approach combined workers from several different organizations in a confined, risky work environment. Two aspects of the safety management approach at Tono Mine during the SEE Project stand out as exceptional contributors to effective safety management: frequent safety meetings, including the weekly meetings of group leaders and the daily meetings of work groups, and safety education, in particular the KY activities. The KY activities involved all the workers directly with the issue of safety. Identifying risks in hypothetical situations and proposing countermeasures to reduce or

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--> eliminate those risks developed the habit of constantly looking for risks and thinking of ways to address them. This habitual heightened awareness undoubtedly protected SEE Project workers on the job. Safety meetings also heightened the awareness of safety issues. The weekly meetings enabled group leaders to coordinate and schedule project activities and to anticipate and work to prevent any hazards resulting from the week's planned tasks. Daily safety meetings prepared each group for the day's work, made them aware of expected hazards, and reminded them of appropriate safety practices. The most important goals of safety management are to enhance each worker's sense against dangers and teach each worker to avoid dangerous actions. An effective safety management program will focus on these goals.