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Radiation protection lessons learned from the TEPCOFukushima No.1 NPS accidentItsumasa Urabea, Takatoshi Hattorib, Takeshi Iimotoc & Sumi Yokoyamad
a School of Engineering, Fukuyama University, 985 Higashimura, Fukuyama-shi, Hiroshima729-0292, Japanb Radiation Safety Research Center, Central Research Institute of Electric Power Industry,2-11-1 Iwatokita, Komae-shi, Tokyo 201-8511, Japanc Division for Environment, Health and Safety, The University of Tokyo, 7-3-1 Hongo,Bunkyo-ku, Tokyo 113-8654, Japand School of Health Science, Fujita Health University, Toyoake-shi, Aichi-ken 470-1192,JapanPublished online: 08 Nov 2013.
To cite this article: Itsumasa Urabe, Takatoshi Hattori, Takeshi Iimoto & Sumi Yokoyama , Journal of Nuclear Science andTechnology (2013): Radiation protection lessons learned from the TEPCO Fukushima No.1 NPS accident, Journal of NuclearScience and Technology, DOI: 10.1080/00223131.2014.855681
To link to this article: http://dx.doi.org/10.1080/00223131.2014.855681
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Journal of Nuclear Science and Technology, 2013http://dx.doi.org/10.1080/00223131.2014.855681
50TH ANNIVERSARY INVITED REVIEW
Radiation protection lessons learned from the TEPCO Fukushima No.1 NPS accident
Itsumasa Urabea∗, Takatoshi Hattorib, Takeshi Iimotoc and Sumi Yokoyamad
aSchool of Engineering, Fukuyama University, 985 Higashimura, Fukuyama-shi, Hiroshima 729-0292, Japan; bRadiation SafetyResearch Center, Central Research Institute of Electric Power Industry, 2-11-1 Iwatokita, Komae-shi, Tokyo 201-8511, Japan;
cDivision for Environment, Health and Safety, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan; dSchoolof Health Science, Fujita Health University, Toyoake-shi, Aichi-ken 470-1192, Japan
(Received 19 March 2013; accepted final version for publication 10 October 2013)
Lessons learned from the TEPCO Fukushima No.1 NPS accident are discussed from the viewpoint ofradiation protection in the situation of nuclear emergency. It became clear from the discussion that theprotective measures should be practiced by taking into account the time profiles of the radiological dis-aster after the nuclear accident and that the land and coastal sea areas monitoring had to be practicedimmediately after the nuclear accident and the communication methods to tell the public about the ra-diation information and the meaning of protective measures should be developed for mitigation of thesociological aspects of disaster impacts. And it was pointed out from the view point of practicing counter-measures that application of the reference levels, above which it was judged to be inappropriate to plan toallow exposure to occur, played an important role for practicing protective measures in an optimized wayand that the quantities and units used for quantifying radiation exposure of individuals in terms of radia-tion doses have caused considerable communication problems. Finally, the occupational exposures and thepublic exposures that have been reported so far are shown, and it is concluded that there is no conclusiveevidence on low dose exposures that would justify a modification of the radiation risk recommended bythe International Commission on Radiological Protection.
Keywords: radiation protection; time profile of the disaster; land and coastal sea area monitoring; referencerevel; occupational and public exposure; radiation risk
1. Introduction
Radiation protection system should be evolved bylessons learned from the emergency response performedin the early stage of the nuclear disaster in order toreduce the radiation exposure of the people in theemergency exposure situation as low as reasonablyachievable.
From the viewpoint of radiation protection, it is aprinciple not to diffuse a large amount of radioactivematerials outside the nuclear power station (NPS) in theemergency situation. But, on account of losing controlof the diffusion of radioactivematerials from the nuclearpower plants, it is quite possible to meet the situation toreduce radiation exposures of the general public by con-trolling exposure pathway to them as soon as possible.
In the early stage of the nuclear disaster occurred atthe Fukushima No.1 Nuclear Power Station of TokyoElectric Power Company (hereinafter referred to as “TFNo.1 NPS”), it was inevitably required to practice pro-
∗Corresponding author. Email: [email protected]
tective actions urgently and effectively after the occur-rence of nuclear accidents because the intensity of theradioactivity in the environment surrounding NPS var-ied rapidly, and it would be also strongly required to per-form rationally the protective measures by utilizing lim-ited resources for countermeasures against the nucleardisaster. Furthermore, the radiation protection princi-ples and the criteria for the emergency exposure situa-tion recommended by the International Commission onRadiological Protection (ICRP)were applied for the firsttime, and the public concerns on the health effects of lowdose radiation became important for implementation ofthe countermeasures.
Some problems on radiation protection faced in theearly stage of the nuclear disaster at the TF No.1 NPSare clarified and discussed here from the viewpoint ofimprovement of radiation protection practice in theemergency exposure situation caused by severe nuclearaccident.
C© 2013 Atomic Energy Society of Japan. All rights reserved.
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Figure 1. A typical example representing a time profile ofthe radiation dose rate observed around the TF No.1 NPS inthe early stage of the nuclear disaster. Dotted and broken linesrepresent the decreasing characteristics of I-131 and the aver-ages of Cs-137 and Cs-134 which were assumed to be existedequally, respectively. The numbers of I, II, III in the figure rep-resent the periods of the high radiation dose rates with rapidchange, high radiation dose rates mainly by I-131 deposited onthe ground surface, and those by Cs-137 andCs-134 deposited,respectively.
2. Countermeasures taken depending on time profileof the radiological disaster
2.1. Time profile of the radiological disasterA typical example representing time profile of the ra-
diation dose rate observed around the TF No.1 NPS isshown in Figure 1 [1]. As shown in Figure 1, variation ofthe radiation dose rate can be divided into three stageswhich were related to the behavior of radioactive ma-terials released. The first stage shown by number I inFigure 1 represents the high dose rates accompanied byrapid change but is lasted in almost 10 days. The radi-ation dose rate in this stage, which corresponded to theperiod passing of radioactive plumes of noble gases, io-dine, and cesium, showed some differences from thosemeasured at the monitoring stations situated more thana few tens of km far from the TF No.1 NPS [2]. The lat-ter ones did not show the marked change after the rapidincrease of the radiation dose rate. This difference wouldbe due to diffusion properties of radioactive materials inthe air and due to decay characteristics of the radioac-tive materials with shorter half-lives.
