Overview of Small Modular High Temperature Gas-Cooled Reactor … · 2019. 12. 9. · 250 mSv 100...

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Overview of Small Modular High Temperature Gas-Cooled

Reactor Research at Canadian Nuclear Laboratories

David Hummel

2019 December 9


SMRs in Canadahttp://www.cnl.ca/smr

https://smrroadmap.cahttp://www.cnl.ca/site/media/Parent/CNL_SmModularReactor_Report.pdf

http://www.cnl.ca/smr

https://smrroadmap.ca/

http://www.cnl.ca/site/media/Parent/CNL_SmModularReactor_Report.pdf


Vendors Engaged with the Canadian RegulatorPre-Licensing Vendor Design Review with the CNSC

• GE-Hitachi BWRX-300

• NuScale NuScale

• SMR (Holtec) SMR-160

• Westinghouse eVinci

• GFP/USNC Micro Modular Reactor (MMR-5/10)

• Starcore Nuclear Starcore Module

• U-Battery U-Battery

• X-Energy Xe-100

• Moltex Energy Stable Salt Reactor (SSR)

• Terrestrial Energy Integral Molten Salt Reactor (IMSR)

• Advanced Reactor Concepts ARC-100

• LeadCold SEALER

LWR

MSR

HTGR

LMFR

HPR


Canadian Nuclear Laboratories (CNL)

• Canada’s premier nuclear science and technology organization

• Contracted by federal crown corporation Atomic Energy of Canada Limited (AECL) to operate Chalk River Laboratories (CRL) and Whiteshell Laboratories

• 10-year revitalization of CRL underway

• Science & Technology (S&T) capabilities include:

http://www.cnl.ca

• Advanced Nuclear Fuels & Material Research

• Radiobiology, Radioecology & Dosimetry

• Hydrogen & Hydrogen Isotopes Management

• Nuclear Safety, Security & Risk Management

• Nuclear & Systems Engineering• Nuclear Chemistry Applications

http://www.cnl.ca/


Canadian Nuclear Laboratories (CNL)

“demonstrate the commercial viability of the small modular reactor by 2026.”

“recognized globally as a leader in SMR prototype testing and S&T support”

“be a recognized hub for SMRs, where multiple vendor-supported prototypes are built and tests.”

“in the next 10 years … host a prototype”

Small Modular Reactor Strategic Initiative

- Excerpts from CNL’s 10-Year Integrated Plan Summary (www.cnl.ca/strategy)

http://www.cnl.ca/strategy


• Three respondents completed Phase 1 (pre-qualification):• StarCore Nuclear (14 MWe HTGR)

• Terrestrial Energy (195 MWe MSR)

• U-Battery (4 MWe HTGR)

• One respondent entered Phase 3 (land use / contract negotiations):• Global First Power / Ontario Power

Generation / Ultra Safe Nuclear Corporation (5 MWe HTGR)

• Applied for “License to Prepare Site”

CNL Invitation for SMR Demonstrationshttp://www.cnl.ca/smr

https://www.cnl.ca/en/home/facilities-and-expertise/smr/update-on-cnl-s-smr-invitation-process.aspx

http://www.cnl.ca/smr

https://www.cnl.ca/en/home/facilities-and-expertise/smr/update-on-cnl-s-smr-invitation-process.aspx


• New program that supports collaborative SMR research projects with third-party proponents in Canada

• Applicants required to match funds and in-kind contributions made by CNL

• Four projects selected in first round:• Moltex Canada (MSR)

• Kairos Power (FHR)

• Ultra Safe Nuclear Corporation (HTGR)

• Terrestrial Energy (MSR)

• Next call for CNRI proposals expected early 2020

Canadian Nuclear Research Initiative (CNRI)www.cnl.ca/CNRI

http://www.cnl.ca/CNRI


• Funded by AECL under the auspices of the Federal Nuclear Science & Technology (FNST) program• Federal agency stakeholders

• Supporting policy and regulatory decision making

• Research areas include:• Limiting accident source term and consequence

• Benchmark core neutronics and core flow (CFD) modelling

• Severe accident phenomena identification/ranking

• Air ingress in severe accidents

• Materials (starting 2020)

HTGR Research at CNLPast, Present, and Future


• Objectives:

