UConn prof writes clear PBMR overview

Pelindaba, South Africa, pebble bed work site

Professor Lee Langston writes in Mechanical Engineering
University of Connecticut retired professor Lee Langston has just published a very clear, readable history of the pebble bed modular reactor project underway in South Africa. Pebbles Making Waves is the feature article in the April, 2008, issue of Mechanical Engineering, published by the American Society of Mechanical Engineers.

I encourage you to read this overview of the history and status of the Pebble Bed Modular Reactor project in South Africa.

South Africa is planning a Pebble Bed Reactor

PBMR vessel, turbines, and generator

The Pebble Bed Modular Reactor (PBMR) is the terminology for South Africa's specific pebble bed reactor project and company. Pebble Bed Modular Reactor (Pty) Ltd has designed and is building a single module demonstration pebble bed reactor with a capacity of 165 MW. Assuming regulatory approvals, the demonstration plant will begin construction in 2008 with the first fuel load scheduled for 2012. If successful, South Africa intends to produce PBMR units for internal use and for export to Africa and the rest of the world. South Africa is planning to use 20 to 30 165 MW units to meet its own power needs.

The PBMR would be useful in many emerging nations than cannot afford billion dollar 1,000 MW power plants common in the US. Because the PBMR is refueled while in operation without being shut down, it can be a single, reliable electric power source in isolated regions. Exporting PBMRs could be a significant income source for South Africa, which is contemplating exporting 10 units per year, perhaps selling in the $150-200 million range. PBMR Pty Ltd has already taken preliminary steps with the US Nuclear Regulatory Commission to license the PBMR for the US market.

Eskom, the South African utility company, began investigating pebble bed technology in 1993, obtaining a license for the technology first developed in Germany in 1966. Eskom was joined by other investors in 2000, including the Industrial Development Corporation of South Africa, British Nuclear Fuels (BNFL), and the US utility Exelon. Since then Exelon has dropped out and the BNFL role has been taken over by Westinghouse, which BNFL sold to Toshiba.

Progress is being made

Mitsubishi Heavy Industries has been awarded the contract for the basic design of the core barrel assembly of the reactor vessel. According to PBMR Ltd, Mitsubishi will be the integrator and single point supplier for the complete system.


Prototype helium turbine built in Potchefstroom

The gas turbine test rig was built by the engineering department of the University of Potchefstroom near Johannesburg. The main pressure vessel of the test rig is 17.5 meters long and weighs 12 tons. The test rig represents the first closed-cycle, multi-shaft gas turbine in the world.


Uranium fuel kernels production

Pelindaba Labs has created a process for producing the small kernels of UO2 that are the fuel for the PBMR.

Earthlife Africa opposes the PBMR and in 2005 persuaded the court to set aside the positive Record of Decision on the environmental impact study. In January 2007 the Department of Environmental Affairs permitted the project to go ahead with the pilot fuel plant at Pelindaba.

Helium test facility

The project has constructed a helium test facility at Pelindaba near Pretoria. It is to test the complete, high temperature, high-pressure helium cycle. The test facility will also simulate fuel-handling, reactivity control, and shut-down.

Summary

The design and planning of the PBMR demonstration reactor and pilot fuel plant are well underway. Funds have been made available. The fuel plant environmental impact statement has been accepted, but the EIA for the demonstration reactor and the nuclear licensing still have to be finalized. Fuel fabrication, helium testing, and turbine manufacturing are underway. Plans are that the demonstration reactor will start construction in 2008 and be operating in 2012.

MIT drives much pebble bed reactor research

MIT, the Massachusetts Institute of Technology, is a great institution. For example, the MIT Department of Nuclear Science and Engineering has led the study of basic nuclear processes and nuclear engineering for a half century. In light of the fact that the US has not built a nuclear power plant since the 1970s, we are fortunate that the science lives on with in faculty of 28 and senior research staff, 101 graduate and 48 undergraduate students.

Andrew Kadak has the unusual title of Professor of the Practice in this department. He has served the US government looking into issues of nuclear waste and safety. His pre-MIT career within the nuclear power industry included being the CEO of Yankee Atomic Electric. This nuclear power plant in Rowe, Massachusetts was decommissioned in 1992. Click Yankee Rowe to see before and after pictures and learn the fate of the spent fuel.

Much of the current interest in pebble bed reactors sprang from an MIT student summer project in January 1998 advised by faculty advisors Ronald Ballinger and Andrew Kadak. Nuclear Power Plant Design Project involved 6 students and 10 guest lecturers. The students reviewed:

1. Westinghouse AP600 advanced pressurized light water reactor (LWR)
2. ABB System 80+ LWR
3. GE Advanced Boiling Water Reactor (ABWR)
4. General Atomics high temperature gas reactor (HTGR)
5. German AVR pilot pebble bed reactor (a HTGR)
6. Lead bismuth reactor
7. Thorium breeder reactor
8. Liquid metal breeder reactor

They evaluation process considered 26 criteria such as safety, economics, construction time, modularity, efficiency, and lifetime. The process selected the small, modular pebble bed high temperature gas reactor. Some of the identified unique features of the PBR are:

• Inherent safety: no operator actions nor automated systems needed
• Proliferation resistance: reprocessing spent fuel pebbles is impractical
• Short, 36 month construction time
• Modular growth: 100 MW units
• Refueling: no shutdown
• Fuel disposal: spent fuel ready for disposal on removal from core
• High thermal/electric efficiency: no water cooling needed
• On-site assembly/disassembly: components shipped intact to/from factory

Subsequently a number of research projects were conducted and documented at the MIT Pebble Bed Reactor web site. Marc Berte and Andrew Kadak prepared the interesting Modularity Approach of the Modular Pebble Bed Reactor which contains a physical design for a PBR, including designs for all component parts that permit construction in a factory, shipment by rail and truck to a job site, and on-site assembly with no welding required.

I am pleased that in the recent three-decade dark ages of US nuclear power plant construction the US government has funded and MIT has continued research and development in nuclear engineering. Unfortunately it appears that US-sponsored funding of pebble bed reactor research projects at MIT has dropped off in recent years. China and South Africa are both developing pebble bed reactors, attracting the attention of university scientists and engineers. MIT is cooperating and sharing information with Tshinghua University in China. The university now has an operational pilot PBR. Kadak has traveled to China to observe the plant's fail-safe testing, and he is now consulting with the South African project.