In various types of exposures in this period, thyroidequivalent doses caused by inhalation of radioactive io-dine in the air and by ingestion of the iodine depositedon the ground surface might be more important than ef-fective doses by gamma-rays from the radioactive plume,because a large amount of radioactive iodine inferredfrom the data monitored later [3] was expected to be de-posited on the ground surface, vegetables, rivers, and soon, although it depended on the meteorological condi-tion. In this period, the countermeasures were accompa-nied by some difficulties because the release rate of ra-dioactive materials was not provided from the operatorand the insufficient radiation information was obtainedat the monitoring stations in the wide area far from theTF No.1 NPS [4]. So, it was strongly required to estab-lish a measurement or an evaluation system of radioac-
tive materials released to the natural environment imme-diately after the nuclear accident in case the radiologicalinformation could not be obtained as scheduled.
The second stage corresponds to the period duringwhich high exposure rates by radioactive iodine and ce-sium which were spread over the wide area far from theTF No.1 NPS were observed. As is shown by number IIin Figure 1, this stage seems to continue about 30 daysafter the latest large release of the radioactive materialsfrom the NPS. Effective dose rates by the ground andsky shines as well as the thyroid equivalent doses by eat-ing vegetables or drinking water contaminated would beimportant since the variation of exposure dose rates wasmainly due to the radioactive iodine in this period.
Though it is very difficult to make sure the protectiveactions were appropriately performed or not [5,6], if theywere not practiced successfully within about 30 daysafter the accident, it was likely that the effective doseof some people including children might exceed even20 mSv and the thyroid equivalent dose might exceedeven 50 mSv. And it was also apparent that the radioac-tivematerials were released into the coastal sea area and,as a result, the marine contamination was also detectedin this period [7]. This problem became important fromthe viewpoints of not only the disaster management tocontrol consumption and distribution of seafood butalso the issue of international relations. By taking intoconsideration of the total amount of radioactive materi-als released widely from the TFNo.1 NPS and the dura-tion of high exposure dose rates in the air, the emergencyresponse of this period played an important role in thecountermeasures tomitigate the radiological health haz-ard due to the nuclear accident. It was found from theexperience that a nuclear disaster response organizationhad to be established and addressed to the disaster asearly as possible after the nuclear accident.
The third stage shown by number III in Figure 1 isthe period that higher exposure dose rates were continu-ing mainly by the radioactive cesium deposited on theground. The exposure dose rate varied not only withthe half-life of the cesium but also with its migrationin the natural environment that was mainly caused byprecipitations. Localizations of the radioactive materi-als caused the important problems in planning the de-contamination procedures of the living environments. Inthis period, many people in the public tended to pay at-tention to the radiation safety in the daily life, especially,to the long-term health effects by low dose exposures. Asa result, protective measures had to face to address theproblems associated with the restriction of shipment ofthe foods contaminated [8,9] and themanagement of theradioactive wastes generated by the decontamination ofthe living environments [10]. That is, the protective mea-sures in this stage had to be performed so as to minimizethe total detriments originated in the health effects andin the social and economical losses by ensuring the op-timization process of the protective actions. Especially,mutual understanding on the radiation safety goal be-tween the national government and the people affected
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and the reliable implementation of protective measuresplayed an important role for realizing optimization ofradiation protection, that is, stakeholder involvement asa basis for optimization would be the most importantproblem in this period.
2.2. Protective actions in the nuclearemergency situation
Emergency exposure situations will occur unexpect-edly and will require urgent protective actions in orderto avoid or reduce undesirable consequence occurringin the people living in the wide area far from an NPS.In various factors relating to radiation protection of thepeople, the time factor of practicing protective measuressuch as evacuations, limitation of intake of foods har-vested in the contaminated areas is very important be-cause otherwise the people in the vicinity of theNPSwillreceive a large amount of exposure doses in a short pe-riod immediately after the nuclear accident. So, appro-priate decision making for practicing countermeasureswas required at the stages I and II of the TF No.1 NPSdisaster. But, the people as well as the staffs engaged inthe disaster management could not immediately under-stand exactly the abnormal exposure situation althoughthey received information about unusual radiation levelsfrom the monitoring stations, which seemed to be dueto the prejudice caused by a human cognitive bias. So, itwould be reasonable to consider at least the first severaldays after occurrence of the severe nuclear accident to beunder the emergency situation which needed the protec-tive measures to reduce radiation exposure of the peopleregardless of the existence of the radiological informa-tion. But, at the same time, it would be justified to per-form radiation monitoring in the highly contaminatedarea around the TFNo.1 NPS by the well-trained radia-tion protection specialists organized by the GovernmentNuclear Emergency Response Headquarters (NERHQ)even after setting the emergency countermeasure areaconcentrically from the nuclear power station.
From the experience of the TF No.1 NPS accidentit became apparent that the radiation measuring sys-tem to get radiation information at anytime and in any-where had to be prepared for improvement of protectivemeasures in the early stage of nuclear disasters. But, theradiation protection practice such as radiation measure-ments and dose estimations in or around the area con-taminated requires specialized techniques in the samesituation as the medical measures. Furthermore, if thenuclear disaster is accompanied with natural disasterslike tsunami and earthquake and so forth, it is conceiv-able not to be able to get radiation information for longtime as was expected in [4]. In order to obtain reliableradiation information around the NPS in the accidentalcondition, it will be essential to organize an operationalunit of radiation protection, namely, Special Radiolog-ical Protection Force (SRP-Force), in the national andlocal governments that will urgently respond to radia-tion protection issues in emergency exposure situations.
Since the SRP-Force has to play an important role in theemergency exposure situation, it has to be always trainedwell by assuming nuclear emergency situations in orderto work successfully in anywhere in the case of nuclearaccidents.
2.3. Declaration of termination of the nuclearemergency situation
An urgent protective action against unexpected re-lease of radioactivematerials has to be continuously pre-pared as long as the nuclear power plants do not get outof an unstable operation condition. This means that theprotective actions relating to nuclear emergency cannotbe terminated without realizing the safe condition of thenuclear power plants. In case of the accident in the TFNo.1 NPS, it was said that high possibility of the ab-normal discharge lasted about 9 months before achiev-ing safe reactor core condition. This experience showedthat there was a possibility that the emergency exposuresituation defined by the ICRP continued for long time.On the other hand, the period of emergency exposuresituation should be as short as possible if the protectiveactions could be practiced successfully since the coun-termeasures were lots of burden to the people. By takinginto consideration of these factors, it would be reason-able that it was not until the emergency exposure situa-tion ended that the release of radioactive materials fromthe nuclear power plants became under control. TheNu-clear Safety Commission (NSC) showed the standpointfor the termination of the urgent protective actions forthe TF No.1 NPS accident and made clear that the ex-istence of transition period from the emergency expo-sure situation to the existing exposure situation [11,12].Based on the standpoint, the protectivemeasures such asestimation of personal doses or environmental impactsby nuclear disaster planned in the existing exposure sit-uation had to be carried out in parallel with the prepa-ration of the countermeasures that could respond to anunexpected release of radioactive materials from the nu-clear power plants. But, it is to be noted that the termina-tion of emergency situation of the nuclear disaster is notstill declared by the NERHQ though there will be lesspossibility to face to the emergency exposure situation.Since the protective measures in the emergency exposuresituation, partly also in the transitional exposure situ-ation, were greatly different from those in the existingexposure situation, the termination of the nuclear emer-gency situation had to be appropriately declared at thesame time as the declaration of attaining stable reactorconditions in December 2011.
