- Email: [email protected]
Experimental campaign on pressure wave propagation in LLE
Fusion Engineering and Design 136 (2018) 809–814
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Experimental campaign on pressure wave propagation in LLE a,⁎
b
a
c
A. Venturini , M. Utili , D. Martelli , I. Ricapito , A. Malavasi a b c
T
b
University of Pisa, Dipartimento di Ingegneria Civile e Industriale, Largo Lucio Lazzarino 2, 56122 Pisa, Italy ENEA Brasimone, 40032 Camugnano, Bologna, Italy TBM&MD Project, Fusion for Energy, EU Commission, Carrer J. Pla, 2, Builiding B3, 08019 Barcelona, Spain
A R T I C LE I N FO
A B S T R A C T
Keywords: In-box LOCA Pressure wave Water hammer LLE HCLL TBM
Experimental facility THALLIUM was designed and installed at ENEA C.R. Brasimone to reproduce the geometry of the LLE (Lithium Lead Eutectic) loop of HCLL TBM. Within the framework of F4E-FPA-372, an experimental campaign was carried out in ITER relevant conditions. The experiments simulated a pipe rupture in a cooling plate of the HCLL TBM, injecting He from an injection valve connected to He-FUS3 loop. The aim was to study the release of high pressure He in LLE due to In- box LOCA. The fundamental phenomena to be observed are the pressure wave trend in the two pipes reproducing the pipe forest of the HCLL-TBM in ITER and the effectiveness of the mitigation strategy designed for HCLL-TBS. The main parameters that were varied during the experiments are: injection time, actuation of the isolation valves and opening pressure of the rupture disc. In the pipe forest mock-up, the pressure wave showed three distinct peaks, related to the water hammer, to the LLE oscillations in the expansion tank and to He which fills the loop. The isolation valves proved to have a deep influence on the pressure wave propagation also when they do not close, being able to damp the first pressure peaks.
1. Introduction In-box LOCA has been identified among the “incident and accident pressure loads” as an event of Cat. III (leakage) or IV (rupture) for HCLL-TBS (Helium Cooled Lead Lithium Test Blanket System) in the ITER classification system [1]. This system is based on the probability of occurrence of loading conditions. Thus far, only few analyses on this accidental sequence have been carried out and published. Among them, Lee et al. [2] carried out an accident analysis of In-box LOCA for the HCCR TBM (Helium Cooled Ceramic Reflector Test Blanket Module) with the GAMMA-FR code. Aiello et al. [3] performed design analyses limited to the HCLL TBM with loading conditions corresponding to the pressurization following this type of scenario. No experimental activities on In-box LOCA were found from a literature review. Therefore, ENEA designed and built a LLE (Lithium Lead Eutectic, composed by 16 at. % of Li and 84 at. % of Pb) test section, named THALLIUM (Test HAmmer in Lead LithIUM), with the aim to understand the effects of the propagation of a pressure wave on the entire LLE loop of the HCLL TBS. The facility is described in detail in [4], together with an analytical investigation on the sound speed in LLE and the nodalisation and pretest results with RELAP5-3D system code [5]. This nodalisation is currently used to assess the capabilities of the code against the
⁎
experimental results of this campaign. This paper illustrates the experimental procedure and the results of the first five injections performed. 2. Brief description of the facility A short description of the facility is reported here with the aim to allow the comprehension of the following results (further information in [4]). THALLIUM was designed to reproduce the LLE loop of HCLLTBS, using the design proposed in [1] as a reference. Hence, it is composed by a TBM (Test Blanket Module) mock-up, an upper and a lower leg that represent the pipe-forest and an expansion tank. The dimensions of the main components are relevant for the design of the HCLL-TBS (Table 1). The TBM mock-up represents a breeding unit and therefore is divided in two chambers by a plate that has the aim to simulate a stiffening plate of the TBM. Consequently, the walls of the mock-up represent two cooling plates. The upper and lower chambers can communicate by means of a hole that has the same area of the corresponding 4 holes foreseen in the design of the stiffening plate [1]. He is injected in the lower chamber by a pipe immediately below the stiffening plate and it is supplied by the He facility He-FUS3. The rupture of the pipe is simulated by a ball valve installed at 26 cm from the mock-up to limit the dissipation of the shock wave as much as possible. The injection valve is operated by a dedicated compressor and
Corresponding author. E-mail addresses: [email protected], [email protected] (A. Venturini).
https://doi.org/10.1016/j.fusengdes.2018.04.013 Received 29 September 2017; Received in revised form 16 February 2018; Accepted 4 April 2018
Available online 10 April 2018 0920-3796/ © 2018 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 136 (2018) 809–814
A. Venturini et al.
Table 1 Dimensions of the most important components.
Table 2 Test matrix with the experiments already performed.
