Intruder configurations in Ne at the transition into the island of inversion; Detailed structure study of Ne

Wang, H.*; Yasuda, Masahiro*; Kondo, Yosuke*; Nakamura, Takashi*; Tostevin, J. A.*; Ogata, Kazuyuki*; Otsuka, Takaharu*; Poves, A.*; Shimizu, Noritaka*; Yoshida, Kazuki; et al.

Physics Letters B, 843, p.138038_1 - 138038_9, 2023/08

https://doi.org/10.1016/j.physletb.2023.138038

Detailed -ray spectroscopy of the exotic neon isotope Ne has been performed using the one-neutron removal reaction from Ne. Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for Ne and the negative-parity states are identified for the first time. The measured partial cross sections and momentum distributions reveal a significant intruder p-wave strength providing evidence of the breakdown of the N = 20 and N = 28 shell gaps. Only a weak, possible f-wave strength was observed to bound final states. Large-scale shell-model calculations with different effective interactions do not reproduce the large p-wave and small f-wave strength observed experimentally, indicating an ongoing challenge for a complete theoretical description of the transition into the island of inversion along the Ne isotopic chain.

Study on performance evaluation of self-actuated shutdown system for sodium-cooled fast reactor; Investigation on flow field around curie point electromagnet

Aizawa, Kosuke; Hiyama, Tomoyuki; Kobayashi, Jun; Kurihara, Akikazu

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 6 Pages, 2023/05

Self-actuated shutdown system (SASS) is a passive reactor-shutdown system that utilizes a Curie-point electromagnet (CPEM), which features the characteristic of loss in magnetism when the magnet temperature reaches the Curie point. A control rod with SASS is inserted into the core by gravity without recourse to any active shutdown system. To allow the SASS to effectively function, efficiently guiding high-temperature fluid from the fuel assembly to CPEM is important. Therefore, CPEM features a complicated shape such as having 45 fins, and a flow collector is installed upstream of CPEM to direct the flow from the fuel subassembly outlet to CPEM. In this report, the water experiment was performed on the full-scale model that simulates from the outlets of the fuel assemblies to the SASS flow collector, and flow phenomena around the temperature sensing part was analyzed from the data obtained by PIV measurement.

Decommissioning of uranium handling facility for development of nuclear fuel manufacturing equipment

Kageyama, Tomio; Denuma, Akio; Koizumi, Jin*; Odakura, Manabu*; Haginoya, Masahiro*; Isaka, Shinichi*; Kadowaki, Hiroyuki*; Kobayashi, Shingo*; Morimoto, Taisei*; Kato, Yoshiaki*; et al.

JAEA-Technology 2022-033, 130 Pages, 2023/03

JAEA-Technology-2022-033.pdf:9.87MB

Uranium handling facility for development of nuclear fuel manufacturing equipment (Mockup room) was constructed in 1972. The Mockup room has a weak seismic resistance and is deteriorating with age. Also, the original purpose with this facility have been achieved and there are no new development plans using this facility. Therefore, interior equipment installed in this facility had been dismantled and removed since March 2019. After that, the Mockup room was inspected for contamination, and then controlled area in the Mockup room was cancelled on March 29th 2022. A total of 6,549 workers (not including security witnesses) were required for this work. The amount of non-radioactive waste generated by this work was 31,300 kg. The amount of radioactive waste generated by this work was 3,734 kg of combustible waste (103 drums), 4,393 kg of flame resistance waste (61 drums), 37,790 kg of non-combustible waste (124 drums, 19 containers). This report describes about the dismantling and removing the interior equipment in the Mockup room, the amount of waste generated by this work, and procedure for cancellation the controlled area in the facility.

Experimental study on prevention of high cycle thermal fatigue at the core outlet of advanced sodium-cooled fast reactor; Characteristics of temperature fluctuations and countermeasures to mitigate temperature fluctuations at a bottom of upper internal structure

Kobayashi, Jun; Aizawa, Kosuke; Ezure, Toshiki; Nagasawa, Kazuyoshi*; Kurihara, Akikazu; Tanaka, Masaaki

JAEA-Research 2022-009, 125 Pages, 2023/01

JAEA-Research-2022-009.pdf:29.22MB

The design studies of an advanced loop-type sodium-cooled fast reactor (Advanced- SFR) have been carried out by the Japan Atomic Energy Agency (JAEA). At the core outlet, temperature fluctuations occur due to mixing of hot sodium from the fuel assembly with cold sodium from the control rod channels and radial blanket assembly. These temperature fluctuations may cause high cycle thermal fatigue around a bottom of Upper Internal Structure (UIS) located above the core. Therefore, we conducted a water experiment using a 1/3 scale 60 degree sector model that simulated the upper plenum of the advanced loop-type sodium-cooled reactor. And we proposed some countermeasures against large temperature fluctuations that occur at the bottom of the UIS. In this report, we have summarized that the effect of the countermeasure structure to mitigate the temperature fluctuation generated at the bottom of UIS is confirmed, and the Reynolds number dependency of the countermeasure structure and the characteristics of the temperature fluctuation on the control rod surface.

