ML20072T730

Resubmits Summary Description of Rev 1 to Calculations Re Precipitation in Standby Liquid Control Sys Discharge Piping,In Response to NRC Request at 910212 Meeting

ML20072T730
Person / Time
Site:	Grand Gulf
Issue date:	04/10/1991
From:	Cottle W ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GNRO-91-00061, GNRO-91-61, NUDOCS 9104180235
Download: ML20072T730 (13)

Text

-_

g=g Entergy F"'"a *"auaaa 'ac-Operations v April 10, 1991 U.S. Nuclear Regulatory Comminnion Mail Station P1-137 Washington, D.C. 20555 Attention: Document Control Desk Sl'IU TCT : Grand Gul f Nuc ient Stntinn Unit 1 Docket No. 50-416 License No NPP-29 Summary of Calculat ions Rega rding Precipit at ion in t he ShCS Discharge Piping (Revision 1)

GNRG: 91/00061 Gentlemnn:

On Pobruary 12, 1991 f.ntergy Operations, Inc., Grand Gulf Nuclent Station (GGNS) mot with members of the NRC Staf f to discuss the results of calculations performed by GGNS nt the request of the Staf f to confirm that excesniin sodium pent aborate solut ion precipitat ion in t he Standby Liquid Control System (SI.CS) discharge piping does not occur. As a follow-up to that moet ing, the Staf f requested that GGNS submit a summary descript lou of t he calculnt f onal methodology and result s. That summnry was submitted on March 4, 1991.

Subsnquently, as discussed with your Staf f, an er ror was discovered in the calculations. We have . initiated appropriate quality deficiency actionn to address the nrror. While the error did not af fect our conclusions it did require us to modify somewhat our methoslology.

Thereforo, we are resubmitt.ing a summary description of the calculat ional inthodology and results.

i G9102264/SNI.ICPhR - 1 j- [;[

{ (g

- 9104180235 910410 PDR P

ADOCK 05000416 \

_ _ _ _ _ _ _ _ _ _ P D L _ ____ ___ ___ ____ -_------ ----

. April 10, 1991 GNRO-91/00061 Page 2 of 3 We would appreciate your timely review and closure of this issue.

Yours truly, csO CCarx-21.

WTC/I'RS/ m t e attachment: Standby 1.iquid Cont rol System Calculation Summar y (Revision 1) c r. ' Mr. D. C. Ilint a (w/n)

Mr. J. Mathis (w/n)

M r . R . 14 McGehee (w/a)

Mr. N. S. Reynolds (w/n)

Mt. 11. L. Thomas (w/o)

Mr. T. W. Titus (w/n)

Mr. Stewart D.17.bnet er (w/n)

Regional Administrator U.S. Nuclear Regulatory Commission Region 11 101 Marietta St., N.W., Sutto 2900 Atlanta, Georgia 30323 Mr. I., L. Kintner. Project Manager (w/a)

Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 11D21 Washington, D.C. 20555 G9102264/SNh1CI'I.R - 2

Attachment to GNRO ' ',1 4

)

1 l

1 STANDBY LIQUID CONTR01. SYSTEM CALCUI.ATION

SUMMARY

(REY.ISION 1) ,

t i

L t

i 09102264/SNLICFLR - 4

, *r--- r, n .- ._ -.%-,__ _ _ _ ~.. ..w. ....rv......,__-.-_.,-.--m -,..--.-.....-_..m_ -

s,.. . . . -. - - . ,,,,%,.. < - , .. . - , -

Attachment to CNRO 91/00061 STANDDY LIQUID CONTROL SYSTCH CALCULATION

SUMMARY

I. .Qalculationjurpose The current GONS Technical Speciffentions (TS) allow the solution in the Standby 1.1 quid Control System (SLCS) to have n sodium pontaborate concentration of 28.5 weight percent (w/c) when at n solut ion t emperat ure of 130*F. The issue of whether such a solution is enpable of being injected into the renctor vessel without excessive nodium pentnborate precipitation occurring has been raised by the NRC.

