As of the preparation of this newsletter, the tunnel had reached a length of 5500 meters. Total length of the ESF tunnel is planned to be 7780 meters. The DOE has indicated they plan to reach the south portal and complete the ESF tunnel prior to the end of 1996. Alcove drifts off the main tunnel to the thermal test area and to the Ghost Dance Fault have been started.
Tunneling to date has produced some unexpected results which have site suitability implications. Results from analysis of Chlorine-36 samples taken from the tunnel and over 1000 meters of poor quality rock within the Topopah Spring Tuff (the proposed repository host rock) raise questions about the suitability of the site to host a repository.
Researchers at Los Alamos National Laboratory, a contractor to the DOE, have detected elevated levels of Chlorine-36 in rock samples collected from faults and fractures along the ESF tunnel. The elevated levels of Chlorine-36, found at various depths to at least the proposed repository depth, suggest that water carried the Chlorine-36 to the sample locations and likely deeper in less that 50 years. Elevated quantities above background of Chlorine-36 were generated from atmospheric testing of nuclear weapons in the south Pacific in the 1950s. A preliminary report titled "Systematic Sampling For Chlorine-36 In The Exploratory Studies Facility" has been prepared by Los Alamos.
Based on analysis of the Chlorine-36 data, the Department, as indicated in a press release, has not reached a conclusion on the significance of the data or the findings. However Bob Loux, Executive Director of Nevada's Agency For Nuclear Projects, stated that the report and its findings "is just another piece of evidence that the site should be disqualified because it can't meet the groundwater travel time qualifications." Federal regulations published in 1984 state that a disqualifying condition exists at a site if groundwater travel time from the repository to the surrounding environment is less than 1000 years along any pathway of likely and significant radionuclide travel.
Carl Johnson, head of the Agency’s Technical Division, further comments that "it is obvious that vertical faults and fractures, prevalent at Yucca Mountain, provide fast pathways for water infiltrating from the ground surface to reach at least the proposed repository level and likely continue on to the water table." He further states that evidence for fast pathways at Yucca Mountain is not new - in 1994, elevated levels of tritium, the radioactive isotope of hydrogen derived from atmospheric nuclear weapons testing, was detected in perched water bodies below the repository level intercepted by surface-based drilling. He says "The 1994 tritium evidence when combined with the recent Chlorine-36 finding presents a powerful case that the site may not isolate radioactive waste."
From the intersection of the Sundance Fault with the ESF tunnel at station 3993 meters to station 4914 meters, quality of the Topopah Spring Tuff rock has been categorized by the DOE tunnel constructors as poor. The rock is so intensely fractured as to require steel arches around the circumference of the tunnel every four feet with intervening steel lags to keep loose rocks from falling into the tunnel. The DOE admits that this poor rock quality was not expected, as neither surface geologic mapping nor cores from surface-based drilling provided a hint as to the intense fractured nature of the rock. The DOE states that tunnels can be constructed in such material and should not pose an insurmountable problem to repository construction.
The Agency for Nuclear Projects sees two concerns with over 1000 meters of poor quality rock within the proposed repository block. One, it is questionable whether engineered waste emplacement drifts can remain open for post-emplacement monitoring for the complete 100 year preclosure regulatory period. Should tunnels begin to collapse, retrieval of the waste containers may not be possible. Two, intensity of the fractures in an area encompassing approximately one- third of the proposed repository block again raises the question of whether the site can, in fact, isolate radioactive waste from the biosphere.