1Summary report on the lessons about the technical standards for prevention
of radiation hazards in emergency exposure situations and existing
exposure situations after the TEPCO Fukushima Daiichi Nuclear Power
Plant accident
Radiation Council
Advisory board of implementing ministries/agencies
1. Background
Technical standards for prevention of radiation hazards in Japan (hereinafter
referred to as "technical standards") have been historically established with
respecting and incorporating the ideas internationally agreed such as the
International Commission on Radiological Protection (hereinafter referred to
as "ICRP"), the International Atomic Energy Agency and so on. In adopting
the policy, the Radiation Council has confirmed validity and consistency of
technical standards by playing a role in ensuring uniformity among them.
With regard to the adoption of ICRP Publication 103 "The 2007
Recommendations of the International Commission on Radiological
Protection", the Radiation Council had just started the discussion in Japan
before the TEPCO Fukushima Daiichi Nuclear Power Plant (hereinafter
referred to as "TEPCO FDNPP") accident occurred. Relevant Ministries and
Agencies were forced to respond to the accident, and they prioritized the
formulation of various technical standards regarding both emergency
exposure situations and existing exposure situations.
Coping with the TEPCO FDNPP accident, the response by the government
needed unprecedented decision to select various protective actions. However,
if there is a change in the situation over the course of time, the technical
standards need to be reconsidered to appropriately respond to the changed
status.
The Radiation Council did not have the function of voluntary investigation
and recommendation. Act on Technical Standards for Prevention of Radiation
Hazard (Act No.162 of 1958) was revised in April 2017, and then the
Radiation Council came to have authority to investigate and make
recommendations voluntarily. Taking it as a trigger, the Radiation Council
decided to scientifically investigate and review the present situation after the2TEPCO FDNPP accident to summarize relevant reports.
The first proposal report from the Radiation Council has been made out to
summarize the latest fundamental framework of radiological protection
mainly based on ICRP. This report (hereinafter referred to as "Report on the
fundamental RP (radiological protection) policy") contains the concepts and
the principles to be referred to when relevant Ministries and Agencies will
develop technical standards. It was published on January, 2018.
As for the next step, the Radiation Council decided to review the standards
formulated after the TEPCO FDNPP accident following the Report on the
fundamental RP policy. In particular, it focused on the criteria of radioactive
concentration in foods and ambient radiation dose-rates, since more
consideration will be required concerning the relationships between food
contamination/ambient dose rates and individual exposure doses such as
effective dose. After the accident, the change in the situation over the course
of time has been well characterized to review the effectiveness of these
standards and the actual conditions of their operation. Clarification of the
lessons learned from the review will complement the Report on the
fundamental RP policy, and will also be able to use discussion in the Radiation
Council for future development of technical standards in emergency exposure
situations and existing exposure situations.
2. Lessons learned
(1) Importance of correct understanding of assumptions and scenarios
behind numerical standards
Point 1.1: There were cases where the numerical values were used beyond
the originally intended use of them.
The provisional regulation values for food were adopted, which were
numerical values originally developed by the Nuclear Safety Commission
as an indicator that it is appropriate for the Nuclear Emergency Response
Headquarters to start considering whether to take the food and drink
intake restriction measures. The same numerical values were used as a
cancellation requirement of the measures.
In this way, when using numerical values beyond the originally intended3use of them, it is necessary to explain to the society after fully
understanding the positioning and derivation process of such standard
values (for example, it was formulated as a measure of whether the
Nuclear Safety Commission would introduce food intake restriction
referring to the Chernobyl accident, or it took into account the physical
half-life due to natural decay of nuclides under the scenario of exposure
by a single large release, etc.) at the operation stage.
Point 1.2: It has been pointed out that a situation has occurred as "Use of
the criteria can go around independently out of context", that is, only the
numerical values are spread widely without proper understanding of
their backgrounds and meanings.
With regard to the current reference values for food (e.g.100 Bq/kg for
general foods), the requirements for designation of the contamination
status survey area and the requirements for the area for establishing the
decontamination implementation plans under Act on Special Measures
Concerning the Handling of Environmental Pollution by Radioactive
Materials (areas exceeding 0.23 μSv/h), which are derived from 1
mSv/year as additional effective dose, it has been pointed out that a
situation as "Use of the criteria can go around independently out of
context" such as "This food is dangerous because it exceeds 100 Bq/kg",
"It may be dangerous because it may exceed 50 Bq/kg (which is the
standard for infant food) when a food for adults is given to infants", or "If
at least one site in the sites after decontamination has more than 0.23
μSv/h, decontamination is insufficient and it is dangerous, so it must be
re-decontaminated" has occurred.
Point 1.3: In some cases, the meaning or the position of the numerical
standards has not been properly conveyed.
With regard to the requirements for designation of the contamination
status survey areas and the requirements for the areas for establishing
the decontamination implementation plans, in "the interim report of the
study meeting held by the Ministry of the Environment, Reconstruction
Agency and 4 cities in Fukushima prefecture", it is mentioned that their
intention such as "The purpose of radiological protection is to reduce the
exposure dose of individual as low as reasonably achievable.