Component and dimension
Value
Lower leg length Upper leg length Legs nominal diameters Mock-up size Expansion tank internal diameter Expansion tank volume
6.5 m 8.0 m 1″ and 2–1/2″ 44.7 × 25 × 20 cm 54 cm 210 dm3
it can open in about 10 ms. The TBM mock-up can be isolated from the expansion tank by means of isolation valves located on both the lower and upper legs. These pneumatic valves were designed to open in less than 0.2 s. He can flow towards the expansion tank by breaking a rupture disc installed on a dedicated bypass line. The expansion tank is a simplified (no submerged pump) and slightly smaller (DN600, where DN is the nominal diameter [6]) reproduction of the storage/recirculation tank, designed to roughly preserve the gravity driven fluid-dynamics. This tank is equipped with a guided-microwave level meter and a pressure transducer. The expansion tank is protected from an eventual overpressure by means of a passive safety valve (VS215). A filter is installed on the pipe below VS215 in order to prevent that the LLE can block the valve. In order to have the possibility to vary the set point of the release for each test, a different pressure relief valve (VS205) was selected and installed on a branch parallel with the safety one. This valve discharge He into the buffer tank of IELLLO (S03). Finally, a third valve, named EV21, was installed and connected to an He tank. This valve is used during loading and draining to modify the LLE level in the tank. Fig. 1 shows a 3D sketch of the facility.
Test number
Injection time [s]
He pressure [bar]
RD opening P [bar]
IV closure
IV clos. P [bar]
Injection area [m2]
1 2 3 4 5
10 10 15 15 20
80 80 80 80 80
9 9 9 80 –
no no yes no no
– – 5.5 – –
1.257∙10−5 1.257∙10−5 1.257∙10−5 1.257∙10−5 1.257∙10−5
campaign. The main parameters that are varied in the tests are:
• the duration of the injection of He (10, 15 or 20 s); • the breaking of the rupture disc, which is prevented in one test, and its breaking pressure (9 or 80 bar); • the closure of the isolation valves, which has been currently allowed in one test (when the pressure in the mock-up reached 5.5 bar).
These values have been selected because they appear to be relevant with the operating and accidental conditions in HCLL-TBS. The five tests were performed with an injection valve with a 4 mm orifice. The way in which the pressure wave behaves was measured by means of 7 pressure transducers with an acquisition frequency of 1 kHz, while the quantity of He injected was monitored by means of a Venturi flow meter installed on the gas injection line. 4. Results of the injections of the first phase of experimental campaign
3. Description of the experimental procedure and test matrix
Two phenomena were observed as a consequence of the He injection: a shock tube dynamics (shock wave in LLE, travelling interface and rarefaction wave in He) followed by a two-phase bubble mixing and by the forced draining of the liquid. Test #1 and #2 were performed with the aim to confirm the repeatability of the results. In test #3 it was decided to set the input for the closure of the isolation valves (pressure in the mock-up) at 5.5 bar. This value was decided in order to have a sudden closure of the valves, but to also have a margin to avoid unwanted closures due to oscillations in the measurement of the transducer. In this test the injection time was
At the beginning of each test the injection valve is opened, interfacing high-pressure He with low pressure LLE, both at 400 °C. When the pressure in the expansion tank reaches 9 bar a spring-loaded relief valve opens and allows He to flow into a dedicated buffer tank. The test is carried out with stagnant LLE were carried out in stagnant conditions, as no pumping system is provided at the moment. At the beginning of the injection the entire facility is filled with LLE. Table 2 shows the tests performed during the experimental
Fig. 1. 3D drawing of THALLIUM facility. 810
Fusion Engineering and Design 136 (2018) 809–814
A. Venturini et al.
also lengthen up to 15 s. A rupture disc with a breaking differential pressure of 80 bar was installed for the injection #4. Nevertheless, the rupture disc broke even at a lower differential pressure. Therefore, the aim of the last test was to understand how the pressure trends vary if the rupture disc does not break. A block of steel of the same shape and size of the rupture disc, but thicker than it, was prepared to overcome this problem. The injection time was set at 20 s. Fig. 2 shows the quantity of He injected in the five tests. Fig. 3 shows the pressure trend measured by the pressure transducer PT10, which is located in the lower part of the mock-up. The valve opens after 2 s from the “injection” command. For injection #1 and #2, the pressure reaches the maximum value of 52.1 bar in about 83 ms. The first decrease is caused by the breakage of the rupture disc, which occurs almost instantaneously. At about 4.45 s the opening of the relief valve VS205 starts to affect the pressure in the mock-up that drops to about 20.6 bar (5.62 s). The second peak (maximum at about 28.6 bar, 6.34 s) has an unclear origin: it is likely due to LLE oscillations in the expansion tank which are transmitted to the mock-up through the lower leg. He which flows into the mock-up causes the third peak (about 29.6 bar, 12.09 s), followed by a logarithmic decrease after the end of the injection. The loop is in steady state condition when the relief valve closes (i.e. when the pressure falls below 9 bar). The little differences in the experimental trend of the first two injections can be ascribed to small variations in the initial conditions (e.g. the injection pressure was 81.3 bar in the first injection and 79.5 bar in the second one). Comparing the trend of test #3 with the one of the first two injections, the first effect of the closure of the valve is to limit the effects of
