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Topic 2 - Regulatory Agencies

Radiation Protection Standards

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  • Dangers of X rays & radium quickly recognized
  • 1928 ICRP formed by the International Society of Radiology
  • NCRP founded 1929 (as advisory committee on X-ray and Radium protection)

Evolution of Dose Standards

  • Early years - based on skin reddening
    • monthly limit: 1/100th of amount that would cause erythema in acute exposure
  • Roentgen defined in 1930s
    • old limit was 600 R
  • ICRP / NCRP adopted 0.02 / 0.01 R as daily “tolerance” dose for workers

Limits for Occupational Exposure

  • Initial limits were for workers & external radiation
  • Limits on internal emitters began in 1920
  • Benchmarks before WWII
    • 0.1 R/d whole-body
    • 0.1 mCi (3.78 kBq) as maximum body burden of 226Ra
  • These standards set basis for safe handling of radiation at the start of atomic energy program
  • Early standards were adapted to address other unstudied radiations (like neutrons) encountered during the war effort
  • Concept of biological effectiveness (rep, rem) added
  • Rising concern about possible stochastic (e.g., cancer, genetic) effects resulted in lowering of dose to 0.3 rem/wk
  • 1956 - ICRP recommended gonadal & blood-forming organ limit of 5 rem/y
  • Also restricted accumulated dose to 5 (N-18)
  • Limited exposure before age 18
  • Limited dose to 3 rem/13 weeks
  • 1977 next change - limit of 5 rem/y; no lifetime limit
  • Other changes: method used to calculate dose (1977)
    • old method: critical organ (~15 rem) & whole body
    • new method: considered differences in radiosensitivity of organs (tissue weighting factors)
  • Consequence: some difficulty in comparing old and new doses

Limits for Exposure of General Public

  • Public dose not really considered until 1950s
  • General practice to set public limit below occupational levels
  • Concept of “no-threshold” for risks demanded no exposure without expectation of benefit (FRC 1960)
  • ALARA concept also introduced

Radiation Standards for the Public

  • 1955, ICRP, 1/10 of occupational levels
  • 1977, ICRP, public dose limited to 0.1 rem/yr, sometimes 0.5
  • applied to intended release of radioactive materials
  • EPA recently recommended (then rescinded) limiting dose from contaminated sites to 15 mrem (NRC - 25 mrem)

Environmental Radiation Standards

  • NCRP (indoor radon)
  • FAO (radionuclides in food)
  • EPA (air emissions)
  • NRC

Radiation Protection Standards

  • Changes in Concepts of Standard Setting
    • old standards adequate
    • new standards consider ALARA, BAT, acceptable risks
  • How Modern Protection Standards are Established
    • Gather scientific data (NAS/NRC, ICRP, NCRP, UNSCEAR, etc)
    • Fight a lot
    • Do what’s politically expedient
  • Organizations involved in establishing and implementing standards
    • NRC
    • EPA
    • FDA
    • States
    • Municipalities
    • DOT
    • International Agencies
    • Others

Summary

  • Standards have evolved in response to:
    • Increased understanding of radiation response
    • Public & political pressures
    • No “major” shift in standards (in U.S.) since 1950s
      • “minor” calculational change
  • Several categories of standards
    • Occupational
    • Public
    • Environmental
    • Remediated sites
    • Decommissioned sites
  • Many Agencies involved in process
  • Inconsistencies abound
    • Within agencies
    • Between agencies
  • Standards are continuing to evolve

 

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