ML20014C843

Discusses Improvements to Hydrogen Uptake Modeling in FRAPCON-3

ML20014C843
Person / Time
Issue date:	10/08/1998
From:	Scott H NRC (Affiliation Not Assigned)
To:	Eltawila F NRC (Affiliation Not Assigned)
References
NUDOCS 9810270338
Download: ML20014C843 (8)

Text

1. %g\\

p" UNITED STATES mfg NUCLEAR REGULATORY COMMISSION f

WASHINGTON, D.C. 2056f4001 n% *****/

.'OCT 0 g m3 TO:

Farouk Eltawila, Chief Reactor and Plant Systems Branch FROM:

Harold Scott N'N Reactor and Plant Systems Branch i

SUBJECT:

MODEL STUDY AND CALCULATIONS: IMPROVEMENTS TO HYDROGEN UPTAKE MODELING IN FRAPCON-3 The Zircaloy cladding in PWRs and BWRS is oxidized (corroded) by the hot water. In this process, some of the hydrogen liberated from the breakdown of the water molecule is retained in the Zircaloy under the oxide layer.

The update of FRAPCON-3 did not concentrate on BWR cladding hydrogen pickup in the CHUPTK model. The PWR pickup fraction in that model was adjusted by PNNL from 0.12 to 0.15 to reflect new data for Zircaloy-4. On page 4-235 of the MATPRO volume, the hydrogen pickup fraction for BWR cladding (Zircaloy-2) is set equal to 1.0 for posttransition corrosion, and this value is used in FRAPCON-3. This model was last updated 20 years ago.

In running the sample calculation with BWR conditions, I noted that the code was giving unreasonably high results for the concentration of hydrogen in the Zircaloy-2 cladding. I also noted on page A13.5 of volums 3 (FRAPCON-3 Assessment), that it says "The prediction for the hydrogen uptake, however, should prompt closer evaluation of the BWR hydrogen uptake model,...."

in looking at the CHUPTK coding, I found two input flags, ICM for type of cladding and ICOR for type of reactor core chemistry (actually a crud buildup flag). ICOR is used in the radial temperature calculation to set the temperature drop across the crud. Thus a code user may choose ICOR without respect to PWR or BWR, although there is generally more crud on BWR cladding. Also, in a subroutine called prior to execution of CHUPTK, ICOR is changed to reflect whether water is boiling. Therefore, because of the ambiguity in using the ICOR flag, the code does not always operate as expected.

I looked for old and new data that could be used to update the MATPRO model for hydrogen uptake (pickup) in BWR (Zircaloy-2) cladding (see attached reference list).

I; These data are shown in the attached table. In some cases, I assumed the sample i

thickness in order to calculate the per cent pickup. The hydrogen uptake is currently modeled as a fraction of the cladding corrosion thickness. The data scatter for corrosion and hydrogen pickup for BWRs is such that one cannot discern if the pickup Yi m

N 981027o338 981000 RU

,Z CF SUBJ RES-2A-2 CF

i 2

e i

fraction is a function of corrosion thickness. Looking at the atta:hed figures for pickup vs oxide thickness and vs hydrogen concentration, a new correlation is not obvious for Zircaloy-2 (BWR) as it was for Zircaloy-4 (PWR). Further, the properties of Zircalcy-2 I

rods are more sensitive to ingot chemistry and fabrication history than are rods of Zircaloy-4. The literature suggests a wider variability and higher pickup fraction for Zircaloy-2 than for Zircaioy-4.

\\

One purpose in making this update is to get the code ready for FRAPCON calculations of BWR rods to be supplied to ANL for the LOCA program. The corrosion thickness and hydrogen content will be measured for these rods. The literature shows that hydrogen concentration affects the mechanical properties. Since a simple correlation l

is not apparent, I suggest that ANL look into the data and the modeling.

i it appears that additional variables are needed for model correlation and assessment.

