Efficient one-week meeting with the IAEA experts on research reactor design

Within the framework of the IAEA Technical Cooperation Project coded VIE 1010 on "Promoting the Development Program of Reactor Safety - Phase III" led by Dr. Tran Chi Thanh, President of the Vietnam Atomic Energy Institute, The IAEA invited a delegation of three experts from the INVAP Company, Argentina to visit the Dalat Nuclear Research Institute (DNRI) to exchange the topics on Management, Safety and Effective Utilization of research reactors to improve Vietnam's national capacity in the field of design and safety analysis for research reactor, from January 30 to February 3, 2023.

Mr. Nguyen Kien Cuong, DNRI Deputy Director discusses the working program with the expert delegation

Dr. Eduardo Villarino – an expert in neutronics and thermal hydraulics, Dr. Alicia Doval – an expert in thermal hydraulics design and safety analysis, and Dr. Daniel Hergenreder – an expert in experimental and irradiation channels for research reactor applications were the delegation members.

The meeting was chaired by Mr. Nguyen Kien Cuong - Deputy Director of DNRI and participated by the representatives from the Center for Nuclear Physics and Electronics, Center for Research and Radioisotope Production and Reactor Center of the DNRI. Other representatives from institutions belonging to the Vietnam Atomic Energy Institute (VINATOM), including Dr. Pham Nhu Viet Ha and scientific staff from the Institute of Nuclear Science and Technology (INST), as well as Dr. Duong Thanh Tung and scientific staff from the Center for Nuclear Training Center, also participated online.

Meeting scene

The Vietnamese representatives presented the topics on the management, operation, and applications of the 500-kW DNRR, as well as the progress of the Center for Nuclear Science and Technology Project with a new research reactor. After that, the INVAP experts presented several topics related to the neutronics and thermal hydraulics design and safety analysis for the multi-purpose research reactor as follows:

• Core and fuel management for research reactors, including core design technique, design criteria, core parameter calculations, fuel burn-up calculations, and the utilization of MTR fuel type with burnable poisons.
• Advanced computational codes applicable to neutronics calculation for research reactors, including commercial codes such as MCNP and SERPENT…as well as in-house CONDOR, and CITVAP codes developed by the INVAP to calculate parameters such as reactivity balance, control rods worths, feedback reactivity, neutron flux and power distribution, power peaking factor, and kinetics parameters... In addition, the verification, validation, and integration of these calculation codes were also presented in detail.

• The analysis of uncertainty and sensitivity in neutronics, thermal hydraulics, and safety analysis in the design and operation for research reactors, in which various approaches to evaluate uncertainty such as conservative approach, theoretical propagation, best estimate plus uncertainty (BEPU), general perturbation theory... were introduced. Some analyses of uncertainty performed in the design of the OPAL reactor were also presented.
• Multi-physics in research reactors, experiments in multi-physics and safety analysis were introduced. Several examples of multi-physics integration and process simulations were presented, including general multi-physics analysis, neutronics and thermal hydraulics feedback, and neutron detector response after secondary shutdown systems (SSS) triggered, activation dose calculation, combined neutronics and thermal hydraulics calculations for multi-physics as well as best estimates for safety analysis in design calculation for research reactors. Some experiment results at the OPAL reactor were presented to validate the combined codes in multi-physics and safety analysis.

• Computer codes applicable to thermal hydraulics calculations and safety analysis for research reactors, including the codes for steady state calculations only, such as TERMIC, CAUDVAP, and CONVEC and the codes for both transients and steady state, such as RELAP5, THERMAL DESKTOP, and CFD (Fluent, Open Foam). The results of the design calculation of thermal hydraulics and safety analysis for the OPAL reactor were presented as an example.
• Details of the safety analysis for the research reactor in which the deterministic safety analysis method based on the defense in depth from level 1 (Normal operation) to level 4 (Postulated core damage accident); the RELAP5 code was used to analyze some typical hypothetical accidents, such as a hypothetical severe loss of coolant accident (type 2A: complete rupture of the primary cooling system) although this accident is very highly unlikely. The experts confirmed that an accident causing significant core damage is excluded for the Open Pool type research reactor. In addition, a number of response actions based on the lessons of Fukushima accident were also introduced, in which the back-up and replacement systems of cooling water supply and power supply were taken into account.
• Experience in designing horizontal experimental channels with the examples of  22 MW ETRR-2 reactor put into operation in 1998, 20 MW OPAL reactor put into operation in 2007, 30 MW RA-10 reactor under construction and 30 MW RMB reactor with the design phase completed, in which the designs of cold neutron source in the reflector and thermal and cold neutron beam ports for research in material science, nuclear physics, neutron radiography, etc. were presented in detail.
• Experience in designing irradiation channels in the core and at the reflector of the above-mentioned multi-purpose research reactors was explaned as examples. The design of irradiation holes for doping large-sized monocrystalline silicon with diameters of 5 to 10 inches, for producing Mo-99 by low-enriched uranium target, and producing other isotopes such as Lu -177, Y-90, Re-188, Ho-166, Re-186, W-188… and sealed radioactive source Ir-192 were presented in detail.
• Discussion on the design of irradiation and experimental horizontal channels in the reactors with heavy water and beryllium reflectors showed that heavy water reflectors have outstanding advantages in terms of the neutron field uniformity, and the capability to create a large diameter reflector for easy to install irradiation channels. In particular, the heavy water reflector produces a thermal neutron to fast neutron ratio hundreds to thousands of times greater making it easy to design and install irradiation channels for doping high-quality monocrystalline silicon to satisfy customer requirements.

Several photos of the INVAP expert delegation at the DNRI

Mr. Nguyen Kien Cuong presents tokens of appreciation to the IAEA experts

The experts pay a visit to the traditional room

The experts takes photos with the DNRI representatives

Translated by Nguyen Kien Cuong

Source: Dalat Nuclear Research Institute