ML18099A161

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LLC Response to NRC Request for Additional Information No. 402 (Erai No. 9449) on the NuScale Design Certification Application
ML18099A161
Person / Time
Site: NuScale
Issue date: 04/09/2018
From: Rad Z
NuScale
To:
Document Control Desk, Office of New Reactors
References
RAIO-0418-59415
Download: ML18099A161 (4)
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Text

RAIO-0418-59415 April 0, 2018 Docket No.52-048 U.S. Nuclear Regulatory Commission

ATTN: Document Control Desk

One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738

SUBJECT:

NuScale Power, LLC Response to NRC Request for Additional Information No.

42 (eRAI No. 9449) on the NuScale Design Certification Application

REFERENCE:

U.S. Nuclear Regulatory Commission, "Request for Additional Information No.

402 (eRAI No. 9449)," dated March 29, 2018 The purpose of this letter is to provide the NuScale Power, LLC (NuScale) response to the referenced NRC Request for Additional Information (RAI).

The Enclosure to this letter contains NuScale's response to the following RAI Question from NRC eRAI No. 9449:

04.03-2 This letter and the enclosed response make no new regulatory commitments and no revisions to any existing regulatory commitments.

If you have any questions on this response, please contact Darrell Gardner at 980-349-4829 or at dgardner@nuscalepower.com.

y, Sincerely, Zackary W. Rad Director Regulatory Affairs

Director, NuScale Power, LLC Distribution: Samuel Lee, NRC, OWFN-8G9A Prosanta Chowdhury NRC, OWFN-8G9A Bruce Bavol, NRC, OWFN-8G9A : NuScale Response to NRC Request for Additional Information eRAI No. 9449 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvalis, Oregon 97330, Office: 541.360.0500, Fax: 541.207.3928 www.nuscalepower.com

RAIO-0418-59415 :

NuScale Response to NRC Request for Additional Information eRAI No. 9449 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvalis, Oregon 97330, Office: 541.360.0500, Fax: 541.207.3928 www.nuscalepower.com

Response to Request for Additional Information Docket No.52-048 eRAI No.: 9449 Date of RAI Issue: 03/29/2018 NRC Question No.: 04.03-2 GDC 10, Reactor design, requires that the reactor core and associated coolant, control, and protection systems be designed with appropriate margin to assure that specified acceptable design limits (SAFDLs) are not exceeded during any condition of normal operation, including the effects of anticipate operational occurrences. GDC 25, Protection system requirements for reactivity control malfunctions, requires that the protection system be designed to assure that SAFDLs are not exceeded for any single malfunction of the reactivity control systems.

FSAR, Tier 2, Section 4.3.1 states that the control system withdrawal rate is designed to assure that SAFDLs are not exceeded for accidental withdrawal of control rods; FSAR, Tier 2, Section 15.4.1.2 states that the transient analyses assume a maximum allowed control rod assembly (CRA) withdrawal rate of 15 in/min; and FSAR Tier 2, Table 14.2-80 states that Test

  1. 80 will verify that the rod insertion and withdrawal speeds are within design limits. NRC staff did not identify design information regarding a specific limit on the withdrawal speed. NRC staff needs to establish a finding that the transient and accident analyses are performed using suitably conservative values for CRA withdrawal rate. Accordingly, NRC staff requests that the applicant update FSAR, Tier 2, Section 4.3 to specify a design limit on CRA withdrawal rate.

NuScale Response:

The control rod system is designed such that the maximum withdrawal speed of the CRAs is 15 inches per minute, as described in Section 3.9.4.1. The accident analysis is performed assuming the same maximum speed, as noted in Section 15.4.1.2. A pointer has been added in Section 4.3.1.4 to refer to the design maximum withdrawal stepping speed in Section 3.9.4.1.

Impact on DCA:

FSAR Section 4.3 has been revised as described in the response above and as shown in the markup provided in this response.

NuScale Nonproprietary

NuScale Final Safety Analysis Report Nuclear Design 4.3.1.3 Power Distribution The power distribution and the reactor protection system are designed to ensure that the following SAFDLs are met at a 95 percent probability at a 95 percent confidence level:

  • Peak fuel power under abnormal conditions, including the maximum overpower condition, will not result in fuel melting as discussed in Section 4.4.
  • Fuel management is such that the values of fuel rod power and burnup meet the fuel rod mechanical integrity assumptions in Section 4.2.
  • Fuel is not operated at a linear power density greater than the design limit for the fuel.

These restrictions along with the burnup restriction in Section 4.3.1.1 satisfy GDC 10.

The power distribution limits are discussed in more detail in Section 4.3.2.2.

4.3.1.4 Maximum Controlled Reactivity Insertion The NuScale design places limits on the worth of the control rod assemblies (CRAs),

CRA insertion depth, and maximum CRA withdrawal rate. The maximum controlled reactivity addition rate is limited, such that the SAFDLs are not violated during normal operation, AOOs, or postulated accidents.

RAI 04.03-2 For an accidental withdrawal of a bank of CRAs or a single CRA, the maximum withdrawal rate is established such that critical heat flux (CHF) limits are not exceeded as discussed in Section 15.4, consistent with GDC 25. The design maximum rod withdrawal rate is 15 inches/minute as described in Section 3.9.4.1.

The maximum worth of the CRAs and the limits on CRA insertion preclude rupture of the reactor coolant pressure boundary due to a rod withdrawal or rod ejection accident (Section 15.4). The design basis presented in this section satisfies GDC 28. Control rod worth is discussed in more detail in Section 4.3.2.5.

4.3.1.5 Shutdown Margin and Long Term Shutdown Capability The NuScale design employs two independent means for reactivity control: CRAs and soluble boron. The concentration of soluble boron in the reactor coolant system (RCS) is controlled by the chemical and volume control system (CVCS). These two reactivity control systems satisfy the portion of GDC 26 that requires two independent reactivity control systems of different design principles. Each of the two independent means of reactivity control is capable of controlling the reactivity changes resulting from planned, normal operation.

Shutdown margin (SDM) is defined as the instantaneous amount of reactivity by which the reactor is subcritical, or would be subcritical from its present condition, assuming Tier 2 4.3-3 Draft Revision 2

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