Microsoft PowerPoint - 7-Nuclear [相容模式]

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核能技術發展 Ionizing radiation : It can cause damage to matter, particularly living tissue. At high levels it is therefore dangerous, so it is necessary to control our exposure.

At high levels it is hazardous, but at low levels such as we all experience naturally, it is harmless.

Standards for the general public are set about 20 times (Sievert) lower still, well below the levels normally experienced by any of us from natural sources.

1 核能技術發展 Ionizing radiation : It can cause damage to matter, particularly living tissue. At high levels it is therefore dangerous, so it is necessary to control our exposure. Ionizing radiation, such as occurs from uranium ores and nuclear wastes, is part of our human environment, and always has been so. At high levels it is hazardous, but at low levels such as we all experience naturally, it is harmless. Considerable effort is devoted to ensure that those working with nuclear power are not exposed to harmful levels of radiation from it. Standards for the general public are set about 20 times (Sievert) lower still, well below the levels normally experienced by any of us from natural sources. 1 Sv = 1 joule/kilogram - a biological effect. 1 Sv represents the equivalent biological effect of the deposit of a joule of radiation energy in a kg of tissue. (Gray, Gy for material) Types of Radioactive Decay (I) Types of Radioactive Decay (II) The reason alpha decay occurs is because the nucleus has too many protons which cause excessive repulsion. In an attempt to reduce the repulsion, a Helium nucleus is emitted. The way it works is that the Helium nuclei are in constant collision with the walls of the nucleus and because of its energy and mass, there exists a nonzero probability of transmission. That is, an alpha particle (Helium nucleus) will tunnel out of the nucleus. Beta decay occurs when the neutron to proton ratio is too great in the nucleus and causes instability. In basic beta decay, a neutron is turned into a proton and an electron. The electron is then emitted. 1

2 Types of Radioactive Decay (III) 游離輻射游離輻射是指波長短頻率高 (>10^16 Hz) 能量高的射線 ( 粒子或波的雙重形式 ) 輻射可分為游離輻射和非游離輻射, 游離輻射可以從原子或分子裡面電離過程中作用出至少一個電子反之, 非游離輻射則不行游離能力, 決定於射線 ( 粒子或波 ) 所帶的能量, 而不是射線的數量如果射線沒有帶有足夠游離能量的話, 大量的射線並不能夠導致游離 Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon known as a gamma particle. 游離輻射包含 :α 射線 (α 粒子 ) β 射線 (β 粒子 ) 中子 ( 僅出現於反應爐中 ) 等高能粒子與 γ 射線 X 射線等高能電磁波, 而被稱為宇宙射線的高能粒子射線則兩者皆有電磁波 ( 光子 ) 的游離能力, 隨著電磁波譜變化, 其中的 γ 射線 X 射線幾乎可以游離任何原子或分子非游離輻射是指與 X 射線相比之下波長較長的電磁波, 由於其能量低, 不能引起物質的游離, 故稱為非游離輻射如近紫外線與可見光紅外線微波和無線電波等游離能力較弱的電磁波游離輻射游離輻射當重的原子核遭到高速粒子的撞擊就可能會釋放出中子中子和原子大小差不多, 但是中子沒有電荷中子會和原子核反應而釋放出 α 粒子 β 粒子 γ 射線在生物體, 它最常跟水的氫原子和其他分子的氮原子反應具有放射活性的原子核會穩定地釋放出 γ 射線, 而對原來的原子核完全沒有影響人類每年平均會自自然 ( 佔 82%) 與人為 ( 佔 18%) 接受 mrems 的游離輻射自然的來源包括地球及宇宙 ( 宇宙射線 90% 是原子, 其餘為 α 粒子 β 粒子 γ 射線, 只有千分之一會到達地球表面 ), 在海平面每年的游離輻射量約為 30mrem, 若在高山上所接收到的量因為大氣層的稀薄而會是海平面的兩倍至於地球的游離輻射則來自有輻射活性的物質不停的衰變, 如鈾會衰變為鐳 -222 並釋放 α 粒子我們建材也會釋放少量的放射線, 住在石材的方屋中的人平均一年接受的輻射量為 10mrem 鉀對人體是必須的, 但是鉀有一種同位素鉀 -40 是有放射性的, 我們透過食物及呼吸化石燃料燃燒而吸入, 貯存在肌肉中, 每年約接受 18mrem (1 西弗 (Sv)=100 侖目 (Rem)) 而在人為的來源方面, 包括地面核子武器試爆核子反應器及核廢料工業用途醫療用途 ( 林意凡 ) ( 林意凡 ) 雖然假牙和眼鏡可能的游離輻射量很高, 不過因為會暴露的器官並不是敏感的器官, 所以並沒有很大的健康危害 2

