Far-Field Influences Shadow the Effects of a Nuclear Power Plant’s Discharges in a Semi-Enclosed Bay
, Sen Jan 2, Meng-Hsien Chen 1, Li-Lian Liu 1, Jung-Fu Huang 3 and Yiing-Jang Yang 2Round 1
Reviewer 1 Report
This manuscript evaluated that temperature increase around the outlet of cooling water from A 951 MWe nuclear power plant at the semi-enclosed Nanwan Bay in the southern tip of Taiwan based on the results of a long-term monitoring. Authors reported that internal waves bring up cold deep water into the bay and reduce the temperature on the surface by as much as 10 ℃ every day. Further, El Niño - Southern Oscillation or Pacific Decadal Oscillation-related interannual variations in temperature are evaluated as much as 5 °C.
Authors claimed that Typhoons and tropical storm, even passing hundreds of km away form the bay, induced the upwelling of cold subsurface water. However, the cause-and-effect relationship between storm and decrease of temperature is not obvious. Without adding evidence such as cross section salinity distribution suggesting enhanced estuarine circulation or intrusion of offshore water, the relationship between the storms and temperature decrease is too weak to be claimed as one of the main results in abstract and title. I won’t say that authors should remove the speculation from the present manuscript. But the tone should be weakened, if supporting data were not presented. Except for this point, there are not serious issue for publication of the manuscript.
Minor points
1. Caption of Figure 1: It should be explained what indicates the symbol “plus” (ten stations for the biogeochemical team?).
2. Lines 87-89: Is the result of drifter observation shown?
3. Lines 152-154: Three stations and the background stations should be presented as an additional panel in Figure 1.
4. Caption of Figure 4: The date should be presented.
5. Lines 299-304: Why was the difference between Normal operation period and Under Maintenance period in autumn the highest among three seasons?
6. Caption of Figure 8: 500 m from the outlet? In method section, ADCP recoded the current at a water depth of 20 m 300 m south of the outlet.
Author Response
Comments and Suggestions for Authors
This manuscript evaluated that temperature increase around the outlet of cooling water from A 951 MWe nuclear power plant at the semi-enclosed Nanwan Bay in the southern tip of Taiwan based on the results of a long-term monitoring. Authors reported that internal waves bring up cold deep water into the bay and reduce the temperature on the surface by as much as 10 ℃ every day. Further, El Niño - Southern Oscillation or Pacific Decadal Oscillation-related interannual variations in temperature are evaluated as much as 5 °C.
Authors claimed that Typhoons and tropical storm, even passing hundreds of km away form the bay, induced the upwelling of cold subsurface water. However, the cause-and-effect relationship between storm and decrease of temperature is not obvious. Without adding evidence such as cross section salinity distribution suggesting enhanced estuarine circulation or intrusion of offshore water, the relationship between the storms and temperature decrease is too weak to be claimed as one of the main results in abstract and title. I won’t say that authors should remove the speculation from the present manuscript. But the tone should be weakened, if supporting data were not presented. Except for this point, there are not serious issue for publication of the manuscript.
Reply: Thanks for the comment. It is beyond the scope of this manuscript to evaluate the relationship between typhoons and changes in Nanwan Bay and we only quote an earlier study. A sentence has been added in the paragraph beneath Fig. 2: It has been reported [13] that typhoons affect Nanwan Bay. In addition, we have taken the advice to weaken the tone for the relevant sentence in the abstract: Typhoons, even hundreds of km away, could also induce the upwelling of cold subsurface water.
Minor points
- Caption of Figure 1: It should be explained what indicates the symbol “plus” (ten stations for the biogeochemical team?).
Reply: Done.
- Lines 87-89: Is the result of drifter observation shown?
Reply: A sentence has been added in the second to the last paragraph: Hydrological and drifter data indicate that the thermal plume with a temperature 1°C above the background extends at most 1km from the outlet.
- Lines 152-154: Three stations and the background stations should be presented as an additional panel in Figure 1.
Reply: Done.
- Caption of Figure 4: The date should be presented.
Reply: Done.
- Lines 299-304: Why was the difference between Normal operation period and Under Maintenance period in autumn the highest among three seasons?
Reply: This is because autumn is the second busiest season for NPP3 so more heat is released during normal operation.
A sentence has been added: Note that autumn in the second busiest season for the NPP3 so more heat is released during normal operation, causing slightly large difference between normal operation and under maintainance compared with spring and winter.
- Caption of Figure 8: 500 m from the outlet? In method section, ADCP recoded the current at a water depth of 20 m 300 m south of the outlet.
Reply: Thanks for pointing this out: “300” was a typo. It is now corrected to 500m.
Reviewer 2 Report
The paper presents the problem in a comprehensive way. The performed analysis is reliable and sound. Conclusions are supported by results. The authors have profound knowledge about the topic. Well-done.
