Effects of Radiation Exposure on Human Body andRadiological Protection Criteria
May 9, 2011

1. Development of Radiological Protection Criteria
Radiological protection criteria are based on the Recommendation of the International
Commission on Radiological Protection, which reflects the latest scientific knowledge
about health effects of ionized radiation.

Passing through several phases, it iseventually employed as a national standard as shown below.

Basic Scientific Studies

Scientific Evaluations by specialized institution

ICRP Recommendations

Regional & TopicalInternational Safety Standards

Industry Standards

Standards (WHO etc)

(IAEA)(ISO, IEC)

National Regulations

For inquiries, please contact: QandA@aesj.or.jp

1

The ICRP Recommendation issued in 2007 (Publication 103) is currently the latest as
the basic recommendation.

The current Japanese standard is based on the basic

recommendation issued in 1990 (Publication 60), and the discussion as to how Japan
will employ 2007-version is in progress.
The foundation of ICRP Recommendation lies on the radiological protection system
based on the three principles, namely (1) justification, (2) optimization, and (3) theapplication of dose limits, all of which remain unchanged since 1990. Since the prefaceof 2007 Recommendation states that the Commission’s extensive review of the healtheffects of ionizing radiation has not indicated that any fundamental changes are needed
to the system of radiological protection based on the 1990 recommendations, andvalidity of the current Japanese regulations can be considered to remain intact.

(1) The Principle of Justification:
Any decision that alters the radiation exposure situation should do more good thanharm.

(The benefits from introducing a proposed activity outweigh the risks).

(2) The Principle of Optimization:
The likelihood of incurring exposure, the number of people exposed, and the magnitudeof their individual doses should all be kept as low as reasonably achievable, taking into
account economic and societal factors.

(lowering radiological exposure withinreasonable range).

(3) The Principle of Application of Dose Limits:
The total dose to any individual from regulated sources in planned exposure situations
other than medical exposure of patients should not exceed the appropriate limits
specified by the Commission.

(As for medical exposure of patients, benefits fromradiological exposure, such as diagnosis and treatment, outweigh the risks and ismanaged at a physician’s discretion).

For inquiries, please contact: QandA@aesj.or.jp

22. ICRP Recommendation on Dose Causing Detrimental Health Effects
ICRP 2007 Recommendation quantifies radiation dose limit based on the latest scientific findings
including the result of follow-up investigations on atomic bombings of Hiroshima/Nagasaki and thenuclear accident of Chernobyl nuclear power plant.

As the result, the recommendation states that

deterministic effects*1 would not occur if the level of exposure is less than 100 mSv.

Meanwhile,

an assumption that the probability of cancer and heritable effects has a linear dose–response
relationship is scientifically reasonable, even if the exposure level is less than 100 mSv.

Theseeffects for which the probability of occurring is regarded as a function of dose without threshold arecalled stochastic effects of radiation.*2
The risk of stochastic effects below 100 mSv has not statistically been detected, and its
level is assumed to be low as described below:•The risk coefficient for lifetime cancer mortality recommended by ICRP is 5 %/Sv.

•Based on this assumption, the lifetime cancer mortality rate increases by 0.5 %with the dose of 100 mSv.

•Considering that 20 to 30 % of the cause of death in Japan is cancer, the 0.5 %increase would only raise 20 % to 20.5 %.

•This increase would not be significant, given individuals’ different lifestyle habits(dietary habit, smoking etc).

3.

Exposure Situations and Dose Limits in ICRP Recommendation

The 2007 recommendation defines different dose limits for various types of exposure
situations and exposed individuals.

The exposure situations are classified into three

types: planned exposure situations, emergency exposure situations, and existingexposure situations.

As for categories of exposure, the Commission distinguishes

between occupational exposure, applicable to those engaged in the occupation based onjustification principle, and public exposure, applicable to the public other thanoccupational exposure, and medical exposure of patients.

The respective exposure

situations and the dose limits are shown in table 1 and 2.

For inquiries, please contact: QandA@aesj.or.jp

3Table 1.

Dose Constraints and Reference Levels.

Type of Situation

Occupational Exposure*3a) Planned Exposure

Dose Limit

Situations

20 mSv per year, averaged

Public Exposure
Dose Limit

Medical Exposure
Diagnostic Reference Level

1 mSv in a year

over 5 years, with no morethan 50 mSv in any one year.
b) Emergency Exposure

Reference Level *4

Reference Level―

Reference Level―

Situationsc)

ExistingExposure―

Situations

Table 2.

Framework for Dose Constraints and Reference Levels.

Bands of effective dose (mSv)

Examples(Acute or Annual Dose)① 20 ~ 100

Reference level for radiological emergency
including radiological accidents.

