ML25343A205
| ML25343A205 | |
| Person / Time | |
|---|---|
| Issue date: | 12/01/2025 |
| From: | Tanya Smith NRC/NSIR/DPR |
| To: | |
| References | |
| Download: ML25343A205 (0) | |
Text
Lets Talk About Potassium Iodide Todd Smith, PhD U.S. Nuclear Regulatory Commission
Potassium Iodide policy in the U.S.
- U.S. Nuclear Regulatory Commission (NRC) regulations require consideration of KI as a supplemental protective action to evacuation and sheltering-in-place regulations and guidance are specific to large light water reactors
- Federal policy recommends KI to be stockpiled and distributed for emergency workers and institutionalized persons, and considered for the public within the emergency planning zone around large light water reactors
- State and local governments decide whether to use KI for the public Federal Policy on Use of Potassium Iodide (KI), 67 Fed. Reg. 1355, 2002.
U.S. KI policy is evidence-based
- Efficacy and efficiency of KI implementation could benefit from modernization
- KI Subcommittee within the Federal Radiological Preparedness Coordinating Committee (FRPCC) is assessing the need for guidance updates
- KI guidance can benefit from:
US NRC. Literature Review: Evaluation of Implementation Strategies for Potassium Iodide; 2025.
ADAMS Accession No. ML25077A036.
insights on radioiodine release from state-of-the-art consequence analyses lessons from past events adequacy of dietary iodine sufficiency and daily iodine intake advances in nuclear technologies best practice
World Health Organization, Iodine thyroid blocking: Guidelines for use in planning and responding to radiological and nuclear emergencies, WHO 2017. https://www.who.int/publications/i/item/9789241550185 WHO recommends further KI research:
radioiodine biokinetics optimal timing of intake feasibility and acceptability best practices for stockpiling or pre-distribution Quality evidence is needed
KI effectiveness depends on many factors Ilias I.,Rizzo M., Meristoudis G. Potassium Iodide in Nuclear Accidents: Give it Timely, Swiftly and Judiciously. Endocr Metab Immune Disord Drug Targets; 23(6):873-875; 2023.
To be effective against inhalation exposure, KI must be administered within a specific time window
< 12-24 hours before exposure ~90% to 70% effective
< 1-3 hours after exposure ~85% to 50% effective
> 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> after exposure has negligible protective effect Modeling can provide useful insights for informing KI implementation strategies. Factors include:
source term (optimal timing and radioiodine form)
KI time dependency (biokinetics)
iodine sufficiency (biokinetics)
distribution strategy (feasibility)
human factors (acceptability)
state of practice (best practice)
Modeling can inform KI strategies What is MACCS?
- MELCOR Accident Consequence Code System
- Analysis tool for developing realistic estimates of consequences of nuclear power plant incidents
- Developed by NRC and Sandia National Laboratory
- Extensive use by NRC and domestic and international organizations How is MACCS used?
- Consequence studies
- Level 3 Probabilistic Risk Assessment (PRA)
- Cost-benefit analysis
- Risk-informed decision-making
NRC is using MACCS to assess KI strategies Literature Review: Evaluation of Implementation Strategies for Potassium Iodide MACCS models effectiveness of KI implementation:
- KIMODL determines whether to consider KI or No KI
- Linear no-threshold (LNT) dose-response model applied
- Thyroid dose to a population is reduced by a factor 1 x
- where, EFFACY reduces the dose to the thyroid from inhalation (value: [0-1])
POPFRAC is the fraction of a cohort that ingests KI (value: [0-1])
US NRC. Literature Review: Evaluation of Implementation Strategies for Potassium Iodide; 2025. ADAMS Accession No. ML25077A036.
US NRC. Evaluation of MACCS KI Modeling Capability; 2025. ADAMS Accession No. ML25017A059.
Scenarios to model in MACCS No KI KI pre-distributed KI picked up at distribution centers/shelters KI stockpiled - delivered when and where needed
NRC tools demonstrate benefits of masks
KI use depends on the technology
Communication is key NRC Literature review revealed communication is vital part of strategy Accurate information on KI is readily available to the U.S. population Search engines provide information from credible sources (e.g., Federal agencies)
The terms magic pill or anti radiation pill still lead to good information Public interested in KI use during pregnancy and dose to children Federal guidance will be updated to address effective strategies and applicability to advanced nuclear technologies
NRC supports effective KI policy in the U.S.
Contact:
Todd Smith, PhD todd.smith@nrc.gov