Two important variables for BWRs are normal water chemistry vs hydrogen water i

chemistry, and water vs steam oxidation. In the mean time, I suggest interim code j

changes (see attachment):

1. use only the cladding-type flag (delete use of the crud-formation flag)

2. eliminate transition thickness functionality l

3. set the Zircaloy-2 pickup fraction to 0.35 j

Attachments:

Reference Citations Data Table i

Figures Suggestion for Revis= 1 CHUPTK Subroutine l

DISTRIBUTION: DST Chron, RPSB r/f, EJA j $6af Hscott r/f, H Scott, F3Meyer FEltawila, TLKing DOCUMENT NAME:HYDRGN.WPD I

v. e.ew. py or sus e.e nt, massie m m n c c copy wenn neomm copy we.nomm=

w - wo py chwe.,wany: cm._.new Pon DFFICEf RES/ DST /RPSB E

RPSB BC RPSB IMME[ H Scott S$

ROMeyer/[$ FEltka s

DATE? " 10/ 8 /98'-

10/fi/98 10/ /98 file code RES-2A-2

References ia. FRAPCON-3 (1997) 1b. MATPRO (1998)

2. WAPD-TM-411 (1964) Hillner, " Hydrogen Absorption in Zircaloy...."

3. Dresden report (EPRI TR-108782) (1998)

4. STP-1295 p 435 Grigoriev p 865 Ruhmann (1996)

5. STP-1245 p 62 Elmoselhi p 80 Charquet P 709 Garzarolli (1994)

6. STP-1023 p 222 Rudling (1989) j

7. Portland ANS p 248 (1997) Fukazawa, " Development.... Fuel for BWR"

8. Joumalof NuclMaterials v226 p13 (1995) Choo, "... hydrogen uptake..."

j 9.

Nuci Engr & Design v137 p59 (1992) Massih, "... cladding corrosion..."

i

10. Nuclear Energy v 31 p 65 (1992) Garzarolli, " Waterside corrosion...."

{

11. NISTIR 89-4114 (1989) Fraker, " Corrosion of Zircaloy Spent Fuel...."

I i

l c

Zircaloy-2 Hydrogen Pickup micron oxide ppm hydrogen

% pickup RLw Comments 6

20

( 9)

Dresden EPRIreport 10 40 -50 (12) 15 300 (55) see anomaly 20 400 (56) water rod 20 max 3rd cyc fuelrods 6

32 Portland ANS p247 inAW 10 48 autoclave 30 STP-1295 p 865 annenhng 53 per. /.s 2.6 241 (26)

STP-1295 p 431 723-773 K i

5.9 385 -570 (22) 0.81 mm j

6.6 660 (28) j 11.4 720 (18) 7 -20 STP-1245 p 721 2 cyc exposure i

100 30-40 JNMv226 pl3 400 C Zr-Nb 1

i 2.5 662 68 NE&D p59 autoclave 2.0 582 (80)

STP-1023 p 222 400 C 1.8 363 (60) 200 days mg/dm2 hyd j

0.3 1

42 WAPD-TM-411 Eliner 1964 j

0.8 3

51 680 F l.3 5

53 fitofdata Fig 8 i

l 12 - 18 GEAP-4089 1%2 i.

( ) calculated from oxide thelme== and ppm hydrogen.

Some values of oxide tinche calculated from weight gain divided by aude density' (5.78).

1 i

i 1

Zircaloy - 2 100 100 i

i j

90 90 t

80 80 70 O

70 i

g

~

~

xI j

v a

a 60 60 8

o U

c X

Q O

.9 g

50 o

a 1

50 e

s-G X

CD D

C 9

40 40 j

I O

7' 30 O

30 0

20 O

0 20 10 -

O 10 t

O' O

i 0

5 10 15 20 25 Oxide Thickness (M)

,, oc, s iw;3. i

]_

Zircaloy - 2 4

l 100 joo 90 go 80 80 i

~

70 70 m

I i

3R x

60 60 o

i o

x

.9 1

50 50 u

i s-x cm E

J 40 40 I

a BR v

30 O

30 20 20 10 13 jo

n 0

o 0

100 200 300 400 500 600 700 800 Hydrogen (ppm)

- 3,3.,,3.

