ML24215A069
| ML24215A069 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 08/02/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24215A000 | List:
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| References | |
| LO-169995 | |
| Download: ML24215A069 (1) | |
Text
Response to SDAA Audit Question Question Number: A-3.9.4-7 Receipt Date: 10/02/2023 Question:
Figure 4.6-2 depicts a "rod holdout mechanism" and a "remote disconnect mechanism," which are not extensively discussed in the FSAR. Please provide information on these features, with an emphasis on any potential impact they may have on the safety-related function of inserting rods (If none, please provide explanation).
Response
The rod hold out (RHO) and the remote control rod assembly (CRA) disconnect mechanism (RDM) are nonsafety-related and non-risk-significant.
Neither the rod hold out (RHO), nor the remote control rod assembly (CRA) disconnect mechanism (RDM) are used during normal plant operations. The FSAR markups to Section 3.9.4 and Section 4.6.1 describe the RHO and RDM. The RHO and RDM have no impact on the safety-related function of inserting the control rods. The proposed scenario of the RDM coils becoming inadvertantly energized is inconsequential because the RDM is only able to function when the control rod drive shaft is fully inserted, which would have no impact to the safety-related function of inserting the control rods.
Markups of the affected changes, as described in the response, are provided below:
NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Introduction NuScale US460 SDAA 1.1-5 Draft Revision 2 Audit Question A-3.9.4-7 Table 1.1-1: Acronyms and Abbreviations Acronym or Abbreviation Description ABS auxiliary boiler system ABVS Annex Building HVAC system ABWR advanced boiling water reactor AC alternating current ACCS air cooled condenser system ACI American Concrete Institute ACM Availability Controls Manual ACRS Advisory Committee on Reactor Safeguards AEA Atomic Energy Act AFU air filtration unit AFWS auxiliary feedwater system AHJ authority having jurisdiction AHU air handling unit AIA Authorized Inspection Agency AISC American Institute of Steel Construction AISI American Iron and Steel Institute ALARA as low as reasonably achievable ALU actuation logic unit ALWR advanced light water reactor AMCA Air Movement and Control Association International, Inc.
ANB Annex Building ANS American Nuclear Society ANSI American National Standards Institute AO axial offset AOA axial offset anomaly AOO anticipated operational occurrence AOV air-operated valve API American Petroleum Institute APL actuation and priority logic APWR advanced pressurized water reactor AQ augmented quality ARM area radiation monitor ARO all rods out ARS acceleration response spectra ASAI application specific action item ASCE American Society of Civil Engineers ASD adjustable speed drive ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers ASM American Society for Metals International ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATB Administration and Training Building ATJC articulating traveling jib crane ATWS anticipated transient without scram AVT all-volatile treatment AWH auxiliary wet hoist AWS American Welding Society AWWA American Water Works Association BAS boron addition system
NuScale Final Safety Analysis Report Introduction NuScale US460 SDAA 1.1-15 Draft Revision 2 PLM priority logic module PLRS programmable logic requirement specification PLS plant lighting system PLVVP Programmable Logic Verification and Validation Plan PMF probable maximum flood PMP probable maximum precipitation PORV power-operated relief valve POS plant operating state POV power-operated valve PPE personal protective equipment PPS plant protection system PRA Probabilistic Risk Assessment PRHA Pipe Rupture Hazards Analysis PRV pressure relief valve PSCIV primary system containment isolation valves PSD power spectra density PSMS power supply monitoring system PSS process sampling system PST phase separator tank PSTN public switched telephone network PTAC performance and test acceptance criteria band PTS pressurized thermal shock PVC polyvinyl chloride PVMS plant-wide video monitoring system PWHT post-weld heat treatment PWR pressurized water reactor PWS potable water system PWSCC primary water stress-corrosion cracking PZR pressurizer QA quality assurance QAP Quality Assurance Program QAPD Quality Assurance Program Description QPD quadrant power difference QD quick disconnect QHO quantitative health objective QPF quadrant power fractions RAI Request for Additional Information RAP Reliability Assurance Program RAW risk achievement worth RBC Reactor Building crane RBCM Reactor Building components RBVS Reactor Building HVAC system RCA radiologically controlled area RCCA rod control cluster assembly RCCWS reactor component cooling water system RCP reactor coolant pump RCPB reactor coolant pressure boundary RCRA Resource Conservation and Recovery Act RCS reactor coolant system RDM remote CRA disconnect mechanism Table 1.1-1: Acronyms and Abbreviations (Continued)
