ML22210A319
| ML22210A319 | |
| Person / Time | |
|---|---|
| Site: | Hermes |
| Issue date: | 07/29/2022 |
| From: | Kairos Power |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22210A317 | List: |
| References | |
| KP‐NRC‐2207‐009 | |
| Download: ML22210A319 (5) | |
Text
KPNRC2207009 Enclosure 1 Changes to PSAR Chapter 4 and Chapter 6 (NonProprietary)
Preliminary Safety Analysis Report Reactor Description coolant level. The design of the reactor vessel allows for online monitoring, inservice inspection, and maintenance.
4.3.1.1.1 Vessel Top Head The reactor vessel top head (see Figure 4.32) is a flat 316H SS disc bolted and flanged to the vessel shell. This interface is designed for leaktightness but is not credited as being leak tight in safety analyses. The vessel top head controls the radial and circumferential positions of the reflector blocks to ensure a stable core configuration for all conditions (e.g., reactor trip and core motion). The top head contains penetrations, as shown in Figure 4.32 and Table 4.31, into and out of the vessel and provides for the attachment of supporting equipment and components (e.g., reactivity control elements, pebble handling and storage system components, material sampling port, neutron detectors, thermocouples, etc.). The top head supports the vessel material surveillance system (MSS) which provides a remote means to insert and remove material and fuel test specimens into and from the reactor to support testing.
4.3.1.1.2 Vessel Shell The reactor vessel is a 316H SS cylindrical shell that, along with the vessel bottom head, serves to form the safetyrelated reactor coolant boundary within the reactor vessel. It contains and maintains the inventory of reactor coolant inside the vessel. The shell provides the geometry for coolant inlet and vessel surface for the DHRS which transfers heat from the reactor vessel during postulated events. The inside of the shell uses 316H SS tabs to maintain the core barrel in a cylindrical geometry and has a welded connection at the top of the core barrel.
4.3.1.1.3 Vessel Bottom Head The reactor vessel bottom head is a flat 316H SS disc that is welded to the vessel shell. It contains and maintains the inventory of the reactor coolant inside the vessel, supports the vessel internals, maintains the reactor coolant boundary and provides flow geometry for low pressure reactor coolant inlet to the core. Hydrostatic, seismic and gravity loads on the vessel and vessel internals are transferred to the bottom head and are transferred to the RVSS.
4.3.1.2 Reactor Vessel Internals The reactor vessel internal structures include the graphite reflector blocks, core barrel and reflector support structure. The vessel internal structures define the flow paths of the fuel and reactor coolant, provide a heat sink, a pathway for instrumentation insertion, control and shutdown element insertion, as well as provide neutron shielding and moderation surrounding the core. The design of the structures support inspection and maintenance activities as well as monitoring of the reactor vessel system.
4.3.1.2.1 Reflector Blocks The reflector blocks are constructed of grade ETU10 graphite. The reflector blocks provide a heat sink for the core and are restrained ensuring alignment of the penetrations to insert and withdraw control elements. The reflector blocks are buoyant in the reactor coolant. The bottom reflector blocks are machined with coolant inlet channels for distribution of coolant inlet flow into the core. The top reflector blocks are machined with coolant outlet channels to direct the coolant exiting from the core into the upper plenum, from which the PSP draws suction. The top reflector blocks also form a pebble defueling chute, as shown in Figure 4.31, to direct the pebbles from the core to the pebble extraction machine (PEM), allowing online defueling of the reactor (see Section 9.3). The reflector blocks also provide machined channels for insertion and withdrawal of the reactivity control and shutdown elements described in Section 4.2.2.
Kairos Power Hermes Reactor 429 Revision 0
Preliminary Safety Analysis Report Engineered Safety Features The DHRS is designed and located to minimize the probability and effect of fires and explosions by the use of low combustible materials and physical separation. These design features, in conjunction with the fire protection plan described in Section 9.4, provide assurance that the DHRS demonstrate conformance with the requirements in PDC 3.
The DHRS is designed with materials that will withstand the radiation environment of the reactor cavity and environmental temperatures up to 800 °C to ensure the DHRS is capable of performing its safety function under conditions associated with normal operation, maintenance, testing, and postulated events. The DHRS is designed against equipment failures that could result from Flibe spills. Pipe whip and other similar dynamic failures are avoided by the lowpressure design of the DHRS and the use of restraints. Each component of the DHRS is designed such that failure of one component does not cascade and cause failures of nearby safety systems, including other DHRS components. These design considerations demonstrate conformance with the requirements in PDC 4.
