The public can weigh in Wednesday on a plan to stabilize a second Hanford tunnel storing highly radioactive waste.
Work should be done as soon as possible to prevent the possible collapse of the longest tunnel storing highly radioactive waste at the Hanford PUREX plant, according to a Department of Energy contractor assessment included in proposed changes to a state permit required for the work.
If the state permit is approved on schedule, work could start this summer to fill the tunnel with concrete-like grout, according to information posted on the Hanford website.
The work, starting with construction of piping and ventilation systems, is expected to take about a year, according to the proposed changes to the Hanford Dangerous Waste Permit.
The public will have a chance to comment on the plan for the tunnel, as described in the permit modifications, at a meeting at 5:30 p.m. Wednesday at the Richland Public Library, 955 Northgate Drive.
The Department of Energy is proposing filling the 1,700-foot long tunnel with concrete-like grout as a temporary measure.
Eventually a permanent plan to clean up the tunnel — and the 28 rail cars loaded with radioactively contaminated equipment that it holds — would be made.
One option could be cutting up the grout with water jets, wire saws or excavation equipment guided by a detailed excavation plan with specific locations for cuts, according to the proposed permit changes.
The retrieved waste could be moved to the unused PUREX plant, where it could be further cut into smaller pieces and packaged for disposal.
Another alternative may be to leave the grouted waste in place and construct a barrier over the tunnel to prevent water from infiltrating and carrying waste into the soil beneath the tunnel.
The changes to the permit also address the collapse of a 17-foot section of the plant’s older tunnel, which was discovered May 9. The collapse prompted the review of the stability of the second tunnel.
An emergency was declared on May 9 and thousands of Hanford nuclear reservation workers were ordered to take shelter, but no airbone radioactive material was detected.
Between June 1960 and January 1965, eight rail cars were pushed into the first PUREX plant waste tunnel. The rail cars hold 780 cubic yards of equipment contaminated with highly radioactive waste.
The first tunnel, which is 360 feet long, has already been filled with grout.
The work was done under a contingency plan, with the risk of further collapse considered great enough that work proceeded in October and November of 2017 in advance of a change to the state permit and public comment.
Documents included with the permit say the cause of the collapse could have been a combination of factors.
The tunnel’s walls and flat roof were built in 1956 of creosoted timbers, and the wood could have deteriorated from exposure to high levels of radioactivity since the first of eight rail cars loaded with contaminated equipment was pushed into the tunnel in 1960.
Heavy rain on May 4 and 5 could have increased the weight of the eight feet of dirt covering the tunnel. In addition, slight vibrations over the years form thunderstorms and distant, low-magnitude earthquakes could have contributed to the collapse.
Engineers also considered the affect of water infiltrating and pooling along a concrete ledge support at the east end of the tunnel. But the dry climate made that only a “moderately plausible” reason for the collapse, according to a CH2M Hill Plateau Remediation Co. document.
The second tunnel, which is about 1,700 feet long, was built in 1964 in the shape of an arch, with steel ribs supporting corrugated steel plate roof panels.
After two collapses during construction, it was re-engineered to add steel I-beams and reinforced, arched concrete girders over the top.
Between December 1967 and 1996, 28 rail cars were pushed into the second PUREX plant waste tunnel. The rail cars hold 2,883 cubic yards of equipment contaminated with highly radioactive waste.
The tunnel has been in service for more than half a century, which is beyond the typical length of use for similar structures, according to contractor information in the proposed modified permit.
The risk of a partial or total collapse is considered high based based on problems during construction and the stress on some components of the tunnel, according to the contractor information.
The loads on the arched steel rib supports exceed building code design capacities.
Those who cannot attend the Richland meeting on changes to the permit can participate via the internet. Go to www.hanford.gov and open the “Event Calendar” to March 14 for sign-in information.
Public comments may be submitted until April 12. Go to bit.ly/TunnelComments to submit comments electronically or mail them to Daina McFadden, Washington State Department of Ecology, 3100 Port of Benton Blvd., Richland, WA 99354.