OEC Webinar on Nuclear Safety New Airborne Dispersion Modeling and Its Impact on Safety Basis Documentation at a DOE Waste Handling and Processing Facility

OEC Webinar on Nuclear Safety - What Initiated the Need for a New DOE Nuclear Facility Safety Basis Offsite and Onsite dispersion analyses?

OEC Webinar on Nuclear Safety Initially, DOE Office of Health, Safety, and Security issued Safety Bulletin No Accident Analysis Parameter Update, in May The bulletin identified issues related to the use of deposition velocity parameter assumptions when determining the atmospheric dispersion factor (x/Q) that is used in dose consequence modeling Initially, DOE Office of Health, Safety, and Security issued Safety Bulletin No Accident Analysis Parameter Update, in May The bulletin identified issues related to the use of deposition velocity parameter assumptions when determining the atmospheric dispersion factor (x/Q) that is used in dose consequence modeling.

New Airborne Dispersion Methodology Complex-Wide Meetings Took Place. However, there was much discussion throughout DOE sites regarding the best approach for the new assumptions. As such, DOE provided direction to us in two letters (June 24, Site- Specific Dispersion Analysis Parameters, and January 23, Clarifications of Site- Specific Dispersion Analysis Guidance) regarding assumptions to be used in the recalculation of x/Q.

As a result, we modified the previous Documented Safety Analysis (DSA) dispersion methodology in which we calculated new onsite and offsite x/Q (“Chi over Q”) values using the simplified approach outlined in the Nuclear Regulatory Commission (NRC) Regulatory Guide 1.145, Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants. This new approach is discussed in our DSA and is the basis for recalculation of consequences in the Preliminary Hazard Analysis (PHA) tables and all site accident scenarios modeled in our DSA.

Impact… When compared to x/Q used for ground level releases in our previous DSA, the value was increased by a factor of 1.3 at the 100m receptor location; 2.88 times higher at the 900 meter receptor location; and 3.97 times higher at the 1,200 meter location. Staging area fires (outside) in the previous DSA were modeled as buoyant plumes based on various assumed fire sizes, consistent with provisions of DOE-STD When the new ground level release x/Q is compared to these lofted plume x/Q values for fire sizes up to 10 MW, the previous DSA calculated x/Q at the touchdown location of the maximum receptor was increased by a factor of 60 to 80, depending on the site boundary distance being compared (i.e., 900 meters or meters). This means that consequences for all hazard scenarios and accidents in the new DSA were increased according to the requisite increase in x/Q.

Impact… Our DOE review team evaluated the associated assumptions, methodology, and results. This document was also reviewed by the DOE Headquarters Chief of Nuclear Safety and shared with the Defense Nuclear Facilities Safety Board and determined that the revised site atmospheric dispersion model was compliant with Appendix A, of DOE-STD , CN3. Additionally, the newly calculated x/Q values have several inherent conservative assumptions relative to the previous DSA, including:  Modeling of ground-level releases  Default surface roughness length of 3 cm versus previous values of 40 cm  Use of the shortest distance for all 16 sectors, and  Use of a dry deposition velocity value of zero rather than the previous assumed value of 1 cm/s The DOE review team concurred with the new conservative methodology.

Changes in Hazard and Accident Scenarios Several factors resulted in significant changes to the hazard and accident analysis First, atmospheric dispersion analysis methodology changes resulted in an increase in accident consequences reported for events in the PHA tables and the accident analysis. This led to additional events being selected and modeled in the Accident Analysis. As consequences were increased, it also led to more detailed analysis in some cases (e.g., seismic, aircraft crash, various vehicle pool fires).

Changes in Hazard and Accident Scenarios Second, other new events were also modeled based on the incorporation and evaluation of four other new activities that came about as a result of our site’s increased mission and the resultant new conditions. This included consideration of a new suite of accidents. Based on these collective factors, the number of hazard scenarios identified in the PHA table was increased. As a result, the bounding and representative PHA events selected as accident scenarios and further modeled in the accident analysis was increased from 21 events to 40.