Even after declaration of the termination of nuclearemergency situation, it is apparent that there still existsthe area highly contaminated such as farmlands, for-est, houses, and so on, so protective measures have tobe performed continuously by the administrative orga-nization such as the Disaster Reconstruction Manage-mentHeadquarters (DRMHQ) of the national and localgovernment that have been transferred responsibilities
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of the protective measures from the NERHQ. Protec-tive actions by this organization have to be continued toachieve the safety objectives that can be agreed amongthe stakeholders on the recovering of the people’s dailylives.
2.4. Optimization of prolonged disastermanagement
When an unexpected sever accident is occurred at nu-clear power plants, the contamination by radioactive ce-sium will distribute widely far from the NPS and will beprolonged for long time. Under these circumstances, theprotective measures to reduce additional exposure dosesof the people will be practiced on the basis of the dosecriterion that will be set at first with the reference levelrecommended by the ICRP. But setting reference level ishighly affected by the attitude toward the risk of radi-ation exposure of the people, and this often tends to bedetermined politically without taking into considerationof the optimization process of radiation protection. Forexample, protective actions taken in the highly contam-inated area will be selectable from the two measures, along-term relocation of the people and a decontamina-tion of the area contaminated. But, both of these actionsforce to receive the newly occurring health and economicburdens to all the people in Japan as well as the habitantsaffected by the disaster. The former measure will im-pose the inconvenience of daily life of the people and thehealth hazard originated in the protective action itselfand the latter one will impose an enormous economicburden to the nation. So, these two kinds of detrimentsoriginated in practicing protective measures as well asreceiving radiation doses by the nuclear accident have tobe taken into consideration in setting the reference levelfor protective measures and in choosing the protectivemeasure. This problem had to be investigated in the TFNo.1 NPS disaster as early as possible in the transitionalperiod from the emergency exposure situation, since thepeople tended to request the lowest level of the refer-ence level recommended by the ICRP for protective ac-tions in the existing exposure situation. It became clearfrom the Fukushima nuclear disaster that the accept-able reference level would be settled depending on thereliance level of the people to the national governmentand that the NERHQ was obliged to choose the lowestreference level of the dose range for management of theexisting exposure situation [13]. This means that the re-liable relationship between the people and the nationalgovernment was very important for realizing optimiza-tion of the protective action for radiological disaster.One way to improve the reliable relationship would bethat the national government practiced the protectivemeasures with showing the high execution ability forradiation protection and the strong intention to pro-tect the residents from the radiological disaster by set-ting the reference level through the open communicationamong the stakeholders. It also became evident from the
TF No.1 NPS accident that the radiation protection ex-perts played a particularly important role not only in set-ting reference level for protective measures but also inpracticing protective actions in the existing exposure sit-uation in order to form the reliable relationship betweenthe people and the national government.
3. Environmental radiation monitoring
3.1. Objectives of radiation monitoringRadiation monitoring after a nuclear accident pro-
vides significant information for designating evacuationareas to restrict radiation exposure of residents and ar-eas, from which to restrict food, beverages, and the ship-ment of agricultural products, and for estimating theamount of discharged radioactive materials in order tounderstand the accident situation. The objective of ra-diation monitoring after a nuclear accident can be cat-egorized into land area monitoring (including aircraftmonitoring of air radiation dose rates at a height of 1 mfrom ground level and the accumulation of radioactiv-ity in the land surface, and monitoring of tap water andfood) and coastal sea area monitoring. The daily moni-toring of land where people are living has been regardedas a significant target of disaster measures. Coastal seaarea monitoring, however, became an important targetof radiation monitoring after the Tohoku District – offthe Pacific Ocean Earthquake (Great East Japan Earth-quake) and tsunami caused by the earthquake, since theTF No.1 NPS faces the sea, most of the radioactivityreleased into the air fell into the sea, high-level contam-inated radioactive water was discharged through cracksin the concrete, and approximately 10 thousand tonsof low-level contaminated radioactive water was inten-tionally discharged into the sea to free up storage spacefor high-level contaminated water. An overview of howthe radiation monitoring was carried out and the issuesidentified are described below.
3.2. Radiation monitoring of land areaAmong the initial monitoring activities that were
conducted outside the premises of the TF No.1 NPS af-ter the accident,monitoring activities, such asmeasuringradiation dose rates in the air, collecting dust suspendedin the atmosphere, environment samples and soil sam-ples, and aircraft monitoring, were described in detailin the Interim Report (V-1-(1)-b and V-1-(2)-b, Dec. 26,2011) [14] of the Investigation Committee on the Acci-dent at the TF No.1 NPS. The “Basic Disaster Preven-tion Plans” created by theCentralDisasterManagementCouncil (CDMC) stipulates that radiation monitoringin the event of nuclear disaster should be undertakenby local government and that the Ministry of Educa-tion, Culture, Sports, Science and Technology (MEXT),operators of NPS, and designated public institutions in-cluding the National Institute of Radiological Sciences(NIRS) and Japan Atomic Energy Agency (JAEA),
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should support the emergency monitoring by local gov-ernments by mobilizing both a mandatory emergencymonitoring workforce and all necessary equipment todisaster-stricken areas. However, the initial monitoringactivities did not work out as intended owing to a hostof reasons, including hazardous road conditions fromearthquake damage, flat tires, vehicles that had falleninto crevices in the ground, and fuel shortages. In addi-tion, it was difficult to consolidate the monitoring datafor sharing with the Secretariat of the NERHQ andother agencies since the Off-site Center had very lim-ited means of communication as a result of widespreadpower failure.As a result of the earthquake and the ensu-ing tsunami damage, 23 of the 24 monitoring posts theFukushima government had installed in the prefecturewere rendered inoperative. As for aircraft monitoring,the United States Department of Energy (DOE) ana-lyzed radiation dose in and around the TF No.1 NPSon the basis of the data obtained frommonitoring pointson the ground and more than 40 hours of flight using apilotless plane of the US armed forces from 17 Marchto 19 March 2011, and officially announced their esti-mated values on 22 March. On the other hand, MEXTstarted to examine aircraft monitoring from around12 March. However, almost all helicopters were occu-pied in rescue activities following the earthquake andthe ensuing tsunami. Thus, MEXT measured the levelsof radiation in the air beyond 30 km from the TF No.1NPS for the first time on 25March with the cooperationof the JapanAerospace ExplorationAgency (JAXA), anindependent administrative organization.
