Low-Level Waste Classification: 10 CFR Part 61

Introduction

Most nuclear-medicine radioactive waste never reaches a disposal site — decay-in-storage quietly handles it — but the material that outlives the 120-day rule must be classified under 10 CFR 61.55 as Class A, B, or C, and getting that classification and its paperwork right is a core radiation-safety-officer responsibility. The waste-classification system is concentration-based: it sorts waste by how much of specific radionuclides it contains, using two tables and a sum-of-fractions rule, and it determines packaging, stability, and disposal path.

For a medical licensee, the good news is that the physics of short half-lives does most of the work. The workhorse radionuclides of nuclear medicine — Tc-99m, F-18, I-123, Ga-68, I-131, Lu-177, Y-90 — are short-lived enough to decay to background in storage, so they leave the radioactive-waste stream before Part 61 ever applies. What remains is a small but important tail: longer-lived contaminants, certain sealed sources and calibration standards, and long-lived impurities that ride along with therapy isotopes. That tail is where waste classification, manifests, and disposal contracts come into play. ^{1, 3}

This guide explains how 10 CFR Part 61 classifies low-level radioactive waste, how the sum-of-fractions rule works, how decay-in-storage under 10 CFR 35.92 interlocks with Part 61, and what a defensible waste program looks like. DRPS supports these programs through its radioactive material license support and radiation safety officer services across Florida, Maryland, Virginia, Washington DC, California, and beyond.

Topic Explanation

What "low-level radioactive waste" actually means

Low-level radioactive waste (LLRW) is defined by exclusion: it is radioactive material that is not spent nuclear fuel, high-level waste, transuranic waste, or uranium mill tailings. In a medical setting that means contaminated consumables — gloves, syringes, vials, tubing, absorbent pads — plus expired or unwanted sealed sources and calibration standards. It is emphatically not the reactor-style waste the public usually imagines; the overwhelming majority of medical LLRW is very low in activity. ¹

The federal framework has two interlocking parts. Disposal-site licensing and the waste-classification system live in 10 CFR Part 61, which governs land disposal of radioactive waste and defines the Class A/B/C scheme. Operational disposal options for a medical licensee live in 10 CFR Part 20, Subpart K and 10 CFR 35.92, which authorize decay-in-storage, transfer to an authorized recipient, and other pathways. Understanding which rule governs which decision is half the battle. ^{1, 3}

A practical waste program answers a sequence of questions:

• Can this material be handled by decay-in-storage instead of shipment?
• If not, what radionuclides does it contain, and at what concentration?
• What waste class results from those concentrations?
• What packaging and stability does that class require?
• How is the shipment manifested and transported?

For the operational disposal pathways that surround this classification question, see our companion guides on decay-in-storage of radioactive waste and radioactive waste management in nuclear medicine.

Decay-in-storage: why most medical waste never enters Part 61

10 CFR 35.92 authorizes decay-in-storage (DIS): a licensee may hold byproduct material with a physical half-life of 120 days or less until it decays, then dispose of it as ordinary or biomedical waste. This single provision removes the bulk of nuclear-medicine waste from the radioactive stream, because almost every diagnostic and most therapeutic radionuclides fall well under the 120-day threshold. ³

There is a common myth worth correcting. The current rule does not impose a fixed "hold for ten half-lives" period. That language was removed from Part 35 in the 2002 revision. Today the rule sets two binding conditions: ³

• The licensee monitors the material at its surface with an appropriate radiation detection meter set on its most sensitive scale, with no interposed shielding, and determines that its radioactivity cannot be distinguished from background; and
• The licensee removes or obliterates all radiation labels (except labels on materials that will be managed as biomedical waste after release).

