Zero-failure fuel

ABB's SVEA-96/100 fuel is the only fully proven 10 x 10 fuel in the industry which have attained final burnup in reload quantities. The expected improvements are now seen in detailed inspections, Hot Cell Post-Irradiation Examinations (PIEs) of high burnup 10 x 10 fuel, proving very low fission gas release, and PCI free operation. Liner fuel mitigates the risk for PCI failures during power ramp operation at higher burn-up. For protection against severe degradation it is necessary to have a liner that is not only mitigating PCI, but also has good corrosion properties. ABB has therefore developed the Zr-Sn liner, which is the only fully operational proven concept against PCI and long axial splits in the industry. Both steam tests of ABB's Zr-Sn liner and Hot Cell PIE of failed Zr-Sn liner fuel have confirmed a very low cladding rate. Through 1998, ABB has delivered 35 reloads of S96/100 Zr-Sn liner fuel which have been more than one cycle in core and 22 reloads of S96/100 Zr-Sn liner fuel which have been 5 cycles or more in core. The operational experience has been as expected, with no PCI failures and only minor degradation of occasional debris failures. To date, all the identified ABB 10 x 10 fuel failures have been due to debris fretting, except one single event of four failed six cycles fuel rods which were affected by ESSC (Enhanced Spacer Shadow Corrosion) during 1996-97. ESSC is now effectively remedied, which leaves only debris fretting as primary failure cause on ABB 10 x 10 fuel. ABB has now a very good understanding of the cause of primary failures and the generic fuel degradation mechanisms. Based on this understanding, ABB has developed effective remedies both against debris fretting and fuel rod degradation. These remedies include fretting resistant cladding, mitigating of debris from the primary system and fuel assemblies, operation guide lines for operation with a primary leaker in core and other efficient remedies against degradation and fuel washout etc. Immediate and accurate fuel failure detection is also very important for the operation of a nuclear power plant, as well as correct evaluation of fuel failure type and severity. ABB has therefore developed an on-line nuclide specific off-gas monitoring system designed to evaluate the integrity of nuclear fuel by analyzing the activity levels of the reactor off-gas. (authors)