On the basis of such experiences, the following itemscan be listed as issues to be examined: “developmentof alternative or cooperative system in case the Off-siteCenter becomes inoperative, and monitoring cars andaircraft monitoring become unavailable” and “upgrad-ing of monitoring posts with high tolerance to earth-quake and ensuing tsunami.”
The regulation and monitoring of tap water aredescribed in the Interim Report (V-1-(1)-f) [14]. Therestriction of the shipment of agricultural productsand the monitoring of foods are given in the InterimReport [14] and the Final Report (V-5-(1)-g, f and I,Jul. 23, 2012) [15]. Regarding tap water, on 18 March2011, 170 Bq/kg of radioactive iodine was detected intap water that had been collected in Fukushima cityon 16 March 2011. In response to this, the Ministry ofHealth, Labor and Welfare (MHLW) began to discussthe development of regulatory values for tap water, justas they had for food and beverages. On 19 March 2011,the MHLW notified all municipalities to refrain fromdrinking tap water with index values exceeding thoseindicated by the NSC (300 Bq/kg of radioactive iodine,200 Bq/kg of radioactive cesium). The reason why theMHLW used the index values recommended by theNSC is that there previously had been no regulatoryindexes for radioactive materials in tap water. On21 March 2011, the MHLW notified municipalities
that water suppliers should promptly inform citizensto refrain from providing tap water to infants if theirtap water exceeds 100 Bq/kg of radioactive iodine, inorder to make the regulatory value for tap water andprovisional regulatory value for food and beveragesconsistent. Although it was included in the MHLWnotification on 19 March 2011 that the intake of tapwater may not be restricted in a situation where safealternative drinking water is not easily available andthere is serious concern for human health, as a resultof the notification on 21 March, social confusion, suchas the selling out of bottled water, occurred in themetropolitan area and the Tohoku district.
For agricultural products, on 19 and 20March 2011,radioactive material in amounts exceeding the tem-porary regulatory value was detected in (i) raw milkfrom Fukushima prefecture; (ii) spinach from Ibaraki,Tochigi, and Gunma prefectures; and (iii) leafy veg-etables from Gunma prefecture. In response to this,on 21 March, the head of the Government EmergencyResponse Center (GERC) provided the leaders of theFukushima, Ibaraki, Tochigi, and Gunma prefecturalgovernments with instructions to restrict the shipmentof (i) raw milk from Fukushima prefecture, and (ii)spinach and leafy vegetables from Ibaraki, Tochigi, andGunma prefectures. The range ofmonitoring results wasnot always consistent with shipment restrictions. Sub-sequently, many municipalities requested the NERHQto restrict shipment on a per-region basis rather than aper-prefecture basis. For this reason, theNERHQ issuednotices such that regions shall be established on a per-prefecture basis, however, regions shall be divided on aper-block basis if the relevant prefectural or municipaloffice can afford to manage and maintain them.
As for foods, by the end of February 2012, a total of117,737 specimens of food products had been tested andradioactive materials in excess of the provisional reg-ulatory value were detected in 1162 specimens. Fruits,mushrooms, seawater fish, and freshwater fishwere listedamong food products from which the high levels of ra-dioactive materials were detected despite the lapse ofa significant period of time from the nuclear accident.However, the number of measurements of radioactiv-ity in food products was insufficient to alleviate anxi-ety of the public in the early stages of the accident be-cause of shortage in measurement equipment and poordetection performance. In addition, it was observed thatincorrect measurements were carried out by their ownway since measurement methods of agricultural prod-ucts and foods had not been standardized.
Concerning the regulations for tap water, agricul-tural products, sea products, and foods, social confusionarose because the MHLW had no regulations availablefor such foods and beverages after the nuclear accident,and indexes for radioactive iodine in sea products andfor radioactive cesium in tea leaves were not includedin the index values provided by the NSC. New standardradioactivity limits (SRLs) are described in the Final
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Report (Jul. 23, 2012) (V-5-(1)-j) [15]. These limitscannot be utilized in other accident situations, whereinthe other radioactive nuclides are discharged, since theywere specific standards for the Fukushima accident,derived on the assumption of the current accidentsituation.
On the basis of the above experiences, the followingitems can be listed as issues to be examined: “develop-ment of methodology (risk communication method) toinform the public of the meanings of restriction of in-take, shipment and standard limit of foods,” “upgradingof standard limits for foods and beverages taking intoconsideration various accident situations (dischargednuclides, continual release period, etc.),” and “standard-ization of measurement methods of agricultural prod-ucts, sea products and foods, and development of emer-gency radiation monitoring structure to alleviate publicanxiety after accident.”
3.3. Coastal sea area monitoringCoastal sea monitoring in the early stage of the
TF No.1 NPS accident was described in the InterimReport (Footnote 14) [14] and Research InvestigationReport (5-3-7) of the Independent Investigation Com-mission on the Fukushima Daiichi Nuclear Accident(Feb. 27, 2012) [16]. In response to the recommenda-tions of the Advisory Team led by Cabinet SecretariatAdvisor, Professor Toshiso Kosako, MEXT developeda policy for conducting sea area monitoring with the co-operation of the Maritime Safety Agency on 21 March2011 and revealed its “sea area monitoring action pro-gram” on 22 March. Subsequently, the Atomic EnergySociety in Japan (AESJ) also pointed out the importanceof coastal sea area monitoring and announced its in-tent “tomonitor radioactivity concentration in seawater,marine sediment and sea products continuously and tomake radiation dose assessment results widely known”as a proposal in response to the Fukushima accident on20 May 2011. For coastal sea areas, MEXT requestedthe Japan Agency for Marine-Earth Science and Tech-nology (JAMSTEC) to conduct the sampling of seawa-ter and the measurement of the sample since there is aninsufficient number of permanent monitoring posts un-
like land areas. This monitoring was carried out at eightpoints already used in the “Comprehensive evaluationprogram of radioactivity in the marine environment”conducted by MEXT and an additional eight points.However, all these sampling points were set in a sea areawithin 30 km offshore of the TF No.1 NPS. These mon-itoring schemes were unsuitable for issues such as dis-persion of radioactive materials owing to ocean currentsand marine sediment.
On the basis of the above experiences, the follow-ing items can be listed as issues to be examined: “de-velopment of sea area monitoring methods taking intoconsideration the behavior of radioactive nuclides in thesea” and “development of simulation techniques to pre-dict the behavior of contaminated liquid in the sea.”
4. Reference levels for countermeasures
4.1. Role of reference levelsDefinition and main role of reference level are de-
scribed in the following way in the paragraphs of (234)and (284) of the ICRP Publication 103 [17].