Investigation on natural circulation behavior for decay heat removal in reactor vessel of sodium-cooled fast reactor under severe accident condition, 1; Effect of decay-heat conditions on natural circulation behavior under dipped-type DHX operation conditions

Tsuji, Mitsuyo; Aizawa, Kosuke; Kobayashi, Jun; Kurihara, Akikazu

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 6 Pages, 2022/10

In sodium-cooled fast reactors (SFRs), decay heat removal after a core disruptive accident (CDA) is an important issue for the safety enhancement. Therefore, water experiments using a 1/10 scale experimental apparatus (PHEASANT) that simulates the reactor vessel of an SFR are conducted to investigate the natural circulation phenomena in the reactor vessel. In this study, experiments under the operation of the dipped-type DHX were conducted to investigate the effect of the heat generation ratio between the fuel debris on the core catcher in lower plenum and the reactor core remnant on the natural circulation behavior in the reactor vessel. The temperature distribution and the velocity distribution were measured under two heat generation conditions. Thus, the effect of the heat generation ratio between the fuel debris in the lower plenum and the reactor core remnant on the natural circulation behavior was quantitatively grasped under the dipped-type DHX operating conditions.

Magnetic properties and electronic configurations of Mn ions in the diluted magnetic semiconductor BaK(ZnMn)As studied by X-ray magnetic circular dichroism and resonant inelastic X-ray scattering

Suzuki, Hakuto*; Zhao, G.*; Okamoto, Jun*; Sakamoto, Shoya*; Chen, Z.-Y.*; Nonaka, Yosuke*; Shibata, Goro; Zhao, K.*; Chen, B.*; Wu, W.-B.*; et al.

Journal of the Physical Society of Japan, 91(6), p.064710_1 - 064710_5, 2022/06

https://doi.org/10.7566/JPSJ.91.064710

Noise countermeasures for inverter-controlled multi-stage roots vacuum pumps in J-PARC LINAC L3BT

Takano, Kazuhiro; Kotoku, Hirofumi*; Kobayashi, Fuminori*; Miyao, Tomoaki*; Moriya, Katsuhiro; Kamiya, Junichiro

JAEA-Technology 2021-017, 35 Pages, 2021/11

JAEA-Technology-2021-017.pdf:5.32MB

In J-PARC LINAC, the vacuum system of L3BT, which is a beam transport line connecting LINAC and 3GeV synchrotron, uses a turbo molecular pump and roots pump for rough exhaust and an ion pump for main exhaust. In addition, beam dumps are connected to the end of the L3BT at 0 degree, 30 degree, 90 degree, and 100 degree positions via vacuum partition windows. The roots pumps are used as the exhaust system for each beam dump. The roots pump controllers have been installed away from the pump in the accelerator tunnel to avoid radiation damages. Besides, the special controllers, which have no inverter circuit inside, have been used to reduce the electrical noise on the beam loss monitors nearby. However, using the special controller without inverters, several problems have occurred such as the instability or wide variability of the pumping speed. To solve such problems, the roots pump controller with the inverter circuit must be used after reducing the electrical noise. In this report, some countermeasures to reduce the electrical noise from the inverters were investigated. The noise reduction circuit was successfully optimized to the level where the beam loss monitors works unaffected.

Water experiments on thermal striping phenomena at the core outlet of an advanced sodium-cooled fast reactor, 2; Proposal of countermeasures to mitigate temperature fluctuations around radial blanket fuel assemblies

Kobayashi, Jun; Aizawa, Kosuke; Ezure, Toshiki; Kurihara, Akikazu; Tanaka, Masaaki

Hozengaku, 20(3), p.97 - 101, 2021/10

Focusing on the thermal striping phenomena that occurs at a bottom of the internal structure of an advanced sodium-cooled fast reactor (Advanced-SFR) that has been designed by the Japan Atomic Energy Agency, a water experiment using a 1/3 scale 60 degree sector model simulating the upper plenum of the Advanced-SFR has been conducted to examine countermeasures for the significant temperature fluctuation generated around the bottom of Upper Internal Structure (UIS). In the previous paper, we reported the effect of measures to mitigate temperature fluctuations around the control rod channels. In this paper, the same test section was used, and a water experiment was conducted to obtain the characteristics of temperature fluctuations around the radial blanket fuel assembly. And the shape of the Core Instrumentation Support Plate (CIP) was modified, and it was confirmed that it was highly effective in alleviating temperature fluctuations around the radial blanket fuel assembly.

Wettability of pure metals with liquid sodium and liquid tin

Saito, Junichi; Kobayashi, Yohei*; Shibutani, Hideo*

Nihon Kinzoku Gakkai-Shi, 85(3), p.110 - 119, 2021/03

https://doi.org/10.2320/jinstmet.J2020042

Formation of clusters in dilute neutron-rich matter

Tanaka, Junki*; Yang, Z.*; Typel, S.*; Adachi, Satoshi*; Bai, S.*; Van Beek, P.*; Beaumel, D.*; Fujikawa, Yuki*; Han, J.*; Heil, S.*; et al.

Science, 371(6526), p.260 - 264, 2021/01

https://doi.org/10.1126/science.abe4688

By employing quasi-free -cluster-knockout reactions, we obtained direct experimental evidence for the formation of clusters at the surface of neutron-rich tin isotopes. The observed monotonous decrease of the reaction cross sections with increasing mass number, in excellent agreement with the theoretical prediction, implies a tight interplay between -cluster formation and the neutron skin.