# Release of radionuclides to air

This chapter summarizes the Phase III effort to derive a detailed source
term for radionuclides released into the air from Savannah River Site
(SRS) facilities. These radionuclides and the annual quantities released
are listed in [Appendix
B](../Appendix_B_ready%20for%20CDC%20031405.doc).

CDC previously sponsored Phase I and II of the SRS Dose Reconstruction
Project. During Phase I, records necessary for the project were
assembled, including facility release records, monthly and weekly
reports, laboratory notes, research papers, and personnel interviews.
During Phase II, radionuclide and chemical releases were estimated using
the records obtained during Phase I. The Phase II study considered
uncertainties in the SRS reports of historical radionuclide release. For
some isotopes of concern, particularly ^131^I, the Phase II study
provided estimates of release that are notably larger than those
historically reported by SRS (Phase II).

The Phase II study was used as the primary basis for the Phase III
source term. The Phase II estimates were refined for use in Phase III to
achieve greater source term resolution in time and space: i.e., releases
by year and location. This greater resolution was mandated by
geographically distributed scenarios and the concern with temporal
changes expressed in the scenario specifications. Other refinements
related to isotopic composition and chemical form provided for more
precise modeling of health effects.

## Development of Study Source Term

### Approach to Development of Study Source Term

As discussed in [Chapter
1](../Chapter_01_%20ready%20for%20CDC%20031405.doc), the scope of this
Phase III dose reconstruction study was intended to move beyond a
screening analysis to identify biologically significant radionuclides
and dose pathways. In order to produce a dose assessment with the
desired level of detail and confidence, a more refined source term than
was available from Phase II was sought. This refined source term for air
releases addressed specific requirements of the analysis, which included
the following broad themes.

To use the results of Phase II, including the identification of
significant radionuclides by a screening analysis and modification of
historical release data to account for instrumentation deficiencies;

To provide enough spatial definition to the source term so that the
geographical characteristics of the various scenarios (and their
proximity to particular sources on site) would be adequately
represented;

To provide enough temporal definition to the source term so that the
age-related characteristics of scenario members (as they interacted with
the time-varying releases from the SRS) would be adequately represented;

To provide enough detail about the chemical and isotopic characteristics
of the releases so that the dose and risk modeling (treatment of health
effects) would be more precise.

To enhance the completeness and/or accuracy of the source term.

Starting with the Phase II results, a sequence of steps was followed to
obtain as source term for Phase III with the desired qualities. Figure
5-1 outlines this sequence and briefly describes for each step the
requirement or need addressed, the additional input information used,
and the status of the data set representing the source term after each
modification. Each step is described in more detail in the following
sections.

![](media/image1.wmf){width="6.496527777777778in"
height="4.514583333333333in"}

Figure 5‑1 Development of Study Source Term

### Identify Important Radionuclides based on Phase II 

Phase II provided a number of results that became starting points for
Phase III, including: (1) Two screening analyses that established a
reduced set of radionuclides to consider in the dose reconstruction; and
(2) Detailed source terms for these radionuclides, with varying degrees
of spatial definition. These two aspects are summarized in the following
sections.

#### Use Phase II Results (Step 1)

Phase II, Screening Level 1, identified twelve groups of key
radionuclides released to air; Screening Level 2 further refined the
list to include only six radionuclides. To avoid possibly overlooking an
important contributor to the Phase III radiological assessment, all
twelve groups of key radionuclides identified in the Level 1 screening
were modeled in Phase III.

The Phase II screening assessment started with a master list of
radionuclides that had been released into the air from SRS facilities.
Preliminary estimates of their annual average release rates were also
made. But because this list was too large for efficient analysis, a
screening assessment was performed to identify a smaller list of key
radionuclides that were the dominant contributors to radiation dose and
risk (Phase II). This screening assessment was performed using a
two-step method recommended by the National Council on Radiation
Protection and Measurements (NCRP) for prospective evaluation of a new
facility. The method featured (1) a screening considering the summation
of six possible exposure pathways, and (2) a screening considering each
of the exposure pathways plus the sum total of all six pathways (1),
(2).

In both screening steps significant simplifications included:

-   releases were averaged over 36 years (from 1954 to 1989)

-   concentrations at the point of release were used, rather than
    concentrations plausibly at the locations of individuals

-   standard human behavior patterns \-- e.g., consumption rates of
    foods \-- were assumed; and

-   adult rather than age-dependent dose conversion factors were used
    (Phase II).

For these and other reasons, the screening values thus calculated were
not plausible representations of doses to actual humans. Rather, the
screening values were highly conservative estimates meant only to
identify those radionuclides that should be considered in further
analyses.[^1]

For Level 1, a total screening value was calculated representing the sum
of all screening values calculated for each radionuclide. Then those
radionuclides were identified that had screening values contributing at
least 0.1% of the total screening value. Using a cut-off of 0.1% of the
total estimated dose, the initial list of radionuclides was reduced to
twelve. These twelve key radionuclides together accounted for more than
99% of the total screening value (Phase II). The radionuclides thus
identified in the Level 1 of the screening assessments for air release
are listed in Table 5-2. Many of the radionuclides are actually groups
of aggregated isotopes such as combined ^239^Pu and ^240^Pu.

Table 5‑2 Radionuclide Rank from Phase II Level 1 Screening

+-----------------+----------------------------------------------------+
| Radionuclide    | Percent of Total                                   |
|                 |                                                    |
|                 | Screening Value (%)                                |
+-----------------+----------------------------------------------------+
| ^131^I          | 50.6                                               |
+-----------------+----------------------------------------------------+
| ^3^H            | 33.7                                               |
+-----------------+----------------------------------------------------+
| ^41^Ar          | 7.0                                                |
+-----------------+----------------------------------------------------+
| ^239,\ 240^Pu   | 2.6                                                |
+-----------------+----------------------------------------------------+
| ^129^I          | 2.3                                                |
+-----------------+----------------------------------------------------+
| ^103,106^Ru     | 1.1                                                |
+-----------------+----------------------------------------------------+
| ^238^Pu         | 0.7                                                |
+-----------------+----------------------------------------------------+
| ^14^C           | 0.6                                                |
+-----------------+----------------------------------------------------+
| ^137^Cs         | 0.6                                                |
+-----------------+----------------------------------------------------+
| Uranium^\*^     | 0.3                                                |
+-----------------+----------------------------------------------------+
| ^89,90^Sr       | 0.2                                                |
+-----------------+----------------------------------------------------+
| ^241^Am         | 0.1                                                |
+-----------------+----------------------------------------------------+
| Total           | 99.8                                               |
+-----------------+----------------------------------------------------+
| ^\*^Screened in |                                                    |
| Phase II as     |                                                    |
| combined ^235^U |                                                    |
| and ^238^U.     |                                                    |
+-----------------+----------------------------------------------------+

This is the starting list of important radionuclides for Phase III.

#### Phase II Estimates of Radionuclide Release

Phase II provided estimates as annual averages over 36 years of site
operation for all twelve groups of key radionuclides identified in Level
1 of the screening analysis (see Table 5-3). These averages spanned a
period from 1954 through 1989. Annual release estimates were provided
for all twelve radionuclide groups except ^14^C and ^241^Am for which
36-year averages were provided. More detailed estimates were provided on
an annual basis for tritium; ^89,90^Sr; ^129^I; ^131^I; ^137^Cs;
uranium; ^238^Pu; and ^239,\ 240^Pu. The level of detail varied
depending on the isotope. In some cases, for example, releases from
specific SRS facilities (such as specific nuclear reactors) were
identified, and in other cases, releases from SRS Areas or groups of
facilities (such as groups of seepage basins) were identified.

Table 5‑3 Radionuclides Reported in Phase II Study by Facility and Year

+--------------+-------------------------+----------------------------+
| Radionuclide | Annual Estimates        | Estimates Provided as a    |
|              | Provided for a Specific | 36-Year Average Yearly     |
| Group        | Facility or a Group of  | Release from the Entire    |
|              | Facilities?             | Site?                      |
+--------------+-------------------------+----------------------------+
| ^3^H         | Annual                  | Yes                        |
+--------------+-------------------------+----------------------------+
| ^14^C        | Not available           | Yes                        |
+--------------+-------------------------+----------------------------+
| ^41^Ar       | Annual                  | Yes                        |
+--------------+-------------------------+----------------------------+
| ^89,\ 90^Sr  | Annual                  | Yes                        |
+--------------+-------------------------+----------------------------+
| ^103,106^Ru  | Annual                  | Yes                        |
+--------------+-------------------------+----------------------------+
| ^129^I       | Annual                  | Yes                        |
+--------------+-------------------------+----------------------------+
| ^131^I       | Annual                  | Yes                        |
+--------------+-------------------------+----------------------------+
| ^137^Cs      | Annual                  | Yes                        |
+--------------+-------------------------+----------------------------+
| Uranium      | Annual                  | Yes (reported as           |
|              |                         | ^235,238^U)                |
+--------------+-------------------------+----------------------------+
| ^238^Pu      | Annual                  | Yes                        |
+--------------+-------------------------+----------------------------+
| ^239^Pu      | Annual                  | Yes (reported as           |
|              |                         | ^239,240^Pu)               |
+--------------+-------------------------+----------------------------+
| ^241^Am      | Not available           | Yes                        |
+--------------+-------------------------+----------------------------+

###  {#section .unnumbered}

### Change Data Requirements to Better Model Health Effects (Step 2)

The initial list of important radionuclides resulting from the Phase II
Level 1 screening analysis was modified in several ways for use in Phase
III:

1.  Some groups of radionuclides were partitioned into separate
    isotopes. This was done to provide a more refined treatment of dose
    modeling. By treating isotopes individually, health effects
    coefficients specific to those isotopes could be used in the dose
    modeling; if isotopes were aggregated by element, as in the Phase II
    screening analyses, a single coefficient (related to the isotope
    with the greatest health effects) would characterize all the
    isotopes of the element, possibly greatly overestimating doses and
    risks. Table 5-4 shows 16 isotopes modeled.