游離輻射 Atomic and Nuclear Structure 致癌性 : 在高劑量暴露的紀錄中 ( 如二次世界大戰日本廣島的生還者 ),100 侖目的游離輻射暴露會增加 5% 罹患癌症致死的可能 (1 西弗

energy required to disassemble a whole into separate parts.

The fusion of two nuclei with lower masses than iron (which, along with nickel, has the largest binding

3 游離輻射 Atomic and Nuclear Structure 致癌性 : 在高劑量暴露的紀錄中 ( 如二次世界大戰日本廣島的生還者 ),100 侖目的游離輻射暴露會增加 5% 罹患癌症致死的可能 (1 西弗 (Sv)=100 侖目 Rem)) Binding Energy per Nucleon Binding Energy per Nucleon Binding energy is the mechanical energy required to disassemble a whole into separate parts. Binding energy is the mechanical energy required to disassemble a whole entity into separate parts. The fusion of two nuclei with lower masses than iron (which, along with nickel, has the largest binding energy per nucleon) generally releases energy, while the fusion of nuclei heavier than iron absorbs energy. The opposite is true for the reverse process, nuclear fission. 3

4 Nuclear fission Critical Nuclear fission 235 U 原子核的一種裂變過程, 235 U 原子核吸收一個中子, 變成 236 U 原子核, 然後 236 U 原子核分裂成二個快速運動的較小原子核, 並釋放三個中子, 同時也會產生 γ 射線 Chain Reaction Fission vs. Fusion 4

Nuclear Fusion The process by which two or more atomic nuclei join together, or "fuse", to form

energy Large-scale thermonuclear fusion processes, involving many nuclei fusing at once, must

Reactor Safety Design Containment Vessel 1.

thick reinforced concrete Bio Shield 4 foot thick leaded concrete with 1.

5 Nuclear Fusion The process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus Usually accompanied by the release or absorption of large quantities of energy Large-scale thermonuclear fusion processes, involving many nuclei fusing at once, must occur in matter at very high densities and temperatures. Reactor Safety Design Containment Vessel 1.5-inch thick steel Shield Building Wall 3 foot thick reinforced concrete Dry Well Wall 5 foot thick reinforced concrete Bio Shield 4 foot thick leaded concrete with 1.5-inch thick steel lining inside and out Reactor Vessel 4 to 8 inches thick steel Reactor Fuel Weir Wall 1.5 foot thick concrete Core of Nuclear Reactor Controlling Chain Reaction 控制棒有鎘或硼可吸收中子, 減低分裂速度 Fuel Assemblies Control rods 鈾燃料是百分之三的 U235 和百分之 97 的 U238 混合比例經濃縮製成約指頭大小燃料丸並堆積於燃料棒內 Withdraw control rods, reaction increases Insert control rods, reaction decreases 5

Light water reactor (LWR) Boiling water reactor Light water reactor (LWR) Pressurized water reactor The BWR is characterized by two-phase fluid flow (water and steam) in the upper

The hot water is pumped into a heat exchanger called steam generator, which allows the primary coolant to heat up and boil the secondary coolant (shown as the loop steam generator

Nuclear Fuel Cycle Handling Nuclear Waste Waste Reprocessing Recondition for further use as fuel Separates usable elements (uranium, plutonium) from spent nuclear reactor fuels Usable