1. Identify limiting accident scenarios for different types of SMRs

2. Determine limiting accident source terms

3. Perform atmospheric dispersion and dose consequence evaluation, benchmark against previous study with hypothetical CANDU 6 sited at Chalk River

• Radionuclide releases from “limiting accidents” does not align with regulator’s preference for plant-specific source terms derived from PSAs

Source Terms and Dose ConsequencePreliminary Study

Reference: D. Hummel, S. Chouhan, L. Lebel, and A. Morreale, “Radiation Dose Consequences of Postulated Limiting Accidents in Small Modular Reactors to Inform Emergency Planning Zone Size Requirements”, Annals of Nuclear Energy (in press).


Generic HTGR-type SMR

• Helium coolant 4-7 MPa, ≥700°C

• TRISO fuel in cylindrical compacts stacked in graphite blocks

• Core power <50 MWth

• Heavy gas secondary circuit

• Below-grade reactor cavity

• Reactor Cavity Cooling System (RCCS) with air or water natural circulation

• No containment

Basis for Source Term Estimation


Limiting Accident

1. Guillotine break of coaxial coolant inlet pipe, failure to scram, limited core flow due to helium buoyancy

2. Temperature reactivity feedback shuts down reactor, decay heat removal by RCCS

3. Delayed recriticality, damped power oscillations converge to steady core power equal to RCCS heat removal

Depressurized Loss of Forced Circulation

with Failure to Scram and Severe Air Ingress


Limiting Accident (cont.)

4. Penetration of air into core region creates natural circulation flow

5. Graphite oxidation contributes to fuel failure and fission product release

6. Continued graphite oxidation results in collapse of core support structures (not considered)

Depressurized Loss of Forced Circulation

with Failure to Scram and Severe Air Ingress


• Initial radionuclide inventories calculated for 30 MWth core near middle-of-life (based on HTTR)

• Fractional releases determined from literature review and past analysis, release durations imposed in sensitivity study

• CRL site meteorological data

• ADDAM (Atmospheric Dispersion and Dose Analysis Method)• Part of Canadian Industry Standard Toolset and directly based on

Canadian standard N288.2-14

• Gaussian plume model with stochastic meteorological sampling

• Benchmark comparison against CANDU 6 Unmitigated Station BlackOut (USBO) with identical dispersion conditions

Source Terms and Dose ConsequenceMethod Used in Preliminary Study


Source Terms and Dose ConsequenceMethod Used in Preliminary Study

Chalk River Laboratories Site Meteorological Data


Source Terms and Dose ConsequenceResults of Preliminary Study

Reactor TypeMaximum Distance at P90 Dose Level [km]

250 mSv 100 mSv 10 mSv 1 mSv

HTGR (30 MWth) 1.92 3.39 10.71 35.3

CANDU 6 USBO 36.6 44.5 >100 >100

CANDU 6 USBO(30 MWth scaled)

3.5 6.2 25.1 50.3

Dose Results for 72 h Release Duration and 15 m Release Height


Source Terms and Dose ConsequenceResults of Preliminary Study

72 h release duration 36 h release duration

Dose Results for 15 m Release Height


• Smaller radionuclide inventories compared to large plants inherently reduces dose consequences of limiting accidents

• Advanced reactor technologies seemingly reduce dose consequences of limiting accidents

• Substantial justification for smaller EPZ sizes compared to contemporary large plants

Source Terms and Dose ConsequenceConclusions from Preliminary Study


HTGR Severe Accident PIRT

• Preliminary literature reviews show knowledge gaps in severe accident phenomenology that could be addressed with R&D

• PIRT process is a structured method for establishing R&D priorities:

Phenomena Identification and Ranking

1. Define the issue2. Define the specific objectives3. Define the hardware and

scenario4. Compile and review information5. Define the Figure(s) of Merit

(FOM)

6. Identify plausible phenomena7. Rank the importance of

phenomena8. Rank the knowledge level of

phenomena9. Document the PIRT results



• D-LOFC with failure to scram and significant air ingress

• Information from academic literature, past PIRT reports, no HTGR vendor-specific information

• Figures of Merit:

1. Fuel temperature - Phase 1, up to the point of fuel failure or core temperatures up to 1600°C

2. Radioactivity release to the environment - Phase 2, after fuel failure or core temperatures beyond 1600°C

• Phenomena list based on previous PIRT reports (ORNL NGNP, UNSC TRISO, ANL and INL VHTR, AECL CANDU6)

PIRT Execution


HTGR Severe Accident PIRTPhenomena Importance Ranking Scale

Rank Definition

High (H)The phenomenon has a controlling impact on the FOM. Highly accurate prediction of the phenomenon is critical.

