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Intra model of ITER-FEAT and accident analysis for GSSR
Fusion Engineering and Design 58 – 59 (2001) 1017– 1020 www.elsevier.com/locate/fusengdes
Intra model of ITER-FEAT and accident analysis for GSSR J. Andersson a,*, H. Jahn b, J. Eriksson a a
b
Studs6ik Eco and Safety AB, Association Euratom-NFR, SE-611 82 Nyko¨ping, Sweden Gesellshaft fu¨r Anlagen-und Reaktorsicherheit (GRS) mbH, Forschungsgela¨nde, DE-85748 Garching bei Mu¨nchen, Germany
Abstract A number of analyses and calculations of ITER reference accident sequences in the first wall (FW) and divertor coolant systems of the 1998 ITER design have previously been carried out for the Non Site Specific Safety Report (NSSR) of the 1998 ITER design. Model updates with new calculations are now ongoing to comply with the new ITER-FEAT design and provide input to the Generic Site Safety Report (GSSR). A wet containment bypass calculation has been performed assuming an in-vessel small pipe break on a FW cooling loop. The result is a smooth scenario with no high over-pressures and in the long run slow system heat loss causing a continuous pressure decrease. © 2001 Elsevier Science B.V. All rights reserved. Keywords: ITER-FEAT; In-vessel; Vacuum vessel (VV)
1. Introduction
2. Calculation model
Model developments and calculations reported here concern the category IV wet bypass accident sequence, ‘in-vessel pipe break and vacuum vessel (VV)/cryostat penetration bypass’ defined for the new ITER-FEAT design [1]. Similar analyses have previously been carried out for the Non Site Specific Report of the 1998 ITER design. The new calculations will provide input to the Generic Site Specific Safety Report (GSSR).
The main calculation is performed using the INTRA [2] code which has been developed for safety analyses of Tokamak type fusion reactors. The code predicts pressures, temperatures and fluid flows in cases such as the present one of water ingress in the VV following a double ended break on one of the many 10 mm coolant tubes in plasma facing structures. The base case calculated here considers a break in the FW at about the mid plane of the VV. 1. The model uses the VV boundary conditions case specified in [1]. 2. Break occurs and concurrently by failure a thin tubular penetration into a ‘generic bypass room’ opens.
* Corresponding author. Tel.: + 46-155-22-1868; fax: + 46155-22-1616. E-mail address: [email protected] (J. Andersson).
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 5 3 6 - 1
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J. Andersson et al. / Fusion Engineering and Design 58–59 (2001) 1017–1020
3. At 110 kPa VV pressure valves on bleed lines to the suppression will open. 4. At 150 kPa VV pressure rupture disks open to the suppression tank. 5. If the VV pressure reaches 160 kPa finally a bypass from the DV sump to a drain tank will open. Since the INTRA code is less applicable for the break flow calculations involving jet evaporation a simplified ATHENA model was set up to supply the break flow characteristics data needed for the INTRA calculation.
2.1. Break flow The VV injection flow characteristics following a double-ended 10 mm tube breach were separately calculated using the ATHENA code [3]. A simplified model was developed for one PFW/ BLK cooling loop. The main items of the model are [4]: 1. Level tracing pressurizer of 12.8 m3 volume. It is initially filled with steam and 8.1 m3 saturated water at 4.3 MPa. 2. The pressurizer line is top connected to two equivalent, level tracing, volumes with total water hold up 140 m3 divided into two vertical coolant branches with temperatures 100 and 152 °C, respectively. 3. At the bottom of each branch a short discharge 10 mm line is connected. 4. Each of the two break flows enter a series of small volumes with increasing areas to reach two-phase water/steam equilibrium before entering the main VV. 5. Relevant heat structures are included.
Fig. 1. INTRA node modelling scheme of ITER-FEAT.
The model updates concern mainly time or pressure dependent system boundary conditions.
3. Calculation results The rates and steam qualities of the two mass flows entering the VV after occurrence of the double ended break are shown in Fig. 2 as results from the ATHENA calculation. Both the rate from the 100 °C branch and the rate from the 152 °C branch are 5 kg/s or higher until about 500 s when a period of loop fast cooling pressure drop ends as Fig. 3 shows. At that time instead an increase in steam qualities occur.
2.2. Vacuum 6essel The ITER-FEAT model for INTRA is an update version of a general ITER-FEAT mode, Fig. 1. It comprises the (VV) including space below the divertor, VV pressure suppression system (VVPSS), a generic depressurization room and a bottom drain tank [5]. The model includes all heat structures facing the VV space and has an optional tabulation for coolant injections defined by flow, temperature and steam quality at the open ends of the tube breach, see previous section.
Fig. 2. VV injection flow rates and qualities after the doubleended break of a FW cooling channel (ATHENA calculation).
J. Andersson et al. / Fusion Engineering and Design 58–59 (2001) 1017–1020
Fig. 3. Depressure behaviour in the FW cooling loop.
