SNR 300 fast breeder reactor: steel containment - design, erection, testing

Nuclear Engineering and Design 97 (1986) 255-267 North-Holland, Amsterdam

255

S N R 300 F A S T B R E E D E R R E A C T O R : S T E E L C O N T A I N M E N T DESIGN, ERECTION, TESTING * G. Z E I T Z S C H E L ,

M. T E N N I E , . C. B U R D U C E A ,

M. G E R S C H ,

-

P. W E R N E R

Kraftwerk Union A G, Postfach 962, 6050 Offenbach, Fed. Rep. Germany and H. O E Y N H A U S E N

International Natrium-Brutreaktorbau GmbH, Postfach D-5060, Bergisch-Gladbach, Fed. Rep. Germany Received 8 January 1986

The Kalkar Nuclear Power Plant which is equipped with an 300 MW fast breeder reactor is being built by a Consortium mainly comprising German, Belgian and Dutch companies. The components of the fast breeder reactor are enclosed in a concrete containment which is designed to withstand severe external and internal loading. The concrete enclosure is surrounded by a steel containment which is designed to prevent the release of radioactivity following a postulated accident involving the nuclear components inside the concrete containment. The paper describes the solutions adopted for the different parts of the steel containment, the calculations verifying the suitability of the designs, the erection and the steel containment pressure and leak tests. The tests were performed with successful results in 1984.

1. Introduction The Kalkar Nuclear Power Plant which is equipped with a 300 M W fast breeder reactor is being built by a Consortium mainly comprising German, Belgian and Dutch companies. The reactor equipment is located inside a reinforced concrete containment (CC) designed to withstand severe external and internal loading. The CC is enclosed in a steel containment (SC) which is designed to prevent the release of radioactivity following a postulated accident involving the nuclear components inside the CC. The SC is anchored to the walls of the CC by means of anchor plates and sway struts. The SC and the walls of the CC are separated by a space (reventing gap) of 608 m m which allows access to the anchoring elements as well as the inside surface of the SC for purposes of

* Invited lecture of the 8th International Conference on Structural Mechanics in Reactor Technology (SMIRT-8), Brussels, Belgium, August 19-23, 1985.

inspection. In some places, the gap is only 154 m m or 250 m m (at recesses). At the top steel plate, a gap of 1100 mm is provided to facilitate welding work at the plate. Fig. 1 shows a section through the plant. In case of an accident the air valves of the CC (2) are automaticaUy closed and a subatmospheric pressure of 3 mbar (300 Pa) is established by ventilators in the reventing gap, preventing unchecked leakage of unfiltered radioactive gas. The eventual air penetration into the reventing gap through the SC determines the rise of the pressure in the CC. If the admissible value of the overpressure is reached, the exventing installation will evacuate the gas through the filters 6 into the ambient atmosphere and in consequence the overpressure will not exceed the admissible value of 250 mbar (25 kPa). The steel used today for the SC is the German steel 15MnNi63 (R~H = 370 N / m m 2, R m = 5 1 0 . . . 630 N / r a m 2 ) . The steel wall is 12 mm thick with some exceptions in the lower part and at the recesses where it is thicker. Special steels were used for the expansion joints and for the anchoring elements. Fig. 2 shows the principal dimensions of the CC. The

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Fig. 1. Kalkar reactor building, elevation; (1-2) concrete containment (1:room filled with inert gas, 2:ventilated room), (3) reventing gap, (4) protection building, (5) reventing installation, (6) exventing installation, (7) steel containment.

reactor is situated near wall 137 and the steam generators are located outside the CC, near wall 126. Fig. 3 shows details of the two containments with the recesses. 93.35

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erected at the b o t t o m of the CC (6: e m b e d d e d part of the SC).

2. Basic principles for the design of the steel containment Table 1 shows the conditions for which the SC was designed. The m a x i m u m pressure acting on the SC is A p = 250 mbar. This pressure may occur in the case of a fault involving the nuclear components. The m a x i m u m value of 250 m b a r covers the pressure peaks occurring during the development of the fault. The m a x i m u m pressure of the ambient air may cause a differential pressure of 80 m b a r across the steel containment. The differential pressure of 30 m b a r is a regulation limit of the self-acting pressure regulator. The temperature of the SC will oscillate during the operation of the reactor within the limits 50°C (summer) and 5 ° C ( w i n t e r ) . The m a x i m u m temperature of 50°C could be possible during the operation of the p o w e r plant in the summer-time, supposing a fault of the air exhaustors of the protection building (4 in fig. 1) occurs. The calculation of this temperature was p e r f o r m e d according to the following hypotheses: - the air exhaustors are completely off and this state has a duration of some days, - this fault occurs o n one of the hottest summer-days (one of average temperature 28°C).