the rupture disc. In fact, the initial depressurization of the mock-up is opposed by the wave reflected by the valves and by the lack of two paths for the release of pressure. After a steep decrease from the maximum at 57.3 bar (2.12 s) to 44.1 bar (2.29 s), the pressure increases again and reaches a new maximum at about 63.1 bar (3.13 s). This increase is clearly related to the closure of the valves which appears to be completed 210 ms after the full opening of the injection valve. After a plateau, which is caused by the incoming He, the pressure decreases at about 5.00 s as a consequence of the opening of the relief valve, similarly with what happened in the two first injections. The minimum is reached at 6.60 s (25.9 bar). The two peaks are at 39.8 bar and 6.77 s, corresponding to the peak of injections #1 and #2, and at 47.8 bar and 8.63 s (after a valley at 26.4 bar and 7.22 s). The final pressurization related to the continuous injection of high pressure He starts at 30.5 bar and 9.7 s and ends with the closure of the injection valve at about 17 s. The behavior of the system in test #4 was the same of the two first injections, with the only differences of the higher value of the first peak (58.5 vs 52.1 bar), caused by the longer time needed so that the rupture disc breaks, and of the longer injection time (15 s) which causes higher pressures in the final part of the transient. The pressures in the mock-up and in the expansion tank (Fig. 4) for test #5 have a similar general aspect to the ones of the previous tests but with many oscillations and a more chaotic trend. This trend is likely related to the fact that He is injected in the expansion from the two legs and, thus, from below the free level of LLE, while in the other tests He could expand in the gas dome. As a consequence, the LLE in the expansion tank was shaken and thrown in every part of the facility. The clearest proof of this is that the gas lines above the expansion tank were found filled with frozen LLE at the end of the experiment. The filter could not stop such a chaotic flow, while there is evidence that the filter worked fine in the first four injections. Fig. 4 shows the pressure trend in the expansion tank. The pressure starts to quickly increase at about 4.47 s, after the opening of the rupture disc. The presence of the isolation valves prevent the creation of one or more peaks in the first seconds, even if they are kept open for the whole transient. The negative peak, which begins at 5.65 s and 16.9 bar and has its lowest point at 6.36 s and 15.8 bar, is almost coincident with the one seen by the PT10 in the mock-up and it is likely produced by the same reflected wave. The pressure trend in the expansion tank for test #3 is almost the same to the one of the two first injection, with three main differences: the first peak has a higher value, the negative valley is wider and deeper, the final increase is slower and reaches a higher maximum. For tests #4 and #5 the same considerations for the pressure in the mock-up are also applicable for the expansion tank. Figs. 5–7 show the pressure measured by the three pressure transducers installed on the upper leg. The first two figures refer to
Fig. 3. Pressure in the TBM mock-up measured by PT10 in the five tests.
Fig. 4. Pressure in the expansion tank measured by PT21 in the five tests.
Fig. 2. He mass flow rate injected in the TBM mock-up.
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Fig. 8. Pressure in the lower leg upstream of the isolation valve measured by PT15 in the five tests.
Fig. 5. Pressure in the upper leg downstream of the TBM mock-up measured by PT11 in the five tests.
These two trends are comparable to the one of the mock-up. Instead, the transducer PT13, shown in Fig. 7, is located downstream of the isolation valve and shows a different behavior, which is closer to the one measured in the expansion tank. A similar behavior occurs in the lower leg: the PT15 (Fig. 8) is located upstream of the isolation valve and measures a pressure trend similar in shape to the one measured by PT10; the PT14 (Fig. 9) is located downstream the isolation valve and highlights a behavior comparable with the expansion tank. The isolation valves proved to have a deep influence on the pressure wave propagation also when they do not close. Particularly, they are able to damp almost entirely the peaks related to the first wave, while they obviously allow the pressure increase related to the arrival of He. Figs. 5 and 6 show another characteristic: the “first peak” pressure is marginally influenced by the distance from the injection valve, while the “second peak” and the “final peak” pressures are lower for the farther measurement points. As far as the legs for test #3 are concerned, the five trends shown from Figs. 5–9 are analogous in the shape to the ones of injections #1 and #2, with the exception of the peak highlighted in Fig. 8 that is not present in the first two injections and which is almost equal to the peak measured by PT10 (Fig. 3). The behavior of the pressures of the two legs is consistent with the hypothetical effects of the isolation valves: the peaks measured in the third test by PT11, PT12 and PT15 are higher than the corresponding values for the first two tests, while the pressures
Fig. 6. Pressure in the upper leg upstream of the isolation valve measured by PT12 in the five tests.
Fig. 7. Pressure in the upper leg downstream of the isolation valve measured by PT13 in the five tests.
transducers which are located upstream of the isolation valve: the PT11 is near the mock-up, while the PT12 is about 80 cm before the isolation valve. The pressures measured have similar trends with a small difference in the timescale (it was estimated to be between 50 and 60 ms).
