COMMISSARIAT A L'ENERGIE ATOMIQUE

DIRECTION DES APPLICATIONS MILITAIRES

DEPARTEMENT DE RECHERCHE SUR LES MATERIAUX NUCLEAIRES

SERVICE RECHERCHE EN NEUTRONIQUE ET CRITICITE

OCDE/NEA

EXPERT GROUP ON CRITICALITY ACCIDENT ANALYSIS

SILENE PULSED EXPERIMENTS

SILENE-HEU-SOL-STEP

S1-300 / S2-300 / S3-300

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REACTOR CORE MAIN DIMENSIONS

• The reactor core is an annular cylinder which main dimensions are :

➘➘➘➘ External diameter : 360/368 mm ➘➘➘➘ Internal diameter : 70/76 mm ➘➘➘➘ Bottom thickness : 36 mm ➘➘➘➘ Cover thickness : 30 mm ➘➘➘➘ Vessel height : 1036 mm

REACTOR CORE MATERIAL DATA

• The core material is stainless steel which main characteristics are :

➘➘➘➘ Stainless Steel : grade Z2 CN 18-10 ➘➘➘➘ Density : 7.9 g/cm3

➘➘➘➘ Weight fraction of Chromium : 18 ± 1% ➘➘➘➘ Weight fraction of Nickel : 10 ± 1% ➘➘➘➘ Weight fraction of Manganese : ≤ 2% ➘➘➘➘ Weight fraction of Silicon : ≤ 1% ➘➘➘➘ Weight fraction of Phosphorus : ≤ 0.04% ➘➘➘➘ Weight fraction of Sulphur : ≤ 0.03% ➘➘➘➘ Weight fraction of Carbon : ≤ 0.03% ➘➘➘➘ Weight fraction of Iron : 68.9% (balance)

• The Z2 CN 18-10 composition is as follows :

Isotopes Atoms / barn-cm

IronChromiumNickelManganeseSiliconPhosphorusSulphurCarbon

5.8694 10-2

1.6469 10-2

8.1061 10-3

1.7319 10-3

1.6939 10-3

6.1438 10-5

4.4640 10-5

1.1883 10-4

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FISSILE SOLUTION

• The reactor fissile solution is uranium nitrate which main characteristics are :

➘➘➘➘ Total Uranium concentration : 70.78 g/l ➘➘➘➘ Density : 1.1588 g/cm3

➘➘➘➘ Acidity : 2N ➘➘➘➘ Weight fraction of U234 : 0.57 ± 0.01% ➘➘➘➘ Weight fraction of U235 : 92.74 ± 0.1% ➘➘➘➘ Weight fraction of U236 : 0.25 ± 0.01% ➘➘➘➘ Weight fraction of U238 : 6.44 ± 0.1%

• The fissile solution composition is as follows :

Isotopes Atoms / barn-cm

HydrogenNitrogenOxygenUranium 234Uranium 235Uranium 236Uranium 238

6.2381 10-2

1.56682 10-3

3.56511 10-2

1.03811 10-6

1.68181 10-4

4.51443 10-7

1.15312 10-5

• For uranium nitrate solution, the specific heat has been determined from experimentscarried out in the Valduc laboratory :

Cp = 1 – 0.0008154 x CUt - 0.06 H+

➘➘➘➘ Cp : specific heat (cal.g-1.°C-1) ➘➘➘➘ CUt: uranium total concentration (g.l -1) ➘➘➘➘ H+ : acidity (N). ➘➘➘➘ for CUt = 71 g.l –1 and H+ = 2N , Cp = 0.8221 cal.g-1.°C-1

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CONCRETE CELL

• The reactor core is in a large concrete cell 1910 cm long, 1210 cm wide and 1000 cmhigh.• The thickness of the concrete side walls is 145 cm.• The thickness of the concrete floor is 40 cm.• The thickness of the ceiling vary from 70 cm (side) to 110 cm (middle).• The distance between the zero level of the solution and the concrete floor is 103.6 cm.• The distances between the reactor core axis and the 1910 cm long side walls are 585 cmand 625 cm.• The distances between the reactor core axis and the 1210 cm long side walls are 771 cmand 1139 cm.

