Accident assessment for DCLL DEMO design

1. Accident assessment for DCLL DEMO design Susana Reyes TBM Project meeting, UCLA, Los Angeles, CA March 2-4, 2005 Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

2. Outline • Preliminary accident analysis for DCLL DEMO • Decay heat removal results for DCLL TBM • Summary of cross-section uncertainty analysis for DC DEMO activation results

3. Preliminary accident assessment of DCLL DEMO concept • Created MELCOR thermal-hydraulics model for DCLL DEMO accident assessment • Model represents ¼ of the full-scale reactor • Dimensions and nuclear heating values from M. Sawan; decay heat results from M. Youssef • Values for temperatures, mass flows and pipes taken from S. Malang’s memo (8/16/04) • Several iterations needed to adjust the balance of plant, heat exchangers, etc

4. Top View Outboard Inboard High Temp shield Vacuum vessel(VV) IB Blanket OB Blanket High Temp shield Vacuum vessel(VV) Secondary Secondary Pressurizer Drain tank Model is 1/4th of full reactor PbLi temperatures 460/700°C PbLi mass flow 329 kg/s He temperatures 360/460°C He mass flow 20 kg/s Radial View Outboard Inboard Blanket Blanket High temp High temp shield LiPb HX shield Accumulator chamber Plasma VV VV He HX LiPb pipes He pipes

5. High Temp shield IB Blanket OB Blanket High Temp shield Vacuum vessel(VV) Outboard Inboard Vacuum vessel(VV) In-blanket He LOCA has been modeled • Preliminary accident analysis for a loss of He coolant (LOCA) into the breeder blanket • Model assumes break of one FW cooling channel and leakage of He gas (8 MPa) to first LiPb breeder channel (1 MPa) • Reactor is scrammed and pumps coast down on a high blanket pressure signal, immediately after accident • We want to assess pressurization of the blanket during the accident Plasma chamber

6. MELCOR results for in-blanket LOCA • MELCOR results show pressurization of blanket occurs in only ~ 4 seconds • Drain line opens 100 s after the accident occurs • FW temperature cools down by radiation to vacuum vessel after drain line opens

7. 600 TBM FW (high performance) 500 ITER FW 400 Temperature (C) TBM FW (baseline) 300 200 8 10 0 2 4 6 Time (d) Assessment of DCLL TBM Passive Decay Heat Removal • ITER safety requirement is that decay heat removal should be achieved by thermal radiation to the basic machine • CHEMCON 1D heat transfer model of DC TBM was used for this analysis with decay heating from M. Youssef • Adequate decay heat removal demonstratedby thermal radiation to ITER in-vessel structures • Maximum FW temperature ~ 595 °C at 1 hr due more to thermal equilibration rather than decay heating CHEMCON Results

8. Analysis of effect of cross-section uncertainty on DEMO FW activation • Completed uncertainty analysis using Monte Carlo procedure included in the ACAB code • Method uses simultaneous random sampling of all XS probability density functions involved in the problem • Nuclear data from European Activation File (EAF-2003): EAF_XS (Cross sections), EAF_UN (XS Uncertainty), EAF_DEC(Decay Data) • Inventory predictions for 60Co and 94Nb, are responsible for significant errors at long cooling times (>8 yrs, significant for waste management) • The XSs 59Co(n,g-m) 60mCo and 93Nb(n,g-m) 94mNb have been identified as those need of improvement for an overall reduction of the uncertainty

9. Summary • Preliminary in-blanket LOCA analysis for DCLL DEMO design shows pressurization of blanket module would occur~ 4 seconds • LOFA assessment for DCLL TBM demonstrates adequate decay heat removal by thermal radiation to ITER in-vessel structures • Completed activation cross section uncertainty analysis for DEMO FW and identified cross sections 59Co(n,g-m) 60mCo and 93Nb(n,g-m) 94mNb as those need of new measurements for overall improvement of FW activation predictions