Fig. 9. Pressure in the lower leg downstream of the isolation valve measured by PT14 in the five tests. 812
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effect of the isolation valve (almost one third of the pressure measured by PT12, located immediately upstream of the valve). The pressure measured by PT15 in the lower leg has a different behavior with respect to the one measured by PT12, the transducer symmetrical of PT15 on the upper leg. This difference is linked with the presence of the rupture disc on the upper leg. In fact, when the rupture disc breaks, LLE can be discharged directly in the gas dome of the expansion tank. Instead, the level of LLE in the tank prevents this from happening in the lower leg. Hence, pressure in the upper leg is generally lower and has a different trend than in the lower leg (also hydrostatic pressure has a small influence as it is about 1 bar).
5. Discussion and conclusions The results of the five injections which constituted the first phase of the experimental campaign are presented in this paper, showing the injected mass flow rate, the pressures in different points of the system and the level in the expansion tank. The tests performed highlighted that the maximum value of all pressure peaks is significantly lower than the injection pressure. However, this statement is clearly related to the size of the leakage (4 mm in this case) and further experiments are needed to reach a full understanding of the phenomenon. The isolation valves proved to have a deep influence on the pressure wave propagation also when they do not close, being able to damp the peaks related to the first pressure wave. The dynamics of the system is heavily influenced by the relief valve of the expansion tank. The relief valve installed in THALLIUM proved to be effective in quickly discharging pressure (at 5 s in Figs. 5, 6 and 8). Thus, the design of this component, or of an equivalent passive system such as a rupture disc, will be of outstanding importance to mitigate the effects of an In-box LOCA. Figs. 3–9 point out that the injections #1, #2 and #4 provoked the same response of the system, with small differences due to the slightly different initial conditions. The first peak in the experiment #4 is approximately 3 bar higher than the peaks in tests #1 and #2. This difference is related to the slightly longer time needed to break the 80 bar rupture disc. The pressure trends of injection #3 present higher values measured by the transducers upstream of the isolation valves. Instead, the pressures measured by the transducers downstream of the isolation valves are lower than those of the first three experiments, as they are protected by the action of the valves. The negative peaks typical of transducers PT13, PT14 and PT21 are bigger, wider and delayed in the injection #3. Finally, in test #5 the lack of a rupture disc causes a plateau similar to the one shown by the same transducers in the experiment #3, even if lower. In all the pressure trends of this injection there are no clearly distinct peaks, but rather steep and fast oscillations in the first seconds of transient and smooth and slow oscillations in the remaining. These oscillations are likely related to very chaotic transient which occurs in the expansion tank and which affects the whole system. Further experiments are foreseen to test the action of two valves with bigger orifices (6.7 and 11 mm). Additional experiments at 50, 60 and 70 bar have been scheduled too. The data described in this paper will be used to validate the nodalisation developed for RELAP5-3D [5] and to assess the capability of the code to reproduce this kind of transient.
Fig. 10. LLE level in the expansion (test #1).
measured by PT13 and PT14 are lower as they are located after the valves which isolate them. Fig. 10 shows the LLE level in the expansion tank in the first 30 s of data acquisition for the first test of this campaign. Similar trends were found in the other tests. The data were filtered to reduce the oscillations related to the accuracy of the instrument. The maximum level is reached after about 8.25 s from the start of the data acquisition and measures 249.3 mm, even if a certain error can be expected due to the large fluctuations that are still present. However, this value is interesting because it corresponds to the time required in order that all the LLE is drained inside the expansion tank (or at least all the LLE of the upper part of the loop: it is imaginable that a small portion of the lower leg is not emptied during the transient). After the maximum, the level decreases because the LLE starts to flood again the lower leg. The steady state level is reached after about 48 s from the injection and it is about 230 mm. Fig. 11 shows how the pressure wave propagates in the facility, presenting an enlargement of the first pressure peak measured by the pressure transducers in the mock-up (PT10), in the upper leg (PT11 and PT12 are located upstream of the isolation valve, while PT13 downstream of it) and in the lower leg (PT15, upstream of the isolation valve). The fast decrease after the first peak is linked with the breaking of the rupture disc on the bypass line. The rupture disc proves to be effective to passively limit the maximum pressure in every point of the system and, in particular, in the TBM mock-up, where the pressure is higher than in every other position. The pressure measured by PT13 in the upper leg is lower than the others, thus highlighting the dampening
Acknowledgments The work leading to this publication has been partially funded by Fusion for Energy under the specific grant FPA-372-SG02. Special thanks go to our F4E colleagues and ENEA colleagues involved in this project.
Fig. 11. Enlargement of the first peak measured in various locations of the facility (test #1). 813
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References
(2011) 2129–2134. [4] M. Utili, et al., THALLIUM: an experimental facility for simulation of HCLL In-box LOCA and validation of RELAP5-3D system code, Fusion Eng. Des. 123 (2017) 102–106, http://dx.doi.org/10.1016/j.fusengdes.2017.05.049. [5] RELAP5-3D© Code Manual Volume I: Code Structure, System Models and Solution Methods, Idaho National Laboratory, 1999 February. [6] International Standard ISO 6708, Published in 1995, definition is in par. 2.1.