6 Light water reactor (LWR) Boiling water reactor Light water reactor (LWR) Pressurized water reactor The BWR is characterized by two-phase fluid flow (water and steam) in the upper part of the reactor core. Light water (i.e., common distilled water) is the working fluid used to conduct heat away from the nuclear fuel. The hot water is pumped into a heat exchanger called steam generator, which allows the primary coolant to heat up and boil the secondary coolant (shown as the loop steam generator turbine condenser). The transfer of heat is accomplished without mixing the two fluids. Nuclear Fuel Cycle Handling Nuclear Waste Waste Reprocessing Recondition for further use as fuel Separates usable elements (uranium, plutonium) from spent nuclear reactor fuels Usable elements are then reused in a nuclear reactor Other waste products (e.g., radioactive isotopes) must be disposed of Waste Disposal Temporary storage Permanent disposal (usually burial) Funded by power customers (US 0.1 cent ; 台灣 0.17 元 per kwh) ( 核後端基金累積至 2012 年 12 月達 2,331 億元 ) 6

Nuclear Waste Disposal Cooled in a spent fuel pool 10 to 20

available Central permanent buried disposal Decay of Nuclear PP

is that their radioactivity decays dramatically.

than one thousandth of its level at the time the spent fuel is

delay disposal until radioactivity has decayed to such a level.

Nuclear Power Plants, nuclear power capacity 1995-2012 (IAEA

7 Nuclear Waste Disposal Cooled in a spent fuel pool 10 to 20 years Onsite temporary dry storage Until permanent site becomes available Central permanent buried disposal Decay of Nuclear PP Waste The spent rods are placed in the pool next to the reactor, where they can cool down. dry storage The distinctive feature of high-level nuclear wastes is that their radioactivity decays dramatically. After 40 years, the heat and radioactivity has dropped to less than one thousandth of its level at the time the spent fuel is removed from the reactor, providing a technical incentive to delay disposal until radioactivity has decayed to such a level. Meanwhile they are easily and safely stored. Yucca Mountain Burial Site Nuclear Power Policy Worldwide Nuclear Power Plants, nuclear power capacity (IAEA 2014) Number of reactors in operation, worldwide (IAEA 2014) Number of reactors under construction, (IAEA 2014) 7

Nuclear power plants worldwide, in operation and under construction, IAEA as of 11 March 2014 Nuclear Power Policy and Development in USA 104 units in operation Provide 20% of electricity 35 units

Power 2010: to seek NRC approval to build and operate at least one new advanced nuclear power plant --Nuclear Education Long term policy: Advanced Fuel Cycle Initiative Generation IV Nuclear Energy

construction Provide 30% of electricity 8 units to be constructed in the next 5 ~10 years Close fuel cycle policy: reprocess all spent fuels; first reprocessing plant plans to operate in 2007 Long

8 Nuclear power plants worldwide, in operation and under construction, IAEA as of 11 March 2014 Nuclear Power Policy and Development in USA 104 units in operation Provide 20% of electricity 35 units obtained permit from NRC (Nuclear Regulatory Commission) for life extension of 20 years as of September 2005 Nuclear share in electricity generation, 2012 (IAEA 2014) Short term policy: --Nuclear Power 2010: to seek NRC approval to build and operate at least one new advanced nuclear power plant --Nuclear Education Long term policy: Advanced Fuel Cycle Initiative Generation IV Nuclear Energy Systems Initiative Nuclear Hydrogen Initiative Nuclear Power Policy and Development in USA Nuclear Power Policy and Development in Japan (No Running Reactors Now) 55 units in operation; 2 units under construction Provide 30% of electricity 8 units to be constructed in the next 5 ~10 years Close fuel cycle policy: reprocess all spent fuels; first reprocessing plant plans to operate in 2007 Long term planning: development of sodium cooled fast breeder reactor JAEA (Japan Atomic Energy Agency) completed lab test for hydrogen generation using thermochemical process in 2004 with a generation rate of 0.03m 3 /h; pilot plant with generation rate of 30 m 3 /h in 2010; a prototype plant in 2015 with a generate of 1000 m 3 /h; to be commercialized in