Acronym or Abbreviation Description
NuScale Final Safety Analysis Report Introduction NuScale US460 SDAA 1.1-16 Draft Revision 2 RDT reactor drain tank REA rod ejection accident RETS Radiological Effluent Technical Specifications RFI radio frequency interference RFP refueling pool RFT reactor flange tool RG Regulatory Guide RHO rod hold out RHR residual heat removal RHX regenerative heat exchanger RIS Regulatory Issue Summary RL response level RLE review level earthquake RM radiation monitoring RMS fixed area radiation monitoring system RMTS risk-managed technical specifications RO reverse osmosis ROP Reactor Oversight Process RPI rod position indication RPS reactor protection system RPV reactor pressure vessel RRS required response spectrum RRV reactor recirculation valve RSA remote shutdown area RSR results summary report RSS remote shutdown station RSV reactor safety valve RTB reactor trip breaker RTD resistance temperature detector RTM requirements traceability matrix RTNDT reference temperature for nil-ductility transition RTNSS Regulatory Treatment of Nonsafety Systems RTP rated thermal power RTPTS reference temperature, pressurized thermal shock RTS reactor trip system RVI reactor vessel internals RVV reactor vent valve RWB Radioactive Waste Building RWBCR Radioactive Waste Building control room RWBVS Radioactive Waste Building HVAC system RWDS radioactive waste drain system RWMS radioactive waste management system RWSS raw water supply system RXB Reactor Building RXCS reactor core system RXF reactor fuel assembly S&Q staffing and qualifications SAFDL specified acceptable fuel design limit SAM seismic anchor motion SAMDA severe accident mitigation design alternative Table 1.1-1: Acronyms and Abbreviations (Continued)
Acronym or Abbreviation Description
NuScale Final Safety Analysis Report Mechanical Systems and Components NuScale US460 SDAA 3.9-33 Draft Revision 2 detail below. The rods are moved in a controlled manner to maintain control of the power level and power distribution in the core. The CRDM is connected to the CRA at the bottom end of the control rod drive shaft.
The CRDM is capable of a continuous full-height withdrawal and insertion and holding a position during normal operating conditions.
The CRDM components in contact with the primary coolant are designed to operate for a 60-year design life. The CRDMs are designed to be replaceable and freely interchangeable without limitations in function and connections.
Control Rod Drive Shaft The control rod drive shaft is the link and the method of transferring force between the CRDM and the CRA. The control rod drive shaft passes through the upper region of the reactor vessel to allow the CRDM to raise, lower, or hold the CRA. The control rod drive shaft also interacts with the rod position indication sensor coils that communicate the elevation of the control rods. The control rod drive shaft allows for the remote release of the CRA for refueling purposes.
The control rod drive shaft is analyzed to the guidance of ASME,Section III, Nonmandatory Appendix F for linear type supports and is evaluated to not adversely affect the integrity of the core support structures in accordance with NG-1122(c).
Martensitic stainless steel materials used in the control rod drive shafts are Cv tested in accordance with NB-2331.
Drive Coil Assembly The drive coil assembly has four main coils: the lift coil, the upper gripper coil, the lower gripper coil, and the load transfer coil. The drive coil assembly is a part of the external assembly that slides over the pressure housing and sits on a ledge at the base of the pressure housing. The drive coil assembly is depicted by Figure 4.6-3.The direct current generated by the control cabinets is sent through a coil that generates a magnetic field; this magnetic field engages the flat-face plunger magnet of the latch arm assembly, which moves the latch arm to engage the control rod drive shaft. The rate at which the upper gripper coil, the load transfer coil, the lower gripper coil, and the lift coil are energized determines the speed of the control rod drive shaft. The motive power supply from the alternating current distribution system to the CRDM control cabinet is interrupted when the reactor trip breakers open, causing the control rods to be inserted via gravity. The CRDS safety function of rapid insertion of the control rods is accomplished when power is removed from the CRDM. Rod movement logic tracks the speed of the control rods, which utilizes direct rod position indication.