2.  Because the releases of Ruthenium were relatively small, all
    releases were modeled as ^106^Ru.

3.  Uranium isotope ^234^U and ^236^U were added to account for
    production of these isotopes in the nuclear reactors.

4.  One radionuclide, ^240^Pu was dropped from consideration. The data
    upon which the Phase II estimates of releases were based did not
    list ^240^Pu releases separately, but always combined with other
    isotopes. Furthermore, the health effects coefficients for ^239^Pu
    and ^240^Pu are very close, so modeling ^240^Pu as ^239^Pu will have
    little effect on the dose estimates. Since there appeared to be no
    basis and no motivation for differentiating these two isotopes,
    separate consideration of ^240^Pu was dropped.

5.  It was considered appropriate to include as releases radioactivity
    measured as unidentified alpha or unidentified beta-gamma activity.
    Although the SRS had recorded releases of such material over the
    years of site operation, an explicit treatment in Phase II was not
    apparent. Therefore two additional categories were added for these
    types of releases. However, to provide bounding estimates of their
    health effects, the unidentified alpha activity was added to the
    releases for ^239^Pu and the unidentified beta-gamma activity was
    added to the releases for ^90^Sr. These two classes are added to
    Table 5-4 to indicate that these activities were compiled and
    tracked separately.

6.  At this point the need to refine the treatment of certain
    radionuclides by defining their chemical form was established. Two
    radionuclides: tritium and ^131^I can have substantially different
    behavior in the environment depending on their chemical form. The
    methods used to partition these radionuclides into different
    chemical forms are described in Section 5.1.8.2. Methods used to
    partition some elements into different isotopes are described in
    Section 5.1.8.1

Table 5-4 Modified List of Radionuclides Considered for Phase III\*

+----------------------------------+-----------------------------------+
| > ^241^Americium                 | > ^238,239^Plutonium†             |
+----------------------------------+-----------------------------------+
| > ^41^Argon                      | > ^89,90^Strontium‡               |
+----------------------------------+-----------------------------------+
| > ^14^Carbon                     | > ^234,235,236,238^Uranium        |
+----------------------------------+-----------------------------------+
| > ^137^Cesium                    | > ^106^Ruthenium                  |
+----------------------------------+-----------------------------------+
| > Tritium (^3^H)                 |                                   |
+----------------------------------+-----------------------------------+
| > ^129,131^Iodine                |                                   |
+----------------------------------+-----------------------------------+

\*Underlined radionuclides were added.

^†^Unidentified alpha-emitters were modeled as ^239^Pu

^‡^Unidentified beta-gamma emitters were modeled as ^90^Sr

### Encode Release Data from Cummins Report (Step 3) 

### The Phase III source term needed definition in space and time so the assessment of radiation doses and cancer risks would be able to reflect differences associated with the seven hypothetical exposure scenarios considered in Phase III. Enhanced spatial definition of the source term allowed the radiological assessment to model and to evaluate the importance of several facets of the Phase SRS dose reconstruction, including: {#the-phase-iii-source-term-needed-definition-in-space-and-time-so-the-assessment-of-radiation-doses-and-cancer-risks-would-be-able-to-reflect-differences-associated-with-the-seven-hypothetical-exposure-scenarios-considered-in-phase-iii.-enhanced-spatial-definition-of-the-source-term-allowed-the-radiological-assessment-to-model-and-to-evaluate-the-importance-of-several-facets-of-the-phase-srs-dose-reconstruction-including .unnumbered}

1.  Different mixtures of radionuclides dominated the releases from the
    major SRS discharge locations, and these locations are often
    separated by several miles.

2.  Radiation doses at different exposure locations specified by the
    scenarios depended on: (1) the quantities of particular
    radionuclides released into the air at the various SRS location
    and (2) direction-related meteorological conditions, such as the
    frequency that the wind blew in the direction of a particular
    exposure location. Several exposure locations are close to the
    release points, relative to the distances between some release
    points.

A more refined definition of the spatial distribution of releases allows
for a more precise estimate of doses compared to a source term with a
single assumed release point to represent all SRS release points.

Enhanced temporal definition of the source term \-- that is, specifying
the amount of release for each radionuclide for each year \-- allowed
the radiological assessment to model and to evaluate the importance of
several facets of the Phase III SRS dose reconstruction:

-   The behavior of the children in each hypothetical scenario changed
    significantly during their childhood; this included breathing rates,
    food ingestion rates, time spent indoors and outdoor;

-   The dose and risk factors for children were adjusted until they
    became adults;

-   The annual release rates of many key radionuclides changed
    considerably over 39 years; of special note were the early years of
    large releases (e.g., 1956).

The source term, the behaviors of the hypothetical receptors, and their
dose and risk characteristics all varied in time; by considering the
annual variation of the source term, the interaction of all these time
variations was considered. A source term that was expressed in terms of
an average over 39 years would not have allowed these important
variations to be adequately considered.

To provide the desired level of spatial and temporal definition in the
source term, historical release data (3), (4) was keyed into an
electronic data base. This data base described radionuclide releases by
isotope, facility, and year. All the data were fully cross-checked and
was subject to a thorough quality assurance program.

### Complete and Correct Data Set (Step 4)

In the initial stages of the Phase III source term data compilation, it
was observed that data were not available in the Phase II report for
annual release estimates for some radionuclides for the years 1954
through 1989 and for most radionuclides for the years 1990 through 1992.
For Phase III, refinements to the Phase II release estimates were made
to obtain a source term for all radionuclides: (1) on an annual basis;
(2) for all 39 years of the study; and (3) on the basis of major SRS
facilities.

For the years 1954 through 1989, when annual release estimates were
given in the Phase II report in sufficient detail, Phase II was used to
determine annual facility-group release rates. Otherwise, data gathered
from SRS references was used. For example, for ^14^C and ^241^Am, the
Phase II report only provided estimates for the entire site as averaged
over 36 years. For ^103,106^Ru, the electronic version of Phase II
provided a supplemental Excel file that listed annual release estimates
for the F- and H-Separations Areas, but not for reactors. Phase II
provided annual release data for ^41^Ar, but the data was not
proportioned among the five reactors that released this isotope.

To apportion release data among the different SRS facilities releasing
radionuclides into the air, the primary reference was (3). In some
cases, information in (3) and other references were given as combined
values for a group of facilities (e.g., reactors). For these cases, SRS
site release history was reviewed and the combined values were
apportioned among facilities in accordance with the processes in the
facilities that resulted in the airborne releases. See Section 5.1.8.1
and [Appendix R](../Appendix_R_Ready%20for%20CDC%20031405.doc) for
further information on how the release data was partitioned.

For the years 1990 through 1992, release estimates were not provided in
Phase II for most radionuclides Therefore, SRS environmental reports and
other environmental data (3), (4), (5), (6), (7), (8) were reviewed for
these three years, and the missing source terms were added when
information was available.

### Merge Data from Fifteen Facilities into One of Four Groups (Step 5)

Section 5.1.4 describes the motivation for refining the spatial
definition of the source term. At this point in the analysis, the source
term was defined in a data base by each radionuclide, year, and
facility. Fifteen separate facilities were considered to be independent
sources of air releases. The types of radionuclide releases from each of
these fifteen facilities are shown in Table 5-5.