In emergency or existing controllable exposure situ-ations, the reference levels represent the level of dose orrisk, above which it is judged to be inappropriate to planto allow exposure to occur, and for which therefore pro-tective actions should be planned and optimized. Thechosen value for a reference level will depend upon theprevailing circumstances of the exposure situation underconsideration.Reference levels, set in terms of individualdose, should be used in conjunction with the implemen-tation of the optimization process for exposures in exist-ing exposure situations. The objective is to implementoptimized protection strategies or a progressive rangeof such strategies, which will reduce individual doses tobelow the reference level. It is the responsibility of reg-ulatory authorities to decide on the legal status of thereference level, which is implemented to control a givensituation.
4.2. Meaning of 1 mSv as a dose criterionIn Table 1, the different types of dose restrictions
used in the ICRP system protection (limits, constraints,
Table 1. The dose constraints and reference levels used in the ICRP system of radiation protection.
Type of situation Occupational exposure Public exposure Medical exposure
Planned exposure Dose limit Dose limit Diagnostic referenceDose constraint Dose constraint leveld (dose constrainte)
Emergency exposure Reference levela Reference level NAb
Existing exposure NAc Reference level NAb
aLong-term recovery operations should be treated as part of planned occupational exposure.bNot applicable.cExposures resulting from long-term remediation operations or from protracted employment in affected areasshould be treated as part of planned occupational exposure, even though the source of radiation is “existing.”dPatients.eComforters, careers, and volunteers in research only.
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and reference levels) are shown with relation totype of exposure situation and category of exposure[17].
For public exposure in planned exposure situations,ICRP continues to recommend that the limit should beexpressed as an effective dose of 1 mSv in a year [17].The consequences of continued additional exposure giv-ing annual effective doses in the range from 1 mSv to5mSv are presented in theAnnexC of ICRPPublication60 [18]. They provide no easy basis for a judgment, butdo suggest a value of annual dose limit not much above1 mSv. On the other hand, other data in the Annex Cshow that, even at a continued exposure of 5 mSv/year,the change in the age specificmortality rate is very small.Excluding the variable exposures to radon, the annualeffective dose from natural sources is about 1 mSv, withvalues at high altitudes above sea level and in some geo-logical areas of at least twice this. On the basis of all theseconsiderations, ICRP recommends an annual limit oneffective dose of 1 mSv under the planned exposure situ-ation. However, in special circumstances a higher valueof effective dose could be allowed in a single year, pro-vided that the average over defined 5-year periods doesnot exceed 1 mSv/year [17].
As far as the setting of reference levels for exist-ing exposure situations resulting from nuclear accidentsand radiation emergencies is concerned, past experiencedemonstrates that typical dose values selected by au-thorities to manage such situations are close or equal to1 mSv per year, corresponding to the desire to reduceprogressively the long-term exposure to the levels thatare close or similar to situations considered normal, i.e.with the band of constraints set for public exposure inplanned situations [19].
4.3. Quantifying radiation exposure4.3.1. Misunderstandings on definition
of dose unit of Sv
Two concepts linking the external radiation field tothe effective dose and to the equivalent dose in the skinare introduced for purposes of environmental and areamonitoring. The first of these concepts, the ambient doseequivalent, H∗(d), is appropriate for strongly penetrat-ing radiations, and second, the directional dose equiva-lent,H’(d), is suitable for weakly penetration radiations.In addition, two other concepts are introduced for pur-poses of individual monitoring. The first of these con-cepts, the individual dose equivalent, penetrating,Hp(d),is appropriate for organs and tissues deeply situated inthe body which will be irradiated by strongly penetrat-ing radiation, and the second, the individual dose equiv-alent, superficial,Hs(d), is suitable for superficial organsand tissues which will be irradiated by both weakly andstrongly penetrating radiation [18].
Concerning all of these doses using units of Sv, thereare significant misunderstandings and confusion afterthe accident. “Report of ICRP Task Group 84 on Ini-
tial Lessons Learned from the Nuclear Power Plant Ac-cident in Japan vis-a-vis the ICRP System of Radi-ological Protection” [20], published on 22 November2012, pointed out some important items to be discussed.In their item No. 3 “Quantifying radiation exposure,”ICRP listed up the communication problems mainlycaused by misunderstandings on definition of unit of Sv.These include the following:
• the differences between the quantities have notbeen well explained and are not well understoodeven by educated audiences;
• the distinction between the quantities used in theradiological protection system and the operationalquantities used for radiation measurement is evenmore difficult to understand in part due to seman-tic problems;
• the use of the same unit for the quantities equiv-alent dose of an organ and effective dose withoutalways specifying which quantity is used has en-hanced confusion further;
• the lack of a formal quantity for a radiation-weighted dose for high doses (such as aneffectiveness-weighted to distinguish from theradiation weight factor) was, fortunately, notan issue in this accident but continues to be anunresolved issue; and
• there is very little understanding for why there areso many different quantities used in radiation pro-tection, not only many dosimetric quantities butalso many radiometric quantities (such as activityand activity concentration).
There are great difficulties to communicate with non-experts like the general public on radiological problemsby using the ICRP system and its quantities. This is aconsequence of rather intricate concepts behind the sys-tem of quantities which uses more than one quantity(equivalent dose and effective dose) and combines phys-ical exposure data with scientific ones on radiation riskfor organs and tissues. In otherwords, the system and thequantities have shown to be well suited for operationalradiation protection but they are much less suited forcommunication with non-experts, particularly in emer-gency situations.
An important confusion has been triggered by thefact that the quantities of equivalent doses and effec-tive doses have a common unit, the sievert (Sv). Theproblem seems to have been particularly relevant in thereporting of thyroid equivalent doses and is related tothe fact that incorporation of radioactive iodine leadsto radiation exposure almost exclusively to the thyroid.Usually the equivalent dose is the relevant quantity forreporting organ doses but, if the dose is reported indicat-ing only the unit, it can easily be confused with effectivedoses. The confusion created by not specifying the dosequantity when giving numerical values in terms of Sv
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Table 2. Standard radioactivity limits for foods in Japan and other countries.
Product Japan USA EU China South Korea
Water 10 200 – 370Milk 50 200 330 370Meat and meat products 100 1200 500 800 370Fish and fish products 100 500 800 370Vegetables 100 500 210 370Baby food 50 – – 370
Data: Public data released by various governments throughout the world (current as of July2012). Note that the EU uses the same limits for imported products from Japan as Japan uses.
merits a careful analysis of possibilities to improve thesituation.