Shortly before 800 s the VV pressure, Fig. 4, has come to the bleed valve opening set point causing a limited blow down into the VV pressure suppression tank. After another 80 s the tank is pressurized and only a minor steady steam flow will continue. The flow via a penetration line to the generic room, initially at 1 bar, to the empty VV leads to reversed flow causing an initial slight pressure decrease in the room. Already after 150 s there is a flow reversal due to pressurising the VV. An other period of inflow from the generic room to the VV starts as the bleed suppression valves open and which effectively is completed 1200 s after the
1019
break. From this time on a minor steady flow continues from the VV to the suppression tank while the exchange between the VV and the generic room ceases. As a consequence of decreasing break flows from some 400 s the steam qualities increase maintaining mainly uniform break steam flows into the VV. At about 4000 s voided upstream coolant starts to enter the broken tubes and a total mass flow drop particularly on the 100 °C branch occurs. In the long term the pressure in the connected volumes is continuously decreasing mainly due to wall heat losses to the surroundings. At 10 000 s the pressure is down at about 0.75 bar. Thus in this case no large area disk breaks occur to the pressure suppression tank or the drain tank, compare Section 2.
4. Conclusions Break flow characteristics calculated by the simplified ATHENA model are not expected to differ sensibly from results obtained using a detailed coolant loop model. However, during the final phase of emptying the loop after bout 4000 s some differences are expected. Attention should also be paid to the break region since wall friction effects particularly due to upstream lengths assumed (here 0.5 m) for the two broken 10 mm tube ends are not negligible. An other detail concerns the ATHENA discharge coefficients which by option were 1.0 here but usually found lower in comparisons with experiments. The base case calculation performed did not show any unexpected effects from the thermal-hydraulic point of view. No radioactive releases were emitted to the environment since no parametric leak was considered.
References
Fig. 4. Pressure scenarios after break (INTRA calculation).
[1] T. Honda, H.-W. Bartels, Accident Analysis Specifications for GSSR (AAS-3), Version 3.1.1, ITER Joint Central Team, Garching, Germany, July 2000.
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J. Andersson et al. / Fusion Engineering and Design 58–59 (2001) 1017–1020
[2] O. Edlund, H. Jahn, INTRA/Mod3.3, Manual and Code Description, Volume 1— Physical Modelling and Volume 2—User’s Manual, Studsvik EcoSafe, January 2000. [3] K.E. Carlson et al., ATHENA Code Manual, EG&G Idaho Inc., Idaho Falls, June 1990.
[4] H.-W. Bartels, L. Topilski, T. Honda, Safety Analysis Data List-3 (SADL-3), Version 2.0, ITER Joint Central Team, Garching, Germany, July 2000. [5] J. Andersson, INTRA Model of ITER-FEAT for GSSR Analyses, Studsvik Eco and Safety, Technical Note, May 2000.
Intra model of ITER-FEAT and accident analysis for GSSR J. Andersson a,*, H. Jahn b, J. Eriksson a a
b
Studs6ik Eco and Safety AB, Association Euratom-NFR, SE-611 82 Nyko¨ping, Sweden Gesellshaft fu¨r Anlagen-und Reaktorsicherheit (GRS) mbH, Forschungsgela¨nde, DE-85748 Garching bei Mu¨nchen, Germany
Abstract A number of analyses and calculations of ITER reference accident sequences in the first wall (FW) and divertor coolant systems of the 1998 ITER design have previously been carried out for the Non Site Specific Safety Report (NSSR) of the 1998 ITER design. Model updates with new calculations are now ongoing to comply with the new ITER-FEAT design and provide input to the Generic Site Safety Report (GSSR). A wet containment bypass calculation has been performed assuming an in-vessel small pipe break on a FW cooling loop. The result is a smooth scenario with no high over-pressures and in the long run slow system heat loss causing a continuous pressure decrease. © 2001 Elsevier Science B.V. All rights reserved. Keywords: ITER-FEAT; In-vessel; Vacuum vessel (VV)
1. Introduction
2. Calculation model
Model developments and calculations reported here concern the category IV wet bypass accident sequence, ‘in-vessel pipe break and vacuum vessel (VV)/cryostat penetration bypass’ defined for the new ITER-FEAT design [1]. Similar analyses have previously been carried out for the Non Site Specific Report of the 1998 ITER design. The new calculations will provide input to the Generic Site Specific Safety Report (GSSR).
The main calculation is performed using the INTRA [2] code which has been developed for safety analyses of Tokamak type fusion reactors. The code predicts pressures, temperatures and fluid flows in cases such as the present one of water ingress in the VV following a double ended break on one of the many 10 mm coolant tubes in plasma facing structures. The base case calculated here considers a break in the FW at about the mid plane of the VV. 1. The model uses the VV boundary conditions case specified in [1]. 2. Break occurs and concurrently by failure a thin tubular penetration into a ‘generic bypass room’ opens.
* Corresponding author. Tel.: + 46-155-22-1868; fax: + 46155-22-1616. E-mail address: [email protected] (J. Andersson).
