ML24348A077

Response to NuScale Topical Report Audit Question Number A-NonLOCA.LTR-59

ML24348A077
Person / Time
Site:	05200050
Issue date:	12/13/2024
From:	NuScale
To:	Office of Nuclear Reactor Regulation
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Download: ML24348A077 (1)

Text

Response to NuScale Topical Report Audit Question Question Number: A-NonLOCA.LTR-59 Receipt Date: 06/28/2024 Question:

LTR Table 7-64 states that letdown is modeled as disabled for the uncontrolled CRA withdrawal at power event (( 2(a),(c) Provide support for this basis for NRC staff review or revise this disposition in the LTR.

Response

TR-0516-49416-P, Revision 4, Non-Loss-of-Coolant Accident Analysis Methodology, Table 7-64 identifies initial conditions, biases, and conservatisms to be applied for analyses of the uncontrolled control rod bank withdrawal at power. Table 7-64 identifies that letdown is disabled ((

}}2(a),(c)

((

}}2(a),(c) Pressurizer spray exists specifically to control pressurizer pressure and maintain it within a range below the high pressurizer pressure reactor trip signal. By varying pressurizer spray modeling for this event (on or off), different sequences of events can be NuScale Nonproprietary NuScale Nonproprietary

obtained. ((

}}2(a),(c)

Demonstration of the effectiveness of the application of this methodology can be seen in the analysis in Section 15.4.2 of the Final Safety Analysis Report (FSAR) for the US460 design. Table 15.4-4 provides the sequence of events for the limiting MCHFR case (a case with spray modeled as on) and shows that reactor trip occurs on high power, not high pressurizer pressure. Figure 15.4-8 shows that, for this case, the reactor coolant system (RCS) hot temperature is also near the analytical limit of 620 degrees F at the time of reactor trip on high power ((

}}2(a),(c) Figure 15.4-7 shows the pressurizer pressure during the transient is maintained below the high pressurizer pressure reactor trip signal. The sawtooth behavior in Figure 15.4-7 indicates the operation of pressurizer spray: pressure increases until spray turns on, decreases during spray operation until spray turns off, then increases again. (( 
}}2(a),(c) power and fluid temperature to continue increasing as shown in Figure 15.4-6 until the high power trip occurs. Although a sequence of events table and transient figures are not provided for the limiting linear heat generation rate (LHGR) case (LHGR is used as the figure of merit instead of fuel centerline temperature as discussed in the FSAR), the case associated with the limiting LHGR result in Table 15.4-7 (( 
}}2(a),(c)

The analysis supporting FSAR Section 15.4.2 is EC-0000-8672, Revision 0, Uncontrolled Control Rod Assembly Bank Withdrawal at Power Transient Analysis, previously provided in the electronic reading room (eRR). ((

}}2(a),(c)

Based on this information, NuScale has addressed the underlying concern in this audit question that control systems that affect pressurizer pressure should be considered for their potential NuScale Nonproprietary NuScale Nonproprietary

(( }}2(a),(c) Note that audit question A-5.4.5-1 requested further information about pressurizer spray setpoints based on the observed sawtooth behavior in FSAR Figure 15.4-7. (( }}2(a),(c) No changes to the SDAA are necessary. NuScale Nonproprietary NuScale Nonproprietary}}