Table 5‑5 Main Sources of Air Releases of Radionuclides at SRS

+-------------+---------------+--------+---------+--------+-----------+
| Facility    | Designation   | Pri    |         |        |           |
| Type        |               | ncipal |         |        |           |
|             |               | R      |         |        |           |
|             |               | adionu |         |        |           |
|             |               | clides |         |        |           |
|             |               | Re     |         |        |           |
|             |               | leased |         |        |           |
+=============+===============+========+=========+========+===========+
|             |               | T      | β-e     | α-em   | A         |
|             |               | ritium | mitters | itters | ctivation |
|             |               |        |         |        | Products  |
+-------------+---------------+--------+---------+--------+-----------+
| *           | C             | X      | X       |        | X         |
| *Reactors** |               |        |         |        |           |
+-------------+---------------+--------+---------+--------+-----------+
|             | K             | X      | X       |        | X         |
+-------------+---------------+--------+---------+--------+-----------+
|             | L             | X      | X       |        | X         |
+-------------+---------------+--------+---------+--------+-----------+
|             | P             | X      | X       |        | X         |
+-------------+---------------+--------+---------+--------+-----------+
|             | R             | X      |         |        | X         |
+-------------+---------------+--------+---------+--------+-----------+
| **          | F Canyon      | X\*    | X       | X      | X         |
| Separations |               |        |         |        |           |
| F           |               |        |         |        |           |
| acilities** |               |        |         |        |           |
+-------------+---------------+--------+---------+--------+-----------+
|             | H Canyon      | X\*    | X       | X      | X         |
+-------------+---------------+--------+---------+--------+-----------+
|             | H Tritium     | X\*    |         |        |           |
|             | Stack         |        |         |        |           |
+-------------+---------------+--------+---------+--------+-----------+
| **Waste     | All Reactors  | X      |         |        |           |
| F           | Seepage Basin |        |         |        |           |
| acilities** | E             |        |         |        |           |
|             | vaporation^†^ |        |         |        |           |
+-------------+---------------+--------+---------+--------+-----------+
|             | CMX-TNX       | X      |         |        |           |
+-------------+---------------+--------+---------+--------+-----------+
|             | D Area        | X      |         |        |           |
+-------------+---------------+--------+---------+--------+-----------+
|             | F & H Seepage | X      |         |        |           |
|             | Basin         |        |         |        |           |
|             | E             |        |         |        |           |
|             | vaporation^‡^ |        |         |        |           |
+-------------+---------------+--------+---------+--------+-----------+
| **Other     | A Area        | X      | X       | X      | X         |
| F           |               |        |         |        |           |
| acilities** |               |        |         |        |           |
+-------------+---------------+--------+---------+--------+-----------+
|             | M Area        | X      |         | X      |           |
+-------------+---------------+--------+---------+--------+-----------+
|             | SRL           | X^§^   | X^§^    | X^§^   |           |
+-------------+---------------+--------+---------+--------+-----------+
| ^           |               |        |         |        |           |
| \*^Releases |               |        |         |        |           |
| for these   |               |        |         |        |           |
| three       |               |        |         |        |           |
| facilities  |               |        |         |        |           |
| are         |               |        |         |        |           |
| combined in |               |        |         |        |           |
| available   |               |        |         |        |           |
| literature  |               |        |         |        |           |
| for         |               |        |         |        |           |
| security    |               |        |         |        |           |
| purposes.   |               |        |         |        |           |
|             |               |        |         |        |           |
| ^†^The "All |               |        |         |        |           |
| Reactors    |               |        |         |        |           |
| Seepage     |               |        |         |        |           |
| Basin       |               |        |         |        |           |
| E           |               |        |         |        |           |
| vaporation" |               |        |         |        |           |
| is already  |               |        |         |        |           |
| a virtual   |               |        |         |        |           |
| source.     |               |        |         |        |           |
| Each        |               |        |         |        |           |
| reactor had |               |        |         |        |           |
| its own     |               |        |         |        |           |
| seepage     |               |        |         |        |           |
| basin. The  |               |        |         |        |           |
| location of |               |        |         |        |           |
| this        |               |        |         |        |           |
| virtual     |               |        |         |        |           |
| source was  |               |        |         |        |           |
| chosen to   |               |        |         |        |           |
| be close to |               |        |         |        |           |
| the         |               |        |         |        |           |
| centroid of |               |        |         |        |           |
| the         |               |        |         |        |           |
| locations   |               |        |         |        |           |
| of the      |               |        |         |        |           |
| reactors.   |               |        |         |        |           |
|             |               |        |         |        |           |
| ^‡^The "F & |               |        |         |        |           |
| H Seepage   |               |        |         |        |           |
| Basin       |               |        |         |        |           |
| E           |               |        |         |        |           |
| vaporation" |               |        |         |        |           |
| is already  |               |        |         |        |           |
| a virtual   |               |        |         |        |           |
| source, but |               |        |         |        |           |
| the seepage |               |        |         |        |           |
| basins for  |               |        |         |        |           |
| F- and      |               |        |         |        |           |
| H-Areas are |               |        |         |        |           |
| only about  |               |        |         |        |           |
| one mile    |               |        |         |        |           |
| apart.      |               |        |         |        |           |
|             |               |        |         |        |           |
| ^§^Releases |               |        |         |        |           |
| from the    |               |        |         |        |           |
| SRL may     |               |        |         |        |           |
| have been   |               |        |         |        |           |
| included in |               |        |         |        |           |
| the A-Area  |               |        |         |        |           |
| releases    |               |        |         |        |           |
| for at      |               |        |         |        |           |
| least some  |               |        |         |        |           |
| years.      |               |        |         |        |           |
+-------------+---------------+--------+---------+--------+-----------+

Although greater spatial definition was desired, these 15 major sources,
as well as several minor sources were too numerous for efficient
analysis considering the number of radionuclides, exposure scenarios,
and exposure pathways to be addressed and the sensitivity and
uncertainty analyses to be performed.

Although spatial simplification of the source term was desirable, any
such simplification needed to preserve the inherent geographical
variation of the air source term and a suitable level of precision in
the dose calculations. Therefore, a two part analysis was performed:

1.  Different combinations of individual sources into groups (virtual
    sources) were evaluated to determine a representative set of
    "virtual" sources. Different numbers of virtual sources were
    evaluated, ultimately settling on four groups of sources (as shown
    in Table 5-6).

2.  A careful evaluation was performed to assure that representation of
    a group of sources by a single virtual source preserved a suitable
    precision in estimating concentrations; as discussed in more detail
    below, the representation of a group of sources by these virtual
    sources was deemed to be sufficiently precise.

Consider a single real source on the SRS, e.g., Reactor L. Since a
static, 20-year average meteorology was assumed, a given release from
this single source will produce a certain concentration at each of the
nine offsite exposure locations of interest, e.g., Girard, GA. First, a
unit release rate (e.g., one Ci/y) was assumed for each of the 15 real
sources in turn; the concentrations that the GENII code estimated were
produced by these unit releases were considered to be the "correct"
value. Second, a unit release rate was assumed for each of the 4 virtual
sources in turn; the concentrations that the GENII code estimated were
produced by these releases were considered to be the "approximate" value
for the sources in each group. Third, the "correct" and "approximate"
releases were compared; the result was an agreement within 18% between
the "correct" and "approximate" values for all sources except one, which
was within 27%. This is considered to be excellent agreement for a very
stringent comparison, given that for most groups the individual sources
do not operate alone. Also recall that the "correct" value is based on
modeling that incorporates many assumptions and uncertainties. For
example, release rates were assumed to be constant over any given year,
when in actuality acute releases caused substantial deviations from this
assumption. When the concentrations induced by the virtual sources were
compared to the concentration induced by a group of sources of equal
strength (e.g., for Group 1 each of the three real sources was assumed
to have a release rate of 1/3 Ci/y, while the virtual source had a
release rate of 1 Ci/y), the comparisons were even closer; the results
agreed within 11%.

This simplification of sources is summarized in [Chapter
6](../Chapter_06_ready%20for%20CDC%20031405.doc) and addressed in detail
in [Appendix A](../Appendix_A%20-%20ready%20for%20CDC%20031405.doc). The
source groupings developed as a result of this analysis are shown in
Table 5-6 and Figure 5-2..

Table 5‑6 Groupings for Four Virtual Sources

  ------------- ---------------------------------------------------------
  Groups        Facilities in Group

  Group 1       A-Area, M-Area, SRL

  Group 2       F-Canyon, H-Canyon, H Tritium Stack, F&H Seepage Basins

  Group 3       C-Reactor K-Reactor, L-Reactor, Reactor Seepage Basin
                release attributable to C-, K-, and L-Reactors, D-Area,
                CMX-TNX

  Group 4       P-Reactor. R-Reactor, Reactor Seepage Basin release
                attributable to P- and R-Reactors
  ------------- ---------------------------------------------------------

The Phase III source term for releases to air, compiled up to this point
for each facility by year and radionuclide, was aggregated based on
these four virtual release points.

![](media/image2.wmf){width="4.875in" height="5.777777777777778in"}

**Figure 5-2 Virtual Source Locations**

### Adjust Data in Accordance With Modifications Made Phase II (Step 6)

Particularly for ^131^I, uranium, plutonium, and tritium the Phase II
estimates of radionuclide release were larger than those historically
reported by SRS (3), (4). Phase II increased the released quantities to
account for deficiencies in instrumentation and recording releases.
Since historical data was used to provide a greater degree of spatial
and temporal definition to the source term, these historical data needed
to be modified for use in Phase III to account for these adjustments
introduced in the Phase II report.

