ML030910600

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Slides: Expansion Cooling Modeling Presented by Fenco at Public Meeting
ML030910600
Person / Time
Site: Davis Besse Cleveland Electric icon.png
Issue date: 05/22/2002
From:
- No Known Affiliation
To:
Office of Nuclear Reactor Regulation
References
FOIA/PA-2003-0018
Download: ML030910600 (19)
v • d • e


Text

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Expansion Cooling Modeling Overview <

. I

' Approach is to determine extent of cooling along the leak path as a function of leak rate using

  • Heat required to vaporize all leaking liquid is the leak rate times the enthalpy increase (from primary water at 613 Btu/lb to saturated steam at atmospheric pressure at 1150 Btu/lb)
  • FEA heat transfer model of conduction within head materials with convection boundary conditions from primary coolant and to space above
  • Correlations for two-phase and single-phase heat transfer coefficients along the leak path
  • ~Extent of cooling affects important parameters including
  • Location of concentrated liquid
  • pH
  • FAC susceptibility Technical Assessment of Davis-Besse Degradation - May 22, 2002 35

Expansion Cooling Modeling Magnitude of Heat Sink 1= 111III 11111 jjjlwgmmm 1"Mil A2=

1,000,000.

100,000. -_

I 10,000.- _

O-1,000.-

100.1- -0.

^ 1. M-0.1 '

0.00001 0.0001 0.001 0.01 0.1 1 0.000001 Leak Rate (gpm)

Technical Assessment of Davis-Besse Degradation - May 22, 2002 36

IT Expansion Cooling Modeling

  • YF -32.286 A-ZS-6 .591 PRECISE HIDfl FEyoe z Terhnical A!

ssessment of Davis-Besse Degradation - May 22, 2002 37

Expansion Cooling Modeling Finite Element Analysis of Head Heat Transfer r= 1:11 11 2111 72111 EEEEEEMMEMM=

ANSYS 5.7 APR 2 2002 12:00:37 NO. 3 LPLOT ELEMENTS

- ~

~~-~4 ~ ~. OMINn--.5682-05 QMAX=0 YV -.700326

~ ,..~. ~ ~ZV --. 189006

  • DIST-16.541

,:Y~ *XF -107.147

  • YF -32.286

~ A-ZS-6.591 f '~ rPRECISE HIDDEN

~-j~4 ~- -1.5682-05

.4 * .441E___

gm -. 3152-05 E - .252E-05

__ 1262-05

- .631E-06 0

Uniform Surface Heat Sink Along the Leak Path Assumed Technical Assessment of Davis-Besse Degradation - May 22, 2002 38

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Expansion Cooling Modeling Finite Element Analysis of Head Heat Transfer TEMP SMN -603.37 SMX -604.996 603.37

- 603.551 Y

Z_'L.V - 603.731

603.912 ME3. 604.093

-- 604.273

-71 604.454

,- 604.635 604.815

- 604.996 Example Calculation for Low Leak Rate (18.6 Btulh Heat Sink:

complete vaporization of 7x10 5 gpm leak)

Technical Assessment of Davis-Besse Degradation - May 22, 2002 39

6> 0 Expansion Cooling Modeling Finite Element Analysis of Head Heat Transfer Iz=_=

rI11-1 I ,7"TMOI' III TEMP SMN =514.122 SMX -604.939

_ 514.122 Y

~%-z _ 524.212 534.303

___ 544.394 Km 55448

-' 564576

=- 574.667 EJ 584.758 594.849

- 604.939 Example Calculation for Moderate Leak Rate (1860 Btulh Heat Sink:

complete vaporization of 0.007 gpm leak)

Technical Assessment of Davis-lBcsse Degradation - May 22, 2002 40

Itl(T C)

. Expansion Cooling Modeling Finite Element Analysis of Head Heat Transfer 650 A45 Deg alf Asre (h-600)

