Evaluation and Measurements of Radioactive Air Emission and Off-Site Doses at SLAC Page: 2 of 8

                                
Evaluation:

SLAC uses CAP88-PC Version 2 [2] to calculate potential effective dose equivalent (EDE) to
MEIs and to the population from the estimated airborne radioactivity released by SLAC.
The potential doses to the MEI and public population are calculated as follows:
1) Saturation activity is calculated using a conservative beam loss on an optimum target,
e.g., from the yield values (Ci/W per meter of air path) in the IAEA Report 188 [1] and a
reasonable air path for each release point of a facility. SLAC has more than 10 facilities
and each facility may have more than one release point. In some cases, Monte Carlo
calculations (e.g., using FLUKA, MARS or MCNPX codes) by simulating actual
beam-target-housing geometry can be performed to obtain more accurate production.
2) Accelerator operational scenarios (length of operation per year and annual beam losses)
and reasonable air exchange rates for accelerator housing are used to estimate the total
radioactivity produced and release per year.
3) For each of the release points, the number of times during the year that potentially
activated air associated with the release point is vented to the atmosphere is determined.
If the air volume is essentially sealed from the atmosphere during normal operations, then
the number of releases is conservatively assumed to be 1 air change per day to take into
account any building ventilation leakages. The total volume of contained air is assumed
to be released per each air exchange. In those cases where the potentially activated air
isn't sealed from the atmosphere, the number of releases is calculated based on the rate of
air changes (from actual measurements or design specifications) per unit time for the
volume of interest.
4) The location of MEI (where off-site public currently resides) that is relevant to each air
release point within SLAC is then determined. There are a total of more than 10 MEI
locations.
5) Based on the annual airborne radioactivity release, the doses to the MEI and the
collective doses to the population up to 80-km from SLAC are calculated using the EPA-
approved atmospheric dispersion and radiation dose calculation computer code, CAP88.
The CAP88 modeling program calculates the average off-site radiation dose to
individuals at specified distances and directions from the SLAC facilities, and
collectively to individuals within each population segment around the SLAC facilities.
6) The Bay Area meteorological data provided for San Francisco Airport (SFO) and the
CY2000 census population distribution are used in the calculations, while default
agricultural values are used. CAP88 also requires information on stack height and
diameter. SLAC conservatively specifies that all releases of airborne radioactivity at
SLAC take place from ground-level points, i.e., from stacks with heights and diameters
of 0 meters.
Finally, the maximum MEI dose and the collective dose to public population are then reported in
the annual NESHAPs. In CY2011, the resulting dose to the MEI was calculated to be