[1] ITER D2.3: Final STR_56. A1. LP. (v.2.1 2014/08/07). ITER PbLi Loop – Final Technical Report. [2] D.W. Lee, et al., Investigation into the In-box LOCA consequence and structural integrity of the KO HCCR TBM in ITER, Fusion Eng. Des. 89 (2014) 1177–1180. [3] G. Aiello, et al., HCLL TBM design status and development, Fusion Eng. Des. 86
814
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Experimental campaign on pressure wave propagation in LLE a,⁎
b
a
c
A. Venturini , M. Utili , D. Martelli , I. Ricapito , A. Malavasi a b c
T
b
University of Pisa, Dipartimento di Ingegneria Civile e Industriale, Largo Lucio Lazzarino 2, 56122 Pisa, Italy ENEA Brasimone, 40032 Camugnano, Bologna, Italy TBM&MD Project, Fusion for Energy, EU Commission, Carrer J. Pla, 2, Builiding B3, 08019 Barcelona, Spain
A R T I C LE I N FO
A B S T R A C T
Keywords: In-box LOCA Pressure wave Water hammer LLE HCLL TBM
Experimental facility THALLIUM was designed and installed at ENEA C.R. Brasimone to reproduce the geometry of the LLE (Lithium Lead Eutectic) loop of HCLL TBM. Within the framework of F4E-FPA-372, an experimental campaign was carried out in ITER relevant conditions. The experiments simulated a pipe rupture in a cooling plate of the HCLL TBM, injecting He from an injection valve connected to He-FUS3 loop. The aim was to study the release of high pressure He in LLE due to In- box LOCA. The fundamental phenomena to be observed are the pressure wave trend in the two pipes reproducing the pipe forest of the HCLL-TBM in ITER and the effectiveness of the mitigation strategy designed for HCLL-TBS. The main parameters that were varied during the experiments are: injection time, actuation of the isolation valves and opening pressure of the rupture disc. In the pipe forest mock-up, the pressure wave showed three distinct peaks, related to the water hammer, to the LLE oscillations in the expansion tank and to He which fills the loop. The isolation valves proved to have a deep influence on the pressure wave propagation also when they do not close, being able to damp the first pressure peaks.
1. Introduction In-box LOCA has been identified among the “incident and accident pressure loads” as an event of Cat. III (leakage) or IV (rupture) for HCLL-TBS (Helium Cooled Lead Lithium Test Blanket System) in the ITER classification system [1]. This system is based on the probability of occurrence of loading conditions. Thus far, only few analyses on this accidental sequence have been carried out and published. Among them, Lee et al. [2] carried out an accident analysis of In-box LOCA for the HCCR TBM (Helium Cooled Ceramic Reflector Test Blanket Module) with the GAMMA-FR code. Aiello et al. [3] performed design analyses limited to the HCLL TBM with loading conditions corresponding to the pressurization following this type of scenario. No experimental activities on In-box LOCA were found from a literature review. Therefore, ENEA designed and built a LLE (Lithium Lead Eutectic, composed by 16 at. % of Li and 84 at. % of Pb) test section, named THALLIUM (Test HAmmer in Lead LithIUM), with the aim to understand the effects of the propagation of a pressure wave on the entire LLE loop of the HCLL TBS. The facility is described in detail in [4], together with an analytical investigation on the sound speed in LLE and the nodalisation and pretest results with RELAP5-3D system code [5]. This nodalisation is currently used to assess the capabilities of the code against the
⁎
experimental results of this campaign. This paper illustrates the experimental procedure and the results of the first five injections performed. 2. Brief description of the facility A short description of the facility is reported here with the aim to allow the comprehension of the following results (further information in [4]). THALLIUM was designed to reproduce the LLE loop of HCLLTBS, using the design proposed in [1] as a reference. Hence, it is composed by a TBM (Test Blanket Module) mock-up, an upper and a lower leg that represent the pipe-forest and an expansion tank. The dimensions of the main components are relevant for the design of the HCLL-TBS (Table 1). The TBM mock-up represents a breeding unit and therefore is divided in two chambers by a plate that has the aim to simulate a stiffening plate of the TBM. Consequently, the walls of the mock-up represent two cooling plates. The upper and lower chambers can communicate by means of a hole that has the same area of the corresponding 4 holes foreseen in the design of the stiffening plate [1]. He is injected in the lower chamber by a pipe immediately below the stiffening plate and it is supplied by the He facility He-FUS3. The rupture of the pipe is simulated by a ball valve installed at 26 cm from the mock-up to limit the dissipation of the shock wave as much as possible. The injection valve is operated by a dedicated compressor and
Corresponding author. E-mail addresses: [email protected], [email protected] (A. Venturini).
https://doi.org/10.1016/j.fusengdes.2018.04.013 Received 29 September 2017; Received in revised form 16 February 2018; Accepted 4 April 2018
Available online 10 April 2018 0920-3796/ © 2018 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 136 (2018) 809–814
A. Venturini et al.
Table 1 Dimensions of the most important components.
