ML19309A555

Chapter 4 of VA Polytechnic Inst & State Univ Research & Training Reactor PSAR, Reactivity Transients.

ML19309A555
Person / Time
Site:	05000124
Issue date:	11/01/1979
From:	VIRGINIA POLYTECHNIC INSTITUTE & STATE UNIV., BLACKSB
To:
References
NUDOCS 8003310427
Download: ML19309A555 (9)

Text

.c -.

[s

'V

4. Pl. ACTIVITY TRANSIENTS 4.1 Fuel Burnup Increasing the maximum power level to 500 KW will result in increased fuel consumption which, in turn, uill affect reactivity. In order to estimate the reactivity effect, it is necessary to estimate the average power level and orarating schedule. Tais projection, based on recent operating history of the reactor facility, is shown in Fig. 4.1. From this figure, it follows that the average energy generated will B'e 180 MW hr per year. The corresponding annual U-235 burnup is given by a

-2 Wgt U-235 = 4.356 x 10 gm/MW hr x P x f U-235

- = 10.4 gm./fr.

Thus the addition of one new fuel plate every two years will compensate fri burnup.

4.2 Power Coefficient of Reactivity 4.2.1 Definitions d!-

The power coefficient of reactivity, , consists of three. components, viz., the li 0 temperature coefficient, (d , the graphite temperature 2

k T)H ~

coefficient, (d Thus d )C andthefueltemperaturecoefficient,[kdT). f kdp "kT " "H + "C + "F where a '

"F " ( )*

H "(kdT)HC "(kdT)C f The magnitude and time-dependence of aH "" "C are scussed in ref. 4.1.

I The measured values are given in Table 4.1.

j Table 4.1 Temperature Coefficients in the VPI & SU Reactor

! Coolant and Fuel GrapTite Coefficient Coefficient Ak f (% /k/oF) (% /k, Q

~

-3

- (5.07 1 0.5) x 10 + (2.37 1 0.?.) x 10 N.11: Graphite coefficient is for the central stringer.

4.1 8003310 %

n i 1

ANNUAL ENERGY GENERATED (MW Hr/Yr)

_ _ ro e O m O o O O O O I I I I

-10 Kw MAX. POWER O

6 g _.

m 5

e

. ----- 100 Kw MAX. POWER L 6 _

er. H 8 O k

9 -<

5 m I 2 >g 5

x nm -

G -

o __

• i

-500 Kw MAX. POWER m .

O L, 1

7 7

l 8

5 _ l m i o l I

i l

I I

- i i

c- t C

O e

9

4.2.2 Fuel Coefficient of Reactivity With the high-enriched uranium (HEU) contained in U-Al alloy in tiie present fuel elements, the fuel coefficient of reactivity is much less than the moderator / coolant coefficient. For the present analysis, tHe fuel coefficient is assumed to be zero.

4.2.3 H 0 Coefficient of Reactivity The modified cooling system for 500 KW operation is designed to maintain the temperature profile in the reactor core very near to tfie profile that exists at 100 KW. (See Chapt. 2) . A comparison of steady ,

state operating conditions is sunnarized in Table 4.2.

Table 4.2

,~

Steady-State Temperatures

-. Power Flow Rate Core at Avg. Inlet T Avg. Outlet T 100 KW 21.5 spn 30 F 135 F 165 F

~

500 KW 90.0 spn 38 F 127 F 165 F Thus, tne average core temperature at 500 EW will Ee 4 lower tHan the value at 100 KW. A net positive reactivity change ofl0.004!

k oF x4 F] = 0.016" will result.

4.3 Xenon Transients The xenon transient expe d at 500 KW was calculated with.the aid of the computer module XETRAN . The module was fit to experimental data on xenon transients observed at the VPI & SU reactor when operated at 100 KW. Two different methods were used in fitting the module to tee.

erverimental data with good agreement between the two. First, critical

vd heights (at lv) were taken for two weeks of daily operation at 100 KW and, second, the transient during a 10 hr. run was observed starting at the fourth hour. The reactivity measurements for the 10 hr. run are summarized in Table 4.3.

4.3

Table 4.3 l Measured Reactivity Transient (100 kw)

Date: 26 July 1978 Run No: 3820 Power Level: 100 kw Avg. U2 0 Temp: 1380F at 0943 Avg. H2O Temp: 139.50F at 1643 l Shim Rod Position: 11.6 in. (70% out)

Safety Rod Position: 16.0 in. (100% out)

Time for fuel and moderator temp. equilibrium: 0943 j Regulating Rod Calibration: 24 July 1978 l

0 Reg. Rod Reactivity Change (% /k)

Ak Time (hrs.) Position (in.) Reactivity (% /k) Measured Calculated 1043 7.3 0.0570 0.000 -

1143 7.6 0.0610 0.004 -

1243 8.1 0.0675 0.0065 0.0065 1343 8.6 0.0740 0.0065 0.0071 1443 9.2 0.0800 0.0060 0.0075 1543 9.8 0.0865 0.0065 0.0078 1643 10.5 0.0935 0.0070 0.0081 The observed power coefficient of reactivity at 100 KW is shown in Fig. 4.2 where Ap/At is plotted as a function of time,t. Since the observed transient reflects both the xenon transient and the graphite heating effect, a correc-tion for the latter must be applied. When this is done, the curve labelled "Purc Xenon Transient" on Fig 4.2 is obtained. The calibration curve for the regulating rod which was used in this experiment is shown in Fig. 4.3.

