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Federal Register / Vol. 86, No. 4 / Thursday, January 7, 2021 / Proposed Rules
Option 2: Conservative ECCS Evaluation Model Alternatively, a conservative evaluation model may be developed in conformance with the required and acceptable features of appendix K, ECCS Evaluation Models, to 10 CFR
part 50. Under appendix K, section I.A., evaluation models must account for various sources of heat during LOCA
conditions including the metal-water reaction rate. In particular, section I.A.5, Metal-Water Reaction Rate, of appendix K requires use of the BakerJust equation to calculate the rates of energy release, hydrogen generation, and Zircaloy cladding oxidation from the metal-water reaction of zirconium with steam, assuming that the reaction is not steam limited.
Petitioners Arguments and Requests Related to Issue 2

occur during a LOCA; and 2
underestimate the rate of Zircaloy cladding oxidation from the metal-water reaction of zirconium with steam and, therefore, underestimate the heatup, heatup rate, and maximum temperature of the Zircaloy cladding during a LOCA.
Therefore, the petitioner requested that the NRC amend RG 1.157 and appendix K to 10 CFR part 50 to require that the rates of energy release, hydrogen generation, and Zircaloy cladding oxidation from the metal-water reaction of zirconium with steam considered in evaluation models used to calculate ECCS cooling performance be calculated based on data from cited experiments, instead of using the Cathcart-Pawel or Baker-Just equations.
Issue 3: Minimum Allowable Core Reflood Rate Background for Issue 3

The petitioner argued that data from multirod assembly severe fuel damage experiments indicate that the equations used to calculate the metal-water reaction rate in ECCS evaluation models that the NRC has determined to be acceptable for use in evaluating ECCS
cooling performance are not conservative. In particular, the petitioner asserted that data from cited experiments indicate that use of the Cathcart-Pawel equation in realistic evaluation models or use of the BakerJust equation in conservative evaluation models would: 1 Overestimate the temperature at which autocatalytic metal-water oxidation reactions would
Section 50.46b of 10 CFR does not include criteria for calculated ECCS
cooling performance pertaining to the core reflood rate following postulated LOCAs.
Petitioners Arguments and Requests Related to Issue 3
The petitioner asserted that a constant core reflood rate of approximately 1
inch per second or lower would not, with high probability, prevent Zircaloy cladding from exceeding the 2,200 F
limit in 50.46b1 if, at the onset of reflood, the cladding temperature was greater than or equal to 1,200 F. In particular, the petitioner asserted that:

1 Although reflood rates would vary throughout the reactor core during a LOCA, local reflood rates could be approximately 1 inch per second or lower; and 2 extrapolation of data from the cited experiments indicates that a constant core reflood rate of approximately 1 inch per second or lower would not, with high probability, prevent Zircaloy cladding from exceeding the 2,200 F limit, if the cladding temperature was greater than or equal to 1,200 F at the onset of reflood.7 Therefore, the petitioner requested that the NRC issue a new regulation that would require minimum allowable core reflood rates in the event of a LOCA.
II. Public Comments on the Petitions II.A. Overview of Public Comments The NRC received a total of 33
comment submissions that collectively included 125 individual comments. The NRC reviewed and considered all 125
comments in its evaluation of the petitions. Table I identifies the number of comment submissions and individual comments submitted, grouped by three main categories of comments. These categories are used only to facilitate presenting a high-level summary and totals for the comments that different stakeholder groups submitted; the NRC
staff used the same approach for addressing all submitted comments, regardless of category or who submitted them. The paragraphs that follow provide a high-level overview of each category of comments.

TABLE INUMBER OF COMMENT SUBMISSIONS AND INDIVIDUAL COMMENTS BY CATEGORY
Number of comment submissions
Category
Number of individual comments
Comments from the Petitioner
Comments from Nuclear Industry Representatives
Comments from Public Interest Groups or Other Interested Individuals

a 13

a 97

3
17

9
19

Total

33

125

a The
petitioner provided nine comment submissions after the public comment period that closed on November 26, 2010. Although not required to do so, the NRC also considered all the comment submissions that were submitted after the public comment period closed.

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Category 1: Comments From the Petitioner Petitioner Mark Edward Leyse provided 13 comment submissions in support of PRM5093 and PRM5095.
He provided nine of these comment submissions after the comment period closed. The NRC considered all 13
comment submissions in its evaluation.
7 Extrapolation of the experimental data was necessary because the referenced tests were started with relatively low initial cladding temperatures.

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In general, the petitioners comments further supported the petitions by either: 1 Repeating information that had already been provided; 2
providing additional details to clarify specific issues; or 3 citing other references that the petitioner believed further substantiated the arguments in the petitions. In some comments, the
petitioner identified additional technical issues that were relevant to the subject matter, but were not directly related to the requested changes to the NRCs regulations. As discussed in Section III, the NRC staff addressed these additional technical issues in its final technical safety analysis report.

The petitioner hypothesized that, if these tests had started with higher initial cladding temperatures, autocatalytic oxidation and failure of the Zircaloy
cladding would have occurred with high probability.

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