To assist in resolving this innue, a calculation was performed to determine how the temperature of the SLCS process flow (start Ing from the SLCS pump discharge) changes due to ambient tempetnture condit ions (in the vicinity of the SLCS discharge piping) when being inject ed into the s enctor vessel. The resulting sodium pentaborate precipitation in calculated and totalled. Figure I contains a schemntic of the St.CS piping layout.

The calculation consisted of two parts:

1) Calculation of the St.CS process flow temperature change under steady stato conditions (i.e., SICS discharge piping warmed to SLCF process flow temperature).

2) Cniculat ion of the SLCS process flow temperature immediately af ter SLCS initiation (i.e. , SLCS discharge piping in t he containment is initially at 70'F and the drywell portion of piping is initially at 110'F) until process flow temperature exceeds anturation temperature of the SLCS solution.

The results of the calculation n' used to demonstrate analyt ically that excessive precipitation does not occur.

II. _ Scoping _Qa_lcula t.f on Before reviewing the cniculations discussed above, it is instructive to take n look at a simple (and highly conservat(ve) calculation which should serve to place an upper bound on the amount of precipitation which could occur in the GGNS SLCS design.

While we do not credit this calculation in resolving the question posed by Lle 3 NRC, it is nonetheless useful in placing the precipitat.lon issue in perspectivo and serving as a check on calculation results.

The scoping eniculation assumes that the SLCS discharge piping (including drywell piping) is init.inlly at 70'F. The SLCS solution is discharged at 130'r and 28.5 w/o sodium pentaborate.

09102264/SNLICFLR - 5 i.

Attachment to GNRO-91/00061 I

We nasume that the dischargo piping must be heated uniformly to approximately 130'r (the steady state temperature reached during St.CS injection). Until the piping reaches 130'r all 81.05 solution )

passing through the piping is assumed to transfer heat. to the

-piping represented by n final solution temperature of 70*P (1.c. , 4 cach lbm of St.CS solution cools down f rom 130'r to 70'P regardless I of the actual piping temperature). The total precipitato is then l calculated based on a SLCS solution temperature of 70'F. I First , we calculate the total amount of heat necessary to raise the St.CS dischatge piping f rom 70'r to 130'F.

The ShCS dischargo piping mast I ist pjameter Leng(h hbmLft Total 2" 4.68' 5.02 23.49 1.5" 166.09' 3.63 602.91 T' 3.25' 10.25 _3h31 659.71 lbm The necessary heat transfer ist i

Q = Mc A7 P l i- where H- a mass of dischargo piping (Ibm) c = stainless steel specific heat'(DTU/lbm'r) '

AT

• finnt - initial pipe temperature ('F)

-* ;(659.71 lbm) (O.12 DTU/1bm*P) (130 - 70'F) ,

= 4750 DTU e

I The HPCS dischargo piping is 1genrod due to the low piping surface contact arca to volume ratio for the ShCS solution and the.

i- resultant low hont transfer.

i 09102264/SNhlCPLR - 6

Attachment to CNRO-91/00061 The heat lost per lbm of SLCS solution is given by:

Q/M = cp AT j

where: H = 1 lbm of SLCS solution c = SLCS solution spec] fic heat (bTV/lbm*F)

AT = Initial - final SLCS solution temperaturo ('F)

=

(0.82488 DTU/lbm*F) (130 - 70*F) 1 a 49.49 BTU /lbm '

l Therefore, t % amount of SLCS solution required to raisn the 1 discharge pli eig temperature to 130'T is t i 1

4750 HTU/49.49 BTU /lbm = 96 lbm At 70*F the sodium pontaborato solution concentration has been roduend to 16 w/o comparnd to the initial concentration of

28.5 w/o. Thn total amount of precipitation 1s t

=

Hp (28.S w/o - 16 w/o) (96 lbm)/100

= 12.0 lbm As will be discussed in more detail lator, this is clearly a negligible quantity of precipitation.

II1. GoneM1.Assump_t1ons Alt. hough the scoping calculation result may be conclusivo, tien and temperature dependent calculations were parlormed.

