Information Notice No. 94-07: Solubility Criteria for Liquid Effluent Releases to Sanitary Sewerage Under the Revised 10 CFR Part 20
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555
January 28, 1994
NRC INFORMATION NOTICE 94-07: SOLUBILITY CRITERIA FOR LIQUID EFFLUENT
RELEASES TO SANITARY SEWERAGE UNDER THE
REVISED 10 CFR PART 20
All byproduct material and fuel cycle licensees with the exception of
licensees authorized solely for sealed sources.
The U.S. Nuclear Regulatory Commission is issuing this information notice to
emphasize the changes in 10 CFR Part 20 with respect to liquid effluent
releases to sanitary sewerage and to encourage you to prepare for these
revisions.* It is expected that licensees will review this information for
applicability to their operations, distribute it to appropriate staff, and
consider actions to prepare for, and incorporate, these changes. Suggestions
contained in this information notice are only recommendations; therefore, no
specific action nor written response is required.
On December 21, 1984, NRC released an information notice documenting several
instances of reconcentration of radionuclides released to sanitary sewerage
(IN No. 84-94, "Reconcentration of Radionuclides Involving Discharges into
Sanitary Sewage Systems Permitted under 10 CFR 20.303"). Several other
instances have since occurred in Portland, Oregon; Ann Arbor, Michigan; Erwin,
Tennessee; and Cleveland, Ohio. The primary contributors, in some of these
cases, appear to have been insoluble materials released as dispersible
particulates or flakes. This issue was addressed again on May 21, 1991, by
NRC, when it published its revision of Part 20 in the Federal Register
(56 FR 23360), which removed insoluble non-biological material from the types
of material that may be released to sanitary sewerage. Relative to this
issue, the NRC Office of Nuclear Regulatory Research is conducting a study to
clarify the mechanisms underlying reconcentration in sanitary sewerage and
sewage treatment facilities.
* Sanitary sewerage is defined by 10 CFR 20.1003 as "a system of public
sewers for carrying off waste water and refuse, but excluding sewage treatment
facilities, septic tanks, and leach fields owned or operated by the licensee
[emphasis added]." .
January 28, 1994
Page 2 of 5
Description of Circumstances
To help prevent further reconcentration incidents at public sewage treatment
facilities, 10 CFR 20.2003(a)(1), effective January 1, 1994, was written as
20.2003 Disposal by release into sanitary sewerage
(a) A licensee may discharge licensed material into sanitary sewerage
if each of the following conditions is satisfied:
(1) The material is readily soluble (or is readily dispersible
biological material) in water; and...
However, this revision to Part 20 did not contain an operational definition of
solubility, and this precipitated many questions, from licensees, concerning
how the solubility of a material may be demonstrated. Without the ability to
demonstrate compliance, these licensees were unable to determine whether new
procedures should be developed, new treatment systems installed, or whether
they should apply for an exemption, based on the principle of maintaining all
doses as low as is reasonably achievable (ALARA).
In some of the known reconcentration incidents, the greatest reconcentrations
appear to have been due to compounds released to sanitary sewerage that were
not soluble. There are many approaches that may be used to determine a
chemical compound's solubility in water. The following discusses two of the
more common approaches:
1. Direct Determination of Compound Solubility Class, Formal Solubility,
or Solubility Product (Ksp)
This approach would be applicable whenever there is sufficient
knowledge of the chemical form of all materials contained in the
liquid effluent at the point of release. With this knowledge, it
would be possible to use one (or more) of the following methods:
(a) Solubility Class Determination:
The solubility class of the compound to be released could be
determined directly from common literature data (e.g., Handbook of
Chemistry and Physics - CRC Press, and Lange's Handbook of
Chemistry - McGraw- Hill Book Company). If a compound is
classified as "v s" (very soluble) or "s" (soluble), this would
indicate the compound is "readily soluble." On the other hand, if
it is classified as "i" (insoluble), "sl s" (slightly soluble), or
"v sl s" (very slightly soluble), this would indicate materials
that are "not readily soluble." Certain compounds are designated
as class "d" (decompose). If the decomposed species of these
compounds are classified as either "v s" or "s," this would
indicate that the parent compound is "readily soluble." If these
decomposed species are simple ions, such compounds (class "d")
should be considered "readily soluble.".
January 28, 1994
Page 3 of 5
(b) Solubility Product (Ksp) Determination:
The solubility product constant of the compound could also be used
to determine if a compound is readily soluble in water. The
solubility product constant, Ksp, for a strong electrolyte MmAa,
is expressed as:
Ksp = [M] [A]
where [M] and "m" are the ionic concentration (mole/liter) and the
number of moles, respectively, of the dissolved cation; and [A]
and "a" are the ionic concentration and the number of moles,
respectively, of the dissolved anion.
