With plant life extensions and power uprates, accurate assessment of neutron damage to reactor pressure vessels (RPVs) beyond the traditional beltline region has become increasingly important. Current guidelines focus mainly on this beltline, but improved predictions of neutron fluence and displacements per atom outside this region are needed. The standard two-step computational approach — involving in-core criticality transport followed by ex-core fixed-source transport — remains widely used in industry due to its practicality, despite the development of more complex high-fidelity methods like, e.g., the internal coupling of VERA with the Monte Carlo Shift code as demonstrated in the DOE CASL activities.
Two key challenges in RPV fluence calculations are the strong flux attenuation between core and vessel and the complexity of neutron source determination which depends on detailed fuel pin modeling and operating conditions. The latter has traditionally received less attention. The proposed activity aims to improve the two-step method by evaluating how neutron source calculations affect ex-core quantities of interest, using the TVA Watts Bar Unit 1 Multi-Physics Benchmark and Oakridge National Laboratory reference solutions. This work supports goals of the Expert Group on Physics of Reactor Systems (EGPRS), particularly regarding uncertainties in reactor physics and transport modelling. Given the anticipated large number of reactors operating beyond their original design life, refining these approximations is essential for ensuring long-term operational safety.
The benchmark will assess the impact of uncertainties in the neutron fission source (due to nuclear data, approximations and physical parameters) on ex-core quantities of interest, such as RPV fluence. Special attention will be paid to the extended beltline region that may be more sensitive to the operating conditions and physical and calculation parameters.
To participate in the benchmark and to gain access to the working area, please fill out the TVA-WB1 Conditions for Release form and e-mail it to wprs@oecd-nea.org.
Details, including specifications and results templates can be found in the working area:
TVA WB1 Benchmark (requires password | reminder)
https://www.oecd-nea.org/tools/ierequest/start/package/NEA-1939%2501The Shielding Integral Benchmark Archive and Database (SINBAD) database contains compilations for more than 100 reactor shielding, fusion neutronics and accelerator shielding experiments.
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