L.

l.

i f

a l

1

! ** COMPUTE CORROSION THICKNESS c

call corros (mmm,tcok,qcim,zro21,zro2o,zoxki,delhs,a(lflux+j-1))

l C

a(lzro2b+j-1) = zro2o/0.3048 l

c update cladding hydrogen content.

c chorg = as-fabricated H2 content in cladding (ppm) dcom = dco (j -1) *cintom i

dcim = dei (j -1) *cintom dpm = dp (j -1) *cintom i

l zro2wg = a (lzro2b+j -1) /0.225e-5 avtemp = (a (ltcodi+j -1) +4 59. 67) /1. 8 ichem = 3 i

if (wt.ge. taat) ichem = 1 j

zoxki = zotcon(avtemp) chydai=a (lec1h2 +j -2 )

j c

t

• • COMPUTE HYDROGEN CONCENTRKfION c

call chuptk (chorg,ppmh2o,dpm,iaaha,dcom,deim,1 chem,zro21, l

1. zro2o,avtemp,qcim,zoxki,chydai,chydbi,huptak) 3 C

• • MATPRO SUBROUTINE

! *dsck chuptk subroutine chuptk (chorg,ppmh2o,dp,1cm,dco,dci,1cor,zro2ai,zro2bi, i

j

+tcoi,qci,zoxki,chydai,chydbi,chcone) chuptk calculates average concentration of hydrogen in zircaloy c

e cladding.

c chconc = output average concentration of hydrogen in cladding at end of time step (ppm) l c chydbi = output hydrogen from coolant in cladding at end c

c of time step (ppm) j c

chorg

= input initial hydrogen in cladding (ppm) j c ppmh2o = input initial fuel water content (ppm) l c dp

= input fuel pellet diameter (m) l c icm

= input cladding material flag (icm = 2 for zircaloy 2,

c icm = 4.for zircaloy 4) j c dco

= input cladding outside diameter (m) l c dei

= input cladding inside diameter (m) e icor

- input variable no longer used

[ Revise]

zro2ai = input oxide thickness at start of current time step (m)

' c zro2bi = input oxide thickness at end of current time step (m) c

c tcoi

= input zro2-coolant interface temperature (k) i c qci

= input axial increment heat flux (watt / meter **2) c zoxki

= input zircaloy oxide thermal conductivity (w/(m-k))

chydai = input hydrogen from coolant in cladding at start c

i c of time step (ppm)

{

the equations used in this subroutine are based on data from:

c

e c

Insert D. D. Lanning's references here

! c j c this model-should not be used outside the temperature range j

c 523.15 - 673.15 k (250 - 400 c).

t i

c chuptk coded by d. 1. h2grmen februnry 1977

• c modifisd by d. 1. hegrman juna 1978 6

modified by h. h. scott september 1998

[ Insert]-

if (tcoi.le.366.5) go to.140 e

if (zro2ai.le.0.0) zro2ai = 1.0e-10 tcoic = tcoi+qci*zro2ai/zoxki (Delete]

wtran = 7.7490e-06*exp(-7.90e02/tcoic)

[ Delete]

if (icor.ge.2) go to 100

[ Delete].

c bwr environment (Delete]

i b = 0.12

[ Delete]

if (icm.le.2) b = 0.29

[ Delete]

l go to 120 (Delete]

i c

Zr-4 environment 15% PICKUP

'[ Revise]

100 b = 0.15 i

c Zr-2 environment 35)% PICKUP

[ Insert].

if (icm.le.2) b = (LJHF.3 5

[ Revise]

110 c = 1.0 l

if (icm.le.2) c = 1.0/b

[ Delete]

l c

find hydrogen uptake from coolant during current time step l

d=

(9.0e+05)*dco/(dco**2-dci**2)

{

if (zro2ai.gt.wtran) go to 130 (Delete].

l if (zro2bi.ge.wtran)'go to 120 (Delete]

c all oxidation pretransition

[ Delete]

chupc = d* (b/8) * (zro2bi-zro2ai)

[ Delete]

go to 150 (Delete]

1 c

part~of oxidation pretransition

[ Delete]-

l 120 chupc = d* ( (b/8) * (wtran-zro2ai) + (c*b/8) * (zro2bi-wtran) )

(Delete]

go to 150

[ Delete]

c-cll oxidation post - transition

[ Delete]

1 130 chupe = d* (c*b/8) * (zro2bi-zro2ai) l go to 150 140 chupc = 0.0 e

sum hydrogen from coolant 4

j 150 chydbi = chydai+chupc i

.c sum hydrogen from alloy, fuel noisture and coolant chconc = chorg+0.186 *ppmh2o* ( (dp* *2) / (dco* *2-dci* *2) ) +chydbi return end l

i l

i

,