ML25233A011
| ML25233A011 | |
| Person / Time | |
|---|---|
| Site: | 99902049 |
| Issue date: | 08/20/2025 |
| From: | Victoria Huckabay NRC/NRR/DNRL/NLIB |
| To: | Haneman M Holtec |
| References | |
| Download: ML25233A011 (1) | |
Text
From:
Monica Haneman Cc:
Clark Shurtleff; p.lashley@holtec.com; Mahmoud -MJ-Jardaneh; David Garmon; John Parillo; Jason White; MNeedham@holtec.com
Subject:
NRC Staff"s Clarification Regarding Assumptions A-1.1 and H-4 in RG 1.183, Revision 1 Date:
Wednesday, August 20, 2025 4:23:00 PM Good afternoon, Monica,
Below is the NRC staffs clarification in response to your question about the basis for the use of pH value of 7 as described in Regulatory Guide (RG) 1.183 Revision 1, Assumptions A-1.1 and H-4.
NUREG-1465, Accident Source Terms for Ligh-Water Nuclear Power Reactors, (Agencywide Documents Access and Management System Accession No. ML041040063)
Section 3.5, Chemical Form, provides a basis for the pH value assumed in RG 1.183, Revision 0. The NRC staff has not departed from that initial regulatory position in Revision 1 of RG 1.183. Section 4.5 of NUREG-1465 provides additional background: on the basis of work in NUREG/CR-5732*, the NRC staff concluded that iodine entering the reactor coolant is composed of at least 95% cesium iodide (CsI) with no more than 5% iodine and hydrogen iodide (I and HI). Once in containment, CsI will dissolve in water pools and plate out on wet surfaces as I (ion). At this point, radiation induced conversion of I (ion) to elemental form I2 will potentially become an important mechanism. If pH is controlled to a level of 7 or greater, conversion will be minimal. However, the only other comparison in the NUREG is made to asystem with no pH control (i.e., slight reduction in pH is only visualized in graphical form, such as the one provided in Figure 3.1 in NUREG/CR-5950 (ML063460464) or left to calculation based on equations that are provided in related studies).
Section 3 of NUREG/CR-5732 provides a detailed approach on how to calculate the conversion from I (ion) to I2. The first column on page 19 states that with a pH of 7, less than 1% of I (ion) is converted to I2. Also, the graph shown in Figure 3.1 confirms that there is a drastic change in iodine behavior seen at 3 < pH < 4, but the radiolytic conversion at pH = 6 is similar to that of pH= 7.
Therefore, the prospective applicant should consider conducting an analysis to demonstrate that, considering its predicted concentration of the iodine, the radiolytic conversion would result in less than 1% conversion of I (ion) to I2 for the chosen pH value, using themethods discussed in Section 3 of NUREG/CR-5732 or the methods described in NUREG-5950.
Additional information and sources for technical bases:
Sandia National Laboratories Report No. SAND2011-0128, Accident Source Terms for Light-Water Nuclear Power Plants Using High-Burnup or MOX Fuel, January 2011 (ML20093F003). Section 4.5 of this report provides a more recent summary and basis for the assumptions used in RG 1.183, Revision 1.
Sandia National Laboratories Report No. SAND2023-01313, High Burnup Fuel
Source Term Accident Sequence Analysis, April 2023 (ML23097A087). Although this report is not directly applicable to Revision 1 of RG 1.183, Section 3.2.8 of this document offers an updated understanding of iodine behavior post-accident and provides a technical basis for a position that the initial assumption of 5% I and HI may be conservative.
J.T. Bell, M.H. Lietzke, and D.A. Palmer, Predicted Rates of Formation of Iodine Hydrolysis Species at pH Levels, Concentrations, and Temperatures Anticipated in LWR Accidents, NUREG/CR-2900 (ML20070J246). This document provides additional background information that may be informative.
- E.C. Beahm, C.F. Weber, and T.S. Kress, Iodine Chemical Forms in LWR Severe Accidents, NUREG/CR-5732 (ORNLTM-11861), prepared for NRC by Oak Ridge National Laboratory, April1992. (ML003726825)
Please let me know if you have questions or require additional information.
Best regards, Victoria
Victoria V. Huckabay Senior Project Manager NRR/DNRL/NLIB (301) 415-5183