Nuclear Power Plants in Japan Nuclear Power Policy and Development in France 59 units in operation Provide 78% of electricity Developing third generation PWR (Pressurized water reactor ) with

and manufacturing of MOX fuels Long term planning: Sodium cooled fast breeder reactor; gas cooled fast breeder reactor Nuclear Power Policy and Development in China 9 units in operation ( 9,110 MWe)

9 Nuclear Power Plants in Japan Nuclear Power Policy and Development in France 59 units in operation Provide 78% of electricity Developing third generation PWR (Pressurized water reactor ) with capacity of 1600 MWe; Finland is constructing one and France plans to build a new one; use MOX (Mixed oxide of U and Pu) fuels With full close fuel cycle plants and provide service of reprocessing and manufacturing of MOX fuels Long term planning: Sodium cooled fast breeder reactor; gas cooled fast breeder reactor Nuclear Power Policy and Development in China 9 units in operation ( 9,110 MWe) providing 2.2% electricity Nuclear Power Policy and Development in China 4 units under construction Nuclear power installation reaching 40 GWe in 2020 (about 40 units) 200 GWe in 2050, possibly a largest nuclear power country, providing 12.5% of electricity Complete design of third generation PWR by 2006 Aggressive sodium-cooled FBR program: 25 MWe CEFR by 2008; 600MWe by 2020; 1000~1500 MWe by 2030 ~ MW High Temperature Gas Cooled Reactor and nuclear hydrogen at Tsing Hua University, Beijing 9

核能事件分級表 (International Nuclear Event Scale, INES)

10 爐心熔毀 1. 爐心熔毀是核反應爐因無法及時冷卻而熔化造成的損毀 2. 爐心熔毀後可引發具有放射性的物質外洩, 並人類及其他生物罹患嚴重後遺症福島第一核電站事故 2011 年 3 月 11 日宮城縣東方外海發生規模 9.0 大地震之後發生之事故, 福島第一核電站 ( 典型沸水反應爐 ) 因此次地震造成部分爐心熔毀核能事件分級表 (International Nuclear Event Scale, INES) o/#/video/world/2011/03/1 4/dnt.japan.reactor.explai ner.nhk?hpt=c2 10

三哩島 (Three Mile Island) 核泄漏事故 March 28, 1979 Partial core meltdown over 5 days Main feedwater pumps failed Backup feedwater system was inoperative Instrumentation failed; operators unaware Should

11 三哩島 (Three Mile Island) 核泄漏事故 March 28, 1979 Partial core meltdown over 5 days Main feedwater pumps failed Backup feedwater system was inoperative Instrumentation failed; operators unaware Should region around TMI be evacuated? No fatalities; little radiation exposure Cleanup lasted 14 years; cost $975 million Public confidence shaken 51 US nuclear reactor orders cancelled 三哩島核泄漏事故核子管制委員會 (Nuclear Regulatory Commission) 對周圍居民進行了連續追蹤研究, 研究結果顯示在以三哩島核能發電廠為圓心的 50 英里範圍內的 220 萬居民中無人發生急性輻射反應周圍居民所受到的輻射相當於進行了一次胸部 X 光照射的輻射劑量三哩島核泄漏事故對於周圍居民的癌症發生率沒有顯著性影響三哩島附近未發現動植物異常現象當地農作物產量未發生異常變化但是, 泄漏事故造成核能發電廠二號堆嚴重損毀, 直接經濟損失達 10 億美元之鉅車諾比核能電廠事故 1986 年 4 月 26 日星期六, 當地時間早上 1 點 23 分 45 秒, 車諾比核電站的 4 號核反應爐功率大規模災難性地激增, 導致蒸汽爆炸, 撕裂反應爐的頂部, 核心暴露, 並散發出大量的放射性微粒和氣態殘骸 ( 主要是銫 -137 和鍶 -90), 使空氣 ( 氧氣 ) 與超高溫核心中的 1700 噸可燃性石墨減速劑接觸 ; 燃著的石墨減速劑加速了放射性粒子的洩漏洩漏原因部分是由於放射性物質並沒有被裝在圍阻體中 ( 不像大多數西方的核電站, 蘇聯的反應爐通常沒有這種裝置 ) 隨後放射性粒子隨風穿越了國界車諾比核能電廠事故意外發生後, 馬上有 203 人立即被送往醫院治療, 其中 31 人死亡, 當中更有 28 人死於過量的輻射死亡的人大部份是消防隊員和救護員, 因為他們並不知道意外中含有輻射的危險於 2005 年九月份, 聯合國國際原子能機構世界衛生組織聯合國開發計劃署烏克蘭和白俄羅斯政府以及其他聯合國團體, 一起合作完成了一份關於核事故的總體報告報告指出事件死亡人數共達 4000 人, 世界衛生組織更包括了死於核輻射的 47 名救災人員, 和九名死於甲狀腺癌症的兒童聯合國於 2006 年四月份公佈世界衛生組織的結果, 也許有另外 5000 多名受害者死於輻射塵地區 ( 包括烏克蘭白俄羅斯和俄羅斯等地 ) 所以, 總數達約 9000 名受害者 11

