Sumi Yokoyama

Radiation protection lessons learned from the TEPCO Fukushima No.1 NPS accident

Lessons learned from the TEPCO Fukushima No.1 NPS accident are discussed from the viewpoint of radiation protection in the situation of nuclear emergency. It became clear from the discussion that the protective measures should be practiced by taking into account the time profiles of the radiological disaster after the nuclear accident and that the land and coastal sea areas monitoring had to be practiced immediately after the nuclear accident and the communication methods to tell the public about the radiation information and the meaning of protective measures should be developed for mitigation of the sociological aspects of disaster impacts. And it was pointed out from the view point of practicing countermeasures that application of the reference levels, above which it was judged to be inappropriate to plan to allow exposure to occur, played an important role for practicing protective measures in an optimized way and that the quantities and units used for quantifying radiation exposure of individuals in terms of radiation doses have caused considerable communication problems. Finally, the occupational exposures and the public exposures that have been reported so far are shown, and it is concluded that there is no conclusive evidence on low dose exposures that would justify a modification of the radiation risk recommended by the International Commission on Radiological Protection.

EVALUATION OF EYE LENS DOSES OF INTERVENTIONAL CARDIOLOGISTS

The effective dose of medical staff members, especially interventional radiologists and cardiologists, is classified as a relatively high level. We measured the dose for interventional cardiologists by using optically stimulated luminescence dosimeters (OSLDs). However, this quantity is not the same as Hp (3). In experiments, the dose at the eye-lens position of a phantom were measured using OSLDs and thermoluminescence dosimeters (TLDs). A conversion factor from dose measured by using TLDs to OSLDs was estimated from these results. In addition, the eye doses of interventional cardiologists in clinical situations were measured, and the effect of eyewear on the eye-lens dose was discussed.

Current situations and discussions in Japan in relation to the new occupational equivalent dose limit for the lens of the eye

Since the International Commission on Radiological Protection recommended reducing the occupational equivalent dose limit for the lens of the eye in 2011, there have been extensive discussions in various countries. This paper reviews the current situation in radiation protection of the ocular lens and the discussions on the potential impact of the new lens dose limit in Japan. Topics include historical changes to the lens dose limit, the current situation with occupational lens exposures (e.g., in medical workers, nuclear workers, and Fukushima nuclear power plant workers) and measurements, and the current status of biological studies and epidemiological studies on radiation cataracts. Our focus is on the situation in Japan, but we believe such information sharing will be useful in many other countries.

Recent activities in environmental science and health physics

Since mid-2011, many studies related to the Fukushima Daiichi Nuclear Power Plant (F1NPP) accident have been published. These studies were useful forworker and resident dose assessment, environmental distribution analysis of radionuclides released into the atmosphere and ocean, and development of decontamination methods in environmental science and health physics fields. However, only limited information exists on the early accident stage. In the future, reducing uncertainty in the dose and environmental distribution of radionuclides presents a significant challenge to environmental science and health physics. Thus, ongoing, high-precision studies are required. Essential environmental monitoring and radiation protection techniques were also published, such as dose rate variation factor and internal dosimetry methodologies. We introduce some papers published from 2012 to early 2014 in the Journal of Nuclear Science and Technology (JNST) and other journals. In 2012, environmental radiation monitoring results related to the Fukushima Daiichi Nuclear Power Plant accident were published by Takeyasu et al. in the JNST [1]. The environmental radiation dose, the air concentration of several nuclides (132Te, 131I, 133I, 134Cs, 136Cs, and 137Cs), and the fallout of 134Cs, 136Cs, and 137Cs weremeasured at Ibaraki Prefecturemonitoring stations (110 km or more from F1NPP) when a large amount of radionuclides was released to the atmosphere on 15, 16, and 21 March 2011. This investigation revealed that the 131I/137Cs concentration ratio in air varied considerably every day. Hosoda et al. investigated the 131I/137Cs and 132I/131I activity ratio in environmental samples collected south of F1NPP at Iwaki City, Fukushima Prefecture. They reported the highest 131I/137Cs, ranging from 49 to 70 [2]. From the viewpoint of initial internal dosimetry, Kurihara et al. reported the radioactivity measurement of 131I in the thyroids of employees involved in the

Exposure for medical staff from patients during/after ⁸⁹Sr therapy (The 12th International Conference on Radiation Shielding (ICRS-12) and the 17th Topical Meeting of the Radiation Protection and Shielding Division of ANS (RPSD-2012)) -- (Radiation Protections)

89 Sr therapy patients. The Hp(10) for medical workers was measured using personal dosimeters and was found to be <1 μSv during the measurement period. Hp(0.07) for medical workers did not exceed 5 μSv per case during routine work, although the dose on the patients skin surface was about 20 times that on the medical staff. To investigate the contribution of electrons to the measured dose, the dose on the patients skin surface as obtained from uniformly distributed 89 Sr in a similar MIRD phantom was calculated using EGS5 code. The peak energy of the incident photons was approximately 0.6 MeV. The estimated Hp(10) and Hp(0.07) doses for the medical staff were 0.43 and 91 μSv/h, respectively. The contribution of electrons to the calculated Hp(0.07) was approximately 200 times that of photons. Thus, the high Hp(0.07) for medical staff is attributed to the strong contribution of electrons.Personal dose equivalent, Hp(10) and Hp(0.07) doses were measured using an ionization chamber and personal electric dosimeters to estimate the exposure dose for medical staff members and carers as received from Sr therapy patients. The Hp(10) for medical workers was measured using personal dosimeters and was found to be <1 μSv during the measurement period. Hp(0.07) for medical workers did not exceed 5 μSv per case during routine work, although the dose on the patient’s skin surface was about 20 times that on the medical staff. To investigate the contribution of electrons to the measured dose, the dose on the patient’s skin surface as obtained from uniformly distributed Sr in a similar MIRD phantom was calculated using EGS5 code. The peak energy of the incident photons was approximately 0.6 MeV. The estimated Hp(10) and Hp(0.07) doses for the medical staff were 0.43 and 91 μSv/h, respectively. The contribution of electrons to the calculated Hp(0.07) was approximately 200 times that of photons. Thus, the high Hp(0.07) for medical staff is attributed to the strong contribution of electrons.