The development of high-fidelity full-core modeling capabilities for LWRs aims to reduce uncertainty in the design margins and to facilitate optimization of reactor operations including fuel management, power uprates, and life extensions. Successful examples for such developments include projects such as CASL (Consortium for Advanced Simulation of LWRs) and Nuclear Reactor Safety Simulation Platform (NURESAFE).

In 2019, the Working Party on Scientific Issues and Uncertainty Analysis of Reactor Systems (WPRS) launched a benchmark, in which the work performed by CASL in their VERA Core Physics Benchmark Progression Problems is extended into a Nuclear Energy Agency code-independent benchmark to encourage Verification and Validation (V&V) of traditional and novel high-fidelity Modelling and Simulation (M&S) from multiple participants. 

The benchmark specifications originate from a selected set of CASL benchmark problems based on data provided by the Tennessee Valley Authority (TVA) and other references available in the public domain. It introduces a benchmark which provides detailed specifications of the WB1 core operations measured by TVA. The data are provided for Watts Bar Unit 1 Cycle 1 (WB1C1), Cycle 2 (WB1C2), and Cycle 3 (WP1C3). Seven exercises cover the key states of WB1C1 to  WB1C3. The exercises span the start-up Zero Power Physics Tests (ZZPT), Hot Full Power (HFP) Beginning of Cycle (BOC) Physical Reactor, depletion of WB1C1, fuel shuffle and decay for Cycle 2 BOC ZPPT, and WBN1C2 depletion, fuel shuffle and decay for WB1C3 BOC ZPPT, and WB1C3 depletion:

• Exercise 1: Validation of stand–alone 3-D neutronics model at HZP conditions
  • This exercise aims to calculate the required parameters of the WBN1C1 ZPPT BOC startup. The loading pattern of this exercise is provided, the fuel assemblies in this exercise are at the beginning-of-life (BOL) conditions and the reactor is at Hot Zero Power (HZP) isothermal conditions. The initial criticality was achieved by inserting bank D while all other banks were fully withdrawn. 
• Exercise 2: Verification of multi-physics steady state model for HFP conditions
  • This exercise aims model WBN1C1 at nominal conditions with the loading pattern and material properties described in the benchmark. In this exercise, bank D is partially inserted while all the other RCCA banks are withdrawn. The prediction of the HFP distribution requires the calculation of the Xenon equilibrium across all the fuel rods in the reactor core. No measured data were provided by TVA for this exercise, therefore the reference results are taken from the calculated MC21/CTD simulation, published in report CASL-U-2015-1010-001. 
• Exercise 3: Validation of multi-physics cycle1 depletion model for Cycle 1
  • The exercise aims to predict the depletion of the WBN1C1 fuel, fission product build-up and decay and material activation within core structures. The averaged operating power history is provided in the benchmark specifications.
• Exercise 4: Validation of fuel shuffle and decay for Cycle 2 BOC ZPPT
  • This exercise focuses on the analysis of the WBN1 refueling and the fuel reactivity at HZP conditions in Cycle 2. The loading pattern of this exercise is described in the specifications. The length of the refueling process between Cycle 1 and Cycle 2 is assumed to be 30 days and isotopic components, including those for boron, are provided.
• Exercise 5: Validation of multi-physics cycle depletion model for Cycle 2
  • The exercise aims to predict the depletion of the WBN1C2 fuel, fission product build-up and decay and material activation within core structures. The loading pattern of this exercise is described in the specifications.
• Exercise 6: Validation of fuel shuffle and decay for Cycle 3 BOC ZPPT
  • This exercise repeats Exercise 4, but for Cycle 3.
• Exercise 7: Validation of multi-physics cycle depletion model for Cycle 3
  • This exercise repeats Exercise 6, but for Cycle 3.

In 2025, the Expert Group on Physics of Reactor Systems (EGPRS) launched a follow-up benchmark to analyse reactor pressure vessel fluence simulations based on the here described TVA-WB1 multiphysics benchmark:

• TVA Watts Bar Unit 1 Reactor Pressure Vessel Fluence Benchmark