Changes in Hazard and Accident Scenarios As a result of increased consequences driven by changes in atmospheric dispersion methodology and other factors, the safety SSCs [Structures, Systems, and Components] and SACs [Specific Administrative Controls] were modified. Two SC [Safety Class] SSCs and seven SS [Safety Significant] safety SSCs were added in the DSA revision, while three other existing SS SSCs were removed. None of these SSCs involved active systems. In the previous DSA, there were 14 Specific Administrative Controls involving inventory limits in various areas of the facility. This number was expanded to 21 SACs in the DSA revision, as staging areas were re- designated with new boundaries and MAR limits in many areas were reduced to offset the increased consequences of the new atmospheric dispersion methodology.

Result  Certain waste transportation containers are now Safety Class.  Vehicle Impact Barriers are now required in areas to protect waste.  Liquid impediments had to be installed around various areas.  Waste staging building construction became credited.  The above-grade nature of some buildings became credited as not allowing fuel to run into the building where the waste is stored.  Various facility/ building MAR [Material-At-Risk] limits were reduced so that no one single fire would involve too much waste.  Vehicle Spotters and Fuel Attendants (think “escorts”) are required during movement of waste in certain areas.  Credit was taken for various ground/asphalt slopes, grades, and drainage around the site so that fuel cannot run into buildings storing waste.  Various specific waste container design criteria became credited.  Various waste staging area configurations became credited.

Result Various new Specific Administrative Controls (SACs) were required including:  New lower inventory limits were assigned to certain facilities.  Some waste containers now have to be overpacked in secondary containers.  No internal combustion-type vehicles /forklifts can be used to transport waste: only electric forklifts or manual-type, i.e., pallet jacks.  Fuel (greater than a specific quantity) cannot be present within 75 feet of waste being transported. This required traffic reconfiguration controls, use of additional boundaries such as gates, chains, and posting of new signage.  Establishment of new “fuel exclusion zones”.  Crane use restrictions near waste.  More restrictive container stacking limitations were established.  Concrete Jersey Barriers are now required around certain areas.

Implementation of These Controls Involved:  Site physical configuration modifications.  Over 50 operational and administrative documents being revised.  Conduct of an internal Management Self-Assessment (MSA) and Implementation Verification Review (IVR), and DOE-witnessed practice evolutions using the new controls, documents, and configurations.  Cooperative efforts with other contractors at adjacent sites.  Minor impacts to adjacent sites’ safety basis documents.  Training Program updates and rewrites.  Extensive training classes and practice evolutions.

Implementation of These Controls Involved: By far, the most significant efforts as a result of the new release criteria were:  Updating the safety basis  Rewriting over 50 procedures and other documents  Purchasing and installing the additional equipment (vehicle barriers, etc.)  Developing and presenting to all employees training on the new controls.

 The DOE review team evaluated the TSRs and determined that:  TSRs were consistent with the set of newly identified controls identified in the DSA.  Affected sections of the TSR were appropriately updated as needed.  Overall, the team concluded that definitions were complete and appropriate to support controls in other sections of the TSR.  Minimum staffing was modified as needed to implement new SACs.  SACs were updated with sufficient clarity to support proper implementation.  Bases were provided and were complete for each SAC to facilitate proper implementation.  Design Features captured the appropriate performance criteria derived in the DSA.  Interfaces with other contractor TSRs were consistent with that derived in the DSA and ensure compliance with new site waste staging restrictions and planned operations.  The DSA incorporates the appropriate changes associated with new dispersion methodology and brings closure to outstanding actions related to Safety Bulletin No , Accident Analysis Parameter Update.

THANK YOU OEC …. for the opportunity to present this information..  We have been very privileged to be among the leaders in this safety basis upgrade effort.  Through a significant training effort our site personnel have embraced the need for the upgrades.  Equally important, the DOE and project management have dedicated the resources we needed to accomplish this large and challenging initiative.