In Phase II, additional detailed analyses of historical estimates of
release were performed for iodine, plutonium, uranium and tritium. These
Phase II analyses compensated for several factors that may have caused
the reported site releases to be smaller than the releases that actually
occurred, including the use of different samplers over time, sampler
collection efficiencies, errors associated with counting equipment, and
the chemical forms of the released radionuclides. Based on a model of
the transmission of effluents in sampling lines and Monte Carlo
analyses, Phase II provided revised estimates for iodine, uranium, and
plutonium that were generally larger from those reported over the years
by SRS (Phase II). Of particular note was ^131^I: The Phase II estimates
were significantly larger than releases historically reported by
SRS.[^2] Phase II also observed that releases for the early years of
operation (through about 1961) were more uncertain than later releases.
Phase II developed probability distributions describing the releases for
key radionuclides for each year modeled in Phase II. These probability
distributions showed more spread (larger ratios of standard deviations
to the mean value) in earlier years than in later years.

In order to incorporate the release values adjusted for uncertainties
that were developed in Phase II, the adjusted values of release by year
and by facility were imported from spreadsheets attached to the Phase II
report (Phase 2, Directory titled Supporting_Files). Adjusted data were
used for plutonium, uranium, and iodine releases. Adjusted data were not
used for tritium releases in Phase III.

### Partition Data to Account for the Mix of Isotope and Chemical Form (Step 7)

In some cases, the radionuclide releases studied in Phase II were
compiled on a combined basis, e.g. all isotopes of uranium, all chemical
forms of tritium. In order to enhance modeling of the health effects of
air releases from the SRS in Phase III, some of these combined releases
were partitioned further into specific isotopes or chemical forms. The
following sections describe how certain combined releases were separated
further into specific isotopes or specific chemical forms.

#### Isotopic Partitioning

Several radioactive constituents that were reported in the Phase II
study and in SRS environmental reports were apportioned from the
combined activities stated by these sources into release estimates for
individual isotopes. For example, the release estimates provided in the
Phase II study for ^89^Sr and ^90^Sr combined, were partitioned into
release estimates for each of these isotopes by considering the nuclear
processes occurring at the facilities that generated these isotopes.
These constituents included:

-   ^89^Sr, ^90^Sr

-   ^134^Cs, ^137^Cs

-   Uranium

-   Plutonium

-   Unidentified alpha

-   Unidentified beta + gamma

Table 5-7 summarizes the sixteen radionuclides that were determined from
this partitioning process for release to air. Source terms for Phase III
were developed for each of these sixteen radionuclides. Table 5-8
summarizes how the total activity of each constituent was partitioned
into constituent isotopes for each SRS site area. Additional technical
information and general assumptions for the partitioning process are in
[Appendix C](../Appendix_C%20-Ready%20for%20CDC_031405.doc).

Table 5‑7 Radionuclides Considered in Phase III Compared to Those Cited
in Phase II

  -------------------------------- --------------------------------------
  Radionuclides Identified in Step Radionuclides Considered in Phase III
  1 of Phase II Screening          Air Release Assessments

  ^3^H                             ^3^H

  ^14^C                            ^14^C

  ^41^Ar                           ^41^Ar

  ^89,\ 90^Sr                      ^89^Sr & ^90^Sr

  ^103,106^Ru                      ^106^Ru

  ^129^I                           ^129^I

  ^131^I                           ^131^I

  ^134,137^Cs                      ^137^Cs

  Uranium                          ^234^U, ^235^U, ^236^U, & ^238^U

  ^238^Pu                          ^238^Pu

  ^239,240^Pu                      ^239^Pu

  ^241^Am                          ^241^Am
  -------------------------------- --------------------------------------

Table 5‑8 Summary of Assumed Isotopic Distributions for Air Release

  -----------------------------------------------------------------------
  Constituent           SRS Area      Isotopic Distribution by Activity
  --------------------- ------------- -----------------------------------
  ^89,\ 90^Sr           F&H Areas     75% ^89^Sr; 25% ^90^Sr

                        A Area        100% ^90^Sr

                        D Area        100% ^90^Sr

                        Central Shops 100% ^90^Sr

  ^134,\ 137^Cs         D Area        100% ^137^Cs

  Uranium               Reactor Areas 91.73% ^234^U; 1.79% ^235^U; 6.45%
                                      ^236^U; 0.03% ^238^U

                        F Area        1.27% ^235^U; 98.73% ^238^U

                        H Area        91.73% ^234^U; 1.79% ^235^U; 6.45%
                                      ^236^U; 0.03% ^238^U

                        M Area        49.49% ^234^U; 2.25% ^235^U; 48.26%
                                      ^238^U

                        A Area (SRL)  91.44% ^234^U; 1.8% ^235^U; 6.4%
                                      ^236^U; 0.36% ^238^U

                        CMX/TNX       49.49% ^234^U; 2.25% ^235^U; 48.26%
                                      ^238^U

                        D Area        91.73% ^234^U; 1.79% ^235^U; 6.45%
                                      ^236^U; 0.03% ^238^U

  Total Plutonium       All Areas     100% ^239^Pu

  Unidentified Alpha    All Areas     100% ^239^Pu

  Unidentified          All Areas     100% ^90^Sr
  Beta-gamma                          
  -----------------------------------------------------------------------

Radionuclides identified as ^89,90^Sr in the Phase II report were
apportioned into ^89^Sr and ^90^Sr. For most facilities, the activity
was assumed to be ^90^Sr. For the separations area, the activity was
apportioned into 75% ^89^Sr and 25% ^90^Sr based on Cummins et al (3).

Radionuclides identified as ^134,137^Cs in the Phase II report were
assumed to all be ^137^Cs because the fission-yield of ^134^Cs in
nuclear reactors was determined to be very small in comparison with
^137^Cs (see [Appendix
C](../Appendix_C%20-Ready%20for%20CDC_031405.doc)).

Radionuclides identified as ^103,106^Ru in the Phase II report were
assumed to all be ^106^Ru. This assumption was consistent with the
screening analysis used in the Phase II report to identify key
radionuclides.[^3] This assumption will conservatively estimate doses
from ingestion and inhalation.

Radionuclides identified as uranium in Phase II were apportioned into
four uranium isotopes: ^234^U, ^235^U, ^236^U, and ^238^U. The Phase II
report only considered the uranium isotopes ^235^U and ^238^U when it
performed its screening analysis. For Phase III, however, ^234^U and
^236^U were included. ^234^U contributes much of the activity of natural
or slightly enriched uranium. ^236^U is produced from neutron
bombardment in nuclear reactors, and would have been present in uranium
released from the separations areas, among other areas at SRS.

Radionuclides identified as ^239,240^Pu in the Phase II report were
assumed to all be ^239^Pu. The fractional activity of ^240^Pu for
weapons grade plutonium was determined to be small compared to that for
^239^Pu (see [Appendix
C](../Appendix_C%20-Ready%20for%20CDC_031405.doc)). Radioactive releases
at SRS were often reported as unidentified alpha activity, unidentified
beta-gamma activity, or undifferentiated plutonium activity. In most
cases, the unidentified constituents would have been a combination of
several isotopes. The fractions of total activity that individual
isotopes represented probably varied from one release event to another.
For simplicity, unidentified alpha activity was conservatively assumed
to be ^239^Pu because it was one of the more prevalent isotopes created
at SRS, and because it is more radiotoxic than uranium isotopes for many
of the exposure pathways. Other transuranic isotopes that have been
produced and used at the SRS (such as ^237^Neptunium, ^244^Curium and
^252^Californium) may have contributed to unidentified alpha activity,
but these isotopes were produced primarily during brief periods.

Unidentified beta-gamma activity was modeled as ^90^Sr, which was
commonly reported in environmental release reports at SRS. ^90^Strontium
has a half-life that is sufficiently long (28 years) that it may persist
in the environment for many years after release. On the other hand, the
health effects of ^90^Sr will exceed those of other radionuclides for
important dose pathways (e.g., doses per unit of activity from
inhalation and ingestion will be greater for ^90^Sr than for ^60^Co).

Undifferentiated plutonium (occasionally found in SRS reports) was
assumed to be ^239^Pu as this was the main plutonium isotope produced at
the site.

#### Chemical Forms of Radionuclides

For the Phase III study two types of releases were partitioned according
to their chemical form: tritium and iodine. Section 5.1.8.2.1 discusses
Phase III assumptions about the chemical forms of tritium released to
air. Section 5.1.8.2.2 discusses Phase III assumptions about chemical
forms of iodine isotopes released to air.[^4]

##### **Tritium**

Tritium was one of the major nuclear materials produced at SRS. The
Phase II report identified two chemical forms of release: an elemental
form (usually HT) and an oxide form (usually tritiated water -- HTO).
Tritiated water poses a much greater radiological risk than in the
elemental form: (1) because water vapor is much more easily taken into
the body than elemental tritium and (2) because tritiated water and
water vapor readily enter into the food chain, while elemental tritium
does not.