Causes of Chernobyl No containment building Poor reactor design (unsafe) Inserting control rods initially increased reactor energy generation Operators were careless & violated plant procedures

(boiling water reactor)+ 核 3 廠 2 PWRs (Pressurized water reactor )] Providing 20% of electricity (8% of energy) 2 units under construction : 核 4 廠 2 ABWRs (Advanced Boiling Water Reactor) Policy:

Total Life-cycles Costs CO2 Emission Fuel Consumed Every Day for a 3000MW Power Plant "By life-cycle costs, I mean the total costs of building, operating, maintaining, fueling and decommissioning a

12 Causes of Chernobyl No containment building Poor reactor design (unsafe) Inserting control rods initially increased reactor energy generation Operators were careless & violated plant procedures Switched off many safety systems Withdrew too many control rods Causes still in dispute by various parties Nuclear Power Policy and Development in Taiwan 6 units in operation [ 核 1 與核 2 廠 4 BWRs (boiling water reactor)+ 核 3 廠 2 PWRs (Pressurized water reactor )] Providing 20% of electricity (8% of energy) 2 units under construction : 核 4 廠 2 ABWRs (Advanced Boiling Water Reactor) Policy: Nuclear Free Homeland but keep the existing plants running until the end of their lives and complete the construction of 4th plant and operation of the plant there after. Total Life-cycles Costs CO2 Emission Fuel Consumed Every Day for a 3000MW Power Plant "By life-cycle costs, I mean the total costs of building, operating, maintaining, fueling and decommissioning a thermal power plant, a solar array, a wind farm or hydroelectric dam over its life, that is, 15 years for a wind turbine, 40 years for a fossil fuel plant, 60 years for a nuclear plant, or 80 years for a large hydroelectric dam. Dividing those total costs by the amount of energy actually produced, not theoretically possible or installed capacity but actually produced, gives a life-cycle cost in /kwhr. How we finance this cost is a totally different issue, one at which we generally fail as a society." ( James Conca of Forbes, 2012) 12

