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CFD and machine learning based hybrid model for passive dilution of helium in a top ventilated compartment

  • Pavan K. Sharma EMAIL logo , Vishnu Verma and Jayanta Chattopadhyay
Published/Copyright: November 15, 2023
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Abstract

For hydrogen management in the containment of Nuclear Power Plants (NPPs), besides the Passive autocatalytic Recombiners (PAR), the passive dilution of lighter gas plays an important role. This could be an attractive option to optimize the containment design and to estimate the extent of dilution. Passive dilution has many other applications in nuclear industry. The experimental studies of air entrainment in the upward rising helium plume and the resulting dilution of helium gas by the Canadians in terms of Volume Flow Magnification Factor (VFMF) have been utilized for Computational Fluid Dynamics (CFD) validation. The CFD based Fire Dynamics Simulator (FDS) predicted values of VFMF found to be in good agreement with the test data. After FDS code validation, parametric study has been carried out to generate a data base of VFMF for range of hydrogen injection, side opening area and opening height. In present study various Machine Learning (ML) models are evaluated based on two-parameter relationship i.e. non dimensional hydrogen injection and VFMF using the CFD code generated database. The trained ML models were used for the predictions of the mass flow rate of gas entrainment (through opening) in the rising buoyant plume in terms of VFMF. The ML predictions were in good agreement with the predictions against test data. Multivariate Adaptive Regression Splines (MARS) based ML model found to performed best and discussed in the paper. The paper highlights details of methodology of numerical simulation, results of the CFD studies and machine learning based predictions.


Corresponding author: Pavan K. Sharma, Reactor Safety Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India, E-mail:

  1. Research ethics: Not applicable.

  2. Author contributions: The authors have accepted responsibility for the entire content of this manuscript and approved its submission

  3. Competing interests: The authors state no conflict of interest

  4. Research funding: None declared

  5. Data availability: Not applicable.

Appendix

Step 0: Problem analysis

Variables considered in the model are (i) non dimensional hydrogen injection (ii) VFMF. In this problem, various models are utilized i.e. Liner regression, Decision Tree regression, Lasso regression, Ridge regression, Random Forests regression and finally MARS regression which will study the correlation between the non dimensional hydrogen injection and non-dimensional VFMF.

Step 1: Importing the libraries

The first step will always consist of importing the libraries that are needed to develop the ML model. The NumPy, matplotlib and the Pandas libraries are imported.

  • import numpy as np

  • import matplotlib.pyplot as plt

  • import pandas as pd

Step 2: Preparing and importing the dataset

Before importing the data, the data was prepared using the digitisation of graphs available in open literature data. The objective of the present work is to prepare a safe and reasonably conservative correlation for regulatory application. In this step, we shall use pandas to store the data prepared and store it as a Pandas DataFrame using the function ‘pd.read_csv’. In this, we assign the independent variable (X) to the ‘non dimensional hydrogen injection’ column and the dependent variable (y) to the ‘VFMF’ column.

Step 3: splitting the dataset into the training set and test set

In the next step, dataset is splitted as usual into the training set and the test set. In present study, 256 non dimensional VFMF data (as a function of non dimensional hydrogen injection) for training and 86 VFMF data for ML testing.

  • from sklearn.model_selection import train_test_split

  • train, test=train_test_split(gdpdata)

Step: 4, 5, 6, 7, 8, 9: training for various models

Liner regression, Decision Tree regression, Lasso regression, Ridge regression, Random Forests regression and finally MARS regression model were used on the training set. The DecisionTreeRegressor class imported from sklearn.tree and assigned it to the variable ‘regressor’. Then X_train and the y_train have been fit to the model by using the regressor.fit function.

  • #:Linear Regression

  • from sklearn.linear_model import LinearRegression

  • model=LinearRegression().fit(train.iloc[:,:1],train.iloc[:,1:])

Step 10: Predicting the results

In this step, the results predicated of the test set with the model trained on the training set values using the regressor.predict function and assign it to ‘y_pred’.

  • y_pred = regressor.predict(X_test.reshape(-1,1))

Step 11: Comparing the Real Values with Predicted values

In this step, comparison and display of the values of y_test as ‘Real Values’ and y_pred as ‘Predicted Values’ is to be carried out in a Pandas dataframe.

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Received: 2023-08-14
Accepted: 2023-10-17
Published Online: 2023-11-15
Published in Print: 2023-12-15

© 2023 Walter de Gruyter GmbH, Berlin/Boston

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