Safety in the Underground Construction and Operation of the Exploratory Studies Facility at Yucca Mountain (1995)

Olle Zellman

In Sweden, industrial safety is formally governed by the Work Environment Act (WEA) and a number of agreements and directives. Under the WEA, the proprietor of a work site has coordinating responsibility for that site, although this responsibility is often transferred to the contractor.

Safety in underground work begins with the planning and design phase. A layout can be made safe by relatively simple means, for example, the location of turnaround niches or transformers. Underground facilities have very few exits, often only one. A combination of shaft and ramp greatly improves the opportunities for evacuating personnel in the event of an emergency.

Good communication is necessary in all safety work. Knowledge and understanding of each other's activities is perhaps especially important between scientists and rock workers conducting completely different tasks in the same areas. This is accomplished with all employees at regularly scheduled information meetings and before the start of major research activities.

At the Äspö Hard Rock Laboratory (HRL) in Sweden, the greatest risk of underground accidents involves transports. The reason is, of course, that vehicles and people have to share a small space that is usually dark. Nevertheless, it is possible to greatly reduce this risk by simple, inexpensive means, such as, a good safety manual and a high safety awareness.

The greatest resources in safety work should be concentrated on the prevention of accidents. But should an accident occur, it is important that all personnel have the right knowledge and equipment at their disposal. Everyone must know, for example, how to alert the surface facility, where the nearest fire extinguisher is, and how oxygen masks work.

Unfortunately, it is impossible to eliminate all safety risks by means of legislation. By raising each individual's level of safety awareness, however, it is possible to reduce

the risks considerably. The safety manual will not do any good unless everyone is familiar with its contents.

The Swedish Nuclear Fuel and Waste Management Company (Svensk Kärnbränslehantering AB, or SKB) is a wholly owned subsidiary of the four companies that produce nuclear power in Sweden. SKB's main duty is to safely manage and dispose of the radioactive waste that results from the operation of nuclear power plants. The company is also responsible for the nuclear waste from medicine, research, and industry.

To perform this duty, SKB has developed and built a complete waste disposal system. For the operational waste, there is an underground final repository in Forsmark, about 100 km north of Stockholm. The spent fuel is stored in water pools in an underground, interim storage facility outside Oskarshamn in southeastern Sweden. Since all Swedish nuclear power stations are situated on the coast, all transports take place by sea on a specially built ship.

A deep repository is planned to accommodate the long-lived waste. The Äspö HRL is one of several links in the chain leading to this repository. The research and development activities in the Äspö HRL have the following main goals:

• test the quality and appropriateness of different methods for characterizing the bedrock with respect to conditions needed for a deep repository;
• refine and demonstrate methods for adapting a deep repository to the properties of the rock in connection with design, planning, and construction; and
• collect material and data important to the safety of the deep repository.

Seven organizations from the United States, Canada, Japan, the United Kingdom, France, and Finland are also participating in the project.

The Äspö HRL can be likened to a dress rehearsal for the construction of the deep repository. This paper describes the safety work during the construction of the tunnel part of the laboratory.

The Äspö HRL is situated in southeastern Sweden, an area dominated by Precambrian granites that are 1.7 billion to 1.8 billion years old. North and south of the laboratory there are younger, diapir-like granite structures that intrude underneath the laboratory. A fine-grained granite found in the area is often fractured and water-bearing.

The underground part of the facility, when finished in early 1995, will consist of a 4-km tunnel down to a depth of 500 m. The tunnel connects with the ground surface through three shafts—one for an elevator and two ventilation shafts. The raise-bored shafts are being excavated in several stages, the first of which is complete.

The tunnel's cross-sectional area is 25 m² except on the curves, which have been designed as meeting places and where the area is over 40 m². The gradient is 1:7, which approaches the maximum gradient conventional vehicles can negotiate.

Tunneling is being carried out by conventional drill-and-blast methods. But the Tunnel Boring Machine (TBM) method will be tried out during the last 400 m. The diameter will then be 5 m, while the gradient of 1:7 will be retained, which is very unusual for TBMs.

