According to the abstract, the paper presents major findings from the UMAN deliverable "Uncertainty identification, classification and quantification". As these results have already been published, the authors' own further reflections are of particular importance for the scientific value of the publication. Where results from UMAN are presented and where the authors' own reflections come into play should therefore be more clearly labelled.

The glossary represents a significant added value of the paper. In addition, the glossary should explain what understanding of risk the publication is based on: Is risk only associated with negative effects that need to be assessed or also with positive effects? What role does the probability component play? Against this background table 1 should be reconsidered.

The article is explicitly focussed on numerical uncertainties, but - as mentioned in chapter 4 - does not deal with the mathematical handling of uncertainties. It would therefore be appropriate to further clarify the question of whether numerical uncertainties can be clearly distinguished from non-numerical uncertainties and what advantages the focus on numerical uncertainties brings for the publication. The authors declare that they want to concentrate on parameter uncertainties. In the text, however, much space is given to other uncertainties, in particular model uncertainties.

While there is general reference to RWM at the beginning of the publication, later statements concentrate mainly on the (long-term) safety of deep geological repositories. A clearer definition of the scope of the paper would be helpful.

The statement in line 64/65 "Uncertainty creates an uncomfortable position for a large part of the public (anxiety)" is not clearly supported by the social science literature. If the topic is not dealt with in more detail in the paper, this sentence should therefore at least be supported by a reference to the literature.

At the beginning of section 2.1, it is not clear what the cost-benefit ratio refers to. "Relevance can be inferred from priority for further investigation" can be read as a circular argument.

Table 2 should be verified. What is the difference between a large and a high amount of knowledge?

In line 418/419 there is the statement "Finally, further research activities should elaborate possible ways to treat uncertainties resulting from human behaviour numerically, taking into account that their impact on the safety could be significant." Was this statement made against the background of the relevant social science literature? A corresponding reference would be valuable.

General comments

In this paper, the results of the EURAD project UMAN are described with a focus on uncertainties in numerical models. The paper effectively highlights the uncertainties and provides options for managing them, such as using a fishbone structure. However, the paper seems to rely too heavily on a EURAD report, which has essentially been adapted with only minor adjustments to fit the format of a paper. For instance, the outlook states that “A thorough survey in other EURAD deliverables issued so far is recommended for indicators that may help to rank the importance of FEPs and their associated uncertainty.” However, I believe much more literature exists on this topic beyond EURAD deliverables. Additionally, the paper notes that “A revision of ranking and order of various uncertainties might also be necessary for the current EURAD Themes definition.” This again focuses solely on EURAD, while there is likely a wealth of other relevant papers on this subject. Therefore, I believe the paper should reference a broader range of other papers and reports. It is also recommended that the authors review the text, as in some instances, they still refer to “this report” instead of “this paper.”

It is also unclear whether the uncertainties discussed in this paper pertain specifically to the safety assessment or safety analysis of a GDR, or if they are related to numerical modeling in general. I suspect it is the former, but the paper does not make this clear. This distinction should be clarified, and an introduction to the subject might be necessary. Additionally, I believe the paper would benefit from including examples with references. For instance, in section 2.1, the authors refer to textbooks that might provide an in-depth discussion, but they do so without citing specific examples. In other sections, they mention certain methods that can be used. Including a reference to a book or other source in the text would be very beneficial for readers who do not have a background in this area. Lastly, I found that there was little on the different stages of a program and how that would influence the uncertainty.

Specific comments

Abstract

R9: Safety analysis is mentioned here but later on in the introduction, it is also referred to as safety assessment. Better use one word and maybe explain what it means.

R14: I am wondering if “for the report” is correct here. In general, I would refer to it as paper.

R17: RWM is not defined.

• Introduction

Overall the introduction looks good, but it can be shortened by focusing on what is done in the paper rather than describing in length was is not done. This will help to make it clearer what the paper is about and it will reduce the length of the introduction and make it clearer.

R25: Safety assessment of the DGR?

R26: Here, radioactive waste management for the first time in the introduction, so maybe introduce the abbreviation here rather than later on.

R29:Is the safety assessment the same as the safety analysis in this context?

R31: I am a bit wondering how various stages of radioactive waste management influence the safety analysis.

R63: Deliverable or paper?

R68: What kind of decisions?

2.0 methodology            

I like that the authors start with a list of definitions. I do, however, wonder how their definitions are compared to others.

R103: pdfs?

R151: The abbreviation WMO is already defined somewhere else.

R117: Both strategy and structure are red underlined. Is that for a reason?

R130: It is mentioned that they are used for a multitude of complex applications in science and society, but could some examples be given?

R186: Again report and what is exactly meant by sources being identified and used in this report are listed in the references section.

R205: Sea level changes instead of water transgression?

R244: I don’t think guess is good to say here: it is always based on something.

R251: Design concept of the DGR?

R276: What are first two columns in table 4 in this paper use for? Do they serve any purpose?  

3.0 Categorization of uncertainties             

R327: The abbreviation FEP is not explained here (or earlier; only later).

R343: EURAD is currently almost finished. So, is there no final version of the EURAD roadmap?

4.0 Categorization of uncertainties             

R375: Not the topic of this report? Paper probably.

R376: RW?

5.0 Outlook: What are the gaps in understanding, quantification and processing of uncertainties?      

R394: Task 3 deliverables?

R410: Why would it be challenging to convince modellers and programmers? I think most of them want to but cannot do it due to time.