ML24222A441
| ML24222A441 | |
| Person / Time | |
|---|---|
| Issue date: | 08/21/2024 |
| From: | Vivanco R NRC/NRR/DNRL/NRLB |
| To: | Jardaneh M NRC/NRR/DNRL/NRLB |
| References | |
| Download: ML24222A441 (13) | |
Text
August 21, 2024 MEMORANDUM TO:
Mahmoud Jardaneh, Chief New Reactor Licensing Branch Division of New and Renewed Licenses Office of Nuclear Reactor Regulation FROM:
Ricky V. Vivanco, Project Manager
/RA/
New Reactor Licensing Branch Division of New and Renewed Licenses Office of Nuclear Reactor Regulation
SUBJECT:
U.S. NUCLEAR REGULATORY COMMISSION
SUMMARY
OF THE JULY 10, 2024, PUBLIC MEETING TO DISCUSS THE CONCEPTUAL DESIGN OF DEEP FISSIONS DEEP BOREHOLE PRESSURIZED WATER REACTOR The U.S. Nuclear Regulatory Commission (NRC) staff conducted an observation public teleconference meeting with Deep Fission, Inc. (Deep Fission), on July 10, 2024. The purpose of the meeting was to discuss the conceptual design of Deep Fissions Deep Borehole Pressurized Water Reactor (DB-PWR).
The meeting notice can be found in the Agencywide Documents Access and Management System (ADAMS) Accession No. ML24192A194. The meeting notice was also posted on the NRC public website.
CONTACT: Ricky Vivanco, NRR/DNRL 301-415-0021
M. Jardaneh 2
Enclosed are the meeting agenda (Enclosure 1), list of attendees (Enclosure 2), meeting summary (Enclosure 3) and NRC staff observations (Enclosure 4). The documents mentioned in the meeting summary can be found under ADAMS accession nos. provided below.
Deep Fissions letter dated June 14, 2024, submitting the White Paper titled, Conceptual Design Review of the Deep Borehole Pressurized Water Reactor (DB-PWR)
ML24172A288 Deep Fissions White Paper titled, Conceptual Design Review of the Deep Borehole Pressurized Water Reactor (DB-PWR)
ML24172A286 Deep Fissions briefing material presented at the July 10, 2024, public meeting ML24191A372 Docket No. 99902126
Enclosures:
- 1. Meeting Agenda
- 2. List of Attendees
- 3. Meeting Summary
- 4. NRC Staff Observations cc w/encl.: Deep Fission, Inc. Listserv
ML24222A441 *via email NRR-106 OFFICE NRR/DNRL/NRLB: PM NRR/DNRL/NLIB: LA NRR/DNRL/NRLB: BC NRR/DNRL/NRLB: PM NAME RVivanco*
SGreen*
MJardaneh*
RVivanco*
DATE 8/9/2024 8/12/2024 8/15/2024 8/21/2024
U.S. NUCLEAR REGULATORY COMMISSION OBSERVATION PUBLIC TELECONFERENCE WITH DEEP FISSION, INC. (DEEP FISSION)
TO DISCUSS THE CONCEPTUAL DESIGN WHITE PAPER FOR DEEP FISSIONS DEEP BOREHOLE PRESSURIZED WATER REACTOR Meeting Agenda Time Topic Speaker 1:00 p.m. EST Introduction NRC 1:05 p.m. EST Discussion of Conceptual Design White Paper for DB-PWR Deep Fission 2:50 p.m. EST Opportunity for Public Comment Public 3:00 p.m. EST Adjourn NRC
OBSERVATION PUBLIC TELECONFERENCE WITH DEEP FISSION, INC. (DEEP FISSION)
TO DISCUSS THE CONCEPTUAL DESIGN WHITE PAPER FOR DEEP FISSIONS DEEP BOREHOLE PRESSURIZED WATER REACTOR List of Attendees Name Organization Stacy Joseph U.S. Nuclear Regulatory Commission (NRC)
Ricky Vivanco Mahmoud Jardaneh Sam Lee Jenise Thompson Jeff Correll Anderson Wolfe Tami Dozier Kerri Kavanagh Joey McPherson Nicholas Armstrong Barbara Hayes Amy D'Agostino David Rudland Chris Van Wert Cliff Munson Tim McCartin Theresa Buchanan Michelle Sutherland Alina Schiller River Rohrman Malcolm Thompson Deep Fission Ingrid Nordby Supna Zaidi Richard Muller Liz Muller Alex Spire Rosemary Muller John Butler Nuclear Energy Institute Steven Pope ISL Kenneth Fossum Idaho National Laboratory Tim Polich RoPower
U.S. NUCLEAR REGULATORY COMMISSION OBSERVATION PUBLIC TELECONFERENCE WITH DEEP FISSION, INC. (DEEP FISSION)
TO DISCUSS THE CONCEPTUAL DESIGN WHITE PAPER FOR DEEP FISSIONS DEEP BOREHOLE PRESSURIZED WATER REACTOR MEETING
SUMMARY
On July 10, 2024, the U.S. Nuclear Regulatory Commission (NRC) staff conducted an observation public teleconference meeting with Deep Fission, Inc. (Deep Fission), to discuss the conceptual design White Paper for Deep Fissions Deep Borehole Pressurized Water Reactor (DB-PWR).
