Working Paper Article Version 2 This version is not peer-reviewed

A DNBR Analysis to Patterns of Subchannel Control Volume

Version 1 : Received: 16 September 2019 / Approved: 17 September 2019 / Online: 17 September 2019 (06:17:27 CEST)
Version 2 : Received: 15 December 2020 / Approved: 15 December 2020 / Online: 15 December 2020 (13:11:26 CET)

How to cite: Kim, B.; Moon, K.; Kim, K.; Lim, J. A DNBR Analysis to Patterns of Subchannel Control Volume. Preprints 2019, 2019090183 Kim, B.; Moon, K.; Kim, K.; Lim, J. A DNBR Analysis to Patterns of Subchannel Control Volume. Preprints 2019, 2019090183

Abstract

The sensitivity of DNBR(Departure from Nucleate Boiling Ratio) values to approaches of subchannel control volume selection has been investigated for the TS01 and TS03 out of HIPER17 CHF(Critical Heat Flux) tests. In general, the coolant-centered subchannel method is applied to subchanel analyses for fuel bundle. When it comes to predicting for CHF of high quality region, however, the rod-centered subchannel method was better over high quality region. As a result, the rod-centered subchannel method were more suitable at a conservative point of view than the coolant-centered subchannel method comparing major properties. Also, it was confirmed that the radial subchannel locations at the minimum DNBR were similar when comparing both analysis results by two kind of methods.

Subject Areas

DNBR; Subchannel Control Volume; CHF; 5x5 rod bundle

Comments (1)

Comment 1
Received: 15 December 2020
Commenter: Byeungseok Kim
Commenter's Conflict of Interests: Author
Comment: [Reviewer 3] 
This manuscript could be considered as a "communication" or a "technical note," because it covers a very limited computational aspect ("rod-centered channel" versus "coolant-centered channel"). Furthermore, the authors' conclusion that "The results with rod-centered subchannel are more conservative than those with coolant-centered subchannel in a point of view of DNBR", are based on computations performed with a single code (THALES), without providing any information about the correlations in this code that are relevant to the computational results and conclusions presented in the manuscript.   The authors should have used at least two different sub-channel codes to perform their "rod-centered channel" versus "coolant-centered channel" computations. Some of the statements made by the authors are ambiguous, to put it mildly. The "Conclusions" Section is reproduced below, in order to highlight how ambiguous it is: "The results with rod-centered subchannel are more conservative than those with coolant-centered subchannel in a point of view of DNBR. The locations at which minimum DNBR occurs are similar. So, rod-centered subchannel control volume analysis is more efficient with for CHF tests with HIPER16 and HIPER17 fuel. This reliable rod-centered approach will be considered as an alternative to the more rigorous approach used for CHF prediction in a rod bundle.  Also, the sensitivity of transverse momentum parameter was investigated, but its effect was not so much to DNBR for very high mass velocity. The each subchannel can be considered separately without considering the effects of its adjacent subchannels." Only one sentence makes sense; the others (highlighted in italics) can be interpreted in more than one way, which makes them altogether meaningless. 

[Response for Reviewer 3] The conclusion which you commented is modified as follows; In subchannel analysis with rod bundle at nuclear power plant, two methods of rod-centered method and coolant-centered method exist traditionally. There is no method other than current two-methods in subchannel analysis using lumped node, unlike CFD(Computational Fluid Dynamics) analysis, which simulates a real geometry. By comparing the results using THALES subchannel code with two methods, it was confirmed that rod-centered method used currently for core thermal-hydraulic design is still valid. The differences between other subchannel codes were not found with their results. The results with rod-centered subchannel are more conservative than those with coolant-centered subchannel in a point of view of DNBR. The radial subchannel locations at which minimum DNBR occurs are similar. So, rod-centered subchannel control volume analysis is more efficient with for CHF tests with HIPER16 and HIPER17 fuel. This reliable rod-centered approach will be considered as an alternative to the more rigorous approach used for CHF prediction in a rod bundle. Therefore, it is recommended that the rod-centered approach is applicable for the next CHF correlation development with new fuel.Also, the sensitivity of transverse momentum parameter was investigated, but its effect was not so much to DNBR for very high mass velocity. The each subchannel can be considered separately without considering the effects of its radially adjacent subchannels.

[Reviewer 2]
The manuscript is accepted with major revision requested. Namely English editing must be improved and new review is necessary, Namely1) the last 3 lines of abstract are not (easily) understandable2) the rationale for M/P should be discussed3) clear objectives for the activity should be fixed in introduction4) proper conclusion must be written  

[Response for Reviewer 2]

1)
Before

Also, it was demonstrated that when the both results produced from each subchannel analysis were compared, the subchannel locations at which DNBR occurred were very similar.

After
Also, it was confirmed that the radial locations at the minimum DNBR were the same comparing both analysis results by two kind of methods. 

2) Before

M/P is measured heat flux over predicted heat flux.

After
M/P provides some information how well CHF correlation predicts CHF while retaining the conservatism. In general, it is a conservative result when the prediction by CHF correlation is lower than measured CHF. 



3)
Before
(add and delete point) Also, it will be shown that how the locations at which minimum DNBR occurs are different. The determined subchannel control volume will be used in the CHF correlation development for HIPER16 and HIPER17 fuels CHF tests.

(add point) including the radial location of minimum DNBR. (delete point)  The main objective is to suggest the appropriate approach for subchannel analysis between two methods and to apply for the next CHF correlation development with new fuel. 

4)
Before
This reliable rod-centered approach will be considered as an alternative to the more rigorous approach used for CHF prediction in a rod bundle.

After
(add point)(add point) Therefore, it is recommended that the rod-centered approach is applicable for the next CHF correlation development with new fuel. 

[Reviewer 1] 

The DNBR value, the quality, and mass velocity of the rod-centered subchannel analysis is compared with the coolant-centered subchannel analysis for finding the efficient, effective, and conservative setup. The study reveals that the rod-centered subchannel are more conservative than those with coolant-centered subchannel in a point of view of DNBR. It also finds the location for minimum DNBR. A sensitivity analysis is also performed. However, the study requires the following revision before can be accepted for publication: The introduction lacks if any similar study was performed in recent times. The Introduction section requires how this two methods are selected and how they compare with other existing methods or other proposed methods. A short background of HIPER16 and HIPER17 fuels would play a great role. In general, the Introduction section does not provide enough evidence for the importance of this study. Also, a lot more references are required to support the claims in the Introduction. Need abbreviation for all the terms for the first time use For example, DNBR (Departure from Nucleate Boiling Ratio) is used in the title of the manuscript. It was also used in the abstract. However, it was abbreviated in line 26 of the manuscript.  

[Response for Reviewer 1] 
The introduction lacks if any similar study was performed in recent times. --> We don't have recent explicit examples available on this subject. That's why we did.  The Introduction section requires how this two methods are selected and how they compare with other existing methods or other proposed methods. --> a subchannel approach is a special case of a generic porous media approach for a specific nodal layout. This nodal layout defines volumes of a size equivalent to a single fuel rod and its associated fluid. There are only two choice to formulate single subchannel, channel-centered and rod-centered. For a lumped channel, which grouping two or more subchannels upto whole assembly, it is a porous media approch.  short background of HIPER16 and HIPER17 fuels would play a great role.--> ??  Need abbreviation for all the terms for the first time use For example, DNBR (Departure from Nucleate Boiling Ratio) is used in the title of the manuscript. It was also used in the abstract. However, it was abbreviated in line 26 of the manuscript.--> The abbreviation for DNBR will be written in the abstract of revised manuscript.

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