The familiar ten-half-lives figure survives only as a practical ALARA planning guideline — a reasonable estimate of how long storage will take before the survey passes — not as a regulatory holding period. Records of each DIS disposal (date, survey instrument, background level, surface reading, and surveyor) must be retained for three years under 10 CFR 35.2092. ³

What cannot go through DIS is what Part 61 governs: material with a half-life greater than 120 days. A vivid modern example is the long-lived nuclear isomer Lu-177m, a trace impurity in Lu-177 therapy products, with a half-life of roughly 160 days. Its presence means Lu-177 therapy waste cannot simply decay away on the usual timescale, and departments must plan for extended storage or classified disposal. ¹²

Key Technical Principles

The two classification tables

10 CFR 61.55 classifies waste using two radionuclide tables. Table 1 lists long-lived radionuclides; Table 2 lists shorter-lived radionuclides, with three concentration columns corresponding to Class A, B, and C. The core codified limits, unchanged for decades, are summarized below. ¹

For Table 1 nuclides the classification logic is: if the concentration is ≤ 0.1× the Table 1 value, the class is determined by the Table 2 nuclides (Class A if none are present); if it is > 0.1× but ≤ 1× the value, the waste is Class C; and if it exceeds the Table 1 value, the waste is greater than Class C (GTCC) and generally not acceptable for near-surface disposal. Note the unit split — the first six rows are volumetric (Ci/m³), while the transuranic rows are mass-based (nCi/g). ¹

Table 2 uses three columns for its short-lived nuclides. Two rows medical physicists encounter most often are strontium-90 and cesium-137: ¹

For the first several short-lived entries (the total of all nuclides with less than 5-year half-life, H-3, and Co-60), Table 2 establishes only a Class A limit; there are no Class B or C limits for those rows, so such waste is Class B by default unless other nuclides drive it higher. The practical takeaway for a medical program is that its waste concentrations sit far below even the Class A column, which is why almost all medical LLRW is Class A. ¹

The sum-of-fractions rule

Real waste is a mixture, so 10 CFR 61.55 provides the sum-of-fractions rule for combining radionuclides. Divide each nuclide's concentration by its limit — all taken from the same column of the same table — and add the fractions. The waste qualifies for that class if the sum is less than one: ¹

$$\sum _{i=1}^n\frac{C_i}{L_i}<1.0$$

where $C_i$ is the concentration of radionuclide $i$ and $L_i$ is its concentration limit from the chosen column. The regulation's own worked example makes the mechanics concrete. Consider waste with Sr-90 at 50 Ci/m³ and Cs-137 at 22 Ci/m³, tested against the Class B column: ¹

$$\frac{50}{150}+\frac{22}{44}=0.33+0.50=0.83<1.0\Rightarrow \text{Class B}$$

Because the sum is below one for the Class B column (and would exceed one for the Class A column), the waste is Class B. When a waste contains both Table 1 and Table 2 nuclides, you evaluate Table 1 first — it can force Class C or GTCC on its own — and then apply the Table 2 columns. ¹

Waste characteristics: what each class must satisfy

Classification determines not just where waste can go but how it must be packaged, under 10 CFR 61.56. All classes, including Class A, must meet minimum requirements: no cardboard or fiberboard containers; liquids solidified or packaged with enough absorbent to soak up twice the liquid volume; free-standing liquid held to no more than about 1% of volume; void spaces minimized; and the waste must not be explosive, pyrophoric, or hazardously biological or toxic. ²

Class B and Class C waste carry an additional stability requirement: the waste form must be structurally stable — from the waste itself, from processing, or from a disposal container that provides stability after disposal. Class C waste must additionally incorporate measures against inadvertent intruder access. Because medical waste is almost always Class A, the stability engineering rarely applies, but knowing the boundary matters when a program handles an unusual long-lived source. ²

Clinical Impact

The operational reality for a medical program

For a nuclear-medicine or radiopharmaceutical-therapy program, the classification system has a reassuringly simple bottom line most of the time: decay what you can, and the small remainder is Class A. The physics of short half-lives, combined with the low activities handled in medicine, means the classification tables are rarely a binding constraint. But "rarely" is not "never," and the exceptions are exactly where programs get into trouble. ^{1, 11}

The exceptions cluster around a few situations:

• Long-lived sealed sources and standards — flood sources, dose-calibrator reference standards, and check sources with half-lives beyond 120 days cannot decay in storage and must be transferred to an authorized recipient or manufacturer.
• Long-lived impurities in therapy isotopes — the Lu-177m impurity in Lu-177 products is the canonical case, forcing extended storage or classified disposal that a naive DIS plan would miss. ¹²
• Mixed and legacy waste — historical accumulations, or waste that is both radioactive and chemically hazardous, complicate both classification and the disposal contract.