From the Phase II data, it was assumed for Phase III that all tritium
released into the air from SRS was either in an elemental (HT) or oxide
(HTO) form. Most tritium releases occurred from the reactor areas and
from the tritium facilities located in the separation areas. Smaller
quantities of tritium were released from other areas such as D-Area.

**Reactor areas.** In other SRS reports and studies, tritium losses from
reactor areas were estimated to be 100% in the oxide form (10), (11),
(12). Westinghouse (13) has indicated that releases from reactors were
due to evaporation of tritiated water and virtually all evaporated waste
was released into the air through the reactor facility stacks. Balancing
this with other information,[^5] it was assumed that all tritium
released from the five reactors was in the oxide form.

Tritium was also released into the air from evaporation of water from
the reactor seepage basins. Tritium released from the reactor seepage
basins was assumed to be in the oxide form.

**Separations facilities.** In the SRS separations facilities, the
chemical form of the released tritium depended on the nature of the work
performed at the facilities. The chemical form of the released tritium
was determined by using information from Murphy (14) and the inadvertent
release and incident histories summarized in the Phase II report.
Specific information on the tritium release form was often provided for
acute and unplanned accidental releases, especially for incidents of
tritium release exceeding 700 curies. Each year, the activity from all
acute or unplanned releases having known chemical forms was subtracted
from the total tritium activity released for that year. The remaining
activity was assumed to be split evenly between elemental and oxide
forms, based on data from Murphy (14) suggesting that about 50% of the
tritium release was in an oxide form. Then the activity whose chemical
form was known from the acute or unplanned releases for that year was
appropriately added to the activity in each of the above splits.[^6]

Similar to the reactor area seepage basins, small quantities of tritium
were released into the air from evaporation of the separation area
seepage basins. The evaporated tritium was assumed to be in the oxide
form.

**Other SRS areas.** Small tritium releases have been documented in
Cummins et al from A Area, D Area, M Area, and CMX-TNX (3). These
releases were assumed to have been all in oxide forms.

##### **Iodine**

The fission processes in nuclear reactors were the primary sources of
radioiodine production at SRS. The chemistry of iodine in nuclear
facilities and the environment is complicated. The most reactive form of
iodine is elemental iodine (I~2~). This form of iodine has a relatively
high deposition rate. It is important for assessing exposures to the
thyroid through the food chain. Under favorable situations (e.g. the
existence of other reactive elements, and the presence of catalysts),
elemental iodine can combine with other elements and form less reactive
gases such as HI, HOI and IO~3,~ or react with organic compounds forming
even less reactive organic iodides like methyl iodide (CH~3~I). Iodine
existing as an organic molecule contributes to exposure by inhalation
but is relatively unimportant for food chain pathways. Radioiodine can
also associate with particles that can lower its reactivity. The gaseous
radioiodine compound can be absorbed by non-radioactive particulate
matter as well.

Two isotopes of iodine were considered in Phase III: ^131^I and ^129^I.
Annual ^131^I releases were monitored for the H- and F-Area separations
facilities, reactors, and other facilities, mainly SRL. Annual ^129^I
releases were monitored for only the separations areas.

The Phase II report addressed the chemical form of the released iodine.
Phase II release estimates for ^131^I from the F- and H-Separations
areas were apportioned between elemental iodine (I~2~) and organic
iodine (Phase II). Phase II did not similarly partition release
estimates for ^129^I from the separations areas, although one might
expect a similar distribution. For reactors, Phase II cited measurements
of iodine released at commercial pressurized water nuclear reactors by
Pelletier et al (15). From this reference, Phase II estimated that
"about 30% of the total would be elemental iodine and that the remainder
would be divided between less reactive inorganic forms (\~40% of total)
and organic iodides (\~30% of total)."[^7] For ^131^I releases from SRL,
it was suggested in Phase II (p. 4.2-27) that "most of the radioiodine
released from the shielded cells was probably in an elemental form"
(Phase II).

For Phase III, the released quantities of iodine into the air were split
between elemental and organic iodine in a manner consistent with the
information in Phase II and summarized in [Appendix
B](../Appendix_B_ready%20for%20CDC%20031405.doc). However, data indicate
that the chemical forms of released iodine change as the iodine is
transported through the air (16). Therefore, the computations in Phase
III for transport, dispersion, and deposition of iodine were performed
assuming that the iodine was a mixture of chemical forms -- i.e., 40%
particulate, 30% reactive gas (elemental), and 30% nonreactive gas
(organic).[^8] These fractions were built into the GENII code by its
creators based on their experience with modeling iodine releases (17).
The manual for the RATCHET[^9] computer code, which was used for the
thyroid dose reconstruction work for the Hanford Reservation, observes
the following regarding the transport and mid-air partitioning of
elemental iodine (16):

> *In the time that it took the iodine to travel 3200 meters (2 miles),
> about two-thirds of the iodine had changed form. Approximately
> one-third of the iodine was in organic species and the remaining third
> was associated with particulate material. The partitioning of iodine
> at 3200 in Ludwick's experiments is consistent with the results of the
> measurement of iodine in plumes from the stacks at the Hanford
> Site...with the partitioning of iodine in the plume following the
> Chernobyl reactor accident.*

### Compare Final Source Term to Phase II Level 1 (Step 8) 

To assure consistency between the Phase II release estimates and the
Phase III source term, the total release of each radionuclide over 39
years, as determined in Phase III, was compared with the 36-year total
release estimate used in Phase II for the screening assessment. This
comparison is shown in Table 5-9. The information herein cited for Phase
II was obtained from the Excel spreadsheets included with the Phase II
report. As discussed in greater detail in [Appendix
C.4](../Appendix_C%20-Ready%20for%20CDC_031405.doc), the source term
used for Phase III is generally consistent with Phase II. Some groups of
isotopes, however, deserve comment:

Table 5-9 Comparison of 39-Year Phase III Total Releases (Ci) to 36-Year
Phase II Releases Used for Phase II Screening Assessment (Ci)

  ----------------- ------------- ------------- -------------- ----------------- --------
  Radio-nuclide     Phase III     Phase II      Difference     Percent           Note
                    Total from    Total         (Phase III --  Difference (Phase 
                    All virtual                 Phase II)      III --Phase II) x 
                    Sources                                    100/Phase III     

  ^241^Am           5.88x10^-3^   0             5.88x10^-3^    \+ 100            X

  ^41^Ar            6.36x10^+6^   6.36x10^+6^   \- 1.00x10^+3^ \- 0.02           

  ^14^C             2.97x10^+3^   3.00x10^+3^   \- 30.0        \- 1.01           

  ^137^Cs           3.51          3.51          3.72x10^-3^    0.11              

  ^3^H              2.51x10^+7^   2.69x10^+7^   -1.80x10^+6^   \- 7.17           

  ^129^I            5.67          5.65          2.20x10^-2^    0.39              

  ^131^I            4.91x10^+4^   4.90x10^+4^   5.42x10^+1^    0.11              

  ^238^Pu           2.08          2.08          4.8x10^-3^     0.23              X

  ^239^Pu           13.2          13.14         6.03x10^-2^    0.46              X

  ^103,106^Ru^\*^   1.58x10^+2^   1.58x10^+2^   -0.31          \- 0.20           

  ^89,90^Sr^\*^     47.0          1.54          45.5           96.73             X

  Uranium^\*^       3.51          1.00          3.29x10^-2^    0.94              X

  \*In the Phase II                                                              
  study, Ru-103,106                                                              
  was screened                                                                   
  assuming that all                                                              
  activity was                                                                   
  Ru-106, Sr-89,90                                                               
  activity was                                                                   
  screened assuming                                                              
  that all activity                                                              
  was Sr-90, and                                                                 
  uranium activity                                                               
  was screened                                                                   
  assuming that all                                                              
  activity was                                                                   
  U-235. For Phase                                                               
  III, activity                                                                  
  reported as                                                                    
  uranium was                                                                    
  apportioned among                                                              
  the uranium                                                                    
  isotopes U-234,                                                                
  U-235, U-236, and                                                              
  U-238.                                                                         
  ----------------- ------------- ------------- -------------- ----------------- --------

**^241^Am:** The citation of zero for Phase II in Table 5-9 reflects the
fact that a 36-year screening total was not provided in the Phase II
Excel spreadsheets for ^241^Am. However, other entries in this table
suggest that the value used in Phase II may well have been 5.60x10^-03^
Ci over 36 years, which is only slightly smaller than the 39-year total
for Phase III of 5.88x10^-03^ Ci.

**Plutonium isotopes:** The Phase III source term is slightly larger
than the Phase II release estimates because unidentified alpha activity
was assumed to be ^239^Pu. Because the unidentified alpha activity only
summed to 0.08 curies, this adjustment to ^239^Pu was not a significant
change to the Phase II release estimate.