For a simple electrolytic compound, with one mole of a dissolved
cation species and one mole of a dissolved anion species, a Ksp
greater than 1.00 E-05 mole /liter would indicate that a compound
is "readily soluble." For other compounds with more complex
dissolution reactions (i.e., more than one mole dissolved for each
species and/or more anionic or cationic species present in the
dissolved products), the Ksp constant would increase
exponentially, based on the number of moles and/or the number of
dissociated species. For example, if three moles are present (two
for the anion and one for the cation), the unit of Ksp would be
3 3 3/2
mole /liter , and the corresponding Ksp would be (1 E-05) or
3.2 E-08 mole /liter ; the same principle could be applied for
more complex dissolution reactions.
(c) Formal Solubility Determination:
Compound solubilities (g/100 ml or mole fraction per 100 ml) are
also listed in the chemical literature. From a review of general
scientific literature, "formal solubilities"** greater than 0.003
mole/liter would indicate that a compound is "readily soluble."
** The general relation between the formal solubility, Sf, and the
solubility product, Ksp, of a strong electrolyte MmAa in water is given by:
m a 1/(m+a)
Sf = (Ksp/(m a )),
where Ksp is the solubility product, [M] is the molar concentration of the
metal ion (cation), [A] is the molar concentration of the anion, "m" is the
number of moles of dissolved cation per mole of dissolved substance, and "a"
is the number of moles of the dissolved anion per mole of dissolved substance.
For further discussion on the determination of solubility products and formal
solubility, refer to Chapter 6, "Precipitation and Dilution," from Water
Chemistry, by Vernon L. Snoeyink and David Jenkins (John Wiley and Sons: 1983)
or texts relating to physical and/or analytical chemistry..
January 28, 1994
Page 4 of 5
Formal solubilities less than 0.003 mole/liter would indicate
compounds that are "not readily soluble."
It should be pointed out that all values mentioned above (e.g.,
solubility class, formal solubility, and solubility product)
correspond to measurements taken under standard conditions (e.g.,
25�C, 101.3 kPa, pH of 7, and Eh of 0).
2. Filtration and Radiometric Analysis of Suspended Solids
This approach may be used if knowledge of the chemical form of all
materials contained in the liquid effluent at the point of release is
incomplete. It is most applicable when releases are made in a batch
mode. This approach involves the use of standard laboratory
procedures to test representative samples of the waste stream for the
presence of suspended radioactive material.
The following two laboratory procedures were developed specifically to
determine the suspended solids content of water: ASTM Method D 1888-
78, "Standard Test Methods for Particulate and Dissolved Matter,
Solids, or Residue in Water," and the American Public Health
Association's Method 7110, "Gross Alpha and Gross Beta Radioactivity
(Total, Suspended, and Dissolved)" from Standard Methods for the
Examination of Water and Wastewater. It should be noted that ASTM
Method D 1888-78 was developed to measure the total suspended solids
content of water, not just the radioactive portion. In either case,
activity in the suspended solids portion of effluent greater than that
found in similarly processed background water samples would indicate
the presence of insoluble radioactive material.
Whether one of the above approaches or a self-developed alternative is used,
it is a good health physics practice to document this approach in the form of
a procedure. Procedures such as these usually include provisions for the
documentation of any models, calculations, analytical measurements, and/or
quality control measures used. This information is usually maintained with
the applicable release records, to demonstrate that the developed procedure
will ensure compliance with the regulations.
If material to be released would not qualify as being "readily soluble,"
10 CFR 20.2003(a)(1) would prohibit release to sanitary sewerage unless an
exemption has been granted. Exemptions will be judged on a case-by-case
basis, when it is demonstrated that release to sanitary sewerage is in
accordance with the ALARA principle, consistent with applicable regulations,
and in the public interest.
It is expected that licensees will review this information for applicability
to their operations, and consider actions, as appropriate to their licensed
activities. However, suggestions contained in this information notice are not
NRC requirements; therefore, no specific action nor written response is
January 28, 1994
Page 5 of 5
If you have any questions about the information in this information notice,
please contact one of the technical contacts listed below or the appropriate
/s/'d by RFBurnett /s/'d by CJPaperiello
Robert F. Burnett, Director Carl J. Paperiello, Director
Division of Fuel Cycle Safety Division of Industrial and
and Safeguards Medical Nuclear Safety
Office of Nuclear Material Office of Nuclear Material
Safety and Safeguards Safety and Safeguards
Technical contacts: Rateb (Boby) Abu-Eid, NMSS
Cynthia G. Jones, NMSS
1. List of References
2. List of Recently Issued NMSS Information Notices
3. List of Recently Issued NRC Information Notices.
January 28, 1994
Page 1 of 1
Annual Book of ASTM Standards. Volume 11.01, "Water (I)." American Society
for Testing and Materials, Easton, MD, 1989.
CRC Handbook of Chemistry and Physics. CRC Press, Inc., Boca Raton, FL, 65th
Lange's Handbook of Chemistry. McGraw-Hill, Inc., New York, NY, 13th ed,
Snoeyink, Vernon L. and David Jenkins, Water Chemistry. John Wiley & Sons,
Inc., New York, NY, 1980.
Standard Methods for the Examination of Water and Wastewater. American Public
Health Association, Washington, DC, 17th ed, 1989.
Page Last Reviewed/Updated Thursday, August 20, 2020