Natural circulation in the reactor core transfers decay heat from the fuel to the reactor vessel shell when normal cooling is not available, as described in Section 4.6.3. Thermalhydraulic calculations demonstrate that the DHRS is capable of passively removing a sufficient amount of decay heat from the reactor vessel for at least 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following postulated events such that the reactor vessel temperature remains below its design limit of 816 °C and is decreasing by the end of the 72hour period. In addition, fuel temperatures remain below their design limits. The DHRS is designed with sufficient redundancy, leak detection capability, and isolation to ensure the safety function can be performed assuming a single failure. The system includes four independent loops and maintains the ability to perform its function with the loss of a single loop. Isolation of the four water storage tanks from one another ensures that damage at one tank location does not result in a total loss of DHRS inventory. The thimbles, separators, and thimble feedwater and steamreturn piping are all contained within the leak barrier. The leak barrier provides leak detection capability and ensures that a failure of the primary DHRS pressure boundary does not prevent the system from performing its heat removal function. These DHRS design features, along with the natural circulation characteristics of the reactor core, demonstrate conformance with the requirements in PDC 34 and PDC 35.
The DHRS design includes the capability for online monitoring of leaks to monitor for system integrity and to ensure that DHRS inventory remains sufficient to perform the safetyrelated heat removal function. The water level in the storage tanks is also capable of being monitored to ensure that sufficient inventory is present at the onset of a postulated event to provide sufficient cooling capacity. The DHRS is also sufficiently accessible to perform inspections for system integrity. These features satisfy PDC 36.
When the reactor is above threshold power, the DHRS is an always on operating condition which provides an ongoing demonstration of system availability. The transition from normal to postulated event operation can also be functionally tested. These features demonstrate conformance with the requirements in PDC 37.
6.3.4 Testing and Inspection The details of the inspection and testing program for DHRS to satisfy the applicable portions of ASME Section XI, Division 1 and 2, Rules for Inservice Inspection of Nuclear Power Plant Components (Reference 2) will be described in the application for an Operating License.
Water storage tank inventory is monitored to ensure the DHRS operability. The DHRS continuous operation is also monitored to ensure DHRS availability when demanded. DHRS operability is controlled by a technical specification, as described in Chapter 14.
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Preliminary Safety Analysis Report Engineered Safety Features 6.3.5 References
- 1. American Society of Mechanical Engineers, ASME Boiler and Pressure Vessel Code, Sec. III Div. 5, BPVC Section IIIRules for Construction of Nuclear Facility ComponentsDivision 5High Temperature Reactors, 2019.
- 2. American Society of Mechanical Engineers, ASME Boiler and Pressure Vessel Code, Sec. XI Div. 1 and 2, BPVS Section XIRules for Inservice Inspection of Nuclear Power Plant Components, 2019.
3.2. American Society of Civil Engineers, ASCE/SEI 4319, Seismic Design Criteria for Structures, Systems, and Components in Nuclear Facilities, 2020.
4.3. American Society of Civil Engineers, ASCE/SEI 416, Seismic Analysis of SafetyRelated Nuclear Structures, 2017.
5.4. American Concrete Institute, ACI 34913, Code Requirements for Nuclear SafetyRelated Concrete Structures and Commentary, 2014.
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Preliminary Safety Analysis Report Engineered Safety Features Table 6.34: Applicable Design Codes and Standards for the DHRS Code Title Applicability ASME Sec. III Div. 5 Class B ASME Boiler and Metallic pressure boundary and supports. In (Reference 1) Pressure Vessel Code general, low temperature service corresponds to
- High Temperature the requirements of ASME Sec. III Div. 1 Reactors subsection NC. This applies to most DHRS components. The risers are an exception and must follow rules for hightemperature service.
These provide additional modifications to Div. 1 rules.
ASME Sec. XI Div. 1 and 2 Rules for Inservice Provides rules and guidelines for testing and (Reference 2) Inspection of Nuclear inspection of DHRS pressure boundary and Power Plant structural components.
Components ASCE 4319 (Reference 23) Seismic Design Provides design criteria for seismic analysis of Criteria for reactor components (including DHRS).
Structures, Systems, and Components in Nuclear Facilities ASCE 416 (Reference 34) Seismic Analysis of Provides additional design criteria for safety SafetyRelated related systems (including DHRS) that expand Nuclear Structures upon ASCE 4319.
ACI 34913 (Reference 45) Code Requirements Applicable to cavity support structures for DHRS for Nuclear Safety panels and potentially the condenser pool Related Concrete construction.
Structures and Commentary Kairos Power Hermes Reactor 613 Revision 0