Average Metal Surface Temperature 045 Deg HalrArc(h-110) 600 Along the Leak Path A 22 5 Deg Hair Arc (h-600)

  • 225 Deg Half Am (h- 110)

I-. 550 0 500 T - .0 02537Q + 604.55678

.40 Sink irposed on total 90° arc surface 450 2

,hon inside head - 600 Btu/h.fl -°F 0

.4 a- 400

'I

a. T - -0 02670Q + 604 55110 2 I \Sink imposed on total 90° arc surface 1, 2 h on inside head - 110Btu/h-fl -TF 350 T = -0 03505Q + 604.54874 04 Sink imposed on total 45° arc surface 2

1.4 300 h on inside head - 600 Btu/h-fl -°F V4, T - -003647Q + 604 39390 / \ \\

Sink imposed on total 45' arc surface 250 on inside head - 110 Btu/h-f2°F 0 2,00 4,0\,0\,00 1,0 200 400 1, 200 0 2,000 4,0w0 6,0w0 8,000 lo,ooo 12,000 14,000 16,00o 5SDIO Magnitude of Heat Sink, Q (Btulhr) 1

¶'"?echnical Assessment of Davis-Besse Degradation - May 22, 2002 41

Volume of Boric Acid Deposits on the Vessel Head Methodology

>' Integrate the leaking boron mass over the fuel cycle

> Calculate the volume of leaked boron based on the density of boric acid (H3BO3 ) or boric oxide (B2 03 ) crystals, conservatively assuming no porosity

> The fraction of precipitated boron compounds that deposits on the head adjacent to the leaking nozzle may be affected by

  • Droplet entrainment into the steam flow

Technical Assessment of Davis-Besse Degradation - May 22, 2002 48

Volume of Boric Acid Deposits on the Vessel Head

. Example Integration of Boron Mass ...

NWENNNM--

.mm INUM-_

25,000

  • M 20,000 x

._O 15,000 cl 4._

UrA 10,000 t0 0

0 5,000 0

0 1 2 3 4 5 6 EFPYs After Start of First Cycle Technical Assessment of Davis-Besse Degradation - May 22, 2002 49

-> Boric acid solutions and dry crystals

  • The end results depend upon the rate of concentration and drying

- If drying is fast, boric acid powder will result

- If drying is slow, a single irregularly shaped mass is likely

> Molten boric acid /

  • When heated above 340-3650 F, solid boric acid melts to form a highly viscous liquid that will fuse into a single mass and flow under the influence of gravity
  • Molten boric acid can contain 8-14% water by weight and is known to be corrosive

. > Solid boric oxide I

  • Above 302'F boric acid is subject to a dehydration reaction to form boric oxide
  • The resultant crystalline mass is an anhydrous, white, opaque, non-glasslike, stony solid

> Molten boric oxide >

  • Above 6170 F boric oxide begins to soften and at about 8420 F becomes a highly viscous liquid Technical Assessment of Davis-Besse Degradation - May 22, 2002 50

I)  !-~

C)

Boric Acid Morphology and Properties Key Temperature Behavior .

100%

0 80%

60%

-.0_

¢ 40%

Po 20%

0%

0 100 200 300 400 500 600 Temperature (0F)

Technical Assessment of Davis-Besse Degradation - May 22, 2002 51

Boric Acid Morphology and Properties Partial Vapor Pressure 11

__, r&UawISEm7_M11"

_ 1..

250 200 - Calculated Using Raoult's Law u' 150 C 100 ALm 50 inn b Ann 4A0n 5s0 600 700 800 900 Technical Assessment of Davis-Besse Degradation - May 22, 2002 52

e' .- I 0 Boric Acid Morphology and Properties General pH Effects without Large Local Cooling NUMImm-

> For low concentration factors, the solution becomes slightly alkaline, having a small effect on crack growth rates

> For high concentration factors, the solution becomes acidic with a high-temperature pH of 4.5 according to MULTEQ calculations

> The initial high ratio of crevice surface area to volume may allow some buffering by the iron in the head material