**^89,90^Sr:** The Phase III source term for ^89,90^Sr increased by 45
curies over the Phase II estimates because unidentified beta-gamma
activity was assumed to be ^90^Sr.

**Uranium:** The 39-year total uranium value used for Phase III is
larger than the 36-year Phase II screening value. After performing the
screening assessment, the Phase II study increased the estimated
releases of uranium from SRS over that reported by SRS to account for
sampling and measurement inefficiencies (see Chapter 4.4 of the Phase II
report). The Phase III source term reflects these increased Phase II
estimates as well as releases during the years 1990 through 1992.

## Phase III Source Term by Groups of Radionuclides

This section contains summaries of the assumptions and procedures used
to develop the source term for each radionuclide released into the air
and listed in Table 5-9.

Tables of the annual quantities of these radionuclides released from
each of the four virtual sources identified in Section 5.1.6 are
provided in [Appendix B](../Appendix_B_ready%20for%20CDC%20031405.doc).
Uncertainties associated with these release estimates are addressed in
[Chapter 12](../Chapter_12_ready%20for%20CDC_031405.doc).

### Tritium

The main sources of tritium release to the air from SRS were the
reactors and the separations areas. Phase II provided tritium release
estimates for reactors and the separations areas for almost the entire
period of interest. There is good agreement between the Phase II release
estimates and SRS data for the reactor and the separations areas (Phase
II.). For Phase III, however, sources were added that were not addressed
in detail in Phase II. These sources included tritium that evaporated
annually from the reactor and separations areas seepage basins, as well
as annual releases from the A-, M- and D-Areas, SRL, CMX-TNX. The
information on annual release of tritium from these additional areas,
facilities, and seepage basins was obtained from Cummins et al (3).

Seepage basin evaporation data in Cummins et al were presented as totals
for all reactor and separations areas seepage basins (3). Annual
quantities of tritium evaporated from the reactor seepage basins had to
be apportioned into two virtual groups of reactor facilities consistent
with Table 5-6. It was assumed for Phase III that evaporation from the
seepage basins was linked to the tritium inventories that were
discharged to the reactor seepage basins in liquid form. Since tritium
losses by evaporation are expected to be proportional to the
concentration of tritium in the seepage basin, assuming that these
releases to air are proportional to the tritium inventory
[discharged]{.underline} to the basin, conservatively neglects changes
in concentration from seepage of tritium into the ground; nevertheless,
this seepage of tritium is then accounted for in the liquid source term.
For each year, the total tritium inventory that was released into all
reactor seepage basins was determined. The fractions of this total
tritium inventory that were released into each of two groups of reactor
seepage basins was also determined (C-, K-, and L-seepage basins in one
group and P- and R-seepage basins in another). Then these fractions were
assumed for the annual release of evaporated tritium into the air from
each group of reactor seepage basins. These two fractions were
multiplied by the total annual amount of tritium evaporated from reactor
seepage basins to arrive at annual releases from both virtual groups of
reactor facilities.

In addition, for Phase III, environmental report data for 1990 through
1992 was used rather than the reactor estimates for these years from
Phase II. The combined totals from these environmental reports are
somewhat larger than those listed in Phase II. This may be due to
limited data in early studies. For these years, tritium release data
were reported in the SRS environmental reports as combined releases from
all reactors (4), (5), (6). Information from Phase II was used to group
the tritium released from all reactors into two virtual groups of
reactor facilities.

### ^131^I

As noted in Section 5.1.8.2.2 annual ^131^I releases were determined in
this Phase III study for the H- and F-Area separations facilities,
reactors, and for SRL, and were grouped into the four virtual sources
summarized in Table 5-6. Annual release information for the years 1954
through 1989 was obtained for these facilities from Phase II. For the
separations areas and reactors, the median values from the Excel
spreadsheets published with the electronic version of Phase II were
used. Annual release information for the years 1990 through 1992 was
obtained from environmental reports (4), (5), (6). Information from (3)
was used to partition the ^131^I estimates from Phase II, which are
given for all reactors, into two virtual sources consistent with the
reactor groupings in Table 5-6.

### ^41^Ar

^41^Argon is an activation product that was created in large quantities
during reactor operations. It is a noble gas having a short (1.83 hours)
half life.

For Phase III, as in Phase II, all ^41^Ar released into the air was
assumed to come from the SRS reactors. Information from Phase II, from
Cummins et al (3), and from Savannah River environmental reports (4),
(5), (6) for the years 1990 through 1992 was used to partition ^41^Ar
release from the five reactors into the two reactor virtual source
groupings listed in Table 5-6.

### ^241^Americium

For Phase III, annual ^241^Am release data was obtained for the years
1977 through 1989 from Cummins et al (3). This reference identified
^241^Am only for the F- and H-Separations Areas. For the years 1999
through 1992, additional data were available from SRS environmental
reports (4), (5), (6) and from (18).

### ^14^C

For Phase III, estimates of ^14^C released into the air were made for
the separations areas and for the reactors. For the separations areas,
data was available from Cummins et al. for the years 1955 to 1989 (3).
Data from SRS environmental reports were used for 1990 through 1992 (4),
(5), (7).

For the reactors, data was available from Cummins et al for the
following time frames (3):[^10]

-   C-Reactor: 1955 through 1985.

-   K-Reactor: 1955 through 1988.

-   L-Reactor: 1955 through 1968, 1987, and 1988.

-   P-Reactor: 1955 through 1988.

-   R-Reactor: 1955 through 1964.

After 1988, information on ^14^C release from nuclear reactors was
available in the SRS Environmental Report for 1992 as summed over all
reactors (6). For 1992, the ^14^carbon released from the reactors was
apportioned the C-, K-, L-, and P-Reactors in equal fractions.[^11]

### ^137^Cs

For Phase III, annual releases of ^137^Cs were estimated for all years
from the separations areas and for a few years from the reactors.

Most of the SRS atmospheric release of ^137^Cs occurred from the F- and
H-separations Areas (Phase II, 3). To develop source terms for ^137^Cs
release from the separations areas, information from these references
was used for the years 1954 through 1989, and data from SRS
environmental reports was used for the years 1990 through 1992 (4), (5),
(6).

For reactors, ^137^Cs release was not reported for the years 1954
through 1989 (3). ^137^Cs releases from reactors were reported, however,
in SRS environmental reports for the years 1990 and 1992 (4), (6). These
releases were small (on the order of 0.00002 Ci in 1990 and 0.00003 Ci
in 1992), but were added to the source term for completeness. For 1990,
the released activity was apportioned equally among C-, K-, L-, and
P-Reactors. For 1992, the activity was all released from L- and
K-Reactors. This was done because for 1992, data was available that
apportioned the total released ^137^Cs activity (3.05x10^-5^ Ci) between
these two reactors (7).

### ^129^I

For Phase III, consistent with the information in the Phase II study and
in Cummins et al., it was assumed that all release of ^129^I to the air
came from the separations areas (Phase II, 3). For Phase III, the annual
^129^I release estimates from the Phase II study were compared with the
smaller annual release estimates provided in Cummins et al. (3). For the
Phase III study, the Phase II estimates were used rather than the
Cummins et al estimates. As discussed in Chapter 4 of the Phase II
report, the historical SRS reports may have underestimated the true
release because of sampling line loss, sampler collection efficiency,
and counting errors (Phase II).

For 1990 through 1992, annual release estimates from SRS environmental
reports were used for the separations areas (4), (5), (6).

### ^103,\ 106^Ruthenium

For Phase III, annual release estimates for ^106^Ru were made for the F-
and H-Separations Areas. For the years 1955 through 1989, release data
were obtained from an Excel worksheet linked to the electronic version
of Phase II (Phase II). For the years 1955 through 1968, data were
provided as combined ^103,106^Ru for both the F- and H-Areas. For the
years 1969 through 1989, data was separately provided for ^103^Ru and
^106^Ru (Phase II).

For Phase III, releases documented in Phase II for the years 1955
through 1989 of ^103^Ru, ^106^Ru, and combined ^103,106^Ru were assumed
to be entirely ^106^Ru. This assumption was consistent with that used in
the Phase II screening analysis (Phase II) and provides conservative
estimates of dose by inhalation and ingestion. Releases of ^106^Ru for
the years 1990 through 1992 from the separations areas were obtained
from SRS environmental reports (4), (5), (6).

The Phase III source term also includes ^106^Ru release from the reactor
areas for the year 1990. This release was documented in the SRS
Environmental Report for 1990 (4). Although the release was small (about
0.00003 Ci), it was included for completeness. This release was
apportioned among the reactors.

### ^89^Strontium and ^90^Strontium with Unidentified Beta-Gamma

For the Phase III study, ^89^Sr and ^90^Sr were anticipated to have been
released into the air from the separations areas. ^90^Sr was anticipated
to have been released into the air from the reactors and from the
A-Area.

