Stress corrosion cracking of stainless steels in the primary water of pressurized water reactors is one issue threatening the safety of a nuclear power plant. To improve safety, researchers from Khalifa University’s Nuclear Engineering Department are investigating the role of the carbides produced when heat-treating steel.��

Pyungyeon Cho, Research Assistant in the Department of Nuclear Engineering, has developed a project to investigate the main role of the carbides (carbon-metal alloys) produced when stainless steel and nickel-based alloys are heat-treated.

Nuclear power plants use stainless steels in the various structures of the reactor for robustness, but the environment in a nuclear reactor is uniquely stressful. Materials subjected to reactor conditions for long periods of time begin to corrode and crack. Cho’s project is expected to show how the carbides produced at the boundary between the particles in the steels act during stress corrosion cracking in one area of the reactor.

“The stress corrosion cracking of austenitic stainless steels and Ni-based alloys in the primary water of pressurized water reactors is one issue threatening the safety of a nuclear power plant,” explained Cho. “A number of studies have been performed on the primary water stress corrosion cracking (PWSCC) of austenitic stainless steels and Ni-based alloys, and several mechanisms have been proposed to explain the observations. However, the exact mechanism remains open to debate.”

Cho’s project sets out to verify the role of the grain boundary carbides in PWSCC. To isolate one factor leading to carbide formation and chromium depletion, stainless steel 347 is used and nickel-based carbides are precipitated without chromium depletion. In the first stage, optimized heat treatment conditions are determined and in the second stage, PWSCC tests are performed. After these tests, microstructures and crack morphology are examined.

All thermal reactor designs require the fast fission neutrons to be slowed down to interact with the nuclear fuel and sustain a chain reaction. Pressurized water reactors (PWRs) use ordinary water as a coolant and neutron moderator (a medium to reduce the speed of fast neutrons), leaving them as thermal neutrons with only minimal kinetic energy. PWRs are by far the most common type of reactor in use today. Kept under high pressure and not allowed to boil, the primary water (the water in contact with the uranium fuel) passes through a heat exchanger, where it transfers its heat to a second loop of water at a lower pressure. This secondary water transforms into steam used to spin turbines that produce electricity.

The secondary water is not in contact with radioactive elements and can be recycled after having been condensed. The plume of steam escaping from the tower of a nuclear power plant comes from a third loop of tertiary water that cools the condenser. PWRs are among the cleanest of the nuclear power reactors, as a radioactive product would need to make its way through the zircaloy shell of the fuel rod, into the primary water, into the secondary water, and then into the tertiary water. The safety provided by these multiple barriers comes at the additional cost of build complexity.

The structure around the reactor and associated steam generators is designed to protect it from outside intrusion and to produce those outside from the effects of radiation in case of any serious malfunction inside. Typically, this is a metre-thick concrete and steel structure.

“Austenitic stainless steels and nickel-based alloys have been widely used in PWR primary coolant systems, such as reactor internals, steam generator tubing, reactor pressure vessel inlet and outlet nozzles and so on, because these alloys satisfy the requirements for primary side components,” explained Cho. “However, stress corrosion cracking on Ni-based alloys and their welds in primary water conditions has been observed since the 70s. Since 1997, we’ve even had reports of cases of intergranular stress corrosion cracking on cold-worked austenitic stainless steels in primary water conditions.”

Primary water conditions are characterized by their high temperature, high pressure, low dissolved oxygen, added hydrogen, and other additives such as boric acid and lithium hydroxide. Boron and cadmium control rods are used to maintain primary system temperatures at the desired point and an operator can control the steady state operating temperature by adding boric acid.

The high temperature water coolant with boric acid dissolved in it is corrosive to carbon steel, which limits the lifetime of the reactor and the systems that filter out the corrosion products. However, stainless steel should not be affected.

“PWSCC is influenced by a number of factors: chemical compositions (carbon, nickel, chromium), grain size and grain boundary orientation, carbide precipitation, cold-work, stress, temperature, pH, and hydrogen partial pressure, among others. Studies show some unique features of cracking behaviour, for example, the cracking of the alloys in the primary side is almost intergranular, and cold-work enhances the susceptibility of alloys to PWSCC.”

A grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. They are 2D defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material.

It has been observed that PWSCC is suppressed by the microstructural changes in both austenitic stainless steels and Ni-based alloys after sensitization heat treatment, but it is unclear how this happens. Cho theorized that the carbides precipitated by this treatment play a main role in the microstructural changes of the stainless steel.