In spite of the difficulties learned, it should be em-phasized that the quantities and units of the ICRPsystem of radiation protection have a record of suc-cessful application in practical radiation protection. Astrict and consequent application of a simplified dosereporting (e.g. organ dose, effective dose) could help toimprove the situation in cases of emergencies, thoughthey might not be well suited for communication andprobably for decision making in emergency and post-emergency situations. It should be remembered andstressed that the ICRP protection quantities have notbeen introduced for individual or collective risk assess-ments but for planning radiation protection in the lowdose range and for verifying compliance with individualdose restrictions.
The above description is exactly quoted from the re-port of the ICRP Task Group 84 [20].
4.3.2. Standard radioactivity limits (SRLs)
Food intake regulation for prevention of internal ex-posure of the people in a nuclear emergency situationhad been set by the NSC for the guidelines of radiologi-cal disaster management. The reference values for regu-
lation of food intake should be used to judge whether arestriction of food intake was necessary or not, becausethe regulation levels, which were estimated based on thethyroid equivalent dose of 50 mSv/year and the effec-tive doses of 5 mSv/year, were very conservative owingto the assumptions that the people continuously eat thecontaminated foods for one year [21].
The reference levels recommended by the NSC wereapplied as provisional regulation levels immediately af-ter the accident. However, new regulation levels calledstandard radioactivity limits (SRLs), which were deter-mined based on the lifetime effective dose of 100 mSv(about 1 mSv/year), were applied for limitation of foodintakes after April 2012 [22].
The SRLs set for the foods in Japan and those ofother countries are listed in Table 2 [23]. The JapaneseSRLs, which were relatively low compared to the stan-dards of other countries, were determined as follows.
Figure 2 shows the concept of deriving the SRLfor “General foods” including categories of meat, fish,and vegetables. First of all, operational interventionlevel (reference level) for all foods and drinks was de-termined as 1 mSv/year. In line with WHO’s guidancelevel for radioactive cesium in drinking water, the stan-dard limit for “Drinking water” was determined as10 Bq/kg which corresponded to the effective dose of
Figure 2. The conceptual diagram of the determination process of the SRL for general foods. The new SRLs were enforced on1 April 2012.
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about 0.1 mSv/year. So, the effective dose to be as-signed to “General foods” was determined as about 0.9mSv/year by subtracting the effective dose for “Drinkingwater” (about 0.1 mSv/year) from the operational inter-vention level (1 mSv/year). Since the effective dose wasdetermined as follows:
Effective dose = Radioactivity for food (Bq/kg)× Intake of food according to age-category× Dose Coefficient according to age-category
SRLs for foods could be calculated by dividing theeffective dose by the intake of food and conversion co-efficient according to age-category under the assump-tion of contamination ratio of 50% for all the marketedfoods.
Standard limits for radioactive cesium were estab-lished for effective dose of radionuclides (includingSr-90, Ru-106, Pu) not to exceed 1 mSv/year. Becauseevaluating radioactive materials other than Cs-134 andCs-137 requires much longer time, following procedurewas taken to determine the new SRLs. Analyzing themi-gration ratio of each radionuclide according to migra-tion pathway, deriving the contribution of radioactivecesium according to both foods- and age-categories, andestablishing standard limits for radioactive cesium, thenthe sum of effective does not exceed 1 mSv/year.
Additional special limit for infant foods was also de-termined. This is based on the statement by Food SafetyCommission, pointing out possibility of higher risk onradiation exposure of infants. This statement caused touse the safety factor of two into the determination oflimit for infant foods.
Wide range of arguments relating these SRLs forfoods have occurred. Among them, for example, the firstis an argument on the timing to change the rule of lim-its for foods. Immediately after the accident, Japanesegovernment declared to use the temporally radioactiv-ity limits for foods calculated based on the annual doseof 5 mSv. Reflecting social confusion with anxious voiceand requests mainly from mothers with young children,Japanese government could not help change the limitvalue after about one year from the accident. This is-sue raised an important problem on the radiation pro-tection that the setting of the reference level is stronglyassociated with a political agenda to balance science-based risks and anxiety of the people against the radi-ation health effects. Though it is very difficult to elimi-nate the anxiety formed in the people, it was suggestedfrom the experience that the protective actions should bepracticed on the basis of a better balance of these twofactors by taking into consideration of the total detri-ments caused by the nuclear disaster. And it becameclear that stakeholders involved in the disaster man-agement as well as radiation protection experts have toexplain the scenario or assumptions behind the SRLsderived as a reference revel and the health and social im-pacts of the operation of the SRLs as early as possible.
4.3.3. Basic principle and target dose fordecontamination activity
The followings are quoted from the national basicprinciples on target doses for decontamination [24,25]:
• In the area where the additional exposure dose isless than 20 mSv/year, it shall be aimed to reducethe additional dose to 1 mSv/year or lower as thelong-term goal.
• As for the area where the additional exposure doseis 20 mSv/year or higher, it shall be aimed to re-duce the area with a step-by-step but prompt ap-proach. It should be noted that a long-term effortis required in the area with significantly high ex-posure dose.
Big confusion and argument were occurred immedi-ately after 20 mSv/year was determined by the Japanesegovernment as the first step of reference level for schoolyard. This situation was very similar to the control limitsfor foods mentioned above. That is, this raised an issuein radiation protection “How could we explain the dosereduction scenario using step-by-step approach basedon the optimization procedure of radiological protec-tion to public appropriately?,” since it was very difficultto explain the radiological significance of the differenceof low radiation doses. In order to determine whetherthe target area would need decontamination activity ornot, ambient hourly dose rate of 0.23 μSv/hour is usedas its operational intervention value, which is equiva-lent to the annual dose of 1 mSv/year as a referencelevel. Exposure dose rate of 0.23 μSv/hour consists oftwo components: 0.19μSv/hour for contamination doseand 0.04μSv/hour for natural background dose. Besidesthe misunderstandings and confusion of dose unit ex-plained above, it should be noticed that the hourly-dose-rate management of 0.23 μSv/hour is so effective to re-duce annual dose less than 1 mSv/year since the dosesrate tends to decrease with the time by the protective ac-tions adopted and by the physical and chemical proper-ties of radioactive material.
5. Dose assessment
5.1. Dose assessment and heath managementof the public
On account of the severe accident at the TF No.1NPS, large amounts of radioactive materials were acci-dentally released into the atmosphere and ocean [26,27].Immediately after the accident, the people living in thearea where radioactive materials might pass over ormight be deposited by precipitation had to be evacu-ated because of high possibility of high radiation doses.External effective doses of the people living in the areasmore than 50 mSv/year would be mitigated by the evac-uation instructed appropriately by the NERHQ. Butthe people in the area where the external effective dose
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Table 3. Distribution of effective dose estimated on the basis of the behavior records of the people living inthe preliminary investigation area ∗ of Fukushima Prefecture. External effective doses were integrated from 11March to 11 July 2011.
