According to ISO 4037, the thickness of the inherent filtration for the radiation qualities L-40 to L- 240, N-40 to N-400, W-60 to W-300 and H-80 to H-400 shall be equivalent to 4 mm Al for matched reference radiation fields or adjusted as far as possible to 4 mm Al for characterized reference radiation fields. And for matched reference fields, the tube window must be made of beryllium and its thickness should not exceed 10 mm. In the case of characterized reference fields, the thickness of the beryllium window should not exceed 10 mm, but it is acceptable to use an aluminum window with a maximum thickness of 1.5 mm. 320 KV X-ray tube installed at KHNP-CRI has been designed to equipped with a 3 mm Be for tube window and an additional 4 mm Al to obtain a total inherent filtration equivalent to that of 4 mm Al. In the previous study, the inherent filtration of 320 kV X-ray tube at KHNP-CRI has been verified by MCNP simulation. However, the ISO standards suggest a method for determining the thickness of the inherent filtration by half-value layer (HVL) measurement and spectrometry. In this regard, the inherent filtration was reassessed using HVL measurement. To determine the inherent filtration, 1st HVL of the beam generated by the tube at a tube potential 60 kV was measured. The measurements were conducted with a calibrated spherical ionization chamber (model A3, Exradine) placed at a distance of 1 m from the target, at the center of the radiation field size. The X-ray tube current was set to 2 mA. The thickness of aluminum absorbers was gradually adjusted in subsequent measurements until approached the 1st HVL. 1st HVL were estimated using the linear regression equation computed with the current values for the thickness of the absorbers. As a results, the thickness of the 1st HVL was estimated as 2.845 mm Al. According to the correlation between the inherent filtration and 1st HVL suggested in ISO standard, the value of the inherent filtration was deduced as 4.25 mm Al that is rounded to the nearest 0.05 mm by interpolation. Further studies on the effects of the inherent filtration thickness determined in this study will be conducted.

Since 2018, Central Research Institute of Korea Hydro & Nuclear Power (KHNP–CRI) has been operating an X-ray irradiation system with a maximum voltage of 160 kV and 320 kV X-ray tube to test personal dosimeters in accordance with ANSI N13.11-2009 “Personnel Dosimetry Performance- Criteria for Testing”. This standard requires that dosimeters for the photon category testing be irradiated with the X-ray beams appropriate to the ISO beam quality requirements. KHNP-CRI has implemented the fourteen X-ray reference radiation beams in compliance with ISO-4037-1, 2, and 3. When installing the X-ray irradiation system, KHNP-CRI evaluated the uncertainties of dose conversion coefficients for deep and shallow doses, based on “Catalogue of X-ray spectra and their characteristic data – ISO and DIN radiation qualities, therapy and diagnostic radiation qualities, unfiltered X-ray spectra” published by Physikalisch Technische Bundesanstalt (PTB). A CdTe detector (X-123, AMPTEK) with disk type collimators made of tungsten was used to acquire X-ray spectra. The detector was located at 1 m from the center of the target material in the Xray tubes. Six uncertainty factors for the dose conversion coefficients for the fourteen X-ray beams were chosen as follows; the minimum and maximum cut-off energies Emin and Emax, the air density (ρ), the accuracy of the high-voltage of the X-ray tube, statistics of the pulse height spectra and the unfolding method. For example, uncertainty of each quantity for a HK30 beam was calculated to be 0.3%, 2.32%, 0.19%, 1.25%, and 0.13%, and 0.18%, respectively. The combined standard uncertainty for the deep dose conversion coefficient of the HK30 beam was calculated to be 2.67%. The coverage factor corresponding to a 95 percent confidence interval was obtained as k = 1.8 using a Monte Carlo method, which is slightly lower the coverage factor of k = 1.95 for a Gaussian distribution. This seems to result from that two dominant uncertainties, the unfolding uncertainty and minimum cut-off energy uncertainty, follow a rectangular distribution.

Among the test categories of the personal dosimetry performance test in Korea, the reference neutron radiation field used for the mixed neutron-photon radiation field is generated by a D2Omoderated 252Cf source. There are some differences depending on the standards, D2O-moderated 252Cf source consists of the 252Cf source surrounded by the D2O sphere with a diameter of 30 cm, covered with a Cd shell of thickness approximately 0.051 cm ~ 0.1 cm. In order to optimize the design of the D2O sphere and establish the neutron radiation field for the personal dosimetry performance test in Central Research Institute of KHNP, the neutron spectra have been simulated by MCNP 6.2 code by design conditions and evaluated dose conversion coefficients. In the consideration of neutron irradiation facility, the basic design structure was determined a D2O sphere with a diameter of covered with a Cd shell and a cylindrical well is in the middle of sphere. Neutron source transfer tube is inserted into this well-shaped structure and neutron source was withdrawn from the tube. And by changing the following design conditions in detail, the neutron spectra were evaluated; 1) the entire diameter of the D2O sphere (with or without the diameter of 7.5 cm of well-shaped structure) 2) the location of the neutron source (distance from D2O) 3) thickness of Cd shell 4) purity of D2O. As a source spectrum, the spectrum of bare- 252Cf recommended by ISO 8529-1 was adopted and spectra were tallied using F4 tally at a distance of 120 cm from the neutron source. Finally, the fluence to dose conversion coefficients were calculated using the simulated spectra. As a result of the evaluation, in case that an entire diameter of the D2O sphere with a diameter of the source tube is 37.5 cm, the fluence to dose conversion coefficient was evaluated to about 4.4% lower than an entire diameter of the D2O sphere is 30 cm. And in case that the distance between the D2O and the top of the neutron source was about 3.75 cm which is a radius of well-type structure, it was evaluated to about 1.4% larger than the distance was about 1 cm, and when the thickness of Cd was 0.1 cm, it was evaluated to 0.8% larger than when it was 0.051 cm. Finally, when the purity of D2O was 99.99%, it was evaluated 1.5% lower than when it was 99%. Except for the diameter of D2O sphere, the differences on the other conditions are acceptable considering the uncertainty of the simulation. Therefore, the design of D2O-moderated 252Cf source was determined by considering source integrity, economic perspectives, and dose conversion coefficient given in ISO 8529: a D2O sphere with an entire diameter of 37.5 cm, filled with above 99% purity of D2O, and covered with a cadmium thickness of 0.1 cm. The fluence to dose conversion efficient was evaluated as 110.10 pSv cm2 for ambient dose H*(10), 115.21 pSv cm2 for personal dose Hp(10) respectively.

일본에서는 2000년 고준위방사성폐기물의 심층처분을 위한「특정방사성폐기물의 최종 처분에 관한 법률」을 제정하고 부지선정을 착수하였으나, 부지선정 절차에 참여를 원하는 지자체가 존재하지 않았다. 따라서, 일본 정부는 2015년 문헌조사 단계에 새로운 부지선정을 절차를 개발하고, 지자체의 공모를 촉진하고자 2017년 6월 28일 심층처분을 위한 전국규모 과학적 특성 지도를 발간하였다. 이 지도는 심층처분장 초기 혹은 개념단계에 고려되는 요건 및 기준 등을 제공하고 심층처분을 위한 적합성을 분석함으로써, 공공의 이해도 증진과 지자체와의 의견교환 등을 위해서 유용하게 활용되고 있다.