“When both the alloys are heat-treated at a temperature range of 450 to 850 C for sufficient time, chromium-rich carbides are precipitated at grain boundaries, leading to the depletion of chromium along the grain boundaries,” explained Cho. “Since carbide formation is always accompanied by chromium depletion, it is not easy to identify which one plays the main role in PWSCC.”

So far, the first stage has been completed and the second stage is underway. It is expected that the results from the second stage and the analysis thereafter will provide key evidence for the role of carbides in primary water stress corrosion cracking, with the research contributing to the safety of this industry.

Jade Sterling
News and Features Writer
25 March 2020

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Khalifa University hosted a Workshop on the Best Practices in Nuclear Training and Education Approaches led by Khalifa University Assistant Professor Saeed Al Ameri and Virginia Commonwealth University Assistant Professor Braden Goddard on 17–19 February 2020.

As peaceful nuclear power and technology is developed in the Middle East region, it is important to know the best practices when it comes to human capital development. The event was attended by industry representatives, regulators, and academics from the UAE and Egypt, two of the leading nuclear countries in the region. Participants of the event have taken the material they have gained from the workshop and have started implementing it in their own training and education program to help produce the best nuclear employees.

Ara Cruz
News Writer
1 March 2020

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As part of the ongoing research and education partnership with Emirates Nuclear Energy Corporation (ENEC), five faculty members from the Nuclear Engineering Department at Khalifa University were given a unique opportunity to visit Barakah Nuclear Energy Plant.

During the visit, Dr. Yacine Addad, Dr. Youssef Shatilla, Dr. Akihide Hidaka, Dr. Saeed Al Ameri, and Dr. Ahmed Alkaabi witnessed firsthand the high safety standards that are embedded at the Barakah Nuclear Energy Plant. Upon completion of its four Units, the Barakah plant will generate 5,600 MW of clean electricity, providing up to 25 percent of the UAE’s electricity demand when fully operational, while preventing the release of 21 million tons of carbon emissions annually, equivalent to removing 3.2 million cars off the Nation’s roads each year.

The visit was timely as it came right before the completion of Unit 1 fuel load. The Barakah Unit 1 has since commenced the start-up process following successful completion of fuel loading in March 2020. Over a number of months, power levels will safely and steadily be raised, once reaching full capacity the unit will generate 1,400 MW of abundant baseload electricity.

This milestone reflects the vote of confidence that the plant specifically, and the UAE in general, have received after a lengthy licensing process by the UAE’s independent regulator, the Federal Authority for Nuclear Regulation (FANR). This process is followed for each of the four units.

The KU faculty expressed their gratitude and pride in witnessing this historic moment for the UAE.

Erica Solomon��
Senior��Editor
10 February 2020

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��The new center will support research, innovation and capacity building in the UAE’s peaceful nuclear energy industry

A Memorandum of Understanding has been signed by UAE’s MoEI, and the Korea’s MoFA to cooperate in research projects

��The UAE Ministry of Energy and Industry opened the Emirates Nuclear Technology Center, at Khalifa University’s Sas Al Nakhl Campus in Abu Dhabi, UAE, to support the long-term sustainability of the UAE Peaceful Nuclear Energy Program by creating a dedicated innovation hub for peaceful nuclear technologies.

��A Memorandum of Understanding (MoU) was exchanged by His Excellency Suhail Bin Mohammed Faraj Faris Al Mazrouei, UAE Minister of Energy and Industry, and His Excellency Lee Taeho, Second Vice Minister of Foreign Affairs, Republic of Korea, during the opening ceremony, attended by His Excellency Engineer Mohamed Al Hammadi, Chief Executive Officer of ENEC, Christer Viktorsson Director General of the Federal Authority of Nuclear Regulation (FANR), Dr. Arif Sultan Al Hammadi Executive Vice President of Khalifa University, and senior officials from all five entities.

The MoU between the UAE MoEI and the Ministry of Science, and Information and Communications Technology of Korea, under the UAE-Korea Consultation Committee on Nuclear Technology, outlines the framework of cooperation on research projects between the center’s relevant partners.

The Emirates Nuclear Technology Center will engage in research projects designed and approved by ENEC and FANR, and will be conducted by students, academics and researchers from Khalifa University. The Center’s initial research projects will focus on three areas – nuclear safety and systems, nuclear materials science and chemistry, and radiation safety in the environment.