To provide for the eventuality of a pump breakdown, basin capacity for around 10 hours will be provided at the bottom of the facility. A visitors' niche has been built at the beginning of the tunnel. Visitors can walk along a sidewalk that is separated from the roadway by a railing.

The WEA is the foundation of industrial safety in Sweden. A number of other agreements and directions regulate various activities in greater detail. As far as underground work is concerned, a number of regulations apply. The three most important regulations for the activities at the Äspö HRL are those concerning rock work, blasting work, and personal safety equipment. With the exception of certain visitors, all persons who will be working underground must sign off on the text of these three regulations before they begin work. The literature is unfortunately only available in Swedish, and since the project has many international participants, this can sometimes cause problems. SKB provides an oral briefing on the most important provisions before work begins.

The National Labor Inspectorate, a state authority, uses two labor inspectors (each of whom has certain specialties) to enforce compliance with existing acts and ordinances. The two labor inspectors cover all underground work, which is dominated by mining operations in northern Sweden. One labor inspector visits the Äspö HRL about four times

a year, at which time client and contractor representatives review activities from a safety viewpoint.

According to the WEA, the client has coordinating responsibility for all risky work on the work site. Normally, however, this responsibility is transferred to the contractor, as is the case with the Äspö HRL.

Much of the preventive safety work can be done in connection with the planning and design of the facility, but many different requirements have to be met. This is particularly true in the case of underground facilities where a great deal of research will take place and where the layout must primarily satisfy the researchers' needs. Satisfying some needs is relatively easy, for example, ensuring that the distances between turnaround niches are not too great and that the niches are large enough for all types of vehicles.

The choice of rock reinforcement measures can be more complicated. In the case of the Äspö HRL, the researchers wanted wire mesh reinforcement to be given priority over shotcreting. This request proved difficult to satisfy from a safety viewpoint. The wire mesh became filled with breakouts, which were finally such a great safety hazard that shotcreting was necessary. Furthermore, it is difficult to use wire mesh near the working face, since it usually gets shot apart in the impending blasting round.

Normally, underground facilities have very few escape routes. The Äspö HRL has a ramp and shafts. The primary consideration was not safety, but there is no doubt that the purpose of safety is served.

Ventilation is another key factor to be determined before construction work begins. The main purpose of ventilation is to remove unwanted gases and supply fresh air. In the event of fire, however, it is important to be able to control the ventilation; so the combustion gases do not, for example, rise in a shaft with a stationary elevator full of people. This is relatively easy to arrange in a permanent facility but is often difficult during the construction period.

During the construction period at the Äspö HRL, there is a ventilation tube along the ceiling; there is no means for controlling the ventilation aside from starting and stopping the fans that are used for fresh air ventilation. The two ventilation shafts will not be used until the facility is finished. Construction of the Äspö Research Village is going on directly above the shafts, which makes their use difficult.

A working-environment group with representatives from the client, the contractor, and the labor inspector (sometimes also from the trade union and the municipal rescue service) meets every three months. The labor inspector usually issues directions and advice on how activities should be carried out without lowering the level of safety. Inspections of the facility, rock reinforcement, vehicles, etc., are additional duties of the labor inspector.

Safety delegates come from both the client's and the contractor's organizations. Their duty is to prevent accidents. Their work includes making safety inspection rounds every 14 days together with the production manager. On these occasions, they check virtually everything having to do with safety. Any deficiencies they note must be corrected immediately. A safety delegate finding an immediate danger to life or property has the right to stop the work completely or partially. This is rare and has never happened at the Äspö HRL, but the fact that it can occur has a safety-enhancing effect.

It is common for research work underground to be conducted at night and on weekends when the contractor is not present. To give research personnel added safety, there is a check-in system with the nearby nuclear power station's local guard center. Before personnel go underground, they phone the guard center and state when they plan to return to the surface. Once aboveground, they must phone in again. If they do not check in within 30 minutes of when they were supposed to come up, an alarm is sent to the rescue service, which goes into the tunnel and searches. The system is simple but works well.

