Transnuclear has launched a new model of spent fuel pool rack called NUSTOR. The racks can also be used for storage of new fuel assemblies in dry new fuel storage vault areas. The US EPR will feature the NUSTOR as standard.
“We purposefully designed NUSTOR to be the most economical and versatile rack available, based on ease of fabrication, simplicity of installation and the availability of materials allowing the use of multiple fabricators,” said Transnuclear chief operating officer Bob Grubb.
NUSTOR combines light weight technology with a Metal Matrix Composite (MMC) poison material to provide easy handling for installation and the utmost in criticality control. Transnuclear’s MMC consists of aluminum alloy and boron carbide, with no polymer or organic components and essentially no interconnected porosity. The NUSTOR rack prevents galvanic coupling with the MMC neutron absorber, even under adverse water chemistry conditions. In the absence of the Boraflex neutron absorber, there is no significant source for soluble silica, and aluminum ions in the pool water pose no hazard to plant operations or fuel performance. As a result of these engineering advances we’ve eliminated the major causes of pitting corrosion in MMCs and consequently eliminated the need to anodize.
For the NUSTOR fuel racks, we verified that MMC poison material was appropriate. As part of the selection and qualification, Transnuclear contracted with Structural Integrity Corp. to develop justification for its use in the wet pool environment. This justification is included in the Technical Report prepared by TN and submitted to the NRC as part of its review of the U.S. EPR reactor. The Technical Report includes the material specification and acceptance testing programs that must be satisfied as part of NUSTOR racks. The MMC material specification is based on the adaptation of ASTM C1671 to wet storage. Transnuclear played a key role in the development of this standard, along with representatives of material suppliers and the NRC. The NRC is in the process of accepting ASTM C1671 via draft Interim Staff Guidance ISG-23.
Radiation and corrosion testing of various supplies of MMC conducted by Transnuclear demonstrated that neither gamma nor neutron radiation has any negative effects. Due to the lack of interconnected porosity, MMC is not subject to blistering, swelling, or delamination as a result of corrosion. Testing also demonstrated that relative to pure water, boric acid solutions have no effect on the corrosion of NUSTOR construction metals or MMC, and actually inhibit the rate of corrosion.
Besides testing, TN developed a whole-pool model to show that the NUSTOR rack meets or exceeds all regulatory requirements. We also used state-of-the art computer codes and proven analytical techniques to meet structural/seismic, criticality and thermal hydraulic standards.