Second thoughts on South Africa’s pebble-bed reactor

2 April 2017

South Africa’s state utility and nuclear operator Eskom is looking again at plans abandoned in 2010 to develop a Pebble Bed Modular Reactor (PBMR), according chief nuclear officer David Nicholls. South Africa began working on the PBMR in 1993, and PBMR Pty, the company set up to lead the project, was on the point of beginning construction when the government cut funding and withdrew its support in 2010. It would have been the first Generation IV unit to enter the construction phase. In an interview with EE Publishers on 28 March, Nicholls. A former CEO of PBMR Pty, said Eskom was investigating whether there is now a market for ultra-safe, small, nuclear reactors for power generation, using high-temperature technology. He said Eskom had started looking at the PBMR again with “a clean sheet” and is carrying out a paper study “with limited research funding going into it”.

The PBMR design was based on German technology that was demonstrated in the 1970s and 80s. It was a high temperature gas-cooled reactor (HTGR) with a closed-cycle gas turbine power conversion system. It was graphite moderated and helium cooled. The power conversion unit was based on the Brayton thermodynamic cycle. It has a proposed thermal output of 400MWt and electrical output (net) of 16 MWe. The fuel comprised thousands of small graphite covered pebbles, each filled with thousands of coated LEU kernels. The pebbles had an expected life of three years and were analysed continuously, with each pebble circulating through this analysis check some six times before replacement. 

PBMR Pty was formed in 1993 and in 1995, the South African government lent support to investigate of the project.  South Africa approved a detailed feasibility phase in 2000. The project generated over 100 patents between 1999 and 2004.  PBMR became a national project of strategic importance. Eskom committed to purchase and operate the demonstration reactor; and the South African Nuclear Energy Corporation (Necsa) drew up plans to acquire 24 PBMR reactors over 20 years to contribute 4,000MWe to the southern African grid. The initial investors were Eskom, British Nuclear Fuels (BNFL – then parent of Westinghouse Electric), Exelon (US), and the Industrial Development Corporation (IDC) of South Africa. Subsequent investors were the South African Government, Eskom and IDC. Eskom was both the client and a major shareholder of PBMR. 

About 700 people work for PBMR Pty and another 600 for suppliers. The company had two headquarters buildings in the small city of Centurion, between Pretoria and Johannesburg. There were three test facilities built at the Potchefstroom Campus of North-West University (NWU). The Pebble Bed Micro Model, a closed-cycle gas turbine system, was constructed in 2002 to test power conversion principles using nitrogen rather than helium. The High Pressure Test Unit began operation in September 2006 to help predict fuel temperatures, mass flows, and pressure drops in the fuel pebbles. The High Temperature Test Unit sought to validate the correlations used for different heat transfer and fluid flow phenomena.

In addition, a Helium Test Facility was built at Pelindaba to validate and verify models operating in a helium environment.  The building includes a helium purification facility and heat exchanger. Fuel replacement and fuel handling were through a helium medium with fuel sphere transfers taking place pneumatically. The spent fuel storage system comprised 12 air-cooled tanks able to accommodate 40 operating years worth of fuel. 

A fifth major demonstration facility was the Fuel Manufacturing Plant where PBMR conducted laboratory scale fuel fabrication. In April 2005, PBMR awarded a $20m contract to Uhde (a subsidiary of Germany’s Thyssenkrupp Engineering), to build the demonstration fuel plant at Pelindaba to manufacture the fuel pebbles for the planned demonstration PBMR. RWE Nukem received a two-year contract from PBMR for detailed design of the fuel production processes. Uranium enrichment for the fuel was to take place in Russia, which had been testing the fuel for PBMR.

In 2003, environmental approval was given for construction of the demonstration PBMR unit on the Koeberg NPP site north of Cape Town and for the fuel plant at Pelindaba near Pretoria. In October 2004, the South African government budgeted to allow development of the first PBMR to proceed, only to effectively cancel the project six years later.

The PBMR project was placed under 'care and maintenance' to protect its intellectual property and assets, for which several employees were retained. However, the Fuel Development Laboratory was decommissioned, and the Helium Test Facility mothballed. The facilities at Northwest University were transferred to the university. A total of ZAR9.244bn ($1.3bn) had been invested in the project, with over 80% coming from the South African government. Other funding had come from Eskom (8.8%), Westinghouse (4.9%), Industrial Development Corporation (IDC) (4.9%) and Exelon (1.1%).

Nicholls said the new work has been looking at what has changed since then, and how the PBMR design can to take advantage of this. He said: “Probably the best example is 3D printing. We can now consider 3D printing the ceramic materials, which would have been unthinkable 20 years ago. We are also considering the use of concrete pressure vessels instead of steel, which could reduce the price significantly”.

Another sign of renewed interest in the PBMR was the appointment in 2016 of Nuclear Africa CEO Dr Kelvin Kemm as chairperson of  Necsa. Kemm was one of nine new board appointed with the aim of stabilising the state-owned company, in preparation for South Africa’s planned nuclear newbuild programme. Kemm noted that a private South African team had been working on its own version of the PBMR with a view to exporting it. “We missed the first boat, but hopefully not the second,” he told Fin24 in March 2016. “As far as I am concerned, the PBMR was virtually complete and we should have started building it years ago.”

He added: “We South Africans should have had the courage to start building a prototype PBMR, but it was easier to keep delaying one more year to ‘polish off the edges’ to try to get the final design perfect on paper. We should have built the PBMR and fixed the teething issues along the way. So what if the first one was only 75 or 80% perfect. The second one would have been much better, but we tried to design to 90% plus before digging the first trench. Also, the team did not brag to the public or to the politicians as to what they had achieved. So, foreign nuclear scientists knew more about the South African PBMR than our own cabinet.”

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