Medium (M)The phenomenon has a moderate impact on the FOM. Moderately accurate predictions of the phenomenon are required.

Low (L) The phenomenon has minimal impact on the FOM.

Inactive (I) The phenomenon has insignificant or no impact on the FOM.


HTGR Severe Accident PIRTPhenomena Knowledge Ranking Scale

Rank Definition

4The phenomenon is fully known. Predictions are possible within a small degree of uncertainty.

3The phenomenon is known or at least understood. Predictions are possible within a moderate degree of uncertainty.

2The phenomenon is partially known. Predictions are only possible within large uncertainties.

1There is very limited knowledge of the phenomenon. The level of uncertainty cannot be characterized.

NANot Applicable or Not Assessed. Used if the phenomena has insignificant or no impact on the FOM.

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HTGR Severe Accident PIRTHigh Importance (H), Low Knowledge (≤2) Phenomena

Phenomena Title

Importance Rank

Knowledge Rank

Phase 1 Phase 2 Phase 1 Phase 2

Aerosol growth by condensation I H N/A 2

Fission product chemical speciation L H 2 2

Outlet plenum collapse H H 2 2

Forced-to-natural circulation transition H H 2 2

CO Flame Acceleration (FA) H H 2 2

CO Deflagration-to-Detonation Transition H H 2 2

Gas radiolysis I H N/A 2



• Other phenomena had controlling impacts on FOM but can only be predicted within moderate uncertainties

• Documented in open literature• D. W. Hummel et al., “Results of a Phenomena Identification and Ranking

Table (PIRT) Exercise for a Severe Accident in a Small Modular High Temperature Gas-Cooled Reactor,” CNL Nuclear Review, August 2019 (doi:10.12943/CNR.2019.00006)

• Results have informed Expressions of Interest in the Federal Nuclear Science & Technology program• Investigation into air ingress (forced-to-natural circulation transition)

began 2018 April, experiment under design

Documentation of the PIRT Results

https://doi.org/10.12943/CNR.2019.00006


HTGR Air Ingress ExperimentsOnset of Natural Circulation (ONC)


• Different outlet geometries results in different dominant transport mechanisms and vastly different ONC

HTGR Air Ingress ExperimentsMass Diffusion vs. Density-Driven Stratified Flow

Reference: C. H. Oh and E. S. Kim (2011), “Air-ingress analysis: Part 1. Theoretical approach”, Nuclear Engineering and Design vol. 241 pp. 203-212.

𝐻

𝐻𝑣>8𝜌𝑐𝜌𝐴

𝛾3

1 − 𝛾Eq. (28)


• Intend to perform new experiments in CNL’s LSCF

• 1575 m3, 10 m ceiling

• Previously used for steam-helium-air gas mixing experiments

• Air ingress experiment pre-conceptual design begun April 2018

HTGR Air Ingress ExperimentsLarge Scale Containment Facility (LSCF)


• Measure the delay before initiating natural circulation

• Stainless steel structure

• >1 core block diameter

• >5 m height

• ≥700°C helium/air, atmospheric pressure

• Horizontal or vertical inlet/outlet duct

HTGR Air Ingress ExperimentsDesign Goals


HTGR Air Ingress ExperimentsConceptual Design


HTGR Air Ingress ExperimentsConceptual Design


Conceptual Design

HTGR Air Ingress Experiments


• Conceptual design completed March 2019, detailed engineering design scheduled to be completed March 2020

• Staff visit to United States Department of Energy-funded High Temperature Test Facility (HTTF) scheduled for January 2020 to discuss and potentially coordinate air ingress research

HTGR Air Ingress ExperimentsProgress Update


Thank you. Merci.Questions?

[email protected]

mailto:[email protected]

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Overview of Small Modular High Temperature Gas-Cooled Reactor … · 2019. 12. 9. · 250 mSv 100...

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