• The concrete composition is as follows :

Isotopes Atoms / barn-cm

HydrogenBoron 10OxygenAluminumSiliconCalciumIron

1.035 10-2

1.602 10-6

4.347 10-2

1.563 10-3

1.417 10-2

6.424 10-3

7.621 10-4

• The density calculated from the reported atom densities is 2.4013 g/cm3

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DESCRIPTION OF PULSED EXPERIMENTS

• Solution is pumped into the reactor core with the reactivity rod inserted until a givensolution height.

• With this solution height, the reactor is above critical state when the reactivity rod isremoved from the core.

• Pulsed experiment is started by the rapid removal of the reactivity rod so that thereactivity insertion is like a step.

• The relation between the inserted reactivity and the solution height is determined by thereactivity weight of solution near criticality which is 510 pcm per cm of solution.

DESCRIPTION OF THE REACTIVITY ROD

• The reactivity rod is an annular cylinder which main dimensions and composition are :

➘➘➘➘ rod length : 580 mm

➘➘➘➘ 0 < radius < 30 mm : Air

➘➘➘➘ 30 mm < radius < 31 mm : Stainless Steel grade Z2 CN 18-10

➘➘➘➘ 31 mm < radius < 32 mm : Natural Cadmium (density is 8.65 g/cm3)

➘➘➘➘ 32 mm < radius < 33 mm : Stainless Steel grade Z2 CN 18-10

• The axis of the reactivity rod is the axis of the reactor core.

• When the reactivity rod is completely inserted in the reactor core, the distance betweenthe zero level of the reactivity rod and the zero level of the solution is 10 cm.

• When the reactivity rod is completely inserted in the reactor core, the reactivity weight ofthe rod has been determined experimentaly to 3230 pcm (±60 pcm).

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DESCRIPTION OF THE EXTERNAL SOURCE

• For the S1-300 experiment, an external neutron source was present during theexperiment.

• The external neutron source is a cylinder of Americium Beryllium alloy which is coveredby a cylinder of Stainless Steel (grade Z2 CN 18-10).

• The Americium Beryllium cylinder diameter is 10 mm and the height is 10 mm.

• The Stainless Steel cylinder diameter is 18 mm and the height is 18 mm. The thicknessof Stainless Steel is 4 mm.

• The source emission is isotropic.

• The source strength is 270000 neutrons emitted per second in 4π.

• The source position is under the reactor core bottom.

• The distance between the source center and the core bottom is 1.4 cm.

• The distance between the source center and the zero level of the solution is 5 cm.

• The distance between the source center and the axis of the reactor core is 5 cm.

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1036 mm

368 mm

142 mm142 mm 70 mmSOLUTION SOLUTIONAIR

AIR AIR

SILENE REA CTOR GEOM ETRY

3 mm

1036

mm

368 mm

142 mm142 mm 70 mm

SOLUTION SOLUTIONAIR

AIR AIR

SILENE REACTOR GEOMETRY

3 mm 4 mm

36 mm

30 mm

REACTIVITY ROD CHANNEL

ALL DIMENSIONS IN MILLIMETERS

SOLUTION

HEIGHT

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PULSED EXPERIMENTS CHARACTERISTICS:

Experiments S1-300 S2-300 S3-300

Effective beta 794 pcm 794 pcm 794 pcm

Reactivity step 405 pcm 769 pcm 1832 pcm

Critical height 37,36 cm 37,36 cm 37,36 cm

Experimental height 38,16 cm 38,91 cm 40,96 cm

Initial temperature 22,2 °C 22,1 °C 22,3 °C

Duration 1100 s 265 s 120 s

External source yes no no

• Temperature given in the table is the mean temperature measured by two thermocoupleslocated at 20 cm and 30 cm from the zero level of the solution.

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CALCULATED RESULTS

Experiments S1-300 S2-300 S3-300

Inverse period

First peak power

Energy to the first peak

Energy to the first minimum

First peak time

Final Temperature

Gas release time

Energy

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