Investigation of irradiated fuel elements from the first atomic power station

Investigation of irradiated fuel elements from the first atomic power station

J ownal of Nuclear Energy. Parts A/B, 1964. Vol 18, pp. 85 to 88. Pergamon Press Ltd. Printed in Northern Ireland INVESTIGATION OF IRRA...

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J ownal

of Nuclear

Energy.

Parts

A/B,

1964.

Vol

18, pp.

85 to 88.

Pergamon

Press

Ltd.

Printed

in Northern

Ireland

INVESTIGATION OF IRRADIATED FUEL ELEMENTS FROM THE FIRST ATOMIC POWER STATION* A. P. SMIRNOV-AVERIN, V. I. GALICOV, V. I. IVANOV, V. P. MESHCHERYAKOV, 1. G. SHEYNKER, L. A. STABYENOVA,N. N. KRO~ and A. G. KOZLOV (Receiced

13 September

1960)

Abstract-In the present paper are described results of the examination of spent fuel elements which have operated in the reactor of the first Atomic Power Station for 445 working days. The changes in diameter due to swelling of the fuel appear to reach saturation at high burn-up. The content of transuranic elements in the fuel elements in kg/m of uranium are zssPu -4.10 2”oPu- 1.53 *41Pu-0.64, 242Pu-0.20, and WZm-2.73 x 10-3. CHANGES

OF

DIMENSIONS

OF

THE

FUEL

ELEMENT

DURING external

examination of the surface of the fuel element, no changes were were made of observed except for patches of a thin brown oxide film. Measurements the increases in diameter of the groove and the parts of the tube between grooves. In Fig. 1 are shown values for the mean of two mutually perpendicular diameters for three fuel elements; unirradiated; irradiated for 104 effective working days, and for 445 working days. With increase in burn-up the difference between the values of I.44

I

1.40 i3ottom I,39

-

I l.3Eo

25

50

Length.

FIG. 1.-Curves

100

75

125

150

cm

for changes in diameter of a fuel element. n-Unirradiated. irradiation. o--445 days irradiation.

bl-104

days

the diameter at the ends and in the middle of the fuel element decreases, which indicates the approach of saturation in swelling. More recent observations with a fuel element exposed for 577 working days confirm this observation since there is a constant diameter along the length of the fuel element. The diameter of the groove for all the fuel elements examined remained constant within the specified limits of 15.0 f O-1 mm. CHANGES

IN THE

TOTAL

G(, /? AND

;J-ACTIVITY

Ten specimens were cut out from various positions along the fuel element for radiometric measurements. The specimens were each dissolved in nitric acid and the resulting solution was divided into aliquot volumes, which were used for measurement of c(, ,!I and y-activity. * Translated by S. F. PUGH from Atotnnaw Ener~iya 11, 122 (1961). 85

A. P. SMRNOV-AVERIN et al.

86

The total cc-activity of the solution was measured with a standard piece of equipment, Da-49, and an ionization chamber with 27~ geometry. The P-activity was measured with a 45r counter using aliquot quantities of the solution carried on thin chamber organic metallized films. The a-activity was measured with an ionization calibrated with radium. In Fig. 2 are shown graphs of the changes of the total M,

Length,

FIG. 2.-Change

in total

alpha

(A)

cm

beta (A) and gamma element.

(0)

activities

along

a fuel

/I and y-activities along a fuel element. The curves for change of p and y-activity can be compared with the analogous curves for a fuel element with a burn-up of 124 per cent and a cooling time of 34 years(l). At a burn-up of 124 per cent the ratio of p’to y-activity is constant, but at high burn-up this ratio changes along the length and reaches a maximum at the centre of the fuel element (see Fig. 2). This is connected evidently with activation of the fission products themselves during a long exposure in the reactor.

I

I

1

25

0

50

75 Length,

FG.