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 5 3 6 - 1
1018
J. Andersson et al. / Fusion Engineering and Design 58–59 (2001) 1017–1020
3. At 110 kPa VV pressure valves on bleed lines to the suppression will open. 4. At 150 kPa VV pressure rupture disks open to the suppression tank. 5. If the VV pressure reaches 160 kPa finally a bypass from the DV sump to a drain tank will open. Since the INTRA code is less applicable for the break flow calculations involving jet evaporation a simplified ATHENA model was set up to supply the break flow characteristics data needed for the INTRA calculation.
2.1. Break flow The VV injection flow characteristics following a double-ended 10 mm tube breach were separately calculated using the ATHENA code [3]. A simplified model was developed for one PFW/ BLK cooling loop. The main items of the model are [4]: 1. Level tracing pressurizer of 12.8 m3 volume. It is initially filled with steam and 8.1 m3 saturated water at 4.3 MPa. 2. The pressurizer line is top connected to two equivalent, level tracing, volumes with total water hold up 140 m3 divided into two vertical coolant branches with temperatures 100 and 152 °C, respectively. 3. At the bottom of each branch a short discharge 10 mm line is connected. 4. Each of the two break flows enter a series of small volumes with increasing areas to reach two-phase water/steam equilibrium before entering the main VV. 5. Relevant heat structures are included.
Fig. 1. INTRA node modelling scheme of ITER-FEAT.
The model updates concern mainly time or pressure dependent system boundary conditions.
3. Calculation results The rates and steam qualities of the two mass flows entering the VV after occurrence of the double ended break are shown in Fig. 2 as results from the ATHENA calculation. Both the rate from the 100 °C branch and the rate from the 152 °C branch are 5 kg/s or higher until about 500 s when a period of loop fast cooling pressure drop ends as Fig. 3 shows. At that time instead an increase in steam qualities occur.
2.2. Vacuum 6essel The ITER-FEAT model for INTRA is an update version of a general ITER-FEAT mode, Fig. 1. It comprises the (VV) including space below the divertor, VV pressure suppression system (VVPSS), a generic depressurization room and a bottom drain tank [5]. The model includes all heat structures facing the VV space and has an optional tabulation for coolant injections defined by flow, temperature and steam quality at the open ends of the tube breach, see previous section.
Fig. 2. VV injection flow rates and qualities after the doubleended break of a FW cooling channel (ATHENA calculation).
J. Andersson et al. / Fusion Engineering and Design 58–59 (2001) 1017–1020
Fig. 3. Depressure behaviour in the FW cooling loop.
Shortly before 800 s the VV pressure, Fig. 4, has come to the bleed valve opening set point causing a limited blow down into the VV pressure suppression tank. After another 80 s the tank is pressurized and only a minor steady steam flow will continue. The flow via a penetration line to the generic room, initially at 1 bar, to the empty VV leads to reversed flow causing an initial slight pressure decrease in the room. Already after 150 s there is a flow reversal due to pressurising the VV. An other period of inflow from the generic room to the VV starts as the bleed suppression valves open and which effectively is completed 1200 s after the
1019
break. From this time on a minor steady flow continues from the VV to the suppression tank while the exchange between the VV and the generic room ceases. As a consequence of decreasing break flows from some 400 s the steam qualities increase maintaining mainly uniform break steam flows into the VV. At about 4000 s voided upstream coolant starts to enter the broken tubes and a total mass flow drop particularly on the 100 °C branch occurs. In the long term the pressure in the connected volumes is continuously decreasing mainly due to wall heat losses to the surroundings. At 10 000 s the pressure is down at about 0.75 bar. Thus in this case no large area disk breaks occur to the pressure suppression tank or the drain tank, compare Section 2.
4. Conclusions Break flow characteristics calculated by the simplified ATHENA model are not expected to differ sensibly from results obtained using a detailed coolant loop model. However, during the final phase of emptying the loop after bout 4000 s some differences are expected. Attention should also be paid to the break region since wall friction effects particularly due to upstream lengths assumed (here 0.5 m) for the two broken 10 mm tube ends are not negligible. An other detail concerns the ATHENA discharge coefficients which by option were 1.0 here but usually found lower in comparisons with experiments. The base case calculation performed did not show any unexpected effects from the thermal-hydraulic point of view. No radioactive releases were emitted to the environment since no parametric leak was considered.
References
Fig. 4. Pressure scenarios after break (INTRA calculation).
[1] T. Honda, H.-W. Bartels, Accident Analysis Specifications for GSSR (AAS-3), Version 3.1.1, ITER Joint Central Team, Garching, Germany, July 2000.
1020
J. Andersson et al. / Fusion Engineering and Design 58–59 (2001) 1017–1020
[2] O. Edlund, H. Jahn, INTRA/Mod3.3, Manual and Code Description, Volume 1— Physical Modelling and Volume 2—User’s Manual, Studsvik EcoSafe, January 2000. [3] K.E. Carlson et al., ATHENA Code Manual, EG&G Idaho Inc., Idaho Falls, June 1990.
[4] H.-W. Bartels, L. Topilski, T. Honda, Safety Analysis Data List-3 (SADL-3), Version 2.0, ITER Joint Central Team, Garching, Germany, July 2000. [5] J. Andersson, INTRA Model of ITER-FEAT for GSSR Analyses, Studsvik Eco and Safety, Technical Note, May 2000.