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Table 1 Calculation loads Load cases

Dead weight

MF DP 1 DP 2 DP3 NB ST1 ST2 ST3 ST4 ST 5 ST6

x x x x x x x x x x x

Internal overpressure (mbar)

Internal subatmos. pressure (mbar)

250 80 3 3 3 30 3 160 250 80

Temperature (global) (°C)

External loads

T > 5° T > 5° 5°
x x x x x x x x x x

Live load

Design basis earthquake

a Note: MF: Erection; DP: Pressure Test; NB: Normal Working State; ST: Failure State.

Differential displacement (ram)

Frequency of occurrence

35 35

50 10 2 4 1 5

35 35 35

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The rise of the temperature within the CC occurring in case of a fault involving the reactor components leads to the thermal dilatation of the CC walls. The anchoring elements with sway struts have a movement capability of 35 mm to make the relative displacement of the CC walls possible. The embedded part of the steel containment will be stressed by the concrete containment (in consequence of its thermal dilatation). The strain in the embedded part of the SC, calculated in accordance with the thermal movement of the concrete structure, is 0.6 %~.

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The loading and ambient conditions used in the SC calculation are shown in table 1. The design of the SC depends both on these conditions and on other factors as: - clear height of the SC is around 48 m, - the anchors plates are not located on the same vertical straight line, - friction at the anchoring elements could produce significant forces, - the penetrations are fixed unlike the SC expands, - the transition zone at the interface between the em-

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G. Zeitzschel et al. / Steel containment of the SNR 300

bedded SC and the free standing walls is stressed by large forces. 3.1. Steel containment design concept

A comparison was made of a number of design concepts, after which the actual concept shown in fig. 4 was adopted. The SC walls are reinforced by means of 160 × 20.5 mm horizontal profiles located at a distance of 1264 mm, respectively 868 mm. The anchoring elements are provided with sway struts or roller bearings and the pipe penetrations with expansions joints. The comers of the SC are elastic i.e. not reinforced in order to allow free movement (due to thermal expansion) of the SC walls and the top plate. The embedded part of the SC is reinforced by a 20.5 ram-thick steel bandage so that the forces caused by deformation of the concrete structure are transmitted to the vertical walls by means of a horizontal plate also 20.5 mm thick. This zone is called transition zone. Fig. 5 shows the anchoring elements for the normal gap (a), and for the walls recesses (b). The anchoring elements have the movement capability in a plane parallel to the CC walls. This concept assures a parallel movement of both walls (concrete wall and steel wall). 3.2. Computational models and calculations of the steel containment

Computations showed that the thermal expansion of the concrete structure produces a vertical deformation of the steel wall and this deformation varies according to a parabolic function depending on the wall length and on the extent of deformation of the concrete structure. This vertical deformation could be prevented by the force Fa (fig. 6), however this force cannot be

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induced in the steel containment. So the vertical deformation will be produced and will cause deformation and stressing of the wall, of the transition zone at the bottom of the SC, and of its embedded part. The subsequent analysis is given in table 2. In view of the complex structure involved, global models of the entire SC were generated and analyzed using the computer programs ANSYS and STARDYNE. Global models were also developed for the SC with the wall recesses. Separate models were generated for the threedimensional comers using the boundary conditions derived from the global models. Calculations based on an overpressure of 250 mbar and a relative displacement of the embedded containment of 0.6%o have confirmed the occurrence of horizontal and vertical deformation (35/15 ram) of the steel walls and have defined the magnitude of the SC stresses and strains. Apart from global calculations, which have confirmed the suitability of the design concept adopted for the SC, detailed calculations have been performed for individual components of the SC such as the steel wails, the anchor plates, the sway struts, the roller bearings, the fixed points located at the bottom in the comer of the wails 133/F, the locks (emergency, material and personnel), the expansion joints at the penetrations for the pipes and some electrical cabling and the anchoring elements in the outer building wall. The allowable stresses were defined in a technical specification in accordance with the German KTA and DIN standards. Stability calculations, performed using ANSYS, have demonstrated the necessity of some vertical reinforcements being provided for the steel walls. 3.2.1. Global model for the steel containment A computation was performed for the entire SC using the second order theory to determine its stresses

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G. Zeitzschel et al. / Steel containment of the S N R 300