The public meeting commenced at 1:00 pm with opening remarks from the NRC and an introduction of participants. Next, Deep Fission began its presentation (ML24191A372) by stating that the purpose of the meeting was to discuss the conceptual design White Paper for (ML24172A286) that was submitted to the NRC on June 14, 2024 (ML24172A288).
Next, Deep Fission discussed the following topics:
Company Information: Deep Fission was incorporated in 2023 by founders experienced in the nuclear industry. Deep Fissions DB-PWR is a PWR using existing supply chain and LEU fuel and natural geology for containment and pressure at ~1-mile depth. The DB-PWR is modular and scalable with each reactor delivering from 1 to 15 MWe and additional reactors can be added to a site to greater than 1 GWe. Deep Fissions vision is low-cost nuclear power to address climate change, energy security, and access.
Design Overview o Standard PWR Design Features Standard Fuel Assemblies Standard Pressure (160 atm)
Standard Temperature Range (275-315°C)
Primary Loop Contained Standard Pressure for Secondary Loop (65 atm)
Standard Temperature for Secondary Loop (steam at 185°C)
Chemical, Volume, and Pressure Control System Hydrogen Injection o Novel Characteristics Configuration Uses only four () fuel assemblies Tall and narrow steam generator Pressurizer based on hydrostatics Emplacement Reactor core 1 mile below earth surface No high-level radiation at surface during normal operations Primary containment based on geology Pressurization based on depth Ultimate Heat Sink is the host geological formation
2 o Reactor Components, Steam Generator and Chemical, Volume, and Pressure Control System o Regulatory Path Response to Regulatory Issue Summary 2020-02, March 12, 2024 Regulatory Engagement Plan for Deep Fission, March 22, 2024 Pursuing a Standard Design Approval under 10 CFR Part 52 Next, NRC staff asked questions about the design and provided observations regarding Deep Fissions presentation. The NRC staff observations are provided at Enclosure 4. The NRC staff does not require a response to these observations.
The public was provided an opportunity to provide comments and ask questions. There were no questions or comments from the public.
U.S. NUCLEAR REGULATORY COMMISSION OBSERVATION PUBLIC TELECONFERENCE WITH DEEP FISSION, INC. (DEEP FISSION)
TO DISCUSS THE CONCEPTUAL DESIGN WHITE PAPER FOR DEEP FISSIONS DEEP BOREHOLE PRESSURIZED WATER REACTOR NRC STAFF OBSERVATIONS White Paper Section Observation/comment 2.1 There is no discussion of the expected design life of this reactor, or any indication of the level of fluence that may be achieved adjacent to the core.
2.2 The conditions of the steam as it rises to the surface is unclear. What is the temperature loss as it rises? Is the pressure in the steam piping maintained?
2.4.2 The design of the reactor internals is unclear. How is the core secured to the reactor vessel? How is the reactor vessel secured to the casing?
2.4.2 The description includes a heat exchanger. Is that the steam generator or a different component?
2.4.4 The steam generator (SG) is to be manufactured to nuclear standards. What codes and standards are to be used? What is the SG shell material?
2.4.5 Since brine is expected in the rock water, what type of corrosion control is expected to be used for the casing material?
2.4.5 Vessel wall is only thick enough to withstand handling. Typically, nuclear codes will require corrosion allowance, etc.
3.2 The staff would like to understand the fragility of this system. A mile long, 30" pipe would seem to have low fragility unless its well supported.
3.2 "The small parts of the DB-PWR are easily held in place against 1-g or several-g accelerations". What is the author referring to?
3.2 Severing of the bore hole in an accident condition seems somewhat likely, but authors claim risk to public is low. Failure would cause water ingress into the environment. The white paper discusses preliminary analyses but no details are available to understand what was considered.
3.6 The information on the materials used is very limited. What are the design conditions (fatigue, etc.) considered, what degradation mechanisms are being considered?
What design and inspection code and standard will be used? What quality assurance programs are planned? How will the structure, system, and component be categorized for safety?