The following are the major assumptions used in both the steady stato and transient: parts of the calculation:

1) The temperature of the SLCS sodium pentaborato solution (process flow) is assumed to bo 130'F at the SLCS pump dischargo.

2) The SLCS flow rato for two pumps is assumed to ho 82.4 gpm.

3) No credit is taken for insulation on the SLCS discharge piping.

4) The ambient temperaturo in the containment is assumed to bo 70*F (i.e., the SLCS discharge piping in the containment is initially at 70'F).

5) The ambinnt temperature in the drywell is assumed to be 110'F (i.e. , the SLCS dischargo piping in the drywell is initially at 110'F).

G9102264/SNLICFLR =7

Attachment to GNRO-91/00061

6) The initial bodium pentaborate concentration of the process flow is assumed to be 28.5 w/o.

7) The amount of sodium pentaborate precipitation is assumed to vary linearly between ll4'r (28.5 w/o) and 70'F (16 w/o). In other words, a lbm of SLCS solution that is cooled to 70'F will precipitate 0.125 lbs. (0.285 lbs. - 0.16 lbs.) of sodium pentaborate.

8) No credit is taken for redissolving precipitate as the SLCS solutton temperature increases in the drywell.

IV. Steady _ Stat.o Condi. tion Calculation.Hethodology The process flow temperature change due to ambient temperatures was calculated by first determining the total heat transfer rate by free convection and radiation. Then dividing the total heat trannfer rate by the process fluid mass flow rate to obtain the enthalpy change per pound mass (thm). The temperature change is then calculated by dividing the enthalpy change by the specific heat of the SLCS sclution. These calculations were performed separately for each of ten pipe sections of the system piping model.

V. SteadLState Calc.ulat_fon_Results Once the piping reaches steady state tempointures, the total temperature drop from when the solution leaves the pump discharge until it reaches the reactor vessel is only 0.22'F. Therefore, the temperature losses to the ambient are very small and do not cause any excessive sodium pentaborate precipitation to occur since the resulting final solution temperature (129.78'F) remains above the saturation temperature (ll4*F).

VI. Transient _ Condition _ Cal _culation_Hethodology While the drywell piping temperature was assumed to be initially at 110'F, it was necessary to account for the cooling ef fects of the 70*F domineralized water in the containment portion of the SLCS piping. Using methodology similar to that discussed below (but incorporating the physical properties of water), an initial drywell piping t emperature profile was calculated, prior to modeling the injection of SLCS solutlon.

The transient calculation for injecting SLCS solution modeled the SLCS piping from the SLCS pump dischargo to the reactor vessel in variable length increments. F,ach increment contained 0.8685 lbm of SLCS solution, which corresponds to a one foot increment in 1.5 inch diameter piping. The calculation also verified that the SLCS flow was turbulent at all locations in the discharge piping so as to assure that no thermal stratification occurred.

G9102264/SNLICFLR - 3

1-Attachment to GN5t0-91/00061 y .

1 .

The first. step was to calculato the transit time through the pipo increment. The SLCS flow rato used was 82.4 gpm for the common dischargo. piping and 41.2 spm in the piping which is apstream of the point where the dischargo piping from each SLCS puap meets.

4 Dividing the SLCS flow rato by the cross sectional aren far the appropriato pipe internal diameter gave the SLCS solution velocity through the piping. Dividing the increment's piping length by the

,_ solution velocity gave the transit time for that pipe inctement.

The second stop was to calculate the area that the sluf, of SLCS solution had in contact with the pipe wall for the appropriato )

diameter of dischargo piping. l EThe third step was to calculate the heat transfer rate por it' of cont.act area for cach increment of piping. The calculation for the ]

heat transfer rate was performed using a computer program. The j heat transfer rate was calculated for each inctement of piping.

4 The enthalpy change was then calculated as a product of the heat transfer rato and the transit timo divided by the slug mass (0.8685 lbm). The temperature change of t.he SLCS solution was calculatea by dividing the enthalpy chango by the specific heat of

the SLCS solution. The temperature change of the piping was similarly calculatod by dividing the amount of heat t ransferred (D

• transit time) by the product of the mass of stool for the pipe section and the piping specific heat (it

• c ).