Audit Question A-3.9.4-7
NuScale Final Safety Analysis Report Mechanical Systems and Components NuScale US460 SDAA 3.9-34 Draft Revision 2 The remote disconnect mechanism coils together with the magnets and internal components of the control rod drive shaft are capable of remotely connecting and disconnecting the control rod drive shaft from the CRA, as the control rod drive shafts are not accessible during NPM disassembly.
Pressure Housing The pressure housing includes components of the CRDM that form the pressure boundary for the reactor coolant. The pressure housing is an ASME BPVC,Section III, Subsection NB component. The pressure housing consists of the single-piece pressure housing (bolted to the reactor vessel head), and the top plug assembly. The removable top plug assembly is threaded onto the top of the pressure housing to complete the RCPB seal.
Latch Mechanism Assembly The basic functions of the latch mechanism assembly are to grip, release, lift, and lower the CRA. The lifting and lowering functions are referred to as stepping, and these steps are in 0.375-inch increments. The latch mechanism assembly contains two sets of latches, the upper gripper and lower gripper latches, as shown in Figure 4.6-5. The latches grip the control rod drive shaft when the teeth of the latch arms are engaged within the grooves in the upper segment of the control rod drive shaft.
The latch assembly is secured into the bottom of the pressure housing.
Rod Position Indicator Assembly The rod position indicator assembly contains the rod position indication coils and interfaces with the CRDM seismic support plates. The coil assembly is a part of the CRDM external assembly and slides over the pressure housing and sits on the rod disconnect mechanism coil housing. The sensor coil assembly is shown in Figure 4.6-4.
Audit Question A-3.9.4-7 Remote CRA Disconnect Mechanism Audit Question A-3.9.4-7 The CRDM includes a remote CRA disconnect mechanism (RDM) that is used during startup and shutdown when the control rod drive shaft is fully inserted to remotely couple and uncouple the control rod drive shaft to and from the CRA hub, as the control rod drive shafts are not accessible during NPM disassembly. The RDM is composed of two major portions: magnetic and mechanical features that are part of the control rod drive shaft assembly and two electrical coils, which are outside of the RCPB. The RDM coil assemblies are in a fixed position and are operated by a direct current sent through the coils that generates a magnetic field. When the RDM portion on the top of the control rod drive shaft is in alignment with the external RDM coils, which only occurs when the control rod drive shaft is fully inserted, this magnetic field
NuScale Final Safety Analysis Report Mechanical Systems and Components NuScale US460 SDAA 3.9-35 Draft Revision 2 engages the flat-face plunger magnets on the RDM portion on the top of the control rod drive shaft. The upper RDM coil actuates locking and unlocking features and the lower RDM coil raises or lowers the control rod drive shaft internal operating rod to engage or disengage the control rod drive shaft coupling with the CRA hub. The RDM feature is only able to be effectively activated when the CRA is being connected or disconnected. When the RDM coils are de-energized or are non-effective, the internal operating rod and shaft coupling are mechanically locked in place to ensure the CRA cannot be disengaged.
Audit Question A-3.9.4-7 Rod Hold Out Device Audit Question A-3.9.4-7 The CRDM includes a rod hold out (RHO) device used only during refueling operations to secure the control rod drive shaft fully withdrawn in the upper portion of the CRDM pressure housing, which allows the control rod drive shaft to be removed with the upper NPM assembly. The RHO is composed of two major portions: the ball grip assembly inside the top of the CRDM pressure housing and one electrical coil outside of the RCPB. The RHO is engaged only when the CRA is uncoupled from the control rod drive shaft by withdrawing the control rod drive shaft beyond the normal range of travel until the tip of the drive shaft is held by the RHO ball grip assembly. It is not physically possible for the control rod drive shaft to engage with the RHO ball grip assembly without the CRA first being decoupled from the control rod drive shaft because the RHO is positioned in the top of the pressure housing beyond the normal operating travel range of the control rod drive shaft. The CRDS alignment cone at the top of the RVI guide tubes physically limits the withdrawal of the CRA, preventing a control rod drive shaft with coupled CRA from reaching the RHO ball grip. The RHO coil is only utilized for RHO disengagement. RHO engagement and holding is performed by mechanical means. The RHO coil is operated by a direct current sent through the coil that generates a magnetic field. This magnetic field engages the flat-face plunger magnets on the RHO ball grip to allow the control rod drive shaft to be disengaged and returned to its normal range of travel.
