# Bypass Flow Computations using a One-Twelfth Symmetric Sector For Normal Operation in a 350 MWth VHTR

## Abstract

Significant uncertainty exists about the effects of bypass flow in a prismatic gas-cooled very high temperature reactor (VHTR). Bypass flow is the flow in the gaps between prismatic graphite blocks in the core. The gaps are present because of variations in their construction, imperfect installation and expansion and shrinkage from thermal heating and neutron fluence. Calculations are performed using computational fluid dynamics (CFD) for flow of the helium coolant in the gap and coolant channels along with conjugate heat generation and heat transfer in the fuel compacts and graphite. A commercial CFD code is used for all of the computations. A one-twelfth sector of a standard hexagonal block column is used for the CFD model because of its symmetry. Various scenarios are computed by varying the gap width from zero to 5 mm, varying the total heat generation rate to examine average and peak radial generation rates and variation of the graphite block geometry to account for the effects of shrinkage caused by irradiation. The calculations are for a 350 MWth prismatic reactor. It is shown that the effect of increasing gap width, while maintaining the same total mass flow rate, causes increased maximum fuel temperature while providing significant coolingmore »

- Authors:

- Publication Date:

- Research Org.:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)

- Sponsoring Org.:
- DOE - NE

- OSTI Identifier:
- 1050540

- Report Number(s):
- INL/JOU-11-21852

Journal ID: ISSN 0029-5493; NEDEAU; TRN: US1204836

- DOE Contract Number:
- DE-AC07-05ID14517

- Resource Type:
- Journal Article

- Journal Name:
- Nuclear Engineering and Design

- Additional Journal Information:
- Journal Volume: 251; Journal ID: ISSN 0029-5493

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; BYPASSES; COMPUTERIZED SIMULATION; FLOW RATE; FLUID MECHANICS; GAS COOLED REACTORS; GRAPHITE; HEAT; HEAT TRANSFER; NEUTRON FLUENCE; REACTOR OPERATION; SHRINKAGE; TEMPERATURE RANGE 1000-4000 K; VHTR REACTOR; BYPASS; CFD; VHTR

### Citation Formats

```
Johnson, Richard W, and Sato, Hiroyuki.
```*Bypass Flow Computations using a One-Twelfth Symmetric Sector For Normal Operation in a 350 MWth VHTR*. United States: N. p., 2012.
Web. doi:10.1016/j.nucengdes.2011.10.070.

```
Johnson, Richard W, & Sato, Hiroyuki.
```*Bypass Flow Computations using a One-Twelfth Symmetric Sector For Normal Operation in a 350 MWth VHTR*. United States. https://doi.org/10.1016/j.nucengdes.2011.10.070

```
Johnson, Richard W, and Sato, Hiroyuki. 2012.
"Bypass Flow Computations using a One-Twelfth Symmetric Sector For Normal Operation in a 350 MWth VHTR". United States. https://doi.org/10.1016/j.nucengdes.2011.10.070.
```

```
@article{osti_1050540,
```

title = {Bypass Flow Computations using a One-Twelfth Symmetric Sector For Normal Operation in a 350 MWth VHTR},

author = {Johnson, Richard W and Sato, Hiroyuki},

abstractNote = {Significant uncertainty exists about the effects of bypass flow in a prismatic gas-cooled very high temperature reactor (VHTR). Bypass flow is the flow in the gaps between prismatic graphite blocks in the core. The gaps are present because of variations in their construction, imperfect installation and expansion and shrinkage from thermal heating and neutron fluence. Calculations are performed using computational fluid dynamics (CFD) for flow of the helium coolant in the gap and coolant channels along with conjugate heat generation and heat transfer in the fuel compacts and graphite. A commercial CFD code is used for all of the computations. A one-twelfth sector of a standard hexagonal block column is used for the CFD model because of its symmetry. Various scenarios are computed by varying the gap width from zero to 5 mm, varying the total heat generation rate to examine average and peak radial generation rates and variation of the graphite block geometry to account for the effects of shrinkage caused by irradiation. The calculations are for a 350 MWth prismatic reactor. It is shown that the effect of increasing gap width, while maintaining the same total mass flow rate, causes increased maximum fuel temperature while providing significant cooling to the near-gap region. The maximum outlet coolant temperature variation is increased by the presence of gap flow and also by an increase in total heat generation with a gap present. The effect of block shrinkage is actually to decrease maximum fuel temperature compared to a similar reference case.},

doi = {10.1016/j.nucengdes.2011.10.070},

url = {https://www.osti.gov/biblio/1050540},
journal = {Nuclear Engineering and Design},

issn = {0029-5493},

number = ,

volume = 251,

place = {United States},

year = {2012},

month = {10}

}