3.7 Under casing, the white paper says the casing will probably be carbon steel. How will corrosion of the casing be treated? The white paper says the fresh water will be tested. Will it be tested on a periodic basis, and what will be the mitigation if corrosion product is found?
3.11 There is very limited detail on pre-service or in-service inspection. The plans for these inspections are unclear. Do you plant to follow an internationally recognized code and standards? What will and wont be inspected and why? If something is found, how will it be mitigated?
2 White Paper Section Observation/comment 2.1 The system is modular, so more power can be generated by adding more boreholes with separated reactors. This spacing would allow multiple reactors per acre with early geologic studies finding that most locations have suitable geology.
Ø Uniform geology is not easy to find and having multiple boreholes in close proximity can create problems in connecting fault an fracture zones between boreholes that could compromise safety. There is very little discussion regarding how the effects of a nest of reactors will impact heat flow of a specific borehole or the potential for multiple to compromise the integrity of the site and safety concept.
Ø For Yucca Mountain, the DOE have a very specific plan for ensuring a uniform heat load for disposing of spent fuel so as not to compromise the integrity of the mined repository as rock properties do not do well with non-uniform temperature gradients. Although part of the concern for a uniform heat load for a mined repository was for maintaining rock stability during operations for a mined opening, multiple reactors that could be at different operating and temperature conditions could have a significant effect on rock properties (mechanical and chemical) in the case of reactors in deep boreholes that could impact operations and subsequent disposal safety.
2.1 The DB-PWR concept leverages geology and depth, not only for pressure, containment, and security, but also for the ultimate heat sink, the host rock of the formation. There is an emergency core cooling system (ECCS) in the mile of water in the borehole that sits above the reactor. There is added safety from the fact that there is no ready supply of gas to displace the reactor water. If it should boil, and the pressure from the mile of water is maintained, then the density of the steam produced is sufficiently high (about 160 atmospheres) to provide high heat removal to the surrounding rock.
Ø There seems to be a strong belief that the geologic formation will provide a great heat sink and will simply conduct the heat away quickly. The white paper references journal papers but there is very little discussion on this topic in the white paper. Once again, heat load was a very significant factor at Yucca Mountain and the geology at Yucca acted like a blanket and while some heat was conducted away, the geology was more like a blanket and repository was expected to continue to heat up and the facility was highly ventilated to remove heat and keep temperatures reasonable.
Again, a very different situation that the borehole reactor but rock is rock, and the reactor will be acting at much higher heat loads than spent fuel that has already cooled in the pool prior to disposal.
Ø Heat conduction in a geologic formation may not be as significant as it seems to be implied by the report and certainly for multiple reactors. The staff would like to see the technical basis for this assertion and including how conduction will change with time (i.e., over the lifetime of the reactor) and the impact on when multiple reactors are operating.
2.1 The DB-PWR concept is that the reactor will be stored in place as the initial waste heat is dissipated to the host rock. When that has happened, there are two choices:
- It can be stored in that mile deep location until a disposal method is chosen.
- It can be lowered into a storage region that had been pre-drilled prior to the original emplacement of the reactor. The secondary loop can be cut or otherwise detached above the heat exchanger and the pipes removed. The reactor and steam generator can be lowered into the storage area and covered for permanent disposal.
Ø There is no basis provided for what would be done to get regulatory approval for storage and disposal of the reactor in a deep borehole. The NRC would need to consider rulemaking and/or exemptions which would be a major effort.
3 White Paper Section Observation/comment 2.3 Defense in depth: there are about 10 billion tons of rock in the 45-degree cone above the nuclear reactor. This natural containment environment provides a radiation barrier and an impediment for radioactive material to reach the public.
Ø For a completely intact formation would appear reasonable, but for the borehole concept and especially for multiple boreholes, the boreholes do create a breach in this barrier of 10 billion tons of rocks that has been compromised, in part, due to the boreholes and of course there will be heterogeneities in most if not all rock formations.
2.3 The ability to ship a prepackaged reactor to a site where boreholes can be drilled within days with emplacement and operation of the reactor within weeks of delivery.
Ø The basis for this statement is not clear. Based on experience with Yucca Mountain, investigations that included excavations at depth to evaluate the geologic conditions took a significant amount of time - - well beyond the days for drilling and weeks for emplacement and operation stated above.
2.4.5 For these reasons, in the DB-PWR, the reactor pressure vessel is termed simply the reactor vessel. Its walls need only be thick enough to provide strength to withstand use and surface handling impacts.
Ø If the reactor is left in place for storage and/or disposal there would need to be an understanding of how this would be impacted for use in storage and/or disposal.