3.9.4.1.2 Operation of the Control Rod Drive Mechanisms The CRDM mechanical and operational requirements are discussed in Section 4.6. The following describes the different modes of CRDM operation.
Reactor trip, consisting of full insertion of the CRAs into the core at design conditions, is achievable during the CRDM operating modes described below.
When a reactor trip signal occurs, the operating coils are de-energized.
De-energizing causes the latch mechanism assembly magnets to separate, retracting the latches from the drive shaft grooves and allowing the drive shaft and the CRA to drop into the reactor core under gravity.
Control Rod Insertion
NuScale Final Safety Analysis Report Functional Design of Control Rod Drive System NuScale US460 SDAA 4.6-1 Draft Revision 2 4.6 Functional Design of Control Rod Drive System The control rod drive system (CRDS) performs the following safety-related functions:
releases the control rod assemblies (CRAs) during a reactor trip maintains the pressure boundary of the reactor pressure vessel (RPV)
The CRDS performs the following non safety-related functions:
latching, holding, and maneuvering the CRAs during reactor startup, power operation, and shutdown provides rod position indication 4.6.1 Description of the Control Rod Drive System The CRDS includes the control rod drive mechanisms (CRDMs) and associated equipment used to operate the CRDMs. The CRDM includes the control rod drive shaft, which extends to the coupling interface with the CRAs in the RPV. The CRDS supports the CRAs by latching, holding, and maneuvering the CRAs during reactor startup, power operation, and shutdown in response to signals from the control rod drive power converter and controller assembly, and in releasing the CRAs during a reactor trip. The CRDS also includes the rod position indicator cabinets and cables, CRDM power cables, and cooling water supply and return piping inside containment.
The mechanical design of the CRDM is described in Section 3.9.4 and the design of the CRA is described in Section 4.2.2. The instrumentation and controls for the CRDS are described in Chapter 7.
Audit Question A-3.9.4-7 Figure 4.6-1 through Figure 4.6-6 illustrate the principal features of the CRDS.
Figure 4.6-1 is a simplified drawing showing an overview of the location of components of the CRDS relative to the RPV and the containment vessel (CNV). The CRDMs are mounted on top of the RPV and laterally constrained in order to limit relative lateral seismic motion, yet allow for unrestricted axial expansion. The control rod drive shafts are located inside the RPV and aligned laterally by CRDS support structures that are part of the reactor vessel internals. Further details are provided in Section 3.9.4. The electromagnetic load transfer across the primary pressure boundary is facilitated by electromagnetic coils on the outside (Figure 4.6-3) that engage a set of magnetic poles connected to latches on the inside (Figure 4.6-5), in order to move the control rod drive shaft in a predetermined stepping sequence (Section 3.9.4). Figure 4.6-2 provides an illustration of the CRDM electromagnetic coils and housings, including the pressure housings. The power and cooling water connectors are located on top of the pressure housing and rod position indication coil stack assembly for ease of access through the removable cover on top of the CNV (Figure 4.6-1). The rod hold out device is composed of a ball grip assembly inside the top of the CRDM pressure housing and an electrical coil on the outside of the pressure housing. The remote CRA disconnect mechanism is located at the top of the control rod drive shaft assembly and is activated using two electrical coils on the outside of the CRDM pressure housing. Further details are provided in Section 3.9.4.
Figure 4.6-3 illustrates the CRDM drive coil and cooling jacket assembly. Figure 4.6-4 shows the layout of the rod position indicator sensor coil assemblies, which are