Dr. Sheikh Tahir Mahmood

Fuel Material

Dr. Sheikh Tahir Mahmood retired from Global Nuclear Fuel in 2012 as a Senior Engineer/Technologist for Fuels Engineering at the Vallecitos Nuclear Center. Earlier he received Masters degrees in Physics and Nuclear Technology from abroad and doctorate in Nuclear Engineering from North Carolina State University. His Post-doctoral work on mechanical anisotropy of zirconium alloys and radiation effects on reactor structural materials was done at NCSU and ORNL, respectively.

At GE Nuclear Energy/GNF, he was actively engaged in fuel performance and materials technology. This activity involved failure root-cause investigations through hot cell PIE of the failed in-core components, and development and evaluation of material property data bases for new materials developed for in-core use. Tahir has particular interest and experience in mechanical metallurgy, mechanical behavior of fuel, cladding and structural materials, and in-reactor behaviour of these materials for improved fuel reliability. He has actively participated in various international nuclear industry research programs.

How did you get started as an engineer?

I did Masters (M.Sc.) in Physics at the Punjab University, Pakistan and won a national scholarship to pursue Masters in Nuclear Technology at the Islamabad University, Pakistan, which I completed in 1976. After teaching nuclear engineering subjects for several years, I completed my Ph.D. degree in Nuclear Engineering at the North Carolina State University (NCSU), USA in 1989. My post-graduate work was on crystallographic texture and mechanical anisotropy of zirconium alloys.

Your career history?

After completing the Ph.D. degree, I worked as post-doctoral fellow at the Nuclear Engineering Department of NCSU. I worked mainly on experimental investigations of properties of zirconium alloys that resulted in a number of journal and conference proceeding publications. In 1991, I joined the Metals and Ceramics division of the Oak Ridge National Laboratory (ORNL) where I worked on radiation effects on reactor pressure vessel steels and aluminium alloys including faster than expected radiation embrittlement of the pressure vessel of the High Flux Isotope Reactor (HFIR) at ORNL. The large magnitude of high energy gamma flux, that was being experienced by the vessel, was found to be responsible for the excessive embrittlement.

In 1994, General Electric Company hired me to work on root cause investigations of the degradation of the failed BWR fuel rods, hot cell investigations of the irradiated fuel bundle components, and development of mechanical property data base for the newly developed products. I was stationed at the GE Vallecitos Nuclear Center in California. One of my last projects at GE was root cause investigations of the excessive bow in Zircaloy-2 channels. Most of the results of these investigations have been published in open literature. At GE, I got a chance to actively participate in various international nuclear industry research programs such as NFIR at EPRI, USA; SCIP at Studsvik, Sweden; Dimensional stability program at RIAR, Russia, and JHIP at CEA, France. I retired from GE in September 2012. I have authored or co-authored over 40 papers in technical Journals and International Conference Proceedings. I am consulting for a few organisations in my areas of expertise.

How did you get introduced to ANT International and the ZIRAT/IZNA Programme?

I was introduced to ANT International by my ex-manager and friend Ron Adamson who himself have been a very active member of the experts team.

How has the field of nuclear fuel issues changed during your career?

When I started to work in the field of BWR materials technology, degradation of the failed fuel rods, with Zr liner, was a major issue for the plant operators and the fuel vendors. This issue was resolved reasonably well by improving the corrosion resistance of the Zr liner through the addition of small quantities of alloying elements. Now many companies are working on SiC cladding for improved reliability and performance.

Increased cycle lengths and bundle burn ups resulted in the issue of Zircaloy-2 channel bow in BWRs. Hot cell investigations pointed to enhanced bow due to hydrogen differential between the channel sides next to and away from the neighbouring control blade. This was the result of shadow corrosion related enhanced corrosion and hydrogen pick up on the channel side next to the blade. Fuel vendors offered Zircaloy-4 channels as the interim solution (due to its low hydrogen pick up properties) while they started working on the more permanent material solution like Zirlo and NSF alloys. During most of my career in this field, UO2 was the fuel of interest. However, work was being done on developing various types of additive fuels. Some vendors have already introduced additive fuels on commercial basis while others are working on these. More recently a lot of emphasis is being placed on SMRs and reactors that use the already used fuel to extract more energy out of it and reduce the volume of the radioactive waste.

What do you foresee the future of the nuclear industry and how does the ZIRAT/IZNA programs fit in?

I think the nuclear industry will continue to grow in spite of the Fukushima accident, and nuclear energy will be a significant part of the energy mix in developed and developing countries. The ZIRAT program provides an excellent platform for technical inter-action between plant operators and other experts to make continuing improvements to operate plants safely and cost effectively. In addition, ZIRAT program also provides basic training for young engineers in this field. The IZNA program provides the fuel vendors and regulators concise summary of the current state of the fuel technology in the form of specialised reports and seminars.

How do you spend your leisure time?

I am an avid fan of poetry in Urdu (a language widely spoken in the Indian subcontinent). Luckily, the UC Berkeley library has a huge collection of Urdu poetry books by classic poets from 18th to 20th centuries. I make good use of these books to prepare for being MC of the monthly Urdu poetry recital programs in the San Francisco bay area. In addition, I always look forward to travelling to visit new places and experience new cultures.