NNSA pursues PF-4 scrutiny

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Structural analysis: All results due by next April

The Defense Nuclear Facilities Safety Board and the National Nuclear Security Administration have been going back and forth regarding the seismic integrity of LANL’s Plutonium Facility.

In a letter to DNFSB Chairman Peter Winokur from NNSA's top security official, DOE Deputy Secretary Daniel Poneman, he tells Winokur the NNSA and LANL have been working methodically to evaluate PF-4 to understand how the facility would perform if subjected to an earthquake.,

“This effort has already resulted in several structural improvements to assure the safe operations of PF-4. As part of a deliberative process outlined in national consensus codes and standards, NNSA and LANL have progressed from relatively simple calculations and modeling approaches to more sophisticated methods (referred to as static nonlinear pushover analysis), to provide additional detail and confidence that we have identified all the facility structural elements that require upgrading.

"The initial results of the nonlinear pushover analysis are complete and have undergone an independent peer review. The final report thoroughly/documenting the methodology and the results will be issued as soon as the peer review comments are addressed,” Poneman wrote.

Poneman went on to say that the “decisions we make regarding this vital facility be of the highest quality and take into account the views of the Defense Nuclear Facilities Safety Board. In that spirit, and as I committed to you in our last phone call on this subject, I am directing that NNSA immediately initiate an action to evaluate PF-4 using a second modeling approach, termed a modal loading analysis. I have also directed the NNSA staff to consult with the DNFSB staff to ensure that the premises underpinning the modal loading analysis take the DNFSB technical perspective into account.”

DNFSB had asked NNSA the following questions in relation to PF-4.

• Provide a description of the identification and technical basis for each key assumption to be applied to the static nonlinear analysis model, with particular emphasis on the nonlinear elements and how the characteristics and parameters for each were selected.

• Provide a detailed description of the approach to be taken in applying loads to the model to simulate the dynamic (degraded) behavior during an earthquake.

• Provide the static analysis acceptance criteria.

In the 12-page memo on the DNFSB website, NNSA outlined a timeline for several activities that need to be completed to ensure that PF-4 continues to meet Department of Energy (DOE) standards,
1. Issue the final report detailing the modeling and results that have been completed thus far (finalize the document provided in draft to the DNFSB).
2.  Complete, review, and revise as necessary the existing LANL model and pushover analysis. This is necessary to ensure there is a high level of confidence that the results of the pushover analysis identify all components that may require structural improvements. (October 2012)
3. Perform additional analysis to evaluate loading in the up direction. (October –November 2012)
4. Develop and execute a second static nonlinear pushover analysis using a modal loading approach. (Start in October 2012)
5. Complete the service chase joint testing and document in a final report. Perform additional analyses as necessary to ensure that the strength of the service chase roof slab joints is modeled correctly. All subsequent model runs will use the strength and stiffness determined from the testing. (December 2012)
6. Evaluate situations where individual components or combined failure mechanisms do not meet or are close to the established performance goal or could lead to facility collapse and identify the safety impact per the requirements in 10 CFR 830 and the September 2012 memo from the Deputy Secretary to the Central Technical Authorities on Adequate Protection. (Initial evaluation completed in September 2012 and updated as new information
is provided based on results of additional analysis)
7. Execute the Nuclear Safety Rule (10 CFR 830) process for potential inadequacy in safety analysis to address applicable requirements of nuclear safety rule and document conditions that assure adequate protection of the public. (October 2012)
8. Identify the set of necessary facility component repairs and establish a prioritized plan for the necessary repairs. Document this plan in revision to the Project Execution Plan. (Initial update to PEP in November 2012 and periodic updates as new information is available)
9. Conduct a comprehensive independent technical review to ensure that the analysis and results are comprehensive and sound and that planned activities are sufficient to resolve identified deficiencies. (Scheduled when all analytical results are available — initial estimate is April 2013)
10. Implement repairs necessary to ensure that needed upgrades are completed. (TBD, the details of individual structural improvement plans will be documented in updates to PEP).
NNSA said the next revision of the PF-4 seismic project execution plan will be issued in November 2012.