Facility Vulnerability with VISAC
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Hazmat Icon VISAC under HPAC (NFAC)

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. NFAC is being developed by the Oak Ridge National Laboratory.

VISAC Icon Installation of VISAC

When VISAC is installed onto a system that already has HPAC 4.03 or higher, VISAC can be used to calculate nuclear power plant releases for an NFAC (Nuclear Facility) incident. Early versions of HPAC cannot make use of VISAC directly. HPAC must be installed before VISAC is installed.

Hazmat Icon VISAC/NFAC Mappings

In order for NFAC and VISAC to "talk" to each other, a mapping must be made from the NFAC facilities of interest to the VISAC facilities. This can be done using VISAC and selecting the menu 'System', option 'Edit NFAC Associations'.

A window will be launched that shows all of the current mappings. If the NFAC facility you are interested in does not appear on the list, you can create a new mapping. Simply select an NFAC plant (by choosing the country, then the reactor) and a VISAC facility model then select the "Make Association" button. Not every nuclear power plant in the world is modeled by VISAC, so you may have to pick a VISAC facility that is similar in design. A dialog box will then ask whether or not this is an exact match and allow you to enter in a short comment about how well the VISAC facility models the NFAC plant. The match can be specified as either "exact" or just "close".

WARNING: Since VISAC has the capability of calculating the effects of blast damage, mapping a real facility in NFAC to a VISAC facility will make VISAC a classified program. If you intend to run VISAC under HPAC for real facilities (as opposed to generic, non-existent plants), you should only do this on computer systems that have been certified to hold "CLASSIFIED - NATIONAL SECURITY INFORMATION" data.

New Facilities

If the VISAC library does not contain an appropriate plant for the NFAC facility you wish to run HPAC/VISAC for, a new VISAC facility can be created. Simply start VISAC and use it as described in Create/Edit Facilities. The facility will be stored in the UserFac directory of VISAC. This new facility can then be mapped to the NFAC plant just as any other VISAC facility from the VISAC library could have been.

The NFAC module of HPAC may also have a shortcut button to launch VISAC in New Facility Mode, which will allow the user to create the new plant and make the NFAC mapping, but will not allow projects to be run. Most likely, this will not happen so if the user wishes to create or edit VISAC facilities, he will have to do so by running VISAC by itself.

Hazmat Icon Running an NFAC Incident

Inside an NFAC incident, first you will choose a reactor. There will be a note as to whether or not a VISAC facility has been mapped to this NFAC plant. If there is a valid VISAC model, under the 'What' tab, select 'Technical Analysis' for the incident type, then select the 'Define Incident' button. In the 'Select Source Term' dialog box will appear with the following choices for the source term:

The 'VISAC' choice will only be enabled if the NFAC reactor you chose has an associated VISAC facility.

Select 'VISAC' from the list and then select 'Next'. VISAC will be launched in single-project mode. The user will only be allowed to add/edit/delete incidents for the project that is automatically started. The user will not be able to edit facilities models. When the user is done defining all of the VISAC incidents and is ready to calculate the final release, select the VISAC menu 'System' and the option 'COMMIT'.

Hazmat Icon Choose Release

After finishing the VISAC project and committing it, a new window will be displayed asking the user to select which release to send back to NFAC. VISAC is a probabilistic code - it calculates what the probabilities are for a variety of outcomes. NFAC is a deterministic code - it calculates what happens for one given release. So, NFAC can only run one release. The user must pick either one of the possible VISAC releases or pick a probability-weighted combination of all possible releases.

The final probabilities of all of your VISAC incidents will be shown, for each aspect that has a consequence that leads to a release (and has a release file).

If there are multiple aspects in the VISAC models, the user must choose which release to use for each aspect. The final release will then be the sum of the releases for each aspect. This may appear odd in NFAC, since some release percentages will add up to greater than 100%.

The "Choose Release" window has the following steps:

  1. Select the Outcome - choose one for each aspect.
  2. Calculate the Final Release - a simple push of the button
  3. View the Results (Optional) - User can view plots of release rates or cumulative release amounts for each of 12 MELCOR groups of fission products.
  4. Return the release to NFAC - simply push the "Submit" button.

The release information will then be transferred back to NFAC.

Oak Ridge National Laboratory, 2004

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