Through the MoU, the ENTC will benefit from sharing of knowledge and expertise from the Korean nuclear energy industry, which has been operating for over 40 years, along with experience in developing nuclear research reactors.

“It is my pleasure to launch the Emirates Nuclear Technology Centre in Abu Dhabi, which is an outcome of our collaborative approach with our South Korean government counterparts and all UAE nuclear stakeholders, who are working to further Nuclear Science & Technology Research and Development. Investing in research and innovation are prerequisites for the long-term success of the UAE’s peaceful nuclear energy industry. It will further position the UAE as an international role model for the development of a peaceful nuclear energy program by building UAE National capabilities and conducting industry-leading research on radiation safety and nuclear energy technologies,” said His Excellency Suhail Al Mazrouei.

“Within the frame of the High-Level Consultation on Nuclear Cooperation, we and our UAE partner are expanding areas of cooperation in the Barakah Nuclear Energy Plant construction and operations, new nuclear energy project in third countries, nuclear R&D, and safety regulations. I believe that the MoU on nuclear energy and R&D cooperation will serve as a catalyst that will further accelerate our bilateral nuclear energy cooperation”, said His Excellency Lee Taeho,.

H.E. Eng. Mohamed Al Hammadi, CEO of ENEC, said: “We are delighted to be part of this initiative to establish the Emirates Nuclear Technology Center. As the UAE’s emerging peaceful nuclear energy industry continues to grow and develop, collaboration and cooperation between academia and industry will allow us to ensure the long-term sustainability of the UAE Peaceful Nuclear Energy Program, as well as enhancing our global competitiveness and high standards of safety. Through its projects and research the Center will provide talented UAE Nationals with the opportunity to work alongside international experts in conducting cutting-edge research, thereby developing their skills and capabilities within the field of peaceful nuclear energy.”

��Dr Arif Sultan Al Hammadi, Executive Vice-President, Khalifa University of Science and Technology, said: “We are delighted to join the official launch of the Emirates Nuclear Technology Center (ENTC), hosted on our campus, in collaboration with our stakeholders including our partners ENEC and FANR. The ENTC reflects another strong commitment from Khalifa University to contribute to enhancing the UAE’s nuclear technology research capability and support our key stakeholder’s goals for the delivery of safe, clean and efficient nuclear technology to meet the UAE 2030 vision. The center will significantly optimize the multidisciplinary capabilities through Khalifa University’s diverse community of faculty and researchers to meet the national objectives.”

“We are delighted to join our national and international stakeholders in launching the Emirates Nuclear Technology Centre. Investing in research and innovation in nuclear technologies is indispensable to ensure the sustainability of the nuclear program. We will work closely with our partners to identify priority areas, focus on strategic nuclear sector research, ensure continuity of projects and provide support to national and international initiatives in line with FANR’s R & D Policy, which was launched in 2017. FANR will support the mandate of the new center by utilizing its Research and Development Program. FANR’s Research and Development Program aims to develop and attract Emiratis by providing opportunities for postgraduate education and research in the nuclear field. It also aims to ensure sound technical basis for all regulatory activities, mitigate risks related to safety, security and safeguards in the UAE nuclear sector,” said Christer Viktorsson, Director-General of the Federal Authority for Nuclear Regulation (FANR) in the UAE.

The establishment of the Emirates Nuclear Technology Center will cement the UAE’s position as an international role model for the development of a new peaceful nuclear energy projects around the globe. Innovation and continuous development are essential to the sustainability and long-term success of the UAE’s peaceful nuclear energy industry, as well as the UAE’s ongoing transition to a knowledge-based economy and society.

The MoU comes at a pivotal time for ENEC, with the 4 Units of Barakah Nuclear Energy Plant more than 93% complete. Unit 4 is over 82% complete, Unit 3 is more than 91% and Unit 2 is more than 95%. Unit 1 construction has been completed and is currently undergoing operational readiness preparations pending regulatory approval and receipt of the Operating License for Unit 1 from FANR, anticipated in early 2020.

After the launch of ENTC and the MoU signing, His Excellency Suhail Al Mazroui, His Excellency Lee Taeho and members of the official delegation from Korea, ENEC, and FANR along with Khalifa University senior management team, faculty members and researchers toured the research facility.

Later, delegation members from the two countries attended the second meeting of the ‘UAE-Korea high-level consultations on nuclear cooperation’.

News Writer
27 November 2019

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