<p>Developed by Idaho National Laboratory (NL), RELAP5-3D is one of the most matured nuclear thermal hydraulics analysis computer software, which has been used for licensing and R&amp;D purpose world widely. Recently, RELAP5-3D became main system analysis software in many R&amp;D projects in US DOE sponsored Light Water Reactor Sustainability (LWRS) program. The application of RELAP5-3D in LWRS program mainly focuses on risk-informed analysis through dynamic probabilistic risk assessment combined with multi-physics uncertainty quantification for various postulated event scenario. However, RELAP5-3D lacks the uncertainty analysis capabilities to perform full best estimate plus uncertainty (BEPU) analysis. The main goal of the development is to modify RELAP5-3D as BEPU ready application. The work scope includes (1) development of initial perturbation model for selected closure laws, (2) testing of suitable probability distribution functions (PDF) for the selected correlations, (3) and validation with selected separate and integral effect cases. The initial development focused on reflood phase of large break LOCA. RELAP5-3D source code has been modified to receive dedicated multipliers to allow perturbing related thermal hydraulics models: interfacial and wall heat transfer, and interfacial friction correlations. Code structure and input deck options are also modified to receive user defied uncertainty propagation data from external logic control software such as RAVEN (Risk Analysis and Virtual Environment), which is also developed by INL. The validation of the model used full-length emergency core heat transfer separate effect and system effect test (FLECHT-SEASET) reflood facility experiment, which uses unblocked bundle with forced and gravity reflood and steam cooling experiments using electrical heater rods to simulate Westinghouse 17 x 17 PWR fuel assembles. RAVEN code is coupled with RELAP5-3D via application programming interface (API). Latin hyper cube sampling scheme was selected and order-statistics was applied to sampling to run total of 153 uncertainty distribution cases based on Wilk's formula. The range of uncertainty distributions for PDF is assumed based on available literature. The results showed uncertainty band, which is comparable to experiment results. Especially, the cladding temperature higher elevation shows better result then non-BEPU simulation. Future work includes expand BEPU capability to blowdown and refill phenomena, and release of official BEPU ready RELAP5-3D.&nbsp; &nbsp;&nbsp;&nbsp;</p>

Development of Best Estimate Plus Uncertainty (Bepu) Application for Relap5-3d

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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