Facility Vulnerability with VISAC |
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VISAC has many capabilities and is used in three different ways.
VISAC currently can be run under the Defense Threat Reduction Agency’s Hazard Prediction and Assessment Capability (HPAC) code. VISAC is launched by HPAC’s nuclear facility module (NFAC) and returns a time dependent source term to HPAC for calculation of the transport and deposition of the radionuclides.
VISAC can also be used to start an MBLM run for calculation of dispersion material involved in a fire.Running projects is the real emphasis behind VISAC - to find out what will happen to a facility when subjected to various types of accidents/incidents. A VISAC project consists of a series of incidents/accidents against a given facility. Incidents can be combined in any order or can happen at the same time. Each of these incidents is just a different way of damaging the critical components of the logic model. The five types of incidents are:
Quick Blast - user selects a location inside or outside the plant and then chooses a charge size and type. For basic models, buildings are damaged. For detailed models, critical components are given fractional damage probabilities. Three types of blast models are available.
Component Damage - individual components are specified and assigned failure probabilities directly by the user. For basic models, individual buildings are assigned these damage probabilities.
Region Damage - facility components within a given area of the plant are completely damaged. User selects the building, the floor of the building, and the size of the region through a graphical user interface.
Quick Blast from Grids - damages components using pre-run Quick Blast calculations. Thousands of such Quick Blast runs are supplied with VISAC for each library plant. User can select an attack based on his desired results. The user can even add to the list of pre-calculated grid points for future use.
Accident - a typical accident that the plant could experience (fails upper level gates in the logic model). User selects an accident from a list of defined accidents.
VISAC calculates the fault trees and event trees for each incident using the cumulative damage to the components. The analysis that VISAC reports consists of one or more aspects - things such as core damage to a reactor, facility kill, material release from the plant, etc. Each of these aspects is described in terms of the consequences listed for the event trees. VISAC is very general, so that users can add fault trees and event trees to model any desired aspect of the plant.
Oak Ridge National Laboratory, 2004