2.4.6 The basic conclusion of these papers is that deep borehole geology offers an exceptional isolation of radioactive isotopes from the human biosphere. The dominant pathways to the surface are diffusion through the rock, advection through the rock and rock fissures, advection up the cemented access borehole after the cement has crumbled, and advection up earthquake faults. The studies showed that advection through a mile of even porous rock took hundreds of thousands to millions of years. An exception might be a site that has a strong pre-existing vertical advective flow; however, any potential site can be studied using natural radioisotopes to determine if long term depth-to-surface flow exists and to measure its velocity and thence deduce safety. A result from these studies is proof of the long-term safety offered even in the presence of earthquake faults, old or new.
Ø Papers have been published by the promoters of deep borehole disposal of radioactive waste, however, it is worth noting that currently no countries are pursuing, in a significant manner, deep borehole disposal of spent fuel and no regulatory agency has published any papers promoting the concept for disposal of spent fuel.
Borehole disposal of spent fuel may be promising but much work will be needed to demonstrate the viability of this concept for spent fuel - certainly the current literature has promotional paper studies that do not represent proof of long-term safety of this concept.
2.4.7 Additional conceptual safety derives from the fact that if the core were to melt though some unexpected mechanism, it is already a mile underground.
Ø The basis for this statement is not clear. It would likely require site-specific analyses to confirm this statement.
3.1 If a site (location and depth) is drilled, and study of the isotopic geology indicates that the vertical migration velocity could lead to unsafe conditions for the public, then that site will not be used for a DB-PWR.
Ø Isotopic geology is only one factor in determining whether this design "could lead to unsafe conditions for the public".
3.2 Faulting
Existing or new earthquake faults do not create fast-paths for radioisotopes to the surface. This has been shown in several peer-reviewed publications, written in
4 White Paper Section Observation/comment support of waste disposal programs but equally applicable here.
Ø This is a site-specific concern and cannot be addressed generically. The impact of a fault will very much depend on site specific conditions and requires some detailed characterization.
3.7 The primary containment for the DB-PWR comes from the mile depth, with only a 30-inch borehole connecting the reactor to the surface. Leakage through the rock has been determined through a series of peer-reviewed scientific papers to be negligible, and so the only issue is whether transport up the borehole is a possible pathway for radioactivity to reach the surface.
Ø Reference to peer-reviewed papers seem to be the primary basis for proof of concept. The NRC staff is not aware of deep boreholes being used for this concept -
peer reviewed papers by individuals/groups that are promotional of the concept are rarely sufficient for regulatory approval. An important question for this concept is what information will be collected and what analyses will be performed to demonstrate the performance of the geologic component of this concept at a site prior to the lowering of the reactor in the borehole.
3.7 Most of the radioisotopes in the spent fuel are not soluble but still might be carried upward by convection. The primary concern would be gases and soluble isotopes such as iodine and chlorine. The casing water is expected to contain these isotopes in dissolved form even if they make it to the upper parts of the reactor borehole.
Ø This statement may oversimplify waste disposal. There are a number of radionuclides in spent fuel that may not be as soluble as iodine but are much more significant for evaluating the safety of disposal. In short, disposal is being done for a host of radionuclides that may not be as soluble as iodine.
3.12 The value of doing this procedure needs to be weighed against the possible accidents that could occur if the reactor with its waste is brought to the surface.
Under some scenarios, with proper licensing, the spent fuel in the reactor is left underground for disposal in situ. In those scenarios there is never any spent fuel near or above the Earths surface, since the unburned fuel is contact safe (can be approached and handled without radiation danger) and if disposed at depth the nuclear waste is never closer than a mile from humanity.
Ø Seems to convey an overly simplified view that 'deep' is all that is needed for safety.
4.2 A second alternative would be to store the reactor with its spent fuel at depth. In this alternative, the borehole serves that role that a dry cask serves for a surface or near-surface reactor.
A third alternative is to leave the reactor in-place, but to sever the secondary loop pipes (but not the cables) just above the steam generator. The primary loop sampling tube would be closed and then cut above the closed section. It might be instead desirable to leave that loop in place to allow sampling of the water in the spent fuel assembly. A new reactor can then be lowered and operated above the previous one.
In this alternative, the lower reactor can be considered to be in storage or in the first stage of disposal.
Ø This seems to assume that the borehole can readily accommodate disposal but much work would be needed to approve disposal. It would appear there is an expectation that one could make a decision about disposal after the reactor has been operating - that is a not a regulatory pathway.