> Precipitation of complex lithium and boron compounds occurs and tends to limit pH swings Technical Assessment of Davis-Besse Degradation - May 22, 2002 53

'-N MULTEQ Modeling Three Main Flow Models Available Step 1: Equilibrium Calculated Using Step 2: Vapor and/or Solids Removed Equilibrium Vapor Constant Liquid Phase Flow Out Variable Volume Water Massl Mass Solution ~ olid Phases, S~i;;/ US Rem ain Flow In Water Mass Flow In (Solution)

Equals Water Mass Flow Out (Vapor)

Static Static with Removal Flowing Technical Assessment of Davis-Besse Degradation - May 22, 2002 54

0, MULTEQ Modeling

^.Available Control Volumes IN__._ I a

Q Only Vapor Only Vapor Flow Out Flow Out 0 Control Mass at Higher Control Concentration Factor Volume with 0 Control Constant G Volume with Liquid Mass Constant 0o1s Liquid ZLP Mass Only Solution I Control Mass at Lower Concentration Factor Flow In I IPI Only Solution Flow In

/V Technical Assessment of Davis-Besse Degradation - May 22, 2002 55

6Ž C)

Example MULTEQ Calculation pH in a Flowing System at 10000 MmJagaikjag 7 0.08 0.07 6

L 0.06 5

0.05 X I

4 004 0:

3 0.03 S 2

0.02 I 0.01 0 !- _4 0 1.E+00 I.E+0I I.E+02 I.E+03 I.E+04 I.E1+05 I.E+06 Concentration Factor Technical Assessment of Davis-Besse Degradation - May 22, 2002 56

(T) I

Molten Boric Acid OrthoboricAcid-H3B03 MetaboricAcid-HBO2 Boric Oxide B203

> Corrosion in molten boric acid largely unstudied

> Degradation:

  • Melting point above the degradation point 0

- Orthoboric acid: melts at 170.9 0C (340TF); degrades to metaboric acid at 169.60 C (337TF)

Metaboric acid: melts at 23600 (457 F); degrades to boric oxide at 23500 (455 F) 0

  • Degradation reaction is slow
  • Effect of degradation products on corrosion largely unknown

- (degradation probably lower in boric oxide, B203, than in either acid)

  • Degradation products highly hygroscopic

- Analysis of deposits not likely to indicate their at-temperature composition

' Solubility issues largely unstudied

  • Miscibility limits unknown
  • For pH calculations, molten boric acid could be an additional precipitate
  • Degradation products not included in MULTEQ Degradation - May 22, 2002 57 Technical Assessment of Davis-Besse

r -N ( I O

Molten Boric Acid Molten Salt Corrosion

____al.k.1 .Imfa

> Molten salt corrosion is electrochemically very similar to aqueous corrosion, depending on a reaction couple:

  • Fe 4 Fe 2 + anodic reaction
  • 02 - OH- or H+ 4 H2 cathodic reaction
  • Additional cathodic reactions unlikely in molten boric acid
  • Typical molten salt corrosion occurs through de-passivation

- Not relevant since LAS and CS are not passive in acidic media

. > Acceleration possible due to high conductivity of molten salts

  • Unlikely to lead to a qualitative difference relative to highly concentrated solutions Technical Assessment of Davis-Besse Degradation - May 22, 2002 58

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Molten Boric Acid Issues Molten Salt Corrosion (continued)

>- Solubility of corrosion products likely to be less in molten boric acid than in water

  • Leads to lower corrosion rates

>- Molten boric acid corrosion likely to be significantly slower than corrosion in aqueous solution

  • Lower 02 and He concentrations (slower cathodic reactions)
  • Possibly lower conductivity
  • Likely lower corrosion product solubility (slower anodic reactions)

>- Corrosion in molten boric acid is a particular case of corrosion in boric acid solutions, not a separate phenomenon Technical Assessment of Davis-Besse Degradation - May 22, 2002 59

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