National Nuclear Security Administration
June 15, 2005
The Honorable A. J. Eggenberger
Defense Nuclear Facilities Safety Board
625 Indiana Avenue, N.W., Suite 700
Washington, DC 20004-2901
Dear Dr. Eggenberger:
On March 18, 2005, the Defense Nuclear Facilities Safety Board (Board) sent a letter to the National Nuclear Security Administration (NNSA) requesting results of a condition assessment and mapping of building leaks and structural cracks at the Device Assembly Facility at the Nevada Test Site. The mapping of building leaks was sent to the Board on May 16, 2005. This letter transmits mapping of the structural cracks. Enclosure 1 to this letter contains a summary of crack locations within each building of the Device Assembly Facility, general orientation, and the largest crack size in each room. Enclosure 2 contains more details of crack locations and floor plans for each building, and cracks that have been monitored over the last several years.
As noted in our previous letter, steps have been taken to start the comprehensive review of the structural capacity of the Device Assembly Facility. To accomplish this goal, we will evaluate the integrity of Device Assembly Facility structures using a phased approach that is outlined below.
Phase I. In this phase, safety related structural elements (walls and slabs, as determined in the Documented Safety Analysis) that contain cracks 0.04 inch or wider will be evaluated using simplified analytical methods. The overall purpose of this evaluation will be to estimate the available design margin considering the cracks, and to determine if a more detailed evaluation is necessary. The evaluation will consider the location and orientation of the cracks, supporting condition of the structural element, reinforcement quantity and pattern, and any cause(s) of the cracking that impacts these factors, if deemed necessary.
The selection of structural elements with cracks 0.04 inch or wider is based on the acceptance criteria defined in Section 5.2 of the American Concrete Institute 349.3R-02, “Evaluation of Existing Nuclear Safety-Related Concrete Structures” and on our crack monitoring program that has monitored 42 cracks for approximately seven years. The crack monitoring program results indicate that these cracks are stable. As we execute Phase I of our evaluation we will discuss the final selection of structural elements with your staff.
Phase II. In this phase we will utilize more refined methodologies to evaluate the structural capacity of structural elements that could not be qualified by the simplified methods used in Phase I. This phase could also include more detailed structural evaluations of other structural elements as deemed necessary. The overall purpose of this phase is to identify those cracked structural elements that may be associated with less than adequate structural capacity to determine if any structural upgrades are necessary.
Phase III. This phase will execute the Seismic Analysis and Evaluation Plan that was mentioned in our May 16, 2005, letter. As noted previously, this plan is expected to be finalized in the near future. NNSA will keep the Board and its staff apprised of the progress on resolving this issue.
If you have any questions, please contact me or have your staff call Ms. Laura Tomlinson at the Nevada Site Office, telephone number 702-295-2588.
Linton F. Brooks
K. Carlson, NSO, w/o attachment
M. Whitaker, DR-1, w/attachment