3.-Activity

I

I

125

100

I50

cm

of the inner surfaces (A) and outer cladding tubes.

surfaces

(A) of the fuel element

During measurement of the activity inside and outside the stainless-steel tubes it was noticed that in the central part of the fuel element, the activity outside the tube was about 30 per cent greater than inside (Fig. 3). The observation is probably due to change of the neutron spectrum along a diameter of the fuel element.

Investigation

of irradiated fuel elements from the First Atomic Power Station DETERMINATION

OF

87

BURN-UP

Burn-up of the fuel element was determined from the absolute activity of fission product caesium separated by an ion-exchange method from the total fission products. Because of the very long time of irradiation of the fuel element a considerable quantity of l%s had accumulated due to activation of the stable product of fission, lz3Cs, which somewhat complicated the determination of burn-up. Usually for determination of burn-up the isotope 13iCs is used, then the task is to find the absolute activity of the 13jCs from knowledge of the total activity of 137Cs and 13*Cs measured with a 4~ counter. For determination of the relative amounts of the isotopes 13iCs and 134Cs scintillation 1% and y-spectrometers were used with a scheme of /+coincidences. To verify the results of the radiometric measurements, specimens were analysed with a mass spectrometer. Figure 4 illustrates the excellent agreement between the 75

i:

c

50 3. d 3 ; ; m 25

t

Bottom

I

I _^

3”

Length, FIG. 4.-Curves

cm

for burn-up of 235U determined spectrometric (0) methods.

by radiometric

(0)

and mass-

235U burn-up values determined by the radiometric method and those determined by mass spectrometry. The mean value of burn-up for the whole fuel element was estimated from the experimental data to be 53 per cent. According to measurements of heat evolution just before removal of the fuel element from the reactor it contained 2.34 per cent 235U instead of initial amount of 5 per cent. This estimate is in good agreement with the results of the measurements described above. DETERMINATION OF THE OF TRANSURANIC

ISOTOPIC CONTENT ELEMENTS

In the previous publication”) were given the results of an investigation of the isotope content of plutonium by a radiometric method in a fuel element with a burn-up of 12;. per cent. In the present work the isotope content of the plutonium was The chamber determined using a mass spectrometer with 60” magnetic deflexion. For analysis a thermionic of the mass spectrometer swung on an arc of radius 150 mm. type of ion source was used. Specimens, as nitrates dissolved in water, were measured out with a micropipette on to the emitter, a tungsten foil 40-p thick and covered with a layer of tungsten sponge. The ion current was measured with an amplifier of constant current with 100

A. P. SMIRNOV-AVERIN et al.

88

per cent feed-back. The masspeaks were recorded on a potentiometer, EPP-09. In addition, the total accumulated plutonium and curium were quantitatively estimated by measurement of the ionization of an s-spectrometer(2). To improve the resolution of the spectrometer, the small collecting electrode was replaced by a gridded ionization chamber. The total K-activity of specimens taken from various positions along a fuel element and the c+spectrum of plutonium separated from these specimens was examined with the a-spectrometer. The quantities of the isotopes of the transuranic elements present in the fuel element are shown in Fig. 5.

Length,

FIG. S.-Curves

cm

of content of isotopes of transuranic

elements.

On the basis of the measurements mean values of the isotope content of a fuel element in kg/m of uranium were 23sPu 4.10, %OPu 1.53, 241Pu 0.64, 242Pu 0.02, 242Cm2.73 x 10-3. The 242Cmcontent was determined 180 days after the end of the irradiation of the fuel element. REFERENCES 1. SMIRNOV-AVERIN A. P. et al., Atomnaya Energiya 8, (5) 446 (1960). 2. SEABORGG. T. and KATZ J. J. (Eds.) The Actinide Elements, McGraw-Hill, N.Y. (1954); SEABORGG. T., KATZ J. J. and MANNINGW. M. (Eds.) The Transuranium Elements, Parts I and II, McGraw-Hill, N.Y. (1949).