[DOE LETTERHEAD]
OFFICE OF RIVER PROTECTION
May 16, 2003
The Honorable John T. Conway
Chairman
Defense Nuclear Facilities Safety Board
625 Indiana Avenue, N.W., Suite 700
Washington, D.C. 20004
Dear Mr. Chairman:
WASTE TREATMENT AND IMMOBILIZATION PLANT
(WTP) CONCRETE SUBSIDENCE ISSUE WTP-03-054
I am attaching a copy of Bechtel National,
Inc. (BNI) High Level Waste Concrete Subsidence Study Phase B (Final Report),
Revision 1, concerning concrete subsidence encountered on some WTP
placements. My staff, including several
of the U.S. Department of Energy, Office of River Protection (ORP) consultants,
have reviewed this report and consider this issue to have been thoroughly
evaluated, the basis of BNI’s conclusions were well founded, and we concur with the
report’s recommendation to
accept as-is all previous basemat and wall placements. Furthermore, we have concluded that no
reductions in design margin need to be made due to concrete subsidence.
The bases for these conclusions are as
follows:
·
All applicable
codes and standards were followed in the design and placement of WTP basemats
and walls.
·
The
methodology for identifying placements that might have significant and
detrimental subsidence was reviewed and verbally approved by the Chairman of
the American Concrete Institute (ACI) Committee 408 on Bond and Development of
Reinforcement during joint discussions.
·
Comparing
as-built lap lengths for all placements having the potential for significant
subsidence shows top bar factors meeting or exceeding the applicable code (ACI
318-99 or ACI 349-01).
·
Additional
calculations were performed assuming a 50% reduction in bond strength from
subsidence, the equivalent of a top bar factor of 2.0. Using the state-of-the-art design provisions
for development length recommended by ACI Committee 408 and approved by the ACI
Technical Activities Committee in the fall of 2002, top bar factors for basemat
placements made to date range from 2.8 to 3.2.
Top bar factors for walls ranged from 2.2 to 2.3. This level of conservatism provides
confidence that existing basemats and walls could handle even extreme and
unrealistic levels of subsidence safely.
Provisions for future placements include:
·
Continuing to
design reinforcement meeting applicable codes (ACI 318-99 or ACI 349-01). These
codes are very conservative for #l1 bars if recommended design provisions of
Committee 408 are followed.
·
All cold
weather placements over 24” in depth will receive revibration per Section 7.4
of ACI 309R. All parties have agreed
that this eliminates subsidence as a concern in cold weather placements.
In summary, I propose closure of this
issue. A video teleconference to
further discuss this issue can be arranged if needed. If you have any questions, please contact me, or your staff may
contact John R. Eschenberg, Manager of the Waste Treatment Plant Project, (509) 376-3681.
Sincerely,
Roy J. Schepens
Manager
cc w/attach:
M. T. Sautman, DNFSB Hanford Site Rep.
M. B. Whitaker, DR-1
J. H. Roberson, EM-I
K. T. Juroff, EM-44
S. P. Schneider, EM-44
S. 0. Stokes, INEL
B. A. Fiscus, RL