The transients predicted for operation at 500 KW were generated by increasing the flux level used in the experimentally fit program by a factor of five. Results are shown in Figures 4.4 and 4.5. The peak in negative reactivity during a standard week of 500 KW operation (5 days at 7 hrs. operation, 17 hrs. shutdown) was found to be 0.47% Ak/k. If longer periods of operation are needed, it can be seen from Fig. 4.5 that 14 hrs. operat4on will result in a reactivity loss of approximately 0.6% Ak/k.

4.4 Excess Reactivity Requirements The current Technical Specifications for 100 KW operation specify a maximum excess reactivity of 0.6% Ak/k. From the foregoing analysis, the same excess reactivity should be sufficient for operation at 500 KW. Con-tinuous operation at 500 KW will be limited to about 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> due to the xenon transient. Long term reactivity losses due to fuel burn-up can be ,

compensated by the addition of the equivalent of one new fuel plate every l two years.

4.4 .

j

i 0009 -

PURE XENON TRANSIENT o.008 - .

u

.c y&

N o o.007 -

J- -

( g,ggg ~d' O O mm mum O

a

<x 0.005 -

o.c04 -

6g o.003 -

<1 0.002 -

i i i i i i i 0.0 01 1043 114 3 1243 1343 1443 1543 1643 i

TIME (hours) 4

! Fig. 4.2 Measured Reactivity Transient

t

.13 -

.12 -

.l l -

^

.10 - -

M N

y .09 - ,

<3 g .08 v

3- .07 -

H

. E .06 -

, O 3 .05 -

o O .04 -

E .

.03 -

4

.02 -

.01 -

1 I I I I l i 2 4 6 8 10 12 14 16 l

lNCHES WITHDRAWN 1 .

i Fig. 4.3 Regulating Rod Calibration d

e

) _ __

P XENON REACTIVITY TRANSIENT OPERATE OPERATE OPERATE OPERATE OPERATE 7 hrs, , 7 hrs , ,7 hrs , ,7 hrs , ,7 hrs ,

i i i i i i i i i SHUTDOWN SHUTDOWN SHUTDOWN SHUTDOWN SHUTDOWN (WEEKEND) 17 hrs 17 hrs 17 hrs 17 hrs

.50 -

Q .4 5 500Kw OPERATION N

M .40 -

>A L o .35 -

L

> .30 -

F-5 .25 -

I o .20 -

<I W

O'

.15 -

i 100 Kw OPERATION

.10 -

! .05 -

i i i i i i i i i i i i i i i i i i i i i e i j 6 12 18 24 30 36 42 48 54 60 66. 72 78 84 90 96 102 108 114 120 126 132 138

! TIME (hours)

Fig. 4.4 Xenon Transients (100 KW and 500 KW)

i . .-

i l

XENON REACTIVITY TRANSIENT 500 Kw OPERATION

.90 -

27 hr OPERATION (x .80 - ,-

,,---~~,,*/,7

<1 .70 -

, 's ' ,-

• b .60

- 14 hr OPERATION '

F- .50 -

5

.40 -

7 hr OPERATION D ~ ,.

-- ~ - . /'-

<t .30 -

s-tu

.EJ -

.10 -

1 I I I I I I I I I I l i I I I I l i 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 TIME (hours)

Fig. 4.5 Xenon Transients (500 KW)

4.5 References 4.1 Parker, J. U. , "A Study of the Reactivity Effects of the VPI Nuclear Reactor," l!.S. Thesis, VPI, April 1969 4.2 Stam, 2., " Performance Characteristics of the VPI Training and Research Reactor (UTR-10)" M.S. Tilesis, VP1 & SU, 1961 4.3 Lamarsh, J. R. ," Introduction to Nuclear Engineering',' Addison-Uesley Publishing Co., 1975 4.4 Chapman, A. S., Heat Transfer, McMillan, New York, 1968 4.5 VP1 & SU, " Thermocouple Data of VPI & SU Reactor Fuel Plate Surface Temperature", 1966 ,

4.6 Tuley, K. D., " Power Excursion Safety Analysis of the VPI & SU Reactor 500 KW Model,"M.S. Thesis, VPI & SU,1976 4.7 Andrews, S. B., " Shielding Calculations for the VPI & SU UTR-10 Reactor at 10 KW", VPI & SU Thesis, Blacksburg, 'la., 1964 4.8 Hurray, R. L. , Dunn, W. L. , Elmaghrabi, M. A. ,

"Xetran, Xenon Transient",

North Carolina State University, Raleigh, N.C. ,1976 4

5 4.9

_ _ _ - - , _ _