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and strains caused by: dead weight, internal overpressure, and differential displacement. This computation also took into account the additional forces of the anchoring elements and the expansion joints on the roof. Model structure. The walls elements measure 10 × 10 m. Triangular plate elements were used for the walls and roof. The stiffness of the comers was simulated by trusses held elastically at their ends. Springs were included in the bottom part of the SC to simulate resistance to lifting of the SC. Fig. 7 shows the model structure of the SC. Gap elements were also included at the bottom, allowing the free displacement upwards and wi.t-hstanding the compressive forces downwards. The nodes of the models are connected by pivoting trusses to the CC. The roof expansion joints were modeled with the aid of springs. Fig. 8 shows the geometry of the lower part of the SC with the idealized supports of the horizontal reinforcements. The horizontal displacements of the model nodes

261

located at the bottom of the SC were computed in relation to the lines of zero displacement. These lines indicate the places of the concrete structure and of the SC at which no thermal movement exist. Fig. 9 shows the lines of zero displacement in the concrete building (marked with 0-0) and its horizontal and vertical thermal displacements (interrupted lines). Results of A N S Y S computation. The deformation of the steel wails, the forces at the bottom part of the SC and the stresses in the steel walls were determined. (a) The deformation of steel wall 137 (the walls of the SC are parallel to the walls of the CC and have the same number) is shown in fig. 10. The deformation values for the wall 137 are shown in fig. 11. It can be seen that in the horizontal direction the bottom of this wall is subject to tensile stresses and the upper part to compressive and tensile stresses. The middle part of wall is subject to compressive stresses in the vertical direction. This stress pattern poses stability problems owing to the compressive forces acting on the middle of the wall. (b) The forces induced into the SC plain by the concrete structure (owing to the embedded part of the SC) are shown in fig. 12. The shear forces induced in the lower part of the SC are transmitted to the comers of the SC and into the fixed points located in the internal corner of the wails 133/F. The stresses acting on the concrete in the external comers were also determined. Fig. 12 refers to the same wall 137 of the steel containment.

3.2.2. Calculation of the SC stability The compressive stresses which occur in the walls of the SC (due to the thermal expansion of the concrete structure) and its dead weight make it necessary to compute the stability of the SC. The overpressure of 250 mbar was also taken into consideration. The forces and the stresses derived from the global model were used for the stability calculation of the SC. The stresses in the lower part of the SC were increased by 20% in order to consider the effect of concentration around the erection openings. The stability computation was performed using the ANSYS program in accordance with the second order theory. The computation model was reduced to the lower middle section of the wall, the force distributing effect of the wall being replaced by a beam of appropriate stiffness. The global model showed that the walls have a lift of about 15 mm at the corners, as a result of which the dead weight is supported at the centre of the wall only. This fact leads to an increase in

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the compressive stresses at this point. It should be added that the internal overpressure has the effect of increasing deflection of the wall between two horizontal reinforcements. The height of the area subject to risk of buckling is about 10 m. The vertical compressive stresses were determined taking into account the biaxial condition of he stresses and correction for the true thickness of the wall. For the model the following were used: triangular plate elements, rectangular plate elements (located where the surfaces remain flat after deformation of the wall) and beam elements. The computation showed that some vertical reinforcements (located there where large compressive stresses occur) are necessary. Calculations were also performed both for the sectors of the wall bounded by two vertical reinforcements and for sectors bounded at

one side only. The distance between two vertical reinforcements is about 5 m. 3.2.3. Calculation o f three-dimensional corners

Using the ANSYS program the corners of the walls A / 1 3 7 / r o o f and F / 1 2 9 / r o o f were computed for the following conditions: - 250 mbar overpressure, deformations in the SC as a result of thermal expansion of the CC which was derived from the global model, and differential displacements of the anchoring elements as a result of thermal expansion of the CC and erection tolerances. Fig. 13 shows the corners of the SC included in the ANSYS computation. The F E M G E N program was used to generate the mesh. -

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The forces and the stresses in these fixed points were calculated using the STARDYNE program, the results of the global model computation being used as boundary conditions. The shear forces are supported by small pipe sections embedded and welded to the 68 mm plate. The tensile forces are supported by steel bars passing through the concrete wall and supported on steel plates on the other side of the wall. The forces produced by thermal expansion of the concrete structure are shown in the same figure. The connection between the fixed point plates and the SC is a 38 mm thick plate.

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Fig. 14 shows the model of the corner A/137/roof. The stiffening effects of the roof expansion joints were also taken into account. The stresses in the SC corners and the forces in the anchoring elements were determined. Fig. 15 shows the geometry of the model of the corner F / 1 2 9 / r o o f 33.

3.3. Earthquake stresses in the walls of the SC

3. 2.4. Calculation of fixed points of internal corner 1 3 3 / F Two fixed points (190/191 and 192/193 in fig. 16), realized using 68 mm thick plates, were provided in the internal corner of walls 133/F.

