Improved power supply after Fukushima and OPC in Japanese BWRs

Transcription

1 BWR-club workshop on Robust Power in Uppsala Improved power supply after Fukushima and OPC in Japanese BWRs May 3 rd, 2017 Hitachi-GE Nuclear Energy, Ltd Masashi Sugiyama Hitachi-GE Nuclear Energy, Ltd All rights reserved.

2 Improved power supply after Fukushima and OPC in Japanese BWRs Contents 1.Current Situation of Japanese BWRs 2.Fukushima trouble experience 3.Improvements 4.Open phase Condition Hitachi-GE Nuclear Energy, Ltd All rights reserved.

3 1-1. Current Situation of Japanese BWRs Unfortunately, None of BWR power plants resume operation after Fukushima accident. We had twenty-eight (28) operating BWRs including Fukushima Daiichi, four (4) units were under construction and four (4) were planning stage power plants before the accident. Eight (8) units including six (6) units of Fukushima Daiichi were decided to be decommissioning. The other units, especially Kashiwazaki-Kariwa unit 7 (ABWR), Shimane unit 2 (BWR5), Onagawa unit 3 (BWR5), and Tokai unit 2 (BWR6) are under assessment to restart. On the other hands, nine (9) units out of twenty-six (26) PWRs have already got the permission to restart. Hitachi-GE Nuclear Energy, Ltd All rights reserved. 2

4 2. Fukushima Trouble Experience On March 11 th All of off-site power was lost due to the earthquake. As for Fukushima Unit 1-4, there were 4 lines of 275kV and 1 line of 66kV, 2 lines of 275kV were lost due to the ACB failures in the switchyard. As for the rest of 2 lines, one line was under construction to replace ACB with GCB and another line was flood affected by Tsunami. The ACBs in the off-site substation were broken caused by earthquake. The cables from 66kV switchyard to unit 1 switchgear were lost due to the earthquake. (The 66kV line itself was available.) 2. All of medium voltage switchgears was flood by Tsunami. Due to the old design, separation between redundant systems was insufficient. 3. All of DGs successfully started as designed after LOPA but they were lost due to Tsunami. 4. DC power supplies except unit 3 was lost due to Tsunami. Hitachi-GE Nuclear Energy, Ltd All rights reserved. 3

5 3-1. Off-site power LOPA by CCF In case of Fukushima, all of off-site power except 66kV line came from only one Substation. The 66kV line was not considered as back-up off-site power for safety systems. The ACBs in the Substation were broken due to earthquake. To confirm at least two independent substations and the independent transmission lines shall be able to feed off-site power to the NPP. To confirm GIS application which has stronger seismic resistance. To confirm separation. Some modification have been done at the cable space under the main control room floor. Hitachi-GE Nuclear Energy, Ltd All rights reserved. 4

6 3-2. On-site power source Improvement against SBO Additional power sources 1) Additional switchgears on the hill. 2) Additional on-site power supply ( GTG etc.) 3) Mobile power sources ( Trucks) with the connection panels for them. 4) Additional batteries for RCIC on the higher floor. Load shedding on the other div. batteries. Extended the design base DC power supplies' coping time from 8hrs to 12hrs. Hitachi-GE Nuclear Energy, Ltd All rights reserved. 5

7 3-3. Improvement against Tsunami Improvement against Tsunami Physical protections 1) Embankment 2) Sea wall 3) Waterproof doors 4) Stagnant at the penetrations ( pipes and trays) Hitachi-GE Nuclear Energy, Ltd All rights reserved. 6

8 3-4. Improvement against the other hazards The other hazards have been estimated. Earthquake Tornado 1)Fixing outside facilities such as DG oil pumps. 2)Enhanced or underground DG fuel tanks Neighborhood fire 1)Fire belt surrounding the buildings. The inner overflow 1) Water proof ( cable and pipe penetrations, Hatch's, HVAC ducts and doors.) 2) Prevention of the counter flow of the floor drains. Hitachi-GE Nuclear Energy, Ltd All rights reserved. 7

9 3-5. Improvement against the other hazards Fire 1) Separation 2) Fire wall Snow Low temperature Eruption of Volcano Lightning Hitachi-GE Nuclear Energy, Ltd All rights reserved. 8

10 4. Open Phase Condition Current Situation Lower risk, compare with the U.S. plants 1) CV cable connections between Switchyard to start-up transformers. No overhead transmission lines nor air insulation points. 2) Multiple overhead transmission lines. The risk of open phase condition of the switchyard bus is low. Protection relay for OPC is now under development. 1) Transformer excitation current, 3 phase currents and 3 phase voltages both magnitudes and angles are detected. 2) Proper logic to detect OPC in any case is under consideration. Hitachi-GE Nuclear Energy, Ltd All rights reserved. 9

11 Thank you for your attention Hitachi-GE Nuclear Energy, Ltd All rights reserved. 10