Finally, the amount of precipitation (if'any) for each slug of SLCS solution was calculated. _ precipitation was assumed to occur if tho solution temperature was loss than ll4*F (the saturation temperature for 28.5 w/o sodium pontaborate solution) and was 1 -calculated separately for the containment and drywell piping.

The preceding steps woro performed separately for each slug of SLCS solution until SLCS solution temperature exceeded Il4*F at the RpV Mnjection point.

An additional calculation was performed to determino the period of timo during which sodium pentaborato precipitation was possible -

in other words, the amount of timo required to heat up SLCS piping sufficiently that SLCS solution is injected into the RpV at a temperature greater than ll4'F. The transient calculation was terminated when the SLCS solution temperature exceeded ll4*F at the RpV. Thorofore, the timo required to pump the solution mass calculated for the transient case, added'to the transit time for nach piping section, datormines the duration of the precipitation transient.

G9102264/SNLICFLR - 9 -

-.- .vw--%-vew_,m m*-m-,--,-._.,m s-.-,._ ._,.--,_m_m_m, -

-. - .w , . - -. - ~ _ - - . - _ , , , - , _ , ., -,m-v-,,~, - ,<r.,,,-rc..n., y.w,,,-aw- ,--r--r-c .c .r r

j '

Attachment to GNRO 91/00061 1- .

4

)

, VII. S a_mp.l.e _T r a n.s i en t, Ca l cu l a t ion i

A samplo calculation demonstrating the above described methods for the first slug of SLCS solution in the last full 1 foot section of common 1-1/2" diameter piping in the drywell follows:

The transit time for this 1 foot increment: ,

T D

= increment length / fluid velocity l

= 1 ft / 14.96 fps = 0.066645 seconds At this location the calculated initini St.CS solution temperature (t is 74.69'F, the pipo temperature-(t ) is 77.161'F, thn SLCS soI)ution velocity ja 14.96 f t/sec, and the internal pipe diameter in 1-1/2". The heat transfer coefficiout 18 given by (Source -

liark 'n St andard llandbook for Mechanjcal 1:nginocre, 8th ed. , page 4-64, equation 6c):

h, = 160*( 14 0. 012 t,)V,' * * / ( D,)' ' 8 Where: h =

mean value of h for entiro surface (BTV/br f tF) tg = film temperature = (t,i t )/2 (*F) t,a pipe wall temperaturo t, = SLCS solution temperature V, e average fluid velocity (ft/sec)

D, = insido pipn diameter (inches)

= 160 * (140.012

• 75.9255)

• 14.96o.a/1.5 8

= 2455.45 BTU /hr ft**F The heat transfer rate at this location is thereforn:

Q=b m* A a* AT where: hy = mean flim coef ficient (BTU /hr f t 'F) 8 A, = surface contact area (f t*)

AT = St.CS solution temperature - pipo temperature (*F)

= 2455.45 BTU /hr ft**F

• 0.3927 ft8 * (-2.471)*F

= -2382.7 BTU /hr = -0.66186 BTV/sec G9102264/SNLICFhR - 10

Attachment to GNRO-91/00061 The enthnipy change per Ibm of St.CS solution while traversing thir. P ipe increment:

AH = h*T oin /H D s where h=hent transfer rate at this location (BTU /sec)

T ,,g = lticroitent trnnait timn (soc)

H, " mnss of solut.lon in this increment (1bm)

= -0.6618611TU/sec

• 0.066845 sec/0.8685 lbm

= -0.051 BTU /lbm The teirporature chnrige across this increment:

AT = All / c P

where: All = enthalpy change (BTU / lbm) c = SLCS solut ion speci f ic hent ( BTU / lbm'F)

= -0.051 IlTU/lbm/0.82488 BTU /lbm*F = -0.06183*F Therefore, the SLCS hlug temperature upon exiting this increment 1s:

