Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia

Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department

of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Dry Cask Simulator Experiments for CFD Validation

Sam Durbin, Eric Lindgren, Abdelghani Zigh*, and Jorge Solis*

* Nuclear Regulatory Commission

SAND2017-4330 C

Overview Purpose: Validate assumptions in CFD

calculations for spent fuel cask thermal design analyses

Used to determine steady-state cladding temperatures in dry casks

Needed to evaluate cladding integrity throughout storage cycle

Measure temperature profiles for a wide range of decay power and helium cask pressures

Mimic conditions for above and belowground configurations of vertical, dry cask systems with canisters

Simplified geometry with well-controlled boundary conditions

Provide measure of mass flow rates and convection heat transfer coefficients

Use existing prototypic BWR Incoloy-clad test assembly

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Underground Storage

Source: ww.holtecinternational.com/productsandservices/wasteandfuelmanagement/hi-storm/

Aboveground Storage

Source: www.nrc.gov/reading-rm/doc-collections/fact-sheets/storage-spent-fuel-fs.html

(m)

(m)

Temp. (K)

Project Structure

Boiling Water Reactor Dry Cask Simulator (DCS)

Partnership between USNRC and DOE Equal cost sharing

NRC staff leads technical review

Mutual benefits Thermal-hydraulic data for validation exercises

Complimentary data for High-Burnup Cask Demonstration Project

Includes thermal lance comparisons to peak cladding temperature (PCT)

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Past Validation Efforts Full Scale

Full scale, unconsolidated

Castor-V/21 cast iron/graphite with polyethylene rod shielding

1986: EPRI NP-4887, PNL-5917

21 PWRs

95 Thermocouples (TC’s) total

Unventilated

Sub-atmospheric (air and He) and vacuum

REA 2023 prototype steel-lead-steel cask with glycol water shield

1986: PNL-5777 Vol. 1

52 BWRs

70 TC’s total

Unventilated

Sub-atmospheric (air & He) and vacuum

Full scale, consolidated

VSC-17 ventilated concrete cask

1992: EPRI TR-100305, PNL-7839

17 consolidated PWRs

98 Thermocouples (TC’s) total

Ventilated

Sub-atmospheric (air and He) and vacuum 4

Past Validation Efforts (cont.) Unconsolidated Fuel

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Small scale, single assembly FTT (irradiated, vertical) and SAHTT (electric, vertical & horizontal)

1986 PNL-5571

Single 15x15 PWR

Thermocouples (TC’s)

– FTT: 187 TC’s total

– SAHTT: 98 TC’s total

BC: Controlled cask outer wall temperature

Atmospheric (air & He) and vacuum

Mitsubishi test assembly (electric, vertical & horizontal)

1986 IAEA-SM-286/139P

Single 15x15 PWR

92 TC’s total, all distributed over 4 levels inside tube bundle

BC: Controlled outer wall temperature of fuel tube

Atmospheric (air & He) and vacuum

Not appropriate for elevated helium pressures or belowground configurations

Current Approach

Focus on pressurized canister systems DCS capable of 24 bar internal pressure @ 400 ◦C

Current commercial designs up to ~8 bar

Ventilated designs Aboveground configuration (This presentation)

Belowground configuration

With crosswind conditions

Thermocouple (TC) attachment allows better peak cladding temperature measurement 0.030” diameter sheath

Tip in direct contact with cladding

Provide validation quality data for CFD Complimentary to High-Burnup Cask Demo. Project

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DCS Pressure Vessel Hardware

Scaled components with instrumentation well

Coated with ultra high temperature paint

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Prototypic Assembly Hardware

Most common 99 BWR in US

Prototypic 99 BWR hardware Full length, prototypic 99 BWR

components

Electric heater rods with Incoloycladding

74 fuel rods

8 of these are partial length

Partial length rods 2/3 the length of assembly

2 water rods

7 spacers

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Nose piece anddebris catcher

BWR channel, water tubesand spacers

Upper tie plate

Thermocouple Layout

97 total TC’s internal to assembly

10 TC’s mounted to channel box 7 External wall

24 in. spacing starting at 24 in. level

3 Internal wall

96, 119, and 144 in. levels

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Radial Array24” spacing11 TC’s each level66 TC’s total (details below)

Axial array A16” spacing20 TCs

Axial array A212” spacing – 7 TC’sWater rods inlet and exit – 4 TC’sTotal of 97 TCs

24”

48”

72”

96”

119”

144”

Internal Thermocouples

a b c d e f g h i

Q

R

S

T

U

V

X

Y

Z

24” & 96” levels 48” & 119” levels 72” & 144” levelsa b c d e f g h i

Q

R

S

T

U

V

X

Y

Z

a b c d e f g h i

Q

R

S

T

U

V

X

Y

Z

CYBL Test Facility

Large stainless steel containment Repurposed from earlier

CYLINDRICAL BOILING Testing sponsored by DOE

Excellent general-use engineered barrier for isolation of high-energy tests

3/8 in. stainless steel

17 ft diam. by 28 ft cylindrical workspace

Part of the Nuclear Energy Work Complex (NEWC)

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Aboveground Configuration

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Pressure

Boundary

BWR Dry Cask Simulator (DCS) system capabilities

Power: 0.1 – 15 kW

Pressure vessel: 3E-3 – 24 bar

Vessel temperatures up to 400 C

~200 thermocouples throughout system

Test conditions presented here

Power: 0.5 – 5 kW

Pressure: 3E-3 – 8 bar

Air velocity measurements at inlets

Calculate external mass flow rate

Internal Dimensional Analyses

Internal flow and convection near prototypic Prototypic geometry for fuel and basket