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horizontal directions a n d 8.4 m / s e in the vertical direction. These values correspond to an amortization of 2% a n d are situated in a frequency range of 1.5 to 3 H z . The lowest frequency of the steel walls in the horizontal direction is 4 Hz a n d in the vertical direction 6 Hz. In this frequency range correspond in the seismic spectrum smaller accelerations t h a n the m e n t i o n e d values, that is 1.6 m / s 2 in the horizontal direction a n d 1.4 m / s 2 in the vertical direction.

The c o m p u t a t i o n results * show that the stresses are small and the uplift of the steel walls is not possible in the case of an earthquake. In the horizontal direction the stresses are smaller than in the load case with 250 . This report gives only the main computations which determined the feasibility of the SC. Detailed calculations were also performed for components of the SC, calculations which are common for steel structures like the SC, but these are not presented here.

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4.

Erection

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The companies MAN/Jarnbes Namur erected the SC between May 1982 and September 1984. The SC

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structure was assembled from standard wall elements (10 x 2 m), the joints of which were welded from each side. The focal areas of erection work were: the bottom part of the SC, the connection with the embedded steel skin, the fixed points, the standard elements of the walls, the plates for the cables and penetrations, the expansion joints, the supports of the protecting building and of the safety cooling stacks, - the supports and anchors for the locks, and the anchoring elements. The standard wall elements were carried from the welding workshop (on the site) to the protecting building (4 in fig. 1), where these elements were lifted up by means of a crane mounted on the roof of this building. Through the mounting openings, these elements were let down into the room between protecting building and the concrete containment, where small cranes carried the elements to their fixed place for welding. Steel stages were mounted in the reventing gap and in the room between the protecting building and the SC to facilitate the welding work on both sides of the wall elements. These steel stages were fixed in the CC walls and in the walls of the protecting building respectively• The total length of the welds made was 42.5 km, approximately 8 km of which were done in the factory and the rest on the site.

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Welds on the site were performed by the WIG (Wolfram inert gas), those in the factory by the UP(submerged arc process). The connection between the SC and the CC was realized by means of about 10000 anchoring elements (sway struts and roller bearings). To avoid large erection tolerances in the anchors (and hence additional forces), the exact geometric position of the anchor plates was measured and adequate holes were made in the horizontal reinforcements of the SC for the sway struts of the anchoring elements. The welds were checked using the following non-destructive methods: X-ray, magnetic powder, ultrasound, halogen, hardness testing, metallographic inspection. The total weight of the SC including the weight of the anchoring elements is about 3500 tons. 5. Pressure and leaks tests

The pressure test was performed on the basis of a pressure diagram (it is the foreseen variation of the applicable pressure to the SC during the timeperiod of the test). The maximum applied pressure was 250 mbar.

During the test, pressure, temperatures and strains were measured. The leak test yielded good results. The maximum allowable rate was specified to be 5.5 m3/h, the maximum leak rate measured was 3.37 m3/h. The locks were both pressure and leakage tested. Fig. 17 is a schematic of the equipment used in checking for leaks of the SC. The internal subatmospherical pressure of 3 mbar (related to the external atmospherical pressure) is realized within the CC by means of the operation ventilators TL01 and TL03. The exventing ventilator (it sucks the air from the reventing gap and pumps it to the chimney) assures an internal subatmospherical pressure of 3 mbar in the reventing gap. The regulation of this ventilator is realized by means of the false air addition. In this way a pressure difference of 3 mbar will act on the SC. The leak rate of the SC was calculated with the help of some corrections (the exventing rate depends on the variation of the temperature and humidity in the reventing gap, the variation of the external air pressure has to be taken into consideration).

G. Zeitzschel et aL / Steel containment of the S N R 300

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The leak rate of the reventing gap, measured by means of the gas counter and corrected with the mentioned influences, represents the leak rate of the steel containment.

6. Conclusion The steel containment of the Kalkar Nuclear Power Plant is designed to prevent the release of radioactivity following a postulated accident within the concrete containment. The calculation of the SC was performed by means of global models for the entire SC to determine its feasibility. Detailed calculations were also performed for components of the SC.

The SC structure was assembled from standard walls elements (10 × 2 m), the joints of which were welded from each side. The connection between the SC and the CC was realized by means of the anchoring elements (sway struts, roller bearings, anchor plates). The pipe and cables penetrations are provided with expansion joints. The pressure and leak tests of the SC, performed at the end of year 1984, yielded good results.

References [1] S.J. Przemieniecki, Theory of Matrix Structural Analysis (McGraw-Hill Book Company, New York, 1968).