General It is advisable to interact early with the NRC prior to submittal to identify any exemptions from Part 52 that are planned. No such exemptions were directly stated
5 White Paper Section Observation/comment in the white paper, so no specific feedback can be provided at this time.
2.4.2 The 2x2 core as described will have a lot of neutron leakage and a very uneven burn.
This will likely result in significant Fq values which might exceed typical tech spec limiting condition of operations. The safety analyses need to address these limiting conditions unless sufficient justification is provided.
3.2 Fuel assembly integrity and the capability to shut down the core is a significant part of seismic analyses. The staff guidance is provided in SRP Section 4.2, Appendix A.
In general, a typical approach is to show that fuel assemblies are not plastically deformed due to externally applied forces. If Deep Fission desires to allow for some amount of plastic deformation, then the capability to accurately predict and analyze the conditions must be demonstrated.
2.4.2 If a neutron reflector is used, be sure to include this in the design description and safety analyses. It will affect the seismic analyses in addition to the core operation and response analyses.
2.4.5 Material compatibility of the reactor vessel with the environment (both during operation and during the stated potential storage term) will require significant review.
The stated brine condition of surrounding host rock can pose significant challenge to material performance.
2.4.2 Depending on the final reactor design, significant neutron leakage could reach the surrounding rock. In this scenario, the potential for activation of surrounding materials (including ground water with dissolved minerals/impurities) will need to be addressed.
3 How many ways will there be to shut the reactor down? GDC 26 requires there to be two independent systems of different design principles. Rod Cluster Control Assemblies (RCCA) were discussed and there appears to be a system for controlling boron concentration, but it was unclear of the boration system was capable of shutting down the reactor.
3 How many RCCAs are planned? GDC 27 requires there to be sufficient capacity to control reactivity changes for postulated accidents with consideration of a stuck rod.
General Although the stated fuel design appears to be a standard 17x17 PWR design, it is not clear from the information provided if it will be operated within the bounds of the fuel performance codes (and safety analysis codes) which have been previously approved. Any future licensing applications should address applicability of any codes/methods to the reactor conditions.
3 Since the DB-PWR is a LWR design, it is expected that the majority of the anticipated operational occurrences and postulated accidents presented in NUREG-0800 would be applicable. The design is significantly different though and Deep Fission might conclude that some events are not credible and should not be considered. In these cases, justification should be provided in a future licensing application explaining why they are not considered. Additionally, Deep Fission should consider the design and determine if new accident conditions are possible which were not considered in NUREG-0800.
6 White Paper Section Observation/comment
3.2 Faulting
Existing or new earthquake faults do not create fast-paths for radioisotopes to the surface. This has been shown in several peer-reviewed publications, written in support of waste disposal programs but equally applicable here.
Ø Regulation (10 CFR 100.23) and guidance requires extensive characterization of local and regional earthquake faults, including capturing the uncertainties in the largest magnitude, the annual slip rate, fault geometry and location, and past activity.
In addition, the potential for faulting on as yet unidentified earthquake faults needs to be taken into account. Ground motion models for the region need to be applied to estimate the accelerations from earthquakes and the local response of the soil and rock to upcoming seismic waves needs to be evaluated to develop a site safe shutdown earthquake (SSE).
3.7 The primary containment for the DB-PWR comes from the mile depth, with only a 30-inch borehole connecting the reactor to the surface. Leakage through the rock has been determined through a series of peer-reviewed scientific papers to be negligible, and so the only issue is whether transport up the borehole is a possible pathway for radioactivity to reach the surface.
Ø Siting a facility a mile below the surface will require extensive geophysical and geotechnical field investigations to determine the subsurface properties of the soil and rock across the footprint of the facility. 10 CFR 100.23 requires that foundation stability, the potential for differential settlement, and soil liquefaction be analyzed.
Downhole geophysics will be needed to characterize the shear wave velocity down to the depth of the facility and below to ensure that the dynamic properties of the rock will be adequately characterized.
3.2 "A complete probabilistic risk assessment of the possible accidents occurring in the case of a large earthquake at or near the DB-PWR will be performed." To perform a seismic PRA to evaluate the potential for accidents from earthquake ground motions requires the development of seismic hazard curves from a probabilistic seismic hazard analysis (PSHA). ANS 2.29, "PSHA" provides guidance on the performance of a PSHA for nuclear facilities. PSHAs are developed from combining a seismic source model, a ground motion model, and site response analysis, with each model capturing the uncertainties in data, models, and methods through logic trees.
3.2 "The small parts of the DB-PWR are easily held in place against 1-g or several-g accelerations". Appendix S to 10 CFR Part 50 requires that systems, structures, and components important to safety will remain functional under SSE ground motion loading and the capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposures.