Volume 85, Issue 2

This article is written to honour the scientific achievements of prof. Eugenijus Ušpuras, who passed away in 2019. Therefore, his colleagues summarized retrospectively main research topics like safety studies for Ignalina NPP, research in nuclear fusion and investigations in energy security prof. E. Ušpuras worked with. Since prof. Eugenijus Ušpuras spent his entire scientific career at Lithuanian Energy Institute (LEI) all these three topics are directly related to the development of the nuclear energy topics and research performed in Lithuania during the last decades.

A comparative analysis of heat transfer characteristic in pulsating flow induced by rolling motion under natural circulation and forced circulation condition was performed. Variation of local and average heat transfer characteristics with rolling motion were also investigated. The results show that the natural circulation time-averaged heat transfer characteristic is enhanced by rolling motion. However, the variation of time-averaged heat transfer characteristic of forced circulation is not significant. In addition, the relationship between the relative pulsation amplitude of Reynolds number and Nusselt number does not present predominant difference in natural and forced circulation conditions.

Pressure vessel in pool layout is usually used in high power and middle pressure research reactor, Flow inversion and residual heat removal is important problem. The heat removal strategy at accident situation for a pressure vessel in pool layout research reactor was studied in the paper, many cases was researched for the ability of heat removal and safety of core.

The pellet-cladding interaction (PCI) is one of the major issues in fuel rod during the power change operation in light water reactors (LWR). The frequent power transient will lead to the PCI failure, which results in the radioactive leakage. Unfortunately, the failure cannot be detected on time during operation. For solving this problem, the PCI results is calculated and predicted before the power transient, and the results is used for optimizing the operation strategy. As everyone knows, the calculation of the fuel is a cumbersome work, which is not fit for online evaluation. At first, we present a PCI online prognosis model in this paper by the method of radial basis function neural network (RBFNN). Based on this online model, an optimal operation strategy is present then. The PCI evaluation results is treated as the feedback of the strategy, which will go to the power control system to decide to carry out the power plan or to modify it. The presented operation strategy used the fast online prognosis model to predict the PCI status, which is used as a feedback signal to the power control system. The optimal operation strategy is tested by the experimental data from the references, and the results demonstrate its effectiveness.

The following work is an attempt to develop a model research reactor based on VVER-440 technologies, primarily for the production of radioisotopes used in nuclear medicine procedures. The article describes the basic design features of the model 10 MW multipurpose VVR reactor, including the features of reactor fuel, core, and related structures. A comparative analysis of targets for maximizing 99 Mo production is also presented.

Small modular reactors (SMRs) are suitable for deployment in isolated underdeveloped areas to support highly localized microgrids. In order to achieve almost autonomous operation for reducing the cost of operating personnel, an autonomous control system with decision-making capability is needed. In this paper, a decision-making method based on Bayesian optimization algorithm (BOA) is proposed to explore the optimal operation scheme under fault conditions. BOA is used to adjust exploration strategy of operation scheme according to observations (operation schemes previously explored). To measure the feasibility of each operation scheme, an objective function that considers security and economy is established. BOA attempts to obtain the optimal operation scheme with maximum of the objective function in as few iterations as possible. To verify the proposed method, all main pump powered off fault is simulated by RELAP5 code. The optimal operation scheme of the fault is applied, the transient result shows that all key parameters are within safe limits and SMR is maintained at relatively high power, which means that BOA has the decision-making capability to get an optimal operation scheme on fault conditions.

Logical loops or circular logics, interpreted as circular supporting relations among systems, remain a longstanding challenge in the probabilistic safety assessment (PSA). Logical loops are commonly found in complex industrial systems. Due to the existence of the logical loops, the minimal cut sets cannot be directly obtained. In order to solve this problem, the logical loops should be broken properly. This paper proposes a graphical method based on multi-tree structure. By constructing the simplified multi-tree, logical loops both in linearly and non-linearly interrelated systems are solved. To illustrate this method, examples of linearly interrelated systems and non-linearly interrelated systems are given in this paper. As a supplement, this method is applied to the well-known complex logical loops in the nuclear power plant. It shows that this method is highly intuitive and efficient by means of graphs.

The 3 rd "Sino-German Symposium on Fundamentals of Advanced Nuclear Safety Technology (SG-FANS)" took place in Xi’an, China, in 2019. Common fields of interests have been identified on both Chinese and German side, such as code benchmarking, common access to experimental facilities and joint experimental data base for nuclear safety analyses.