Why the paperwork is a radiation-safety issue

Waste that leaves the site travels on the Uniform Low-Level Radioactive Waste Manifest — NRC Forms 540, 541, and 542 — under 10 CFR Part 20, Appendix G, and moves under U.S. Department of Transportation hazardous-materials rules as Class 7 radioactive material. ^{5, 8} The generator remains responsible: it must get the manifest to the consignee, obtain an acknowledgement of receipt, and investigate and report a shipment that is not confirmed as received. An unaccounted-for shipment of radioactive material is not a clerical footnote; it is a reportable loss-of-control event. This is why waste tracking sits squarely inside the radiation-safety program, not off in a logistics silo. For the transport side of this workflow, see our guide on transport of radioactive material under DOT rules. ⁸

Packaging and transport class

Most medical LLRW and DIS-destined material ships as a Type A package or as an excepted or limited quantity under DOT rules; the more robust Type B packaging under 10 CFR Part 71 is generally reserved for quantities above the A₁/A₂ limits and is not typically implicated for routine nuclear-medicine waste. Matching the package type to the activity is part of a defensible shipment, and it connects directly to the receipt and wipe-testing practices covered in our package receipt and wipe testing guide. ^{8, 9}

Practical Optimization Tips

A defensible low-level-waste program follows a repeatable decision path.

1. Segregate at the point of generation

Separate short-lived DIS-eligible waste from anything long-lived, and separate radioactive from chemically hazardous waste, at the moment it is generated. Mixed waste created by careless commingling is expensive and difficult to dispose of. Label and date every DIS container so the storage clock is auditable.

2. Let decay do the work — but verify it

For DIS, do not rely on a calendar rule of thumb alone. Survey each container to background on the meter's most sensitive scale with no shielding before release, document the reading, and remove or obliterate the labels. The survey, not the elapsed time, is what the regulation requires. ³

3. Flag the long-lived tail early

Maintain an inventory of every item that cannot decay in storage — sealed sources, standards, and known long-lived impurities — with a disposal plan for each. The Lu-177m impurity problem is the classic trap: a program that assumes all Lu-177 waste decays on a therapy timescale will accumulate an undisposed long-lived stream. ¹²

4. Classify mixtures with the sum-of-fractions rule

When waste contains more than one radionuclide, use the sum-of-fractions calculation with limits from a single column of a single table, and evaluate Table 1 before Table 2. Document the calculation; a defensible classification is a written one. ¹

5. Own the manifest and the acknowledgement

Track every shipment on the Uniform Waste Manifest, retain the manifest and the signed acknowledgement of receipt, and act promptly if a shipment is not confirmed as received. Treat an unconfirmed shipment as a potential reportable event, not a paperwork delay. ⁵

Common pitfalls to avoid

• Believing the "ten half-lives" myth. The rule requires a survey to background and label removal, not a fixed holding period. ³
• Ignoring long-lived impurities. Lu-177m and similar contaminants defeat a naive decay-in-storage plan. ¹²
• Commingling radioactive and hazardous waste. Mixed waste is far harder and costlier to dispose of.
• Classifying by a single radionuclide. Mixtures require the sum-of-fractions rule across all contributing nuclides. ¹
• Treating manifests as logistics, not safety. An unaccounted-for shipment is a loss-of-control issue. ⁵

Regulatory Considerations

A medical low-level-waste program must align disposal decisions with the federal (or Agreement State) rules that govern radioactive-material disposal, and document its classifications and shipments so they are defensible on inspection. ^{1, 3}

Key frameworks to reference:

• 10 CFR Part 61 (61.55 and 61.56) — the waste-classification system (Class A/B/C, the two tables, and the sum-of-fractions rule) and the waste-characteristics/packaging requirements. ^{1, 2}
• 10 CFR 35.92 and 35.2092 — decay-in-storage authorization for byproduct material with a half-life of 120 days or less, and the three-year recordkeeping requirement. ³
• 10 CFR Part 20, Subpart K and Appendix G — general disposal options and the Uniform Low-Level Radioactive Waste Manifest (NRC Forms 540/541/542). ⁵
• 49 CFR Parts 172–173 (DOT) — hazardous-materials classification and packaging for Class 7 radioactive material in transport. ⁸
• NRC NUREG-1556, Volume 9 — program-specific guidance for medical-use licensees, including waste-disposal expectations. ⁶
• NRC Concentration Averaging and Encapsulation Branch Technical Position (Rev. 1, 2015) — current guidance on averaging concentrations to determine waste class. ⁷

