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
- 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- EPA recently recommended (then rescinded) limiting dose from contaminated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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