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butthurt [soylentnews.org] writes:

The Center for Public Integrity [publicintegrity.org] found that several reports, the first in 1980, warned of weakening of the timbers in a tunnel storing radioactive equipment which last month was discovered [soylentnews.org] to have partially collapsed.

The tunnel with the collapsed roof was built in 1956 [...]

It is unclear when contractors running the plant first became concerned that gamma radiation, which changes the molecular structure of wood cell walls, would significantly weaken the first tunnel’s timbers. As early as 1971 the integrity of the wood was checked and determined to be sound. The 1980 study said however that said the wood’s strength had deteriorated to 64.5 percent of its original strength. It predicted that the structure should be sound until at least 1982, by which time the authors anticipated it would be cleaned out.

[...]

In the 1991 report, by Los Alamos Technical Associates, Inc., the authors made clear after conducting an internal inspection of the tunnel that the DOE knew the timbers holding up the roof had been substantially weakened as early as 1980. It predicted that by 2001, they would be at 60 percent of their original strength and recommended another evaluation in 2001. But records indicate that it never happened.

A 2015 report [cresp.org] (PDF) estimated that collapse would occur around 2040 and warned that the wood presents a risk of fire (pages 1215-1216 of PDF, numbered F.4-42 and F.4-43):

PUREX Tunnel 1 was constructed in 1956. Except for a 103 foot section one wall that is composed of 3
foot thick reinforced concrete, the remaining walls and roof of the 358 foot long tunnel were
constructed using 12 inch by 14 inch creosoted No. 1 Douglas Fir timbers, arranged side by side with the
12 inch side exposed. The last evaluation of the structural integrity of the tunnel was made in May 1991 by Los Alamos Technical Associates (LATA). It concluded that there was very low probability of any
degradation of the timbers due to decay or insect attack, but that there was ongoing degradation
occurring from continued exposure to the gamma radiation from equipment being stored there. It
estimated that the strength of the timbers would be 60% of their original strength in 2001. Applying the
same formulas used in that analysis to the year 2014 would indicate that the timbers are currently at
about 55% of their original strength. This study indicates that standard factor of safety will be reached
at 47.5% of original value. It is estimated this could occur sometime about 2040. This wood structure
also offers the potential for a fire in the tunnel that would release its entire 21,200 Ci radiological
inventory to the environment.

Elsewhere (page 11 of PDF, numbered x) the authors acknowledged "large uncertainty" in their estimate of when collapse might occur.

Original Submission