The NRC has also opened rulemaking to modernize Part 61, but that effort is a proposed rule — the existing 61.55 Table 1 and Table 2 limits remain fully in effect, and programs should classify against the current tables. ¹¹

Agreement States administer their own equivalent programs. Among the states DRPS serves, Florida, Maryland, Virginia, California, Nevada, New York, Pennsylvania, and New Jersey are NRC Agreement States that regulate radioactive-material disposal under their own rules, while Washington, DC and Delaware are regulated directly by the NRC. A licensee must verify which authority governs its waste and confirm any state-specific manifest, transfer, or reporting requirements before shipping. For a state-specific view, see Florida radiation safety requirements. ¹

Frequently Asked Questions (FAQs)

What is low-level radioactive waste?

Low-level radioactive waste (LLRW) is radioactive material that is not spent nuclear fuel, high-level waste, transuranic waste, or uranium mill tailings. In medicine it includes contaminated gloves, syringes, vials, absorbent pads, and used sources. Under 10 CFR Part 61 it is classified by radionuclide concentration into Class A, B, or C, with a small remainder that exceeds Class C limits.

What are Class A, B, and C radioactive waste?

Class A, B, and C are waste classes defined in 10 CFR 61.55 by the concentration of specific radionuclides. Class A has the lowest concentrations and the least demanding packaging; Class B and Class C have higher concentrations and must meet structural-stability requirements, with Class C also requiring protection against inadvertent intruder access. Waste exceeding Class C limits is generally not acceptable for near-surface disposal.

How does decay-in-storage relate to Part 61?

Decay-in-storage (DIS) under 10 CFR 35.92 lets a licensee hold byproduct material with a physical half-life of 120 days or less until it decays to background, then dispose of it as ordinary or biomedical waste. Because most medical radionuclides are short-lived, DIS removes the majority of nuclear-medicine waste from the radioactive stream entirely. Only material that cannot go through DIS is classified and shipped under Part 61.

What is the sum-of-fractions rule?

The sum-of-fractions rule in 10 CFR 61.55 handles waste containing more than one radionuclide. You divide each radionuclide's concentration by its classification limit from the same column of the same table, then add the fractions. If the sum is less than 1.0, the waste qualifies for that class. It ensures a mixture is not misclassified by looking at any single radionuclide alone.

Does 10 CFR 35.92 still require holding waste for ten half-lives?

No. The current 10 CFR 35.92 does not set a fixed ten-half-lives holding period. Eligibility is limited to material with a physical half-life of 120 days or less, and the binding requirement is to survey the waste at its surface with an appropriate meter on its most sensitive scale and no interposed shielding and confirm it cannot be distinguished from background, then remove or obliterate the radiation labels. The ten-half-lives figure survives only as a practical ALARA planning guideline.

What class is most nuclear-medicine waste?

Almost all medical low-level waste that must leave the site is Class A. The radionuclide concentrations are typically far below the Class A limits in 10 CFR 61.55, so the waste only needs to meet the minimum packaging requirements of 10 CFR 61.56 and does not require the structural stability engineering imposed on Class B and Class C waste.

Who tracks low-level waste shipments?

Shipments of low-level waste to a licensed land-disposal facility are documented on the Uniform Low-Level Radioactive Waste Manifest (NRC Forms 540, 541, and 542) under 10 CFR Part 20, Appendix G, and transported under U.S. Department of Transportation hazardous-materials rules for Class 7 radioactive material. The generator must maintain the manifest, obtain acknowledgement of receipt, and investigate shipments that are not confirmed as received.