Table 2 Test matrix with the experiments already performed.
Component and dimension
Value
Lower leg length Upper leg length Legs nominal diameters Mock-up size Expansion tank internal diameter Expansion tank volume
6.5 m 8.0 m 1″ and 2–1/2″ 44.7 × 25 × 20 cm 54 cm 210 dm3
it can open in about 10 ms. The TBM mock-up can be isolated from the expansion tank by means of isolation valves located on both the lower and upper legs. These pneumatic valves were designed to open in less than 0.2 s. He can flow towards the expansion tank by breaking a rupture disc installed on a dedicated bypass line. The expansion tank is a simplified (no submerged pump) and slightly smaller (DN600, where DN is the nominal diameter [6]) reproduction of the storage/recirculation tank, designed to roughly preserve the gravity driven fluid-dynamics. This tank is equipped with a guided-microwave level meter and a pressure transducer. The expansion tank is protected from an eventual overpressure by means of a passive safety valve (VS215). A filter is installed on the pipe below VS215 in order to prevent that the LLE can block the valve. In order to have the possibility to vary the set point of the release for each test, a different pressure relief valve (VS205) was selected and installed on a branch parallel with the safety one. This valve discharge He into the buffer tank of IELLLO (S03). Finally, a third valve, named EV21, was installed and connected to an He tank. This valve is used during loading and draining to modify the LLE level in the tank. Fig. 1 shows a 3D sketch of the facility.
Test number
Injection time [s]
He pressure [bar]
RD opening P [bar]
IV closure
IV clos. P [bar]
Injection area [m2]
1 2 3 4 5
10 10 15 15 20
80 80 80 80 80
9 9 9 80 –
no no yes no no
– – 5.5 – –
1.257∙10−5 1.257∙10−5 1.257∙10−5 1.257∙10−5 1.257∙10−5
campaign. The main parameters that are varied in the tests are:
• the duration of the injection of He (10, 15 or 20 s); • the breaking of the rupture disc, which is prevented in one test, and its breaking pressure (9 or 80 bar); • the closure of the isolation valves, which has been currently allowed in one test (when the pressure in the mock-up reached 5.5 bar).
These values have been selected because they appear to be relevant with the operating and accidental conditions in HCLL-TBS. The five tests were performed with an injection valve with a 4 mm orifice. The way in which the pressure wave behaves was measured by means of 7 pressure transducers with an acquisition frequency of 1 kHz, while the quantity of He injected was monitored by means of a Venturi flow meter installed on the gas injection line. 4. Results of the injections of the first phase of experimental campaign
3. Description of the experimental procedure and test matrix
Two phenomena were observed as a consequence of the He injection: a shock tube dynamics (shock wave in LLE, travelling interface and rarefaction wave in He) followed by a two-phase bubble mixing and by the forced draining of the liquid. Test #1 and #2 were performed with the aim to confirm the repeatability of the results. In test #3 it was decided to set the input for the closure of the isolation valves (pressure in the mock-up) at 5.5 bar. This value was decided in order to have a sudden closure of the valves, but to also have a margin to avoid unwanted closures due to oscillations in the measurement of the transducer. In this test the injection time was
At the beginning of each test the injection valve is opened, interfacing high-pressure He with low pressure LLE, both at 400 °C. When the pressure in the expansion tank reaches 9 bar a spring-loaded relief valve opens and allows He to flow into a dedicated buffer tank. The test is carried out with stagnant LLE were carried out in stagnant conditions, as no pumping system is provided at the moment. At the beginning of the injection the entire facility is filled with LLE. Table 2 shows the tests performed during the experimental
Fig. 1. 3D drawing of THALLIUM facility. 810
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also lengthen up to 15 s. A rupture disc with a breaking differential pressure of 80 bar was installed for the injection #4. Nevertheless, the rupture disc broke even at a lower differential pressure. Therefore, the aim of the last test was to understand how the pressure trends vary if the rupture disc does not break. A block of steel of the same shape and size of the rupture disc, but thicker than it, was prepared to overcome this problem. The injection time was set at 20 s. Fig. 2 shows the quantity of He injected in the five tests. Fig. 3 shows the pressure trend measured by the pressure transducer PT10, which is located in the lower part of the mock-up. The valve opens after 2 s from the “injection” command. For injection #1 and #2, the pressure reaches the maximum value of 52.1 bar in about 83 ms. The first decrease is caused by the breakage of the rupture disc, which occurs almost instantaneously. At about 4.45 s the opening of the relief valve VS205 starts to affect the pressure in the mock-up that drops to about 20.6 bar (5.62 s). The second peak (maximum at about 28.6 bar, 6.34 s) has an unclear origin: it is likely due to LLE oscillations in the expansion tank which are transmitted to the mock-up through the lower leg. He which flows into the mock-up causes the third peak (about 29.6 bar, 12.09 s), followed by a logarithmic decrease after the end of the injection. The loop is in steady state condition when the relief valve closes (i.e. when the pressure falls below 9 bar). The little differences in the experimental trend of the first two injections can be ascribed to small variations in the initial conditions (e.g. the injection pressure was 81.3 bar in the first injection and 79.5 bar in the second one). Comparing the trend of test #3 with the one of the first two injections, the first effect of the closure of the valve is to limit the effects of