Downcomer scaling insensitive to wide range of decay heats External cooling flows matched using

elevated decay heat

Downcomer dimensionless groups

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Parameter

AbovegroundDCS

Low PowerDCS

High PowerCask

Power (kW) 0.5 5.0 36.9

ReDown 170 190 250

RaH* 3.1E+11 5.9E+11 4.6E+11

NuH 200 230 200

Downcomer

“Canister”ChannelBox

“Basket”

External Dimensional Analyses

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External

cooling

flow path

Parameter

Aboveground

DCSLow Power

DCSHigh Power

Cask

Power (kW) 0.5 5.0 36.9

ReEx 3,700 7,100 5,700

RaDH* 2.7E+08 2.7E+09 2.3E+08

(DH, Cooling / HPV) × RaDH* 1.1E+07 1.1E+08 4.8E+06

NuDH 16 26 14

External cooling flows evaluated against prototypic External dimensionless groups

1 in.1 cm

Steady State Values vs. Decay Heat

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PCT and air flow as simulated decay heat

Significant increase in PCT for P = 3E-3 bar Due to air in “canister”

instead of helium

Transient Data

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Power = 2.5 kW

Internal pressure = 1.0 bar

Steady state values PCT = 570 K

Q = 673 slpm

CFD Modeling

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Computational fluid dynamics modeling

ANSYS Fluent 16.1

Discrete Ordinates (DO) for radiation heat transfer

Semi-Implicit Method for Pressure-Linked Equations (SIMPLE)

Link for momentum and continuity equations

3-D mesh with symmetric mid-plane

Fuel represented as porous media

Internal laminar flow

External Low-Re k-ε

Modeling performed consistent with best practices and best available data representing fuel properties

NUREG-2152, “CFD Best Practice Guidelines for Dry Cask Applications”

NUREG-2208, “Validation of CFD Methods Using Prototypic Light Water Reactor Spent Fuel Assembly Thermal-Hydraulic Data”

Steady State Comparisons

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Press. (bar) Quantity

Power (kW)0.5 1 2.5 5

Test CFD Diff.Error (%)

Test CFD Diff.Error (%)

Test CFD Diff.Error (%)

Test CFD Diff.Error (%)

1.0PCT (K) 376 378 2 0.5 434 438 4 0.9 570 569 -1 -0.2 715 717 2 0.3Q (slpm) 335 326 -9 -2.7 448 449 1 0.2 673 669 -4 -0.6 874 877 3 0.3

4.5PCT (K) 367 368 1 0.3 426 423 -3 -0.7 545 549 4 0.7 689 698 9 1.3Q (slpm) 306 293 -13 -4.2 415 396 -19 -4.6 603 601 -2 -0.3 830 826 -4 -0.5

8.0PCT (K) 359 362 3 0.8 410 408 -2 -0.5 521 523 2 0.4 659 663 4 0.6Q (slpm) 280 277 -3 -1.1 392 387 -5 -1.3 593 579 -14 -2.4 793 773 -20 -2.5

Agreement within experimental uncertainty for majority of results Only one instance of difference beyond estimated uncertainty

Further analysis shown next

Graphical Steady State Comparisons

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PCT average difference of 2 K across all conditions 95% exp. uncertainty

+/- 1% reading in Kelvin

(UPCT, max = 7 K)

Max. observed difference = 9 K

(5 kW and 4.5 bar)

Air flow rate average difference of -8 slpm for all conditions 95% exp. uncertainty of UQ = 35 slpm

Max. observed difference = -20 slpm

(5 kW and 8.0 bar)

Summary

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Dry cask simulator (DCS) testing complete for aboveground configuration

12 data sets available for pressurized canister conditions

3 data sets available for sub-atmospheric

Comparisons with CFD simulations show favorable agreement

Within experimental uncertainty for nearly all cases

Additional steady state comparisons for basket, “canister”, and “overpack” also show good agreement

EXTRA SLIDES

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Custom TC Lance

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Compliments the TC lance in the Cask Demo Project Same fabricator (AREVA)

“Same” materials and fabrication process

– Closure method for SNL TC lance significantly different

– Sealed using brazing method with water-based flux

TC elevations match BWR assembly TCs Provides direct comparison

between lance TCs and clad TCs

TC Lance

Thermocouple (TC) Lance Anomalies

“Glitches” observed in SNL TC lance Sharp changes in dT/dt

Coincidentally occurring near ~100 oC?

Generally recovered by end of Steady State

Discussions with vendor revealed unique closure for SNL TC lance Hypothesis developed that TC

chamber contaminated with water

Closure formed by brazing with water-based flux

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Proposed Solution: Vent TC Lance

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Pierce lance collar below brazed seal

Introduce vent path for any trapped water

Breach created using rotary tool with grinding wheel

Performed May 2nd, 2017

Well?

Test conditions repeated for 2500 W, 1 bar He

Significant difference in response

Success?

Supports water contamination hypothesis Good news for Cask Demo

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Belowground Configuration

Modification to aboveground ventilation configuration

Additional annular flow path

Currently testing Inlet and outlet based on prototypic

configuration

Scaling analysis completed

Favorable comparisons Modified, channel Rayleigh

number (Ra*)

Reynolds (Re) number

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Cross-Wind Testing

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Wind Machine Output

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Velocity (m/s)

CFD Cross-Wind Streamlines

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Effect of Wind Speed on External Air Flow

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