Around 40 years ago, in the mid-1980s, Swedish government approved the KBS-3 method for the direct disposal of spent nuclear fuels (SNF) in Sweden. Since then, this method has become a reference for many countries including Korea, Republic of. The main ideas of the KBS-3 method are to locate SNF at 500 m below the ground surface using a copper disposal canister and a bentonite buffer. In 2016, our government announced the National Plan (NP 2016) regarding the final management of high-level waste (HLW) in Korea. In 2019, new committee were organized to review the NP 2016, and they submitted the final recommendations to the government in 2021. Finally, the government announced the 2nd National Plan in December, 2021. So far, KAERI has developed the technologies related to the final management of SNF in two directions. One follows ‘direct disposal’ based on the KBS-3 concept, and the other ‘recycling’ based on ‘pyroprocessing-and-SFR’ (PYRO-SFR). Even though Posiva and SKB obtained the construction permits with the KBS-3 method in Finland and Sweden, respectively, there are still several technical obstacles to applying directly to our situations. Some examples are as follows: high burnup, huge amounts of SNF, and high geothermal gradient in Korean peninsula. In this work, we try to illustrate some limits of the KBS-3 method. Within our country, currently, the most probable disposal option is the KBS-3 type geological disposal, but no one knows what the best option will be in 20 or 30 years if those kinds of drawbacks are considered. That is, we compare the effects of the drawbacks using our geological data and characteristics of spent fuels. Last year, we reviewed alternative disposal concepts focusing on the direct disposal of SNF and compared the pros and cons of them in order to enhance the disposal efficiency. We selected four candidate concepts. They were multi-level disposal, deep borehole disposal, sub-seabed disposal and mined deep borehole matrix. As mentioned before, KAERI has developed a pyroprocessing technology based on the SFR to reuse fissile radionuclides in SNF. Even though we can consume some fissile nuclides such as 239Pu and 241Pu using PYRO-SFR cycle, there still remain many long-lived radionuclides such as 129I and 135Cs waiting for the final disposal. The authors review and propose several concepts for the future final management of the long-lived radionuclides.

Korea Atomic Energy Research Institute (KAERI) has investigated Pyroprocessing technology in order to decrease the burden of disposal system and increase availability of useful radionuclides in the spent nuclear fuel (SNF) for future. The treatment and the disposal of SNF, however, are very sensitive issues socially. In addition, under the energy transition policy phasing out nuclear energy gradually there have been demands for alternatives so far. Thus various alternatives should need to be investigated in preparation for unexpected situations. This study has been conducted roughly in effectiveness point of view of alternative pre-managements for SNF, not pyroprocessing technology, in disposal system, consisting of three stages according to the degree of burden in disposal system. Stage I is the case for making safety increase with removing highly-mobile radionuclides from SNF. Stage II is the case for eliminating high-heat radionuclides additionally, alleviating thermal risk in the disposal system. And Stage III is the case for recovering Uranium in addition to Stage II. These options of pre-management are thought to be able to provide an intuitive strategy for effective diversification of the disposal system. Because several types of waste form from pre-management make it possible to develop the effective, newly-composed waste disposal system according to the properties of radionuclides. And the processability of SNF through pre-management might be combination with available core-drilling technology, being able to design various disposal system as well. Even though the whole, detailed unit processes have not designed yet, mass balance and distributions of radionuclides are performed under the appropriate assumption of engineering processes. As a first step the alternative approaches for SNF pre-management for disposal system might be expected to be widely used in implementing SNF management policy in the future.

During normal and off-normal conditions, the concrete structures of dry storage system for spent nuclear fuel must maintain structural integrity. A stress-strain curve is the most important key factor for structural integrity evaluation. The ASTM C39 specifies the concrete specimen geometry for the static compression test. However, there is no standard specimen size for intermediate stain rate, and it is not easy to maintain consistency among all test results because the failure tendency is different from each other. In order to account for the strain rate effects on concrete, the dynamic increase factor (DIF) is conventionally addressed by dividing dynamic strength by static strength. However, the DIF value considers only the strength of concrete and does not describe the overall behavior of concrete, such as a stress-strain relation. The objective of this study is to propose proper specimen geometry for the concrete dynamic compression test by several parametric study. The static compression simulation results with the specimen specified in ASTM C39 showed the constant strain distribution in a cylindrical specimen. However, as the strain rate increases, the strain state in specimen showed a nonuniform with the same geometry of ASTM C39. The non-uniform strain state in the specimen deteriorates the consistency and accuracy of the compression test. Therefore, we presented the specimen shape and size to form a uniform strain state through radial direction by drilling a hole in the axial direction. We analyzed two specimens using ABAQUS with the concrete damaged plasticity model, one with a hole at the center and the other without the hole. As a result, the strain distribution became more uniform than the specimen without the hole. Based on the results, we proposed the specimen shape and size for the intermediate strain rate compression test.