Key Takeaways

• Decay-in-storage handles most medical waste. Radionuclides with a half-life of 120 days or less can be surveyed to background and released, never entering the Part 61 stream.
• The "ten half-lives" rule is a myth. Current 10 CFR 35.92 requires a survey to background on the most sensitive scale and label removal — not a fixed holding period.
• Part 61 classifies by concentration. Table 1 (long-lived) and Table 2 (short-lived) define Class A, B, and C, with a GTCC tail above Class C.
• Use the sum-of-fractions rule for mixtures. Divide each concentration by its limit from one column of one table; a sum below 1.0 qualifies for that class.
• Most medical LLRW is Class A. It needs only the minimum 10 CFR 61.56 packaging, not the stability engineering required for Class B and C.
• Manifests are a safety obligation. Track every shipment on the Uniform Waste Manifest and treat an unconfirmed receipt as a potential loss-of-control event.

Conclusion

Low-level radioactive waste classification looks intimidating from the outside — two tables, three classes, a sum-of-fractions rule, and a GTCC tail — but for a medical program the framework resolves into a clear workflow. Short half-lives and low activities mean decay-in-storage carries most of the load, and the remainder is almost always Class A. The discipline lies in verifying the survey rather than trusting the calendar, flagging the long-lived tail before it accumulates, classifying mixtures correctly, and owning the manifest end to end.

For the RSO and medical physicist, the value of understanding Part 61 is not in classifying reactor waste; it is in knowing exactly where the medical exceptions hide and handling them before they become an inspection finding or an unaccounted-for shipment. A program that treats waste as a tracked, documented process — not an afterthought at the loading dock — protects its staff, its license, and its community.

How DRPS Can Help

Diagnostic Radiation Physics Services helps nuclear-medicine and radiopharmaceutical-therapy programs build waste programs that are practical and defensible: decay-in-storage procedures and survey documentation, long-lived-source inventories and disposal planning, waste-classification and sum-of-fractions calculations, manifest and transport support, and radiation-safety-program integration aligned with NRC and Agreement State requirements.

DRPS provides radioactive material license support, radiation safety officer consulting, and medical physics consulting across our service locations, including Florida, Maryland, Virginia, Washington DC, California, Nevada, New York, Pennsylvania, New Jersey, and Delaware.

A strong waste program is not about passing an inspection. It is about making the compliant disposal path the easy default for the clinical team.

Related Resources

• Decay-in-storage of radioactive waste
• Radioactive waste management in nuclear medicine
• Transport of radioactive material under DOT rules
• Package receipt and wipe testing
• Sewer disposal of radioactive material
• Radioactive material license support
• Radiation Safety Officer consulting
• Medical physicist consulting

References

1. U.S. Nuclear Regulatory Commission. 10 CFR 61.55: Waste Classification. ecfr.gov
2. U.S. Nuclear Regulatory Commission. 10 CFR 61.56: Waste Characteristics. ecfr.gov
3. U.S. Nuclear Regulatory Commission. 10 CFR 35.92: Decay-in-Storage. ecfr.gov
4. U.S. Nuclear Regulatory Commission. 10 CFR 35.2092: Records of Decay-in-Storage. ecfr.gov
5. U.S. Nuclear Regulatory Commission. 10 CFR Part 20, Appendix G: Requirements for Transfers of Low-Level Radioactive Waste and Manifests (NRC Forms 540, 541, 542). ecfr.gov
6. U.S. Nuclear Regulatory Commission. NUREG-1556, Volume 9, Revision 3: Program-Specific Guidance About Medical Use Licenses. nrc.gov
7. U.S. Nuclear Regulatory Commission. Concentration Averaging and Encapsulation Branch Technical Position, Revision 1. 2015. nrc.gov
8. U.S. Department of Transportation. 49 CFR Part 173, Subpart I: Class 7 (Radioactive) Materials. ecfr.gov
9. U.S. Nuclear Regulatory Commission. 10 CFR Part 71: Packaging and Transportation of Radioactive Material. ecfr.gov
10. U.S. Nuclear Regulatory Commission. Backgrounder on Radioactive Waste. nrc.gov
11. Ravichandran R, Binukumar JP, Sreeram R, Arunkumar LS. An overview of radioactive waste disposal procedures of a nuclear medicine department. J Med Phys. 2011;36(2):95-99. doi:10.4103/0971-6203.79692. PubMed
12. Prévot S, Karcher G, Marie PY, Verger A. Dealing with dry waste disposal issues associated with 177mLu impurities: a long-term challenge for nuclear medicine departments. EJNMMI Phys. 2023;10(1):3. doi:10.1186/s40658-023-00524-z. PubMed