**Separations areas.** Annual release data for combined ^89,\ 90^Sr from
the F- and H-Separations Areas were provided in the Phase II report for
1954 -- 1989 (Phase II). In Phase III, the combined ^89,90^Sr activity
was apportioned into 75% ^89^Sr and 25% ^90^Sr (see Section 5.1.8.1). To
this activity was added the activity that was reported through 1989 in
Cummins et al as unidentified beta-gamma activity (3). All this
unidentified activity was assumed to be ^90^Sr (see Section 5.1.8.1).

^89^Sr and ^90^Sr activity was assigned to the years 1990 and 1991 using
information from SRS environmental reports (3), (5). For these two
years, data were reported in these two references as combined ^89,90^Sr,
including unidentified beta-gamma. This combined activity was assumed to
be all ^90^Sr. For 1992, Arnett et al reported 1.62x10^-3^ Ci of
combined ^89,\ 90^Sr with unidentified beta-gamma activity (6). A second
reference reported 2.75x10^-4^ Ci of combined ^89,\ 90^Sr activity
without referencing unidentified beta-gamma activity (6). The difference
was 1.35x10^-3^ Ci. The activity (1.62x10^-3^ Ci) reported by (6) was
partitioned between ^89^Sr and ^90^Sr in a 75%-25% ratio. The difference
(1.35x10^-3^ Ci) was assumed to be ^90^Sr.

**Reactors.** For reactors, ^90^Sr release data were not provided in the
Phase II report (Phase II). However, for the years 1954 through 1989,
annual unidentified beta-gamma activity was released from reactors and
reported in Cummins et al (3). This activity was assumed for Phase III
to be ^90^Sr. Reactor-specific annual ^90^Sr estimates were apportioned
using Cummins (3) data into two virtual source groups consistent with
Table 5-6. For the years 1990 through 1992, the release data obtained
from environmental reports for the reactor areas were equally
apportioned into C-, K-, L- and P-Reactors.

**A-Area.** For the years 1954 through 1989, annual releases from A-Area
that were identified in Cummins et al as unidentified beta-gamma
activity (3) were assumed to be ^90^Sr. For the years 1990 through 1992,
SRS environmental reports were used to develop ^90^Sr release estimates
from A-Area (4), (5), (6).

### Uranium and Plutonium with Unidentified Alpha

For Phase III, annual estimates of uranium released into the air were
made for the F- and H-Separations Areas and for M-Area. Annual estimates
of plutonium released into the air were made for the separations areas,
the reactors, and for A-Area.

**Separations Areas.** The Phase II release estimates were based on
information from Cummins et al (3). However, the Phase II estimates were
increased in earlier years, compared with that reported by Cummins et al
(3), because of concerns about sampling uncertainties. For Phase III,
the Phase II estimates of release of uranium and plutonium from the
separations areas were enhanced using additional data from environmental
reports.

For Phase III, uranium activity was apportioned into four uranium
isotopes based on the isotopic partition assumptions summarized in
Section 5.1.8.1 and Table 5-8. Note that uranium isotopic composition
varied in the F- and H- Separations Areas, because the processes
conducted in each area differed. Uranium data for Phase III were
available for 36 years from Phase II (Phase II) and for three years from
SRS environmental reports (4), (5), (6).

For the years 1954 through 1989, uranium released from the F-Separations
Area was reported separately in Phase II from uranium released from the
H-Separations Area. This information was sufficient to partition the
uranium released from both the separations areas. But for 1990 through
1992, information about uranium released from the separations areas was
provided in SRS environmental reports (4), (5), (6) only as combined
releases from both areas. Isotopic partitioning of uranium was performed
for these years using an SRS report for the year 1992 that provided
uranium release data separately for F- and H-Areas (6). This reference
indicated that 95% of the uranium in 1992 was released from the F-Area
and 5% from the H-Area (6). It was assumed that this 95%-5% uranium
split between F- and H-Areas was also applicable to 1990 and 1991. The
total uranium released from each separations area for these years was
apportioned into isotopic distributions consistent with Table 5-8. Then
the total release of each uranium isotope from both separations areas
was determined for purposes of the virtual source grouping. Finally,
release data for each uranium isotope in F- and H-Area were increased
for Phase III using the same method described in Chapter 4 of Phase II
to compensate for sampling line loss.

For plutonium, Phase II increased its estimates of plutonium released
into the air, relative to that reported by SRS, to compensate for
sampling line loss. The source term adjustment in Phase II for plutonium
air release was done for ^238^Pu and for ^239,240^Pu together. Because
sampling line loss should have been the same for any plutonium isotope,
for Phase III the procedure cited in Phase II to compensate for sampling
loss was applied to both ^238^Pu and ^239^Pu. The total plutonium
activity reported in Phase II before adjustment matched the calculated
plutonium term in Cummins et al (3). Using the isotopic information
provided in (3), plutonium reported as total plutonium in Phase II was
apportioned for Phase III into ^238^Pu and ^239^Pu.

Cummins et al reported unidentified alpha activity released from the F-
and H-Separations Areas (3). For Phase III, this unidentified activity
was included as ^239^Pu. The activity was increased in Phase III,
relative to that reported in Cummins (3), to compensate for sampling
line loss. As discussed earlier, the inclusion of this unidentified
activity as ^239^Pu did not significantly change the plutonium source
term.

**Reactors.** Annual estimates of ^239^Pu released from the nuclear
reactors were made for Phase III using information from Cummins et al
for the years 1973 through 1989 (3). In this case, starting in 1973,
Cummins (3) provided air release data for unidentified alpha activity
for the reactor areas. For Phase III it was assumed that this alpha
activity was ^239^Pu consistent with Section 3.5.4. For 1990 through
1992, information from SRS environmental reports was used (4), (5), (6).
No estimates were made for uranium release from reactors, because such
releases were not identified in Phase II, Cummins (3), or other
documents.

**M-Area.** Annual estimates of uranium isotope releases from M-Area
were made in Phase III using information from (3). This reference listed
annual uranium releases (as U-Nat -- i.e., natural uranium) from 1975
through 1989, except that no releases were listed for 1981 and 1984.
This activity was apportioned among the isotopes ^234^U, ^235^U, and
^238^U. Releases for the years 1990 through 1992 were estimated using
information from SRS environmental reports (4), (5), (6).

**A-Area.** Cummins et al reported annual release of unidentified alpha
activity from A-Area for most of the years from 1961 through 1992 (3).
No release information was provided for 1964-1967, 1972, 1979, 1981,
1982, 1984, and 1985. This unidentified alpha activity was assumed to be
^239^Pu for Phase III. Information from environmental reports was used
to complete the estimates for 1990 through 1992 (4), (5), (6).

## Annual Release of Tritium, ^131^Iodine, and ^41^Argon

As will be seen in [Chapter
11](../Chapter_11_ready%20for%20CDC%20031405.doc), radiation doses
calculated from the air pathway are dominated by tritium, ^131^I, and
^41^Ar. To help shed light on these calculated doses, the source term
assumed in Phase III for these radionuclides is graphically depicted in
the Figures below. The annual release of tritium to air from the four
virtual sources used in Phase III is shown in Figure 5-. The bulk of the
tritium released over the 39 years of nuclear materials production came
from the F-and H-Separations Areas (Virtual Source 2) rather than from
the reactor areas. Annual releases of ^131^iodine from all four virtual
sources are shown in Figure 5-4. Note that the bulk of the ^131^I was
released from the separations areas (Virtual Source 2), and that the
largest ^131^I release from this virtual source occurred in 1956. (Also
note that the y-axis of this graph (Curies of ^131^I released) is in a
logarithmic scale.) Annual releases of ^41^Ar from the four virtual
sources are shown in Figure 5-5. Although ^41^Ar releases rise and fall
over the years, one can see a succession of peaks that gradually
diminish in height. The largest peak occurred over roughly a five-year
period between 1958 and 1963. Successively smaller peaks occurred in the
years 1967 and 1968, in 1973, and in 1986.

![](media/image3.wmf){width="5.135416666666667in"
height="3.2916666666666665in"}

Figure 5‑3 Tritium Release to Air from SRS

![](media/image4.wmf){width="5.145833333333333in"
height="3.3020833333333335in"}

Figure 5‑4 Release of ^131^I to Air from SRS

![](media/image5.wmf){width="5.125in" height="3.28125in"}

Figure 5‑5 Release of ^41^Ar to Air from SRS Reactors

## References

1.  NCRP 1989. National Council on Radiation Protection and Measurements
    (NCRP). Screening Techniques for Determining Compliance with
    Environmental Standards, Releases of Radionuclides to the
    Atmosphere. NCRP Commentary No. 3. Bethesda, MD. 1989.

2.  NCRP 1991. NCRP. Screening Models for Releases of Radionuclides to
    Air, Surface Water, and Ground Water. NCRP Report No. 123.
    Bethesda, MD. 1996.

3.  Cummins 1991a. Cummins CL, Hetrick CS, and Martin DK, 1991.
    Radioactive Releases from the Savannah River Plant 1954-1989,
    Environmental Protection Department Summary. WSRC-RP-91-684, SRS
    Phase II Database MOL199401111.