Number of the people
<1 mSv 1 mSv–10 mSv >10 mSv
The people including those ever engaged in radiation work. 6070 4303 95 (max. 47.2 mSv)The people excluding those ever engaged in radiation work. 5636 4040 71 (max. 23.0 mSv)Less than 20 years old. 1032 660 1 (max. 18.1 mSv)
∗Kawamata (553), Namie (7250), Iidate (1944).Numbers in the parentheses indicate the number of the people responded to the questionnaire excluding radiation workers.
predicted would not fall below 20 mSv/year within fiveyears were not allowed to be returned to the originaldwellings for long time. And even the people living inthe area less than 50 mSv/year had to accept the vari-ous kinds of restrictions such as decontamination of theliving environments [28].
According to the radiological health survey inFukushima Prefecture, external radiation doses esti-mated on the behavioral records of the residents during11 March to 11 July in 2011 were reported as shown inTable 3. As shown in Table 3, 95 persons including radi-ation workers were more than 10mSv and themaximumradiation dose was estimated as 47.2 mSv [29].
With respect to the internal exposure of the peo-ple, it has been considered to be difficult to estimatethe internal doses by short-lived radioactive materialssuch as I-131 because of lack of measuring data per-formed in the early stage of the radiological disaster.But, though it was accompanied by various kinds of dif-ficulties, S. Tokonami tried to estimate the thyroid equiv-alent doses based on the extensivemeasurements and themedian doses were 4.2mSv and 3.5mSv for children andadults, respectively [30]. And internal dose reconstruc-tion in the early stage of the disaster was also tried bythe NIRS by using a limited number of measured dataand the calculated results of atmospheric dispersion ofthe radioactive materials [31]. The preliminary resultswere that the thyroid equivalent dose of the people liv-ing in the highly contaminated area was about 10 mSv atmost.
Measurements of radioactive materials using wholebody counters and estimation of the committed effec-tive dose of the general public have been carried out byFukushima Prefecture after 27 June 2011 [32]. The re-sults are shown in Table 4.
As is evident fromTable 4,more than 99%of the peo-ple inspected were less than committed effective dose of1 mSv and 26 persons were distributed from 1 mSv to3 mSv. These were supported by the other works per-formed by using whole body counters [33,34]. In addi-tion to these whole body inspections, though it was con-sidered the radiation doses would not be very high, thethyroids of children under 18 years old have been exam-ined using an ultrasonography since October 2011 [35].
Table 4. Distribution of committed effective doses of thepeople living in Fukushima Prefecture measured by wholebody counters from June 2011 toMay 2013. The age of 108,112people of the total (132,011) is 4–19 years old.
Committed effective dose
<1 mSv 1 mSv 2 mSv 3 mSv
Number of the people 131,985 14 10 2
This examination will be done every two years until themembers of this cohort reach at 20 years old and willbe done every five years after that age or later. Further-more, mental and physical health examinations such asa blood examination, urinalysis, and detailed questionswere conducted to investigate the radiation and non-radiation effects for residents in the evacuation zone andthe specified area.
So, though it seems to have succeeded in radia-tion dose reduction of the people as low as practica-bly achievable, the difficulty associated with dose assess-ment would be due to the fact that the importance ofdose estimation in the early stage of the nuclear disasterwas not clearly mentioned in the nuclear disaster pre-paredness system. So, it must be emphasized that theearly establishment of dosimetry system will be essentialto nuclear accidents because the safety of the people canbe ensured by knowing the amount of radiation dosesreceived.
From the viewpoint of ensuring the safety of thepeople affected, management of contaminated naturaland living environments and radioactive wastes here-after will be more important to reduce radiation dosesas low as reasonably achievable since there still existswide area highly contaminated by radioactive materialsreleased [36,37].
5.2. Health effects of ionizing radiationAs a result of the nuclear accident, workers for pro-
tective actions in the emergency exposure station and thegeneral public were exposed to the external and internalradiations. Fortunately, the doses of both groups werenot so high as to produce severe radiation injuries. As
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Table 5. Detriment-adjusted nominal risk coefficients(10−2 Sv−1) for stochastic effects after exposure to radiationat low dose rate shown in ICRP Publication 103.
Exposed population Cancer Heritable effects Total
Whole 5.5 0.2 5.7Adult 4.1 0.1 4.2
shown in Table 3 and 4, the public radiation doses pre-liminary estimated were 10 to a hundred times greaterthan that of the natural background during normal op-erations.
After the TFNo.1NPS accident, following problemson the public people’s understanding about radiologicalhealth effects were occurred:
• effective doses of a few tens of mSv were unaccept-able for the people regardless of the developmentof the disaster management and the response ca-pabilities.
• the effects by internal exposure are more severethan those by external exposure regardless of theamounts of effective doses.
• concern for the radiation dose of the children sincethe people know that they aremore sensitive to theradiation exposure than those of adults.
But, many of these misunderstanding against radia-tion exposure was considered to be caused by the factsthat the people have less chance to know the scientificbasis of the protective system of radiological emergency.
For stochastic effects of low doses, the ICRP recom-mended that the combined detriment of excess cancerand heritable defects were about 5% per Sv, as shown inTable 5.
The recent cohort study on radiation-induced can-cer incidence in high background radiation region, Ker-ala in India, for example, is useful in ascertaining theradiation health effect on the general public [38]. The re-sults of this work showed no excess cancer risk from pro-longed exposure of about 600 mSv. The ICRP Commis-sion also reviewed the cancer risk and assumed that thelife-time cancer risk following in-utero exposure wouldbe similar to that of early childhood, which was aboutthree times that of the population as a whole, althoughthe ICRP Commission does not give special values onstochastic effects, as shown in Table 5 [17]. Furthermore,in embryos, fetuses, and children, the risk of tissue re-action and malformation which were reviewed by theICRP were very infrequent below the dose of 100 mGy[39].
Among those who were children or adolescents in1986 in the area affected by the Chernobyl nuclear ac-cident of the former Soviet Union, more than 6000cases of thyroid cancer have been reported. This inci-dence could be attributed to drinking fresh milk con-taminated with the short-lived radionuclide iodine-131
(T1/2 = 8 days) [40]. The United Nations Scientific Com-mittee on the Effects of Atomic Radiation (UNSCEAR)reported that the general population was exposed to ra-diation, but there was no consistent evidence on anyother radiation-related, long-term health effects.
With reference to such reports described above, it islikely that the serious health effects that were worriedabout by the people will not be caused by the radiationdoses due to radioactive materials released in the earlystage of the TF No.1 NPS accident.