74.69 F - (-0.06183)0F = 74.75ar The mass of sodlum pentnborate precipitated from this slug in the SLCS piping:

M = AC

• M, wheret AC = (28.5 w/o - saturation w/o at this slugs lowest solution tempernture)/100 H, = mass of solution in this increment (lbm)

= (28.5 w/o - 17.05 w/o)

• 0.8685 lbm/100

= 0.09944 lbm Finnily. the change in piping temperature is:

AT=(h*T tiin L / tM*L*c)p G9102264/SNLICFI,R - 11

l Attachment to GNRO-91/00061  !

where: All = heat t ransferred by the SLCS alog (BTV)

M = piping mass (Ibm /ft)

L = length of this increment ( f t) i e = stainless steel specific hent (llTV/lbm*F) j

= (-0.66186 liTU/sec

• 0.066645 sec)/(3.63 lbm/ft

• 1 ft.

• 0.12 IITV/lbm'F) j

= -0.1016'F And, the piping temperature after the SLCS slug exits this increment is:

77.161'r + (-0.1016'F) = 77.059'r All of the values calculated above approximato the values calculated by the computer program algorithm.

VIII. Tpnsfont_Ca}culation_Rosults The total amount of sodium pentaborate precipitation was calculated to be 6.993 lbm.

The duration of the precipitation transient was calculated to be 79.4 seconds. After this time, the SLCS solution temperature at the RpV . injection point remains above ll4*F.

IX. Sa f e ty_S i gn.i f.$ c an c e_o ff r o c.i p i.t a t ion SLCS injection is designed to meet a 3% shutdown requirement and includes a 25% margin to allow for uncertainties such as imperfect mixing in the core, leakage, etc. A minimum of 5800 lbm of scxtium pentaborato is necessary to fulfill this requirement. The 6.993 lbm of sodium pontaborate which may precipitato during injection represents only 0.001% of the minimum sodium pentaborate wolght - a negligible amount compared to the 25% margin.

Since lit tle published information exists on the precipitation of scxilum pentaborate, OGNS conducted a controlled laboratory experiment to observe and record the behavior of an approximato 28.5 w/o sodium pentaborato solution when cooled below its saturation temForature of Il4*F. Ilrlofly, a solution of 28.3 w/o sodium pontaborate was prepared and heated to 130 F. The heat source was removed and the solution cooled to room temperature (approximately 77'F). The solution was constantly stirred at rates well below those necessary to reach turbulent flow conditions.

09102264/SNLICFLR - 12

At t achinent to GNRO-91/00061 Various observations were made:

• Visible precipitntion did not occur until approximntely 100'r wheti cooling down e At room temperature the mixture exhibited a cloudy, " milky" tippenrnnce with fine particles of precipitato suspended throughout

• Upon discontinuing agitat ion, a smnll nrnount of precipitate settled in a thin layer on the bottom of the finsk - no plating of precipitate was observed on the finsk walls or bottom surface e Upon rehenting, the precipitate rindily redissolved prior to reachitig its saturation temperature Ensed on these observations, the smn11 amount of enIculated precipitate would not inhibit ShCS injectfon. The precipitate which forms is very fine niid remains in suspension unless flow in stagnant. p!nto-out. does not occur to any obserynhle extent .

Therefore, the precipitate would be injected into the RpV and redissolve upon mixing.

X. Conclus.lo_n The results of this calculat. ion confirm that excessive precipitation of sodlum pentaborate in the dischargo piping will not. occur for the conditions annlyzed. The minor precipitation which may occur would have no offont on the St.CS safety function.

09102264/SNh1CFI,R - 13

SLCS PlPING _AYOUT .

RPV i I

i  :

F SLCS i 2" s 1.5" PUMP A J I 2' 19'lt I ( '

' 14" 1.5" 1.5" o 3" 12' f;

~ ,

62' 71' 3' i  !

t.  ?

' j SLCS 2" % 1.5" j e U  :

PUMP B J! 2' 14'  : ,

i

i r HPCS DISCHARGE P!PE CONTA!NMENT DRW/ ELL

• NOT DRAWN TO SCALE Figure 1

-