(estimated orresidual dose)② 1~ 20・ Constraints for occupational exposure inplanned situations.
・Reference level for radon in dwellings.
・Reference level for evacuation in emergency
situations.

③ 1 or less

Constraints for public exposure in plannedsituations.

As described above, the safety limit of public exposure in a planned exposure situation(e.g., defining the borderline of a radiation facility so that the amount of exposure ofgeneral public falls within the safety limit) is 1 mSv or less, and this is much lower
value compared to the 100 mSv, the level of exposure where the deterministic effects
would not occur with less than this value.

It has been so determined since the lowest

amount of exposure reasonably achievable is based on the principle of optimization ofradiological protection.

For inquiries, please contact: QandA@aesj.or.jp

4Meanwhile, while the ongoing Fukushima Daiichi nuclear accident corresponds to theemergency exposure situation, such categorization was not clearly made in the 1990
Recommendation, the foundation of the current national regulation. Thus national
government and the relevant ministries are assumed to be taking stricter measurescompared to international standard, with the basis stemming from the dose limit(public exposure of 1 mSv or less per year) that corresponds to the planned exposure
situation defined in 2007 Recommendation.

Table 3.

Radiological Protection Criteria.

Intervention Levels

Reference Levels

Occupational Exposure・life-saving

No dose restrictions(informed volunteers)

No dose restrictions if benefit
to others outweighs rescuer’srisk.

・other urgent rescue operations~ 500 mSv; ~ 5 Sv (skin)・other rescue operations－1000 or 500 mSv≦ 100 mSv

Public Exposure
・foodstuffs

10 mSv/year

・distribution of stable iodine

50 － 500 mSv (thyroid)・sheltering

5 － 50 mSv in 2 days

・temporary evacuation

50 － 500 mSv in 1 week・permanent relocation

100 mSv for the first yearor 1000 mSv

・all countermeasures combined－in an overall protection strategy

In planning, typically between
20and100mSv/year

according to the situation.
ICRP recommends that the following actions be taken by Japanese government as theresponse to the Fukushima Daiichi nuclear accident.

For inquiries, please contact: QandA@aesj.or.jp

5Summary of the ICRP Comment(as of March 21, 2011, ICRP ref:4847-5603-4313)•ICRP (hereinafter called “the Commission”) wishes to express the deepest
sympathy to those in Japan affected by the recent tragic events.

•The Commission hopes that the following and recent recommendations will prove
helpful.

For the protection of the public during emergencies the Commission continues torecommend that national authorities set reference level for the highest planned
residual dose (dose amount expected to remain after a complete implementation ofradiological protection) in the band of 20 to 100 mSv.
•Contaminated areas may remain when the radiation source is under control.
Authorities will often implement all necessary protective measures to allow people
to continue to live there rather than abandoning these areas. In this case theCommission continues to recommend choosing reference levels in the band of 1 to20 mSv per year, with the long-term goal of reducing reference levels to 1 mSv peryear.

•Occupationally exposed workers in emergency situations should stay within the500～1000 mSv band to protect their own lives.

•The Commission recommends no dose restriction for lifesaving efforts by informed
volunteers.

The level specified in ① of table 2 is adopted for the situation where radiation dose isuncontrollable, as in the case of Fukushima nuclear accident, and the lower level of ②isused when dose is controllable amongresidual contamination.

Efforts should bemade toward achieving the level noted in ③, which is the ultimate target.

That is, thelevels listed in ① and ② are undesirable, but are applied as a temporary measure sothat the public would bear greater burden or permanently leave their home lands.
Especially, the level specified in ② is also applied for those exposed to high dose from

For inquiries, please contact: QandA@aesj.or.jp

6radon in dwellings and caretakers of patients treated with radiopharmaceuticals,
sometimes applied in a normal circumstances.

Also, this level is commonly applied for

occupationally exposed workers and does not involve adverse health effects.

However,when applying the level noted in ① and ②, specific protection measures should betaken for those with health problems, infants, and pregnant women.
The principles of justification and optimization recommended by ICRP justifies
application of the above concepts, given that there is no deterministic effects with doseof 100 mSv or less and that the risk of stochastic effects is low enough.

*1 Deterministic Effects:

It is caused by high dose of radiation and characterized by a threshold dose for radiation
damages.
*2 Stochastic Effects:

Malignant disease and heritable effects for which the probability of an effect occurring,
regarded as a function of dose without threshold. The effects of low dose of radiation
on human body involve various theories as to the existence of lower limit, which are yet
to be verified.
*3 Measures should be taken so as not to exceed the upper bound.
*4 Since it is a reference value, standards should be adjusted as the situation demands. (See table 2).

For inquiries, please contact: QandA@aesj.or.jp

7