I just recommend tackling at the literature level (short sections with references) the potential problem of radiotoxicity release for NPPs, which is much more serious than thermal pollution. Some literature about the validated tools for source term calculations is available in open-access journals (e.g. https://doi.org/10.1515/nuka-2015-0102 ; https://doi.org/10.3390/en14113094).
Author Response
Comments and Suggestions for Authors
The paper presents the problem in a comprehensive way. The performed analysis is reliable and sound. Conclusions are supported by results. The authors have profound knowledge about the topic. Well-done.
I just recommend tackling at the literature level (short sections with references) the potential problem of radiotoxicity release for NPPs, which is much more serious than thermal pollution. Some literature about the validated tools for source term calculations is available in open-access journals (e.g. https://doi.org/10.1515/nuka-2015-0102 ; https://doi.org/10.3390/en14113094).
Reply: Thank you for the valuable comments but the radionuclide study has been handled by a different team and we do not have access to the data. We have added a sentence to note this fact: Without referring to the often-noticed radiotoxicity problem, what follows studies the all but non-existent thermal pollution at a 951 MWe nuclear power plant located at a semi-enclosed bay at the southern tip of Taiwan (Fig. 1).
Reviewer 3 Report
My comments are in the file attached.
Comments for author File: 
Comments.pdf
Author Response
Review - sustainability-2337299
The manuscript describes an assessment of the effects of the 951 MWe nuclear power plant in terms of thermal pollution at the semi-14 enclosed Nanwan Bay in the southern tip of Taiwan, which started its activity in May 1984. CTD and drifter physical data, and nutrients sampled in water, were collected in stations in the bay where the plant is located. The observations show that seasonal dynamics are able to mitigate the effect of thermal pollution in the area
The manuscript deals with a very important problem concerning the affect of nuclear power plants on ocean, concerning temperature. It is a very interesting topic: I suggest to rewrite some sections to explain better what was done and why the data used do not cover the same time span.
Reply: Thank you for the comments. We have added a sentence to explain why data from different time span was used: Note that in order to highlight the most prominent features what follows do not cover data obtained from the same time span.
In Section 2. Study area and methods, data about tide and their source canto be found. I suggest the Authors to draw a table including the different data, methods of sampling, area and time coverage.
Reply: We have now added the source of the tidal data. The manuscript only highlight some of the most important results and details but all data, methods of sampling, area and time coverage are available; a sentence is now added under “Study area and Methods” to refer interested parties to the link: Data reports are available at https://npp3.nsysu.edu.tw.
In Section 3. Results and discussion, lines 109 - 118 are not results, and should be included in a section describing the dynamics of the study area. At the end of this section I would add a Discussion of the results presented, also summarizing what has been stated in the section.
Reply: Thanks for the valuable comment. We have now added a new section in Dynamics of the Study Area.
In Section 4. Conclusions, I suggest to add a sentence commenting what is described in the Section.
Reply: Thanks for the valuable comment. We have now added a concluding sentence: To conclude, because of the favorable topography strong internal tides bring in cold, subsurface waters to prevent serious thermal pollution from happening in Nanwan Bay.
Round 2
Reviewer 3 Report
Please find the comments in the attached file
Comments for author File: Comments.pdf
Author Response
Comments and Suggestions for Authors: Please find the comments in the attached file
peer-review-29473989.v2.pdf
The manuscript has been partly rewritten, as asked in the comment for the authors, but in order to meet the standards of the Journal something still needs to be clarified. As explained in the file for the Authors, who did not follow all the suggestions, an issue remains concerning the reason why the data used do not cover the same time span: the sentence added in lines 72 - 74, “Note that in order to highlight the most prominent features what follows do not cover data obtained from the same time span”, should be explained: why can they put together observations taken in different moments / years? The research design should be clarified in that sense.
One of the links can't be opened (Line 110)
Reply: Thanks for pointing this out. Many factors such as internal tides, topography, upwelling, stratification, and typhoons affect the distribution of the thermal discharge. For practical reasons bottled samples could only be taken four times a year although temperatures were recorded continuously. More information on the temperature loggers has been added: A NorTek AS Aquadopp current meter equipped with a temperature logger was used to record the current continuously at a water depth of 20 m 500 m south of the outlet. In addition, temperature loggers (HOBO, Water Temp Pro v2; Tinytag, TG-4100) were placed near the cooling water inlet (8 m in water depth), outlet (3 and 9 m in water depth), and at Moubitou (9 m in water depth). Since not all factors occur at the same time in order to highlight the most prominent features what follows do not cover data obtained from the same time span.
The link sometimes does not work when there is a thunder storm. We check the link twice a day during working hours to ascertain that it works.
