Radiation Physics and Engineering
Volume:2 Issue: 3, Summer 2021

The management of high radioactive spent nuclear fuel (SNF) from research and power reactors has become a key topic of discussion in the nuclear communities. Metal casks are used for the management and disposal of spent fuel and all types of radioactive waste worldwide. The spent fuel assemblies-contained casks are stored in interim storage facilities. The present study aims to show the neutronic behavior and neutron/gamma dose rates of a designed hall for storage of the casks as a current technical, economic, safe and flexible solution, adaptable to any long and short-term SNF storage strategy. The hall structure was considered as ordinary concrete with an internal dimension of 5×6×5 m3. The concrete wall thickness was discussed to keep the dose rate limit of 10 μSv/h (neutron and gamma) at its external side when 25 casks are available inside the hall. ORIGEN and MCNPX computational codes were used to model the storage hall contained 25 Tehran Research Reactor spent fuel casks. The carried out calculations showed 30 cm thickness would fulfil total gamma and neutron dose rate limitation after the external surface of the concrete wall. When the hall contains 25 casks (any contains 16 55%-burnup 10-years cooled spent fuel assembly), maximum gamma and neutron dose rates at the external surface of the hall are 3.45 nSv/h and 3.45 μSv/h, respectively. In addition, the carried out calculations showed natural circulation of air could powerfully remove the deposited heat of neutron and gamma rays.

In the present work, a time-dependent neutron diffusion simulator is developed utilizing the second order of average current nodal expansion method. Generally, nodal methods can accurately simulate the reactor core with coarse meshes as long as the sizes of a fuel assembly. In this case, an adopted iterative approach is used for resolving the time-dependent three-dimensional multi-group neutron balance equations coupled with six-group precursor equations. In order to evaluate the implemented methodology, two popular transient problems are used including TWIGL two-dimensional seed-blanket reactor and three-dimensional LMW LWR. For indicating the precision of the method, the numerical results of high (second) order approach also have been compared with the basic methodology i.e. the zeroth order solution. From the comparison of obtained results with references, the suitable and precise simulating of transient schemes can be comprehended using the time-dependent second order average current nodal expansion method. Moreover, the results confirm that the second order solution can treat the coarse mesh dynamic problems with more accuracy relative to the basic approach.

For configuring plasma focus device (PFD), the gap between electrodes is filled out with a gas at low pressure. When discharge is starting at the surface of the insulator, the gas breaks down, leading to the flow of the plasma current sheath toward the anode end. A homogeneous and symmetric current sheath which is essential for ion emission and a proper plasma pinching can be obtained when there is an electrical breakdown along the insulator. Therefore, one of the most important parts of the plasma focus is the insulator. In the present research, the effect of different insulator sleeves on the intensity of ions emitted from a 4 kJ PFD filled with Neon has been studied. Pyrex and Quartz are considered for the insulator materials and the length is varied from 3 to 6 cm for Pyrex and from 3.5 to 5.5 for Quartz. Numerous gas pressures were experimented with voltages of 11, 12 and 13 kV. The results show that both the length and the material of the insulator sleeve can affect the intensity of ions emitted from the device. The length of 4.5 cm seems optimal to yield maximum ion emission for Pyrex insulator. For the Quartz insulator, on the other hand, length of 3.5 cm results in higher ion emission. In addition, in some cases, utilizing Quartz insulator causes more ion emission compared to the Pyrex insulator.

Advantage of non-brazing methods in manufacturing of cavities has been considered in high gradient studies because of the softening of copper by brazing cavities at high temperatures. Recent studies with hard copper cavities have been shown that the harder materials can reach larger accelerating gradients for the same breakdown rate. Shrinking, as a braze-free method for construction of the cavities, was used recently to fabricate and assemble acceleration cavities of an electron linear accelerator at the Institute for Research in Fundamental Science (IPM-Iran). Based on the results obtained in this project, this paper proposes the design of a 3-cell S-band standing wave structure operating at 2.9985 GHz for high gradient tests, considering shrink-fit construction method. The desired cavity consists of three cells so that the maximum gradient in the middle cell is about twice that of the surrounding cells. Simulation with Ansys-HFSS showed that maximum axial electric field 59 MV.m-1 achievable for 2 MW input power in middle cell.

In this study, thermal-hydraulic analysis of partial loss of coolant flow accident in supercritical pressure light water reactor (SCWR) with a new geometric design has been investigated. In the new design, the coolant and moderator circuits are separated. This analysis was performed using the development of a transient-state thermal-hydraulic code in which the equations of mass, momentum, and energy are solved. The porous Media approach is used to solve these equations. By extracting the results of transition modeling, it is observed that in the new geometric design, by separating the coolant and moderator circuits, the maximum fuel clad temperature is lower than the maximum fuel clad temperature value of the previous designs. As in the new design at the end of the transition, the maximum fuel clad temperature has decreased by about 37% compared to the initial state. The result of the calculations in this study shows that the new design, in which the coolant and moderator circuits are separated, has created more safety in a chosen transition.

Addressed herein, a new monitoring method for alpha surface contamination based on the function of a thick gaseous electron multiplier (THGEM) in a self-quenching streamer mode (SQS) has been introduced. SQS mode detectors can detect alpha surface contamination in two dimensions. In the current study, the ability of thick gas electron multiplier detectors in SQS mode for two-dimensional monitoring of alpha surface contamination has been investigated by two Am-241 sources with activities equal to 33 and 150 kBq.m-3. It has been found that the brightness is stronger in front of stronger sources. This may be attributed to the difference in contamination levels. It was also observed that the spatial resolution of the contamination rate depends on the number of holes per unit area of ​​each THGEM. The advantage of this system is the ability to determine both the location and intensity of surface contamination with no need for an electronic multiplier or reader system.