Concrete structures of spent nuclear fuel interim storage facility should maintain their shielding ability and structural integrity during normal, off-normal and accident conditions. The concrete structures may deteriorate if the interim storage facility operates for more than several decades. Even if deterioration occurs, the concrete structures must maintain its unique functions (shielding and structural integrity). Therefore, it is necessary to establish an analysis methodology that can evaluate whether the deteriorated concrete structure maintains its integrity under not only normal or off-normal condition but also accident condition. In accident conditions such as tip over and aircraft collision, both static material properties and dynamic properties of the concrete are required to evaluate the structural integrity of the concrete structures. Unlike the calculated damage results for the static deformation of the concrete structure, it is very difficult to accurately estimate the damage values of the degraded concrete structures where an aircraft collides at a high strain rate. Therefore, the present authors have a plan to establish a database of the dynamic material properties of deteriorated concrete and implement to a Finite Element Analysis model. Prior to that, dynamic increase factors described in a few technical specifications were investigated. The dynamic increase factor represents the ratio of the dynamic to static strength and is normally reported as function of strain rate. In ACI-349, only the strain rate is used as a variable in the empirical formula obtained from the test results of specified concrete strengths of 28 to 42 MPa. The maximum value of dynamic increase factor is limited to 1.25 in the axial direction and 1.10 in the shear direction. On the other hand, in the case of the CEB model, static strength is included as variables in addition to the strain rate, and a constitutive equation in which the slope changes from the strain rate of 30 /s is proposed. As plotting the two dynamic increase factor models, in the case of ACI, it is drawn as a single line, but in the case of CEB, it is plotted as multiple lines depending on the static strength. The test methods and specimen sizes of the previously performed tests, which measured the concrete dynamic properties, were also investigated. When the strain rate is less than 10 /s, hydraulic or drop hammer machines were generally used and the length of the specimens was more than twice the diameter in most cases. However, in the case of Split Hopkinson Pressure Bar tests, the small size specimens are preferred to minimize the inertia effect, so the specimens were small and the length was less than twice the diameter. We will construct the dynamic properties DB with our planned deteriorate concrete specimen test, and also include the dynamic property data already built in the previous studies.

In the present study, we examined if deep uterine artificial insemination (DUAI) can improve the pregnancy rate of artificial insemination (AI) using epididymal spermatozoa (ES) in Hanwoo cattle. The estrus cycles of 88 Hanwoo cows were synchronized, and 17 cows were artificially inseminated using the DUAI method with ES, 20 cows were artificially inseminated via the uterine body (BUAI) method with ES, and as a control, 51 cows were inseminated by using the BUAI method with ejaculated spermatozoa from 1 proven bull after frozen thawing. The pregnancy rate of the DUAI method (58.8%) was higher than that of the BUAI method (25.0%, p = 0.0498). The motility of ES was examined immediately after thawing and after 3 and 6 h of incubation. The rapid progressive sperm motility of the control group was significantly higher than that of the ES group immediately after thawing and after 3 and 6 h of incubation (p < 0.05). The straight line velocity and average path velocity of the ES group after 6 h of incubation were significantly lower than those in the control group (p < 0.05). The linearity and amplitude of lateral head of ES were lower than those at 6 h (p < 0.05). The flagellar beat cross frequency and hyperactivation of ES were lower than the control spermatozoa immediately after thawing and at 3 h (p < 0.05). These motility parameters suggested that ES had a low motility and fertilization ability compared to the control spermatozoa. After frozen-thawing and 3 h of incubation, the percentage of live spermatozoa with intact acrosomes in the ES was significantly lower than that in ejaculated spermatozoa (p < 0.05). Our findings suggested that the DUAI method can overcome the low pregnancy rate of ES, despite the low motility, viability, and fertilization ability of ES.