the rupture disc. In fact, the initial depressurization of the mock-up is opposed by the wave reflected by the valves and by the lack of two paths for the release of pressure. After a steep decrease from the maximum at 57.3 bar (2.12 s) to 44.1 bar (2.29 s), the pressure increases again and reaches a new maximum at about 63.1 bar (3.13 s). This increase is clearly related to the closure of the valves which appears to be completed 210 ms after the full opening of the injection valve. After a plateau, which is caused by the incoming He, the pressure decreases at about 5.00 s as a consequence of the opening of the relief valve, similarly with what happened in the two first injections. The minimum is reached at 6.60 s (25.9 bar). The two peaks are at 39.8 bar and 6.77 s, corresponding to the peak of injections #1 and #2, and at 47.8 bar and 8.63 s (after a valley at 26.4 bar and 7.22 s). The final pressurization related to the continuous injection of high pressure He starts at 30.5 bar and 9.7 s and ends with the closure of the injection valve at about 17 s. The behavior of the system in test #4 was the same of the two first injections, with the only differences of the higher value of the first peak (58.5 vs 52.1 bar), caused by the longer time needed so that the rupture disc breaks, and of the longer injection time (15 s) which causes higher pressures in the final part of the transient. The pressures in the mock-up and in the expansion tank (Fig. 4) for test #5 have a similar general aspect to the ones of the previous tests but with many oscillations and a more chaotic trend. This trend is likely related to the fact that He is injected in the expansion from the two legs and, thus, from below the free level of LLE, while in the other tests He could expand in the gas dome. As a consequence, the LLE in the expansion tank was shaken and thrown in every part of the facility. The clearest proof of this is that the gas lines above the expansion tank were found filled with frozen LLE at the end of the experiment. The filter could not stop such a chaotic flow, while there is evidence that the filter worked fine in the first four injections. Fig. 4 shows the pressure trend in the expansion tank. The pressure starts to quickly increase at about 4.47 s, after the opening of the rupture disc. The presence of the isolation valves prevent the creation of one or more peaks in the first seconds, even if they are kept open for the whole transient. The negative peak, which begins at 5.65 s and 16.9 bar and has its lowest point at 6.36 s and 15.8 bar, is almost coincident with the one seen by the PT10 in the mock-up and it is likely produced by the same reflected wave. The pressure trend in the expansion tank for test #3 is almost the same to the one of the two first injection, with three main differences: the first peak has a higher value, the negative valley is wider and deeper, the final increase is slower and reaches a higher maximum. For tests #4 and #5 the same considerations for the pressure in the mock-up are also applicable for the expansion tank. Figs. 5–7 show the pressure measured by the three pressure transducers installed on the upper leg. The first two figures refer to
Fig. 3. Pressure in the TBM mock-up measured by PT10 in the five tests.
Fig. 4. Pressure in the expansion tank measured by PT21 in the five tests.
Fig. 2. He mass flow rate injected in the TBM mock-up.
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Fig. 8. Pressure in the lower leg upstream of the isolation valve measured by PT15 in the five tests.
Fig. 5. Pressure in the upper leg downstream of the TBM mock-up measured by PT11 in the five tests.
These two trends are comparable to the one of the mock-up. Instead, the transducer PT13, shown in Fig. 7, is located downstream of the isolation valve and shows a different behavior, which is closer to the one measured in the expansion tank. A similar behavior occurs in the lower leg: the PT15 (Fig. 8) is located upstream of the isolation valve and measures a pressure trend similar in shape to the one measured by PT10; the PT14 (Fig. 9) is located downstream the isolation valve and highlights a behavior comparable with the expansion tank. The isolation valves proved to have a deep influence on the pressure wave propagation also when they do not close. Particularly, they are able to damp almost entirely the peaks related to the first wave, while they obviously allow the pressure increase related to the arrival of He. Figs. 5 and 6 show another characteristic: the “first peak” pressure is marginally influenced by the distance from the injection valve, while the “second peak” and the “final peak” pressures are lower for the farther measurement points. As far as the legs for test #3 are concerned, the five trends shown from Figs. 5–9 are analogous in the shape to the ones of injections #1 and #2, with the exception of the peak highlighted in Fig. 8 that is not present in the first two injections and which is almost equal to the peak measured by PT10 (Fig. 3). The behavior of the pressures of the two legs is consistent with the hypothetical effects of the isolation valves: the peaks measured in the third test by PT11, PT12 and PT15 are higher than the corresponding values for the first two tests, while the pressures
Fig. 6. Pressure in the upper leg upstream of the isolation valve measured by PT12 in the five tests.