Though the frequency of stochastic effects, such asradiation-induced cancer and genetic defects appear tobe low or not to be a significant difference, the possi-ble impairment of health and serious economic losses,such as migration, unemployment, and decontamina-tion, caused public uneasiness. Furthermore, the sight-seeing, agricultural, manufacturing, and processing in-dustries in and around Fukushima that did not sufferany direct damages from radiation exposure were nega-tively impacted by rumors. It is necessary for Japanesegovernment to examine the adequacy of the protec-tive measures from the points of view of the socialand economical impacts as well as health effects of theaccident.
5.3. Dose assessment of workersThe effective dose limit of 100 mSv was estab-
lished for workers in emergency situations. However,the Japanese regulatory authority raised this limit to250 mSv because of the expanded measures were neces-sitated by the nuclear disaster at the TF No.1 NPS [14].In the ICRP recommendation 2007 (ICRP Publication103) [5], the ICRP committee recommended that the ref-erence level for urgent rescue operations, other than lifesaving, should be below 500 mSv in a serious accident.The clinical information on the possibility of seriousacute damage at doses below 250 mSv has not yet beenconfirmed. Thus, the Radiation Council of Japan recog-nized that this value would be appropriate. On Novem-ber 2011, the dose limit for emergency workers in the TFNo.1 NPS was thus returned to the former value [41].
The occupational exposures of the workers at the nu-clear power station were reported on the website of theTEPCO [42]. Workers of 25,837 people were engaged inradiation works from March 2011 to January 2013. Inthese workers, the effective dose for six workers exceeded250 mSv (maximum dose is 678.8 mSv) and that of 161was between 100 and 250 mSv (about 0.6%). The dosesof two female working in the quake-proof building ofthe Fukushima Station were 7.49 and 17.55 mSv, whichexceed the limit for the female worker (5 mSv/3 months).However, the dose for most workers was more than10 mSv; their average effective dose was 11.85 mSv. But,since the radiation workers have received relatively highdoses in the emergency works, it is quite important tocontinue the high quality of health care over the lifetimeof the workers.
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6. Conclusions
From the discussions stated above, conclusions areas follows:
(1) By taking into consideration of the time profileof releasing radioactive materials from the TFNo.1 NPS, the urgent protective actions in theearly stage of the disaster played an importantrole in the countermeasures to mitigate the ra-diological health hazard of the nuclear accident.The protective measures in the transitional stagehave to be performed so as to minimize the to-tal detriments originated in the health effects andin the sociological and economical losses by en-suring the optimization process of the protectiveactions.
(2) The reliable relationship between the people andthe national government was very important forrealizing optimization of the protective actionfor radiological disaster. One way to improve thereliable relationshipwill be that the national gov-ernment practiced the protective measures withshowing the high execution ability for radiationprotection and the strong intention to protect thepeople affected from the radiological disaster be-cause the safety goal and the practice of protec-tive measures will be decided depending on thereliance level of the general public.
(3) Since practice of countermeasures depends onthe exposure situation, it will be appropriate thatthe termination of the nuclear emergency situa-tion was declared at the same time as the decla-ration of attaining stable reactor condition.
(4) Radiation monitoring system which can workin anytime and in anywhere and the task forceengaged in radiation monitoring in the affectedarea has to be established for improvement ofpracticing countermeasures in the early stageof the nuclear disaster, especially, the radiationmonitoring methods and simulation techniquesfor prediction of the behavior of radioactive ma-terials in the sea area have to be developed tomake possible to practice protective actions inthe nuclear emergency situation.
(5) Standardization of measurement methods ofagricultural products, sea products, and foodswas needed, and emergency radiation monitor-ing system to alleviate public anxiety after ac-cident and methodology (risk communicationmethod) to inform the public of the meaningsof restriction of intake, shipment, and standardlimit of foods have to be developed for improve-ment of mutual communication of the nationalgovernment and the people affected.
(6) As far as setting reference levels for existing ex-posure situations resulting from nuclear acci-dents and radiation emergencies is concerned, it
was often shown that the typical dose values se-lected by authorities to manage such situationsare close or equal to 1 mSv/year, correspondingto the desire to progressively reduce long-termexposure to levels that are close or similar to sit-uations considered normal, i.e. with the band ofconstraints set for public exposure in plannedsituations.
(7) In the aftermath of the accident, the quantitiesand units used for quantifying radiation dosesof individuals have caused considerable commu-nication problems which have been triggered bythe fact that the quantities of equivalent doseand effective dose have a common unit, the siev-ert (Sv). In spite of these difficulties, it shouldbe emphasized that the quantities and units ofthe ICRP system of radiation protection have arecord of successful application to a simplifieddose reporting in practical radiation protectionof the emergency situation. And it also shouldbe remembered and stressed that the ICRP pro-tection quantities have not been introduced forindividual or collective risk assessment but forplanning radiation protection in the low dose ex-posure and for verifying compliance with indi-vidual dose restrictions.
(8) Standard radioactivity limits (SRLs) for foodsin Japan were enforced on 1 April 2012. But,at first, Japanese government could not help de-termine the limits by reflecting social confusionsand requests mainly from mothers with youngchildren. It was suggested from the experiencethat the protective actions should be practicedon the basis of a better balance between thescience-based risk and the anxiety of the peopleby taking into consideration of the total detri-ments caused by the nuclear disaster. And it be-came clear that the radiation protection expertshave to explain the scenario or assumptions be-hind the SRLs derived from the interventionlevel as a reference revel.
(9) Radiation doses for the public in the early stageof the nuclear accident have been estimatingbased on the behavioral records of the residentsby using the monitored data by Fukushima pre-fecture or the calculation results by National In-stitute of Radiological Science. According to theradiological health survey in Fukushima Prefec-ture, external effective doses of the most peo-ple cumulated during 11 March to 11 July 2011were less than 10 mSv and a maximum one wasestimated as 47.2 mSv. With respect to the in-ternal exposure of the people, preliminary re-sults of the internal dose reconstruction in theearly stage of the disaster reviled that the thy-roid equivalent dose of the people living in thehighly contaminated area was about 10 mSv atmost.
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(10) According to the preliminary dose estimationobtained so far and the dose criteria recom-mended by international organizations, it is con-ceivable that the radiological health effects thatmight be appeared in the public by the radiationexposure in the early stage of the TF No.1 NPSdisaster will be indescribable from other healtheffects. However, in order to achieve higher safecondition of the living environment, there arestrong needs to continue the study on dose re-construction to improve the precision of doseestimation and the management of protectiveactions to the people affected. And it is also im-portant to pay attention to the non-radiologicalhealth effect resulting from the physical andmental stresses appeared in the public andworkers.
AcknowledgementsSeveral sentences in this document are quoted from the fol-
lowing references in order to strengthen our argument. We ex-press our gratitude for all related parties and organizations.
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