Fukushima Nuclear Power Plant Accident and Nuclear Perspectives

Transcription

1 Fukushima Nuclear Power Plant Accident and Nuclear Perspectives Tetsuo YUHARA The University of Tokyo, the Canon Institute for Global Studies Hiroshi UJITA Tokyo Institute of Technology Fengjun DUAN The Canon Institute for Global Studies 1. Introduction Here, the Fukushima Daiichi Severe Accident is described and the direction for nuclear power after the accident is discussed. Energy mixture formation against global warming is further examined. Taking the effort for energy-saving as major premise, carbon-sequestration for fossil fuel, renewable energy and nuclear energy should be altogether developed, which means energy best mix is achieved, under the CO2 constraint around 450ppm atmosphere. 2. Severe Accident of Fukushima Daiichi Nuclear Power Plant 2.1 What happened in the Fukushima Daiichi Nuclear Power Plant East- Japan Great Earthquake is described, as follows; Magnitude of the Earthquake (Mw) is 9.0, which is ranked 4th largest in the world. All 15 plants located east coast of north Japan suffered Earthquake, while every plant was successfully shutdown as same as Kashiwazaki plants suffered large Earthquake in The first and highest tsunami wave was observed at 15:51 (65 min. after the earthquake) of March 11th at a point 50km north of the Fukushima Daiichi Nuclear Power Station. All plants were attacked by Tsunami, while observed Tsunami height only in Fukushima Daiichi Nuclear Power Plant is over actual ground level (or design height), and therefore Loss of Power phenomena have occurred in 3 plants in Daiichi site as summarized in Table 1. Status of the Nuclear Power Stations hit by the Earthquake and the Tsunami, and accident process are summarized as below; (1) On March 11th, there was a huge magnitude 9.0 earthquake that occurred off the Pacific Coast of Japan. All Nuclear Power Plants (NPPs) on the east coast were shut down safely (See Fig.1 (a)). Every emergency cooling function succesfully operated and was cooling the reactor core. (2) About one hour later, a huge tsunami hit Japan. However, all NPPs continued cooling down operations, except for Fukushima Daiichi NPP (1F), where Residual Core Cooling system still operated (See Fig.1 (b)). (3) Because 1F NPP was attacked by a tsunami that was much higher than the plant was designed for, the Sea Water Pumps and Power Supply Systems were flooded and the plant then lost the cooling systems due to a Station Blackout, etc. (See Fig.1 (c)). - Operating units (1F1, 2& 3) lost the Core and Spent Fuel Pool cooling systems - Outage unit (1F4) lost the Spent Fuel Pool cooling systems 1

2 Table 1 Status of the Nuclear Power Plants (NPPs) hit by the quake and the tsunami NPS Unit Type MWe Before Quake After Quake After Tsunami Acceleration (gal) Tsunami Height HigashiDori 1 BWR-5 1,100 Outage Cold Shutdown Cold Shutdown Onagawa 1 BWR Operating Automatic Scram Cold Shutdown 587 [529] Design: 9.1m 2 BWR Reactor Start Automatic Scram Cold Shutdown 607 [594] Ground level: 13.8m (Observed: 13m) 3 BWR Operating Automatic Scram Cold Shutdown 573 [512] Fukushima Daiichi (1F) 1 BWR Operating Automatic Scram Loss of cooling 447 [489] Design: 5.7m 2 BWR Operating Automatic Scram Loss of cooling 550 [438] Ground level: 10m (1F1-4) 3 BWR Operating Automatic Scram Loss of cooling 507 [441] 13m (1F5&6) 4 BWR Outage Cold Shutdown Cold Shutdown 319 [445] (Observed: 14-15m) 5 BWR Outage Cold Shutdown Cold Shutdown 548 [452] 6 BWR-5 1,100 Outage Cold Shutdown Cold Shutdown 444 [448] Fukushima Daini (2F) 1 BWR-5 1,100 Operating Automatic Scram Cold Shutdown 254 [434] Design: 5.2m 2 BWR-5 1,100 Operating Automatic Scram Cold Shutdown 243 [428] Ground level: 12m (Observed: 6.5-7m, 3 BWR-5 1,100 Operating Automatic Scram Cold Shutdown 277 [428] Locally >14m) 4 BWR-5 1,100 Operating Automatic Scram Cold Shutdown 210 [415] Tokai Daini - BWR-5 1,100 Operating Automatic Scram Cold Shutdown 225 [400] Ground level: 8m (Observed: 5.4m) 2

3 Figure 1(a). Accident Progression - just after the earthquake Figure 1(b). Accident Progression - just after the tsumami hit 3

4 Figure 1(c). Accident Progression - Loss of core cooling Figure 1(d). Accident Progression - S/C vent and Water injection 4

5 - Outage units (1F5& 6) successfully achieved cold shutdown through recovery measures. (4) Hydrogen explosions occurred at the units in which cooling function was lost, which may have been caused by a Zirconium-water reaction. In addition, the Reactor Building was damaged (1F1, 3&4) (See Fig.1 (d)). (5) For the units that lost the cooling system, water is continuously being injected from outside (1F1-4) (See Fig.1 (d). (6) Quite a large amount of radioactive material has been released into the atmosphere and sea, and continuous efforts are being made to bring the situation under control. Radiation level decreases gradually for three month to steady level (See Fig.2). Figure2. Radiation dose around the NPP (7) Extensive recovery efforts are being continued. Stable cooling is scheduled to take three months and cold shutdown is scheduled to take another 3 to 6 months (See Fig.3). As the total safety function status is summarized in Fig. 4, shutdown was successfully done, while cooling and containment functions were damaged. International Nuclear and Radiation Scale rating of three accidents are compared in Fig.5, Fukushima is assessed as Level 7 but release amount is one order less than Chernobyl even three units damaged. The reason why Fukushima and TMI is less release than Chernobyl is due to reactivity control capability and fission product containment potential in the water. Figure 6 shows Frequency-Consequence Curves (only for early fatalities) for Severe Accidents in various energy chains, OECD Even the Chernobyl accident, the risk is very small than other energy industries, and we cannot plot Fukushima or TMI accidents because no fatalities (people death). The issue to 5

6 be care in near future would be psychological problem such as Posttraumatic stress disorder for evacuating people, as appeared in Chernobyl case. Figure3. Future Schedule - Roadmap towards Restoration (Red colored: newly added to the previous version, : reported to the government) 2.2 Countermeasures Countermeasures, which are lessons learned from accident, are summarized here. 1. against Station Black-Out 1) Ensuring the water tightness of essential equipment facilities, such as Metal-clad switchgears and Emergency Diesel Generators. 2) Secure power supply system through diversification of Power Supply sources, Fukushima Daiichi Nos. 5 and 6 were safe due to diversification. 3) Secure robust cooling functions of reactor and containment vessel. 2. against Severe Accident Severe Accident means core melting and damage of Containment Vessel. So far Severe Accident is considered as Beyond Design Basis Accident (B-DBA), those measures should be extensively evaluated, thorough Accident Management (AM) measures. 1) Enhancement of prevention measures of hydrogen explosion 2) Enhancement of Containment Venting system 6

7 Figure 4. Station Black Out with Loss of Heat Sink Figure 5. INES Rating of three accidents 7

8 Figure 6. Frequency-Consequence Curves for Severe Accidents in Various Energy Chains OECD The causes of accident and countermeasures of safety on the NPP are considered on the aspects of regulations, designs and operations. To protect the Severe Accident under the station black out accident, safety design of NPP is further examined once more. 3. Rethinking nuclear power plant safety issues 3.1 Accident root cause analysis First of all, Fukushima Daiichi accident issues will be presented. "Assuming while not considering such event!" That is the phrase to represent the Fukushima Daiichi Accident problem. First priority for safety related personnel is that Human Factor and Common Mode Failure are always worth keeping in mind. Station Blackout: Loss of offsite Power & Emergency DG failure Site with multiple units, Earthquake and Tsunami multiple events Everything would be done completely, while by formalism Imagination lack on risk or severe condition by responsible personnel There are two items to be discussed, which are considered to be root cause of the Accident. One is Rare Event treatment; the other is Crisis Management problem, while both are due to lack of imagination by responsible personnel. Rare Event is high consequence with low frequency. Low consequence with high frequency event is easy to treat by commercial reason, while it is very difficult to handle the rare event even the risk is just the same. Unexpected event has been used frequently, but it is the risk-benefit issues to assume or not. Tsunami Probabilistic Risk Analysis has been carried out, and safety related personnel knew the severity of the effect well. Regardless of the initiating event, lack of measures to Complete Loss of Power is to be asked. 8

9 There are many Crisis Management problems as follows; Delay in initial response Delay in decision making Delay in external support request Poor collaboration among government (Prime Minister Kan), bureaucrats (NISA, JNES), and interested party (TEPCO) Poor information disclosure in emergency situation After all, it is a matter of organizational culture. Anyway, rare event occurred on one occasion, measures had to be taken. Fukushima Daiichi Nuclear power plants as National Privatization destroyed by large-scale disasters should be treated same as infrastructure systems as a national policy. 3.2 What should be done to improve the safety Safety design principle is Defense in Depth concept as shown below, which should be therefore reconsidered reflecting the accident causes. Preventing damage Failure expansion mitigation: autonomous characteristic, inherent safety (intrinsic safety) Incident prevention: a fail-safe, fool-proof, redundancy, diversity Incident expansion mitigation: confinement, control release Environmental effects mitigation: evacuation Usual systems focus on the forefront function, such as preventing damage, expansion mitigation, or incident prevention, while safety critical systems increases attention to back-up function, if it has a large enough impact on the environment. Common Mode Failure, such as External Initiating Event, which is usually Rare Event, or auxiliary systems failure is difficult to install to Defense in Depth design. Earthquake & Tsunami, Off-site Power & EDG & Buttery Sea Water Cooling Swiss Cheese Model proposed by Reason, J indicates operational problem. Fallacy of the defense in depth has frequently occurred recently because plant system is safe enough as operators not consider system safety. And then safety culture degradation would be happened, whose incident will easily become organizational accident. Such situation requires final barrier that is Crisis Management. Concept of Soft Barrier has been proposed. There are two type of safety barriers, one is Hard Barrier that is simply Defense in Depth. The other is Soft Barrier, which maintains the hard barrier as expected condition, makes it perform as expected function. Even when it does not perform its function, human activity to prevent hazardous effect and its support functions, such as manuals, rules, lows, organization, social system, etc. Soft Barrier can be further divided to two measures, one is Software for design : Common mode failure treatment, Safety logic, Usability, etc. The other is Humanware for operation, such as operator, maintenance personnel, Emergency Procedure, organization, management, Safety Culture, etc. 4. Mitigation of global warming by optimum energy mixture 9

10 Setting and meeting the common target of CO2 emission and energy mix are proposed on the basis of climate science and engineering model simulations. The feasible target for emission scenario named over-shoot and zero emission is proposed. International cooperation would enable the practical mitigation against global warming, based on cost minimum optimization over the world. Innovative and useful technologies should be introduced with well balances among renewable energy, nuclear energy and fossil energy. Target of emission scenario and long term energy vision against global warming is discussed here. Feasible CO2-emission scenario of the world, based on scientific concept is set as the target. To meet the target, world energy mix fitting to this CO2 emission scenario was optimized well-balanced between investment and merit of fuel savings. International system on simple and transparent corporations, excluding speculation for carbon offset has been proposed. Alternative and feasible global emission pathway by scientific analysis based on target of global mean temperature rise, to limit the global surface temperature rise to approximate 2 degree C compared to pre-industrial levels, to decrease the CO2 concentration by zero emission after a peak over the target concentration by Global Emission Pathway: Z650 as shown in Fig. 7(a), which means that total accumulation CO2 in this century is 650GtC. Compared with the IPCC 450ppm equilibrium stabilization scenario, the proposed global emission pathway, so called Z650 scenario, allows a relatively large emissions during the near short term as shown in Fig. 7(b). Therefore, the Z650 scenario will generate a higher CO2 concentration in the near future. The concentration will exceed 450ppm in a short period, but it will decrease and stabilize at a lower level. As the result, the Z650 scenario will cause a similar temperature rise with the IPCC 450ppm scenario as shown in Fig. 7(c). Multi gas GHG concentrations: max 2.3 degree C in 2100 and saturating 2 degree C towards Result of simulation is shown below, in which system cost minimum optimization under Z650 restriction all over the world; Total Primary Energy for Z650 shown in Fig. 8(a) continuously increases up to 2100, where both nuclear and renewable energy increase. Peak of fossil fuel consumption is around As the results, portion of Fossil: Nuclear: Renewable is 5: 2: 3 in 2050, while 3: 2: 5, in Region Total Primary Energy for Z650 is also examined as shown in Fig. 8(b). In industrialized countries, total primary energy is almost constant up to 2100, where share of fossil fuel gradually decreases and share of renewable energy mainly increases alternatively. In developing countries, total primary energy continuously increases up to 2100, where peak of fossil fuel consumption is around 2040, and both nuclear and renewable energy increase remarkably. As CO2 emission is summarized in Fig. 8(c), developing countries would be able to release CO2 much until As investment and fuel saving costs are summarized in Fig. 8(d), in industrialized countries (2005 level = 1) investment cost is $5Tri, while earn fuel saving $4Tri, and in developing countries (2005 level = 1) investment cost $8Tri, while earn fuel saving $9Tri. 5. Innovative technology and deployment Innovative technology and deployment to achieve world under CO2 constraint are proposed as follows; 10

11 Figure7. Global Emission Pathway - Z650 (a) CO2 emission; (b) Concentration; (c) Global mean temperature rise Figure 8(a). Total Primary Energy for Z650 11

12 Figure 8(b). Region Total Primary Energy for Z650 (left: industrialized countries; right: developing countries) Figure 8(c). CO2 emissions of Z650 scenario 12

13 Figure 8(d). Result of simulation Investment &fuel saving cost (1) Innovative technology 1) Replacements of clean and highly efficient fossil-power plants (Combined cycles with natural gases and gasified coals) efficiency: η=30% to 50% 60% 2) Introductions of advanced nuclear power plants (3rd + and 4th generation reactor systems) and advanced spent fuel recycle systems 3) Stabilization of unstable renewable energy with large-scaled battery and stable supply with grid networks 4) Fuel alternative in transport sector (Fuel cell vehicle and Electric vehicle) 5) Energy saving in industrial sector, especially steel, cement, paper &pulp and chemical industries (2) Deployment 1) New systems instead of the current CDM s short coming (i.e., additionality) 2) Speedy and fair deployment systems of advanced technology 3) Excluding speculations in carbon offset trading mechanism The feasible target for new emission scenario (Overshoot & Zero-Emission) instead of traditional concept and energy mix against global warming has been proposed. It demonstrated that international cooperation would enable the practical mitigation against global warming, based on cost minimum optimization over the world. It identified that innovative and useful technologies should be introduced over the world. International cooperation should be advanced with new system instead of additionality of CDM in Kyoto Protocol and without speculation of carbon trading. 6. Energy issue and role of nuclear energy after the Fukushima Daiichi Accident Premise here is that "Global warming is an invariant problem!", "Energy security is also the invariant problem!". The long-term energy demand and supply simulation to minimize the total energy system cost was conducted for energy prediction during the 21st Century in the world. Taking the effort for energy-saving as 13

14 major premise, carbon-sequestration for fossil fuel, renewable energy and nuclear energy should be altogether developed, which means energy best mix is achieved, under the CO2 constraint around 450ppm atmosphere. Nuclear phase-out scenario, in which new nuclear plant construction is prohibited, is possible even considering the issue of global warming, from simulation as shown in Fig. 9. Until around 2050, mostly replaced by natural gas. Since 2080, the contribution of the fossil power declined, large-scale introduction of the Fuel Cell. Nuclear phase-out scenario has two problems; increasing energy costs, little room for countermeasure and large uncertainties of technology. Therefore, rational use of nuclear power is requested, that is each country should make decision, Japan and several European countries will be also phase out, while China, India and ASEAN countries will continue to be introduced. If the accident happens again anywhere in, it will become the global phase-out. Therefore, rational unified safety standards (organizational structure, design and operation, regulations) should be reviewed based on the Fukushima Daiichi Problem world-wide analysis and established in the world. Figure 9. Z650 and Nuclear power phase out (no newly established since 2020) Table 2 summarizes the results. In Z650 case, idealized energy mix is obtained, well-balanced between investment and fuel saving. In Nuclear Phase Out (NuPO) case, unbalance between investment and fuels saving, and the burden on developing countries increases largely 7. Conclusion Cause of Fukushima Daiichi Nuclear Accident is simple and primitive, and can be overcome. Main cause was lack of Water tightness of switchgear, and/ or lack of water proof of emergency diesel generator. Evolutions of safety technologies of nuclear power plants, such as emergency residual heat removal system have been in progress for this half a century. The future energy outlook should not be designed by technologies in 1960 s. Now we are in the age of Generation 3+ Reactor system, which have passive safety characteristics. Nuclear power and renewable energy should be two wheels towards low carbon societies against global warming with economical growth. Under the new concept on emission scenario and with feasible advanced technologies, industrialized and developing countries can reach to low carbon societies with the optimized 14

15 energy mix by all-over-the-world-cost minimum simulation. International cooperation system against global warming should be reestablished on the basis of Science, Feasibility, and Fairness. Table 2. Summary of results/co 2 Emission, Additional investment & Fuel savings in REF, Z650, and NuPO References (1) H. Ito, JANTI Report to American Society for Mechanical Engineers, May 12, (2) Burgherr & Hirschberg, 2005, Stefan Hirschberg, , NEA/Paris 13. (3) T. Matsuno et al., Stabilization of the CO2 concentration via zero-emission in the next century, presented at the 1st CIGS Symposium on Oct. 27, (4) RCP Database (version1.0), IIASA Homepage ( (5) T. Yuhara et al., Towards the harmony - Principles for the new climate regime-, presented at the 2nd CIGS Symposium on Sep. 16,