PF-4 a top concern of DNFSB

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By The Staff

On the day before Christmas, the Defense Nuclear Facilities Safety Board took on the role of Scrooge as it made its report to Congress on the status of significant unresolved issues with the Department of Energy’s Design and Construction Projects.

The report cited a couple of projects taking place at Los Alamos National Laboratory.

In a letter from DNFSB’s Peter Winokur to Energy Secretary Steven Chu, the seismic safety issue at the Plutonium Facility took center stage.

Here are the highlights of Winokur’s report about PF-4.

• On Oct. 26, 2009, the DNFSB issued a recommendation, which addressed the need to reduce the potential consequences to the public from a seismic event at PF-4, as analyzed in a Documented Safety Analysis. In October 2011, the National Nuclear Security Administration approved a revision to the PF-4 DSA. The revision included a refined accident analysis for seismically-induced events and asserted that all postulated accident scenarios have mitigated dose consequences to the public that are below the Evaluation Guideline of 25 rem Total Effective Dose The mitigated dose consequence is a key driver for the seismic upgrades planned at PF-4, because it indicates whether additional seismically qualified controls are required to protect the public.

• In a June 18, 2012 letter to NNSA, the board identified several technical deficiencies with the revised DSA, challenging NNSA’s conclusion that the dose consequences to the public do not exceed the Evaluation Guideline. NNSA transmitted its response to the board Nov. 5, 2012. NNSA’s response acknowledged that the PF-4 DSA needs further improvement and committed to perform additional analysis to determine what additional safety controls may be needed. The DNFSB is reviewing NNSA’s response.

• LANL also updated the site’s Probabilistic Seismic Hazard Analysis in 2007 and 2009 and identified that the potential ground motion was significantly higher than analyzed in the DSA. In 2010, LANL initiated the Seismic Analysis of Facilities and Evaluation of Risk project to evaluate the increase in seismic risk resulting from the higher ground motion.

• In 2011, NNSA completed its evaluation of the seismic performance of the PF-4 structure in response to the increased seismic hazard at the site. The evaluation identified nine vulnerabilities that could render the structure unable to maintain its safety-class confinement function during postulated seismic events.

• Responding to those vulnerabilities, NNSA approved a Justification for Continued Operation for PF-4 in July 201l. The JCO served as a temporary change to the PF-4 DSA that allowed operations to continue in light of the seismic vulnerabilities. The JCO identified interim compensatory measures to help mitigate the increased seismic risk of continuing operations and outlined a plan for addressing the structure’s seismic vulnerabilities.
NNSA subsequently completed structural upgrades to address these nine vulnerabilities and exited the JCO in June 2012.

• In addition to the upgrades, NNSA agreed that additional structural analysis, including a static nonlinear seismic analysis of the facility’s structure, was necessary to identify potential additional vulnerabilities that could lead to a loss of confinement or a seismically induced collapse of the structure.

• In a July 18, 2012 letter to the deputy secretary of energy, the board expressed concern that the static nonlinear seismic analysis was proceeding without adequate definition and technical justification. LANL completed the static nonlinear seismic analysis in September 2012. The analysis identified additional structural vulnerabilities, such as roof girders and captured columns that could fail during a seismic event and lead to the collapse of the facility. LANL notified NNSA of these results and submitted a safety basis addendum to NNSA for approval,

• The deputy secretary of energy responded to the DNFSB’s concerns with the analysis on Sept. 28, 2012, and committed to take several actions. NNSA is developing an alternate approach for performing the static nonlinear seismic analysis that will more accurately reflect the building’s behavior and the calculated impact of seismic forces on the structure.

The DNFSB also addressed another problem at LANL — deficiencies in the preliminary safety design report for the Transuranic Waste Facility project. The board identified a number of issues with the report that could impact the identification, design and functional classification of the facility’s safety-related controls.

The report stated, “the project team did not:

• Adopt appropriate release parameters for modeling the consequences of accidents involving radioactive sealed sources,

• Follow DOE’s guidance on deposition velocity and therefore used a value in the accident analysis that was not technically supportable.

• Correctly apply the process established in DOE Standard for evaluating the probability of an aircraft impacting the facility.

• Apply conservative and technically supportable assumptions in deriving the probability for large truck crash accidents.

• Meet DOE guidance for identifying the appropriate controls for protecting the safety-significant fire protection system from freeze-related damage.