Tunneling is done in two shifts using a conventional drilling rig equipped with three drills and a charging basket. The rig is also equipped with a Beaver control for recording various drilling parameters. Normally, one 4-m round is shot per shift. Owing to large earth currents in the rock, bulk explosives are inappropriate. For ignition, non-el, pentyl fuses, and powder fuses are used. The client determines the degree of rock reinforcement, but safety delegates can always demand additional reinforcement. Mucking is done with ordinary trucks equipped with catalytic converters and soot-particle filters to improve the environment in the tunnel. The loader is electric, which is a big advantage. During mucking, no research activities may be carried out in the vicinity of the loading area, and other transports in the tunnel must be limited to those that are absolutely necessary. Visitors may, however, go down into the special visitors' niche.

Conducting Äspö HRL's extensive research work while tunneling is in progress makes special demands on safety awareness. Two different organizations, several different occupational categories, and different opinions on what is important make communication both aboveground and underground very important.

After each blasting round, geoscientists document the newly shot rock. No other activities may be conducted at the tunnel face during this work, which normally takes about an hour. The drilling rig serves as a light source after having been moved back about 10 m. Before the geoscientists go underground, they sign a protocol that has been completed by the contractor's shift boss. It describes the appearance of the tunnel face and states whether any special precautions must be taken, for example, whether the rock must be reinforced. By the time the geoscientists go underground, the tunnel face will have to be scaled, washed clean, and completely mucked out. If the rock conditions are such that reinforcement in the form of shotcreting is necessary, the tunnel face is mapped from a safe distance, normally 5 to 10 m.

After every fourth round, 20-m-long probe holes are drilled to investigate the rock in front of the face. The contractor and scientists cooperate on these drillings. The scientists constantly record what happens during the actual drilling procedure. When the hole is finished, it is packered and tests are performed to determine pressure build-up. At a water pressure of around 35 bar, there are some practical problems with packer setting when the holes contain a great deal of water. A method has been developed whereby the rig helps to put each packer in position. The packers are then chained to the rock, so that they will not act as projectiles if they should come loose.

Prior to investigation drilling where large water flows can be expected, a 3-m-long casing pipe is cemented to the rock and anchored with four concrete bolts through a steel plate. A ball valve is fitted at the far end of the casing. Drilling then takes place through this valve. This makes it easy to stop large water inflows that might exceed the capacity of the pumps. Today the total inflow to the tunnel is about 2,000 liters per minute, and the pump capacity is about 3,500 liters per minute.

Because the contractor has coordinating responsibility for the construction site, the shift supervisor must always give verbal permission before anyone may go underground, along with information on any problems with passage, fan or pump troubles, etc., that might affect safety.

Near the tunnel face, a steel container with an inner wooden cage serves as a rescue chamber. The chamber has a telephone and oxygen for six hours' consumption by six persons. There may only be as many persons between the rescue chamber and the face as can be accommodated in the container. This provides an extra escape route in the event of an emergency.

After discussions with the local rescue service, trials with radio communication have been conducted underground. Due to the layout of the facility, it has been difficult to get this kind of communication to work. Far too much cable would be necessary for the system to have any advantage over an ordinary telephone. Thus, the project participants recently decided to schedule the installation of the permanent internal telephone system earlier than originally planned and to expand it with additional telephones, a solution accepted by the local rescue service.

All vehicles underground are diesel powered, except the drilling rig and the loader, which are electrohydraulic. A fire extinguisher is mounted on every vehicle. In addition, there are oxygen masks on most of the vehicles. Fire extinguishers and first-aid equipment are available in the visitors' niche.

In summary, the patchwork of rules and regulations governing underground work in Sweden has evolved gradually, based in part on experience from several hundred years of underground work. In addition to all the laws and rules, common sense and a firmly rooted safety awareness are essential. The latter can always be raised with training and information. It is also very important that the personnel perceive existing rules to be clear and practically applicable. Otherwise these rules will never be more than just words on pages in a dusty binder in an office.

After Mr. Zellman's presentation, in an exchange about compliance and enforcement, the safety of scientists working during off-hours was questioned. In Sweden, the equivalent of the Occupational Safety and Health Administration has authority to issue directives, copies of which are distributed to everyone working on the project site. Every scientist must go into the tunnel with at least one other person. Also,

to ensure familiarity with the facility, each must first complete a long introductory session. If these criteria are met, scientists may go underground for up to nine hours without mining personnel accompanying them.