ML24346A264
| ML24346A264 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 12/11/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24346A130 | List:
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| References | |
| LO-175762 | |
| Download: ML24346A264 (1) | |
Text
Response to SDAA Audit Question Question Number: A-15.1.1-9 Receipt Date: 05/13/2024 Question:
Provide FSAR markups to describe individual treatments of MTC and DTC for the decrease in feedwater temperature, increase in feedwater flow, and increase in steam flow events. Currently FSAR sections discussing parameters and initial conditions for these events just provide the statement The most limiting EOC reactivity feedback is used to provide a limiting power response. DCA evaluations of these transients discussed the parameters individually. This detail is needed in these sections as treatment of these reactivity coefficients (while potentially limiting for the power response) differs from the general trends discussed in FSAR Section 15.0.0.4, Initial Conditions.
Response
The original response was posted on June 5, 2024. The NRC provided feedback on July 8, 2024. The response to the NRC feedback is provided beginning with the section titled Response to NRC Feedback. No changes to the original response below are made prior to the section titled Response to NRC Feedback.
Discussion of the decrease in feedwater temperature, increase in feedwater flow, and increase in steam flow events is provided in the sections below.
Decrease in Feedwater Temperature In Final Safety Analysis Report (FSAR) Section 15.1.1.3.2 for the Design Certification Application (DCA) of the US600 design, the following was stated regarding reactivity coefficient parameters:
The most limiting end-of-cycle core parameters are used to provide a limiting power response. The most negative moderator temperature coefficient (MTC) of -43.0 NuScale Nonproprietary NuScale Nonproprietary
pcm/degrees F and the most negative Doppler temperature coefficient (DTC) of -2.5 pcm/degrees F are used to provide the largest power response for this event.
In the FSAR for the Standard Design Approval Application (SDAA) of the US460 design, specific reactivity coefficient values were removed from Chapter 15 sections and replaced via reference to the values in Chapter 4. For the decrease in feedwater temperature event, FSAR Section 15.1.1.3.2 states the following:
The most limiting end-of-cycle (EOC) reactivity feedback is used to provide a limiting power response.
This statement is consistent with the first statement in the DCA citation above. To find the specific values used in the analyses, it is necessary to follow the provided cross-references.
FSAR Section 15.0.0.4 describes initial conditions applicable to the Chapter 15 events. As identified in FSAR Section 15.0.0.4, reactivity coefficients used in the Chapter 15 analyses are provided in Table 4.3-2 and Figure 4.3-15. It is also stated in FSAR Section 15.0.0.4 that reactivity coefficients are associated with time in cycle analyzed, where beginning of cycle analyses use the most positive (least negative) value while end of cycle analyses use the most negative value. Because FSAR Section 15.1.1.3.2 identifies that EOC is analyzed, FSAR Section 15.0.0.4 identifies that EOC analyses use the most negative value, and FSAR Section 15.0.0.4 refers to FSAR Table 4.3-2, it then follows that the decrease in feedwater temperature analysis uses the most negative reactivity coefficients in FSAR Table 4.3-2. As indicated in FSAR Table 4.3-2, the most negative Doppler temperature coefficient is -4.7E-03 $/F. Both FSAR Table 4.3-2 and FSAR Section 15.0.0.4 identify that the moderator temperature coefficient is a function of power. Because the decrease in feedwater temperature analysis is performed at full power as described in FSAR Section 15.1.1.3.2, the most negative moderator temperature coefficient for full power is -0.140 $/F per FSAR Table 4.3-2 and FSAR Figure 4.3-15. By following the references contained in the FSAR, the specific values used in the analysis (i.e., Doppler temperature coefficient of -4.7E-03 $/F and moderator temperature coefficient of -0.140 $/F) can be determined without having to repeat the FSAR Chapter 4 values in FSAR Section 15.1.1.3.2. Therefore, the SDAA FSAR provides the same level of information as the DCA FSAR for the reactivity coefficients used for the decrease in feedwater temperature event. No changes to FSAR Section 15.1.1 are required.
Increase in Feedwater Flow The same explanation as for the decrease in feedwater temperature event applies. By following the references contained in the FSAR, the specific values used in the analysis (i.e., Doppler NuScale Nonproprietary NuScale Nonproprietary
temperature coefficient of -4.7E-03 $/F and moderator temperature coefficient of -0.140 $/F) can be determined without having to repeat the FSAR Chapter 4 values in FSAR Section 15.1.2.3.2.
Therefore, the SDAA FSAR provides the same level of information as the DCA FSAR for the reactivity coefficients used for the increase in feedwater flow event. No changes to FSAR Section 15.1.2 are required.
Increase in Steam Flow The same explanation as for the decrease in feedwater temperature event applies. By following the references contained in the FSAR, the specific values used in the analysis (i.e., Doppler temperature coefficient of -4.7E-03 $/F and moderator temperature coefficient of -0.140 $/F) can be determined without having to repeat the FSAR Chapter 4 values in FSAR Section 15.1.3.3.2.
For cases analyzed at less than 100 percent power, the anaysis uses a MTC that corresponds with the power being analyzed (using FSAR Figure 4.3-15). Therefore, the SDAA FSAR provides the same level of information as the DCA FSAR for the reactivity coefficients used for the increase in steam flow event. No changes to FSAR Section 15.1.3 are required.
Response to NRC Feedback The original response above was posted on June 5, 2024. The NRC provided the following feedback on July 8, 2024:
The response states that the most negative Doppler temperature coefficient (DTC) is used in the analysis of decrease in feedwater temperature, increase in feedwater flow, and increase in steam flow events. ((2(a),(c) NuScale reviewed the supporting analyses for FSAR Sections 15.1.1 (EC-104467, Revision 0, NPM-20 Decrease in Feedwater Temperature Transient Analysis), 15.1.2 (EC-0000-8328, Revision 0, NPM-20 Increase in Feedwater Flow Analysis), and 15.1.3 (EC-120241, Revision 0, NPM-20 Increase in Steam Flow/Inadvertent Opening of Steam Generator Relief or Safety NuScale Nonproprietary NuScale Nonproprietary
Valve Analysis). (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
In conclusion, the existing decrease in FW temperature, increase in FW flow, and increase in steam flow event analyses use reactivity feedback based on EOC conditions, which includes most negative MTC and most negative DTC. Use of most negative MTC with least negative DTC, although it could be considered conservative, is not a realistic combination of conditions. The power response modeled in the existing three analyses is sufficiently conservative (( }}2(a),(c) No changes to the SDAA are necessary. NuScale Nonproprietary NuScale Nonproprietary}}