Fig. 7. Pressure in the upper leg downstream of the isolation valve measured by PT13 in the five tests.
transducers which are located upstream of the isolation valve: the PT11 is near the mock-up, while the PT12 is about 80 cm before the isolation valve. The pressures measured have similar trends with a small difference in the timescale (it was estimated to be between 50 and 60 ms).
Fig. 9. Pressure in the lower leg downstream of the isolation valve measured by PT14 in the five tests. 812
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effect of the isolation valve (almost one third of the pressure measured by PT12, located immediately upstream of the valve). The pressure measured by PT15 in the lower leg has a different behavior with respect to the one measured by PT12, the transducer symmetrical of PT15 on the upper leg. This difference is linked with the presence of the rupture disc on the upper leg. In fact, when the rupture disc breaks, LLE can be discharged directly in the gas dome of the expansion tank. Instead, the level of LLE in the tank prevents this from happening in the lower leg. Hence, pressure in the upper leg is generally lower and has a different trend than in the lower leg (also hydrostatic pressure has a small influence as it is about 1 bar).
5. Discussion and conclusions The results of the five injections which constituted the first phase of the experimental campaign are presented in this paper, showing the injected mass flow rate, the pressures in different points of the system and the level in the expansion tank. The tests performed highlighted that the maximum value of all pressure peaks is significantly lower than the injection pressure. However, this statement is clearly related to the size of the leakage (4 mm in this case) and further experiments are needed to reach a full understanding of the phenomenon. The isolation valves proved to have a deep influence on the pressure wave propagation also when they do not close, being able to damp the peaks related to the first pressure wave. The dynamics of the system is heavily influenced by the relief valve of the expansion tank. The relief valve installed in THALLIUM proved to be effective in quickly discharging pressure (at 5 s in Figs. 5, 6 and 8). Thus, the design of this component, or of an equivalent passive system such as a rupture disc, will be of outstanding importance to mitigate the effects of an In-box LOCA. Figs. 3–9 point out that the injections #1, #2 and #4 provoked the same response of the system, with small differences due to the slightly different initial conditions. The first peak in the experiment #4 is approximately 3 bar higher than the peaks in tests #1 and #2. This difference is related to the slightly longer time needed to break the 80 bar rupture disc. The pressure trends of injection #3 present higher values measured by the transducers upstream of the isolation valves. Instead, the pressures measured by the transducers downstream of the isolation valves are lower than those of the first three experiments, as they are protected by the action of the valves. The negative peaks typical of transducers PT13, PT14 and PT21 are bigger, wider and delayed in the injection #3. Finally, in test #5 the lack of a rupture disc causes a plateau similar to the one shown by the same transducers in the experiment #3, even if lower. In all the pressure trends of this injection there are no clearly distinct peaks, but rather steep and fast oscillations in the first seconds of transient and smooth and slow oscillations in the remaining. These oscillations are likely related to very chaotic transient which occurs in the expansion tank and which affects the whole system. Further experiments are foreseen to test the action of two valves with bigger orifices (6.7 and 11 mm). Additional experiments at 50, 60 and 70 bar have been scheduled too. The data described in this paper will be used to validate the nodalisation developed for RELAP5-3D [5] and to assess the capability of the code to reproduce this kind of transient.
Fig. 10. LLE level in the expansion (test #1).
measured by PT13 and PT14 are lower as they are located after the valves which isolate them. Fig. 10 shows the LLE level in the expansion tank in the first 30 s of data acquisition for the first test of this campaign. Similar trends were found in the other tests. The data were filtered to reduce the oscillations related to the accuracy of the instrument. The maximum level is reached after about 8.25 s from the start of the data acquisition and measures 249.3 mm, even if a certain error can be expected due to the large fluctuations that are still present. However, this value is interesting because it corresponds to the time required in order that all the LLE is drained inside the expansion tank (or at least all the LLE of the upper part of the loop: it is imaginable that a small portion of the lower leg is not emptied during the transient). After the maximum, the level decreases because the LLE starts to flood again the lower leg. The steady state level is reached after about 48 s from the injection and it is about 230 mm. Fig. 11 shows how the pressure wave propagates in the facility, presenting an enlargement of the first pressure peak measured by the pressure transducers in the mock-up (PT10), in the upper leg (PT11 and PT12 are located upstream of the isolation valve, while PT13 downstream of it) and in the lower leg (PT15, upstream of the isolation valve). The fast decrease after the first peak is linked with the breaking of the rupture disc on the bypass line. The rupture disc proves to be effective to passively limit the maximum pressure in every point of the system and, in particular, in the TBM mock-up, where the pressure is higher than in every other position. The pressure measured by PT13 in the upper leg is lower than the others, thus highlighting the dampening
Acknowledgments The work leading to this publication has been partially funded by Fusion for Energy under the specific grant FPA-372-SG02. Special thanks go to our F4E colleagues and ENEA colleagues involved in this project.
Fig. 11. Enlargement of the first peak measured in various locations of the facility (test #1). 813
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References
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