Decontamination is one of the means to accomplish it but it is not only.",4"The value 0.23 μSv/h is not a target for decontamination. It is the
numerical value to use in designating the contamination status survey
areas." and "A calculating formula to convert the annual additional dose
1 mSv to 0.23 μSv/h is an estimated value in a specific daily life style."
has not been conveyed correctly to the residents.
Lessons based on the above issues
Although it is natural for technical standards to be formulated with a
certain assumption and scenario in the absence of sufficient data
immediate after an accident, it is necessary for policy makers to define
the position of the viewpoint of radiological protection, to clarify the
target and the period to which the standards should be applied, to
properly understand and operate them, and at the same time to explain
them to the society including the possible advantages and disadvantages
which may be brought about. Then, it is also necessary to explain what
extent the technical standards have the degree of safety margin or
uncertainty depending on the exposure situation, in consideration of the
change of the situation etc.
It is necessary to understand that there were some cases where the
relationship between the assumptions/scenarios and operation of the
standards was unclear in the response to this accident, that safety cannot
be ensured only by lowering the standard values, that at the time of an
accident, it is important to take various protective measures in
consideration of optimization and reduction of the additional individual
doses and to promote the recovery and reconstruction of the society while
considering the effects other than radiation, and that measures by
numerical standards are mere one means for that.
(2) Difference of implications between numerical standard based on
reference levels and dose limits in planned exposure situations
Point 2.1: Some technical standards developed after the accident required
"bellow 1 mSv as an additional annual dose" by means of regulatory
compliance.
As it is judged as a violation of the law if the food is distributed beyond5the numerical standard, the current standards for food are considerably
strict as the technical standards in existing exposures situations and
differ from the concept of reference levels.
Point 2.2: In Japan’s legal system, it seems that adopting the concept of
reference levels contains legislative issues, and regulatory methods by
means of punitive or obligatory actions should not be ruled out uniformly.
On the other hand, when trying to set the numerical standard for an
individual dose in the general public in emergency exposure situations or
existing exposure situations, it is necessary to understand the difference
between the meaning of dose limits and reference levels.
(3) Importance of a process of verifying the validity of the standards
comparing with the original purpose when there is a change in
radiological situation over the course of time or accumulation of data
Point 3.1: It is said that the revisions of technical standards developed
mainly in response to existing exposure situations are difficult because of
concern about the social impact, especially reputational damages.
As for current standard values for food, radioactive concentration in
actual food is much lower than assumed and the estimated internal dose
from food intake is extremely lower than 1 mSv per year. Therefore, it
may be hard to explain the need of continuously using the current
standard value for monitoring from the perspective of radiological
protection.
Point 3.2: From the viewpoint of optimization, it is important to establish
a process of verifying the validity of the numerical standards comparing
with the original purpose when the radiological situation has changed
over the course of time or characterized data have accumulated. In
addition, it is necessary to develop the decision making policy of
transitioning the exposure situation from the emergency exposure
situation to the existing exposure situation.
3. Viewpoint of deliberation in the Radiation Council based on the lessons
Based on the lessons written in 2., it will be fundamental to deliberate the6development of technical standards in emergency exposure situations and
existing exposure situations in the following way. In this regard, however,
when the Radiation Council is actually consulted regarding technical
standards, it will discuss them on a case-by-case basis depending on the
actual circumstances at that time.
(1) When formulating a numerical standard, it is necessary to confirm the
validity of the underlying assumptions and scenarios and the concept of
the margin assumed in the assumptions and scenarios. In order to avoid
social misunderstandings and confusions such that two simple categories
as ‘safety’ and ‘danger’ were observed by "Use of the criteria can go around
independently out of context" diverted away from the original aim of the
standard, appropriate measures should be taken such as adding notes to
the report on matters to be kept in mind when handling the numerical
standard.
(2) When trying to set the numerical standard for an individual dose for the
general public, it is necessary to differentiate the meaning of the dose limit
and the reference level. In particular, if the numerical standard is
implemented by the regulatory method with penalties etc., it should be
checked whether it cannot be secured by other methods.
(3) It is necessary to check whether the process of verifying the validity can
be beforehand incorporated in the system in term of the original purpose,
when there is a change in situation over the course of time or accumulation
of characterized data.
Supplement
This Report is to be primarily used by the Radiation Council for its own
deliberations, and it’s also to be used by relevant Ministries and Agencies for
reference when they formulate technical standards. In addition, it is expected
that it helps the people and experts outside the field of radiological protection
and will serve as a reference for the ongoing efforts to recover from existing
exposure situations.
From now on, when formulating technical standards in emergency exposure
situations or existing exposure situations, it is necessary to pay particular7attention to this Report in addition to the Report on the fundamental RP
policy.
The Report does not intend to disapprove the approach or specific values
regarding the technical standards already formulated based on the TEPCO
FDNPP accident, since the validity cannot be judged only by the uniformity
of technical standards. Basically, the Radiation Council will continue to
compile the documents for preserving the uniformity of technical standards
in the regulatory guide.