4.  Cummins 1991b. C.L. Cummins, D.K. Martin, J.L. Todd. Savannah River
    Site Environmental Report (U). WSRC-IM-91-28. Westinghouse Savannah
    River Company, Environmental Monitoring Section. Savannah River
    Site, Aiken, SC. 1991.

5.  Arnett 1992. M.W. Arnett, L.K. Karapatakis, A.R. Mamatey, and J.L.
    Todd. Savannah River Site Environmental Report for 1991 (U).
    WSRC-TR-92-186. Westinghouse Savannah River Company, Environmental
    Monitoring Section. Savannah River Site, Aiken, SC. 1992.

6.  Arnett 1993a. M.W. Arnett, L.K. Karapatakis, A.R. Mamatey. Savannah
    River Site Environmental Report for 1992. WSRC-TR-93-075.
    Westinghouse Savannah River Company, Environmental Monitoring
    Section. Savannah River Site, Aiken, SC. 1993.

7.  Arnett 1993b. M.W. Arnett (ed.). Savannah River Site Environmental
    Data for 1992. WSRC-TR-93-077. Westinghouse Savannah River Company,
    Environmental Monitoring Section. Savannah River Site, Aiken, SC.
    1993.

8.  Evans 1992. Evans AG, Bauer LR, Haselow JS, Hayes DW, Martin HL,
    McDowell WL, & Pickett JB, "Uranium in the Savannah River Site
    Environment," WSRC-RP-92-315, Rev. 0, 12/09/92.

9.  Heffner 1999. Heffner, J.D. Comments on CDC's Final Draft Report on
    Phase II of the Savannah River Site Dose Reconstruction Project (U).
    ESH-EMS-99-0461. 11 May 1999.

10. Miller and Patterson 1956. Miller, D.A. and C.M. Patterson. Plant
    Manager and Superintendent Health Physics. Letter to G.H. Giboney,
    Atomic Energy Commission. Subject: Crave Project. DPSP-56-842. SRS
    Phase II Database PGV1994042881. 3 August 1956.

11. Longtin et al. 1973. Longtin, F.E., G.W. Earle, J.W. McMahan, and
    G.H. Street. Tritium Control Technology-- Reactor Operations.
    DPSPU-73-30-6. SRS Phase II Database EIW199406031. May 1973.

12. Jacoberson 1973. Jacoberson, W.J., D.A. Orth, and G.W. Earle.
    Tritium Control Technology\--Separations Operations. DPSPU-73-30-7.
    Du Pont. SRS Phase II Database SKR1994020427. 5 May 1973.

13. Westinghouse 1991. Westinghouse. *Description of Samplers and Flow
    Monitoring Devices.* SRS Alternative Methods Information, Item 7.
    Rev. 2. SRS Phase II Database MD199710131. March 21, 1991

14. Murphy 1991. Murphy, C.E., Jr., L.R. Bauer, D.W. Hayes, W.L. Marter,
    C.C. Zeigler, D.E. Stephenson, D.D. Hoel, and D.N. Hamby. Tritium in
    the Savannah River Site Environment (U). WSRC‑RP-90-424-1,
    Revision 1. Westinghouse. SRS Phase II Database MJC1994051310. May
    1991.

15. Pelletier 1978. Pelletier, C.A., J.E. Cline, E.D. Barefoot, R.T.
    Hemphill, P.G. Voillequé, and W.A Emel. Sources of Radioiodine at
    Pressurized Water Reactors. NP-939. Electric Power Research
    Institute, Palo Alto, California. November 1978.

16. Ramsdell 1994. Ramsdell, Jr., J.V., C.A. Simonen, and K.W. Burk.
    Regional Atmospheric Transport Code for Hanford Emission Tracking
    (RATCHET). PNWD-224 HEDR. Prepared from the Technical Steering Panel
    and the Centers for Disease Control and Prevention. Battelle Pacific
    Northwest Laboratories. Richland, WA. 1994.

17. Napier, B.A., et al. GENII Version 2 Software Design Document.
    Pacific Northwest National Laboratory for the U.S. Environmental
    Protection Agency. November 2002.

18. Carlton 1997b. Carlton WH, "Assessment of Neptunium, Americium, and
    Curium in the Savannah River Site Environment," WSRC-TR-97-00266,
    December 1997.

[Previous Chapter](../Chapter_04_ready%20for%20CDC_031405.doc)

[Next Chapter](../Chapter_06_ready%20for%20CDC%20031405.doc)

[Return to Table of Contents](../Chapter_01_ready_for_CDC_031405.doc)

[^1]: A report describing the NCRP screening method notes, on page 4:
    "The assumptions and methods incorporated into all of the screening
    procedures presented in this Report are such that actual doses
    should not be underestimated by more than one order of magnitude. In
    most situations, the actual dose will be significantly less than the
    values calculated for screening" (2).

[^2]: SRS revised its iodine monitoring and sampling systems and
    procedures over time. According to the Phase II report, about 99% of
    the ^131^I released into the air came from the separations areas.
    Until September 1961, only elemental ^131^I was measured at the
    separations areas. SRS estimated organic iodide activity from
    elemental ^131^I release, assuming that organic forms represented
    70-90% of all iodine released from separations. The Phase II report
    addressed measurement uncertainties such as sample collection
    efficiency, and measurement biases resulting from deposition of
    elemental iodine in sampling lines, and concluded that SRS
    underestimated the release of ^131^I to air during early years
    (1950s and early 1960s). For example, for each year from 1955
    through 1960, the Phase II report estimated that the annual total
    iodine released to the air was at least 20 times larger than was
    reported in Cummins (3). For the year 1961 the total iodine released
    to air was 12 times larger. SRS staff (9) have criticized these
    Phase II estimates. After 1961, however, the Phase II estimates of
    ^131^I release more closely correspond to those reported by SRS
    (with few exceptions). Annual ^131^I releases after 1961 were much
    smaller than in earlier years (Phase II).

[^3]: In the supplemental files provided as part of Chapter 3 of Phase
    II, the following notation was made: "We combined all estimates of
    reported releases of ^103^Ru (0.2 Ci), ^106^Ru (0.5 Ci), and
    ^103,106^Ru (\~1 Ci), and then used the screening factor for ^106^Ru
    to ensure a conservative approach" (Phase II).

[^4]: Other radionuclides were not partitioned by chemical form.
    Although health effects may depend upon "the lung clearance class"
    for other radionuclides, only a single class was considered for each
    of these other radionuclides. In addition, the model for uptake of
    tritium by biota depends on the chemical form.

[^5]: For example, in 1992, 65.90 curies of tritium were released from K
    reactor in elemental form compared with 39,200 curies in oxide form.
    The elemental form release accounts for less than 0.2 % of the total
    tritium release

[^6]: As an example, assume that the total tritium release from the
    separations facilities in a given year was 1000 Ci, and this release
    was in an unspecified elemental and oxide form combination, although
    there was reason to believe that about half was either form. That
    year, 200 Ci of tritium was known to have been inadvertently
    released in an elemental form and 300 Ci of tritium was released in
    an oxide form. The 1000 Ci of tritium released that year was assumed
    to consist of 200 + (1000 -- 200 -- 300)/2 = 450 Ci of tritium in an
    elemental form and 300 + (1000 -- 200 -- 300)/2 = 550 Ci in an oxide
    form.

[^7]: Essentially, the Pelletier data indicated that iodine was released
    in a highly reactive form, a moderately reactive form, and a less
    reactive form. For the sake of conservatism, the moderately reactive
    and highly reactive forms could be grouped rather than the
    moderately reactive and the less reactive forms, leading to a split
    of about 70% elemental and 30% organic.

[^8]: Data files containing annual releases of elemental and organic
    forms of 131I were input into the pre-processor and added. The total
    131I was then split between chemical forms in the ratios of 40%
    particulate, 30% elemental, and 30% organic. The revised files from
    the preprocessor were then input to GENII for the air transport,
    deposition, and radiation exposure computations. See Appendix G for
    details.

[^9]: RATCHET: Regional Atmospheric Transport Code for Hanford Emission
    Tracking (16).

[^10]: Recall that R-Reactor shut down in 1964, C-Reactor shut down in
    1985, P-Reactors shut down in 1988, and that L-Reactor was shut down
    in 1968, but was restarted in 1985 and shut down again in 1988.
    K-Reactor was shut down in 1988 but briefly operated in 1992 (Phase
    II).

[^11]: Release from R-Reactor was assumed to have been much smaller for
    the years 1990-1992, compared with other reactors, because it had
    permanently shut down much earlier (at least 21 years) than did the
    other reactors. Because of uncertainty about the fraction of the
    total release that should have been allotted to each of the other
    four reactors, the 1992 ^14^C release (0.183 Ci) was apportioned
    equally among the four reactors. Hence, 75% of the ^14^C was
    released from the C-, K-, and L-Reactor group, and 25% was released
    from the P- and R-Reactor group.