民營再生能源電廠分布圖 Nuclear Power Policy in Taiwan 歷年裝置容量占比歷年發電量占比更新日期 :2013-05-06

其餘國家採 IEA 統計之 2010 年資料 ( 大陸上海深圳採 2011 年資料 ) 中子不帶電荷, 可以無限制地接近原子核, 中子與原子核間可能發生的反應,

當中子具有的能量與中子在原子核內軌道運動的能階差相同時, 特別容易被吸收核分裂反應釋出之中子為快中子 ( 即動能較高, 移動速度較快 ), 能量介於 10 5

中子透過碰撞時之能量交換, 減速成為慢中子 ( 或稱為熱中子, 能量小於 10-2 電子伏特 ), 此類型反應器稱為熱中子反應器, 可以使用鈾 235 含量 (

13 民營再生能源電廠分布圖 Nuclear Power Policy in Taiwan 歷年裝置容量占比歷年發電量占比更新日期 : 電價及單位成本結構比較 ( 台電 ) 中子 1. 資料來源 : 台電公司 2. 南韓係以 2011 年平均單價按 2012 年 ( 整體 +4.9%, 住宅 +3% 工業 +6%) 電價調整幅度估算 3. 臺灣調整前電價採 2011 年平均電價, 調整後電價採估計之 2012 年平均電價 ( 已考量 6/10 調價因素 ) 4. 其餘國家採 IEA 統計之 2010 年資料 ( 大陸上海深圳採 2011 年資料 ) 中子不帶電荷, 可以無限制地接近原子核, 中子與原子核間可能發生的反應, 包括彈性散射非彈性散射中子吸收帶電粒子反應中子產生反應及核分裂等各種反應中子與原子核發生何種反應的機會與核種及中子行進的速度 ( 或中子的動能 ) 有關當中子具有的能量與中子在原子核內軌道運動的能階差相同時, 特別容易被吸收核分裂反應釋出之中子為快中子 ( 即動能較高, 移動速度較快 ), 能量介於 10 5 ~10 7 電子伏特 (ev) 間快中子較不易誘發核分裂反應, 故在設計核反應器時, 需於反應器的爐心置入質量數較輕的核種做作為減速材料 ( 緩和劑 ), 中子透過碰撞時之能量交換, 減速成為慢中子 ( 或稱為熱中子, 能量小於 10-2 電子伏特 ), 此類型反應器稱為熱中子反應器, 可以使用鈾 235 含量 ( 濃縮度 ) 較低的鈾或天然鈾為燃料用石墨為緩和劑的反應器, 分裂產生的快中子在減速過程中, 中子能動減緩較趨近連續, 故較易成為所謂的共振區中子, 為鈾 238 核所吸收, 產生鈽 239 若使用普通水 ( 輕水 ) 為緩和劑, 中子有可能一次碰撞, 即喪失全部動能, 跳過共振區, 成為熱中子 ; 故利用普通水當緩和劑的反應器不適合生產鈽李敏 ( 科學月刊, 2011) 13

反應器 Generation IV Nuclear Energy System 可孕核種 : 吸收中子後可以成為可裂核種的原子核 ; 鈾 235 ; 鈽 239 ( 鈾

: 當核分裂反應是由快中子激發時, 會比慢中子引發之核分裂反應釋出更多的中子, 在維持核分裂反應的同時, 有足夠的中子將鈾 238 核轉換為鈽 239 核,

14 反應器 Generation IV Nuclear Energy System 可孕核種 : 吸收中子後可以成為可裂核種的原子核 ; 鈾 235 ; 鈽 239 ( 鈾 238 原子核吸收一個中子後, 經過二次 γ 衰變 ) ; 鈾 233 ( 釷 232 吸收中子經二次 β 衰變 ) 熱中子反應器 : 消耗的可裂核種 ( 鈾 235), 然而天然鈾中的鈾 235 含量僅占 0.7%, 待鈾 235 用罄後, 剩下的鈾 238 將無法使用僅靠熱中子反應器的核分裂來提供核能, 估計只能使用數十年到近百年現使用之輕水式反應爐均屬此類快中子反應器 : 當核分裂反應是由快中子激發時, 會比慢中子引發之核分裂反應釋出更多的中子, 在維持核分裂反應的同時, 有足夠的中子將鈾 238 核轉換為鈽 239 核, 故在消耗可裂核種的同時, 會產生更多的可裂核種 ( 鈽 239), 亦即有滋生 (breeding) 的效果, 故快中子反應器又稱為滋生反應器李敏 ( 科學月刊, 2011) Generation IV Nuclear Energy System 李敏 ( 科學月刊, 2011) 李敏 ( 科學月刊, 2011) 14

15 GOALS FOR GENERATION IV GOALS FOR GENERATION IV Sustainbility-1: clean air; long-term availability of systems; effective fuel utilization Sustainbility-2: minimize and manage their nuclear waste and notably reduce the long-term stewardship burden; thereby improving protection for the public health and the environment Proliferation resistance and physical protection: increase the assurance that they are a very unattractive and the least desirable route for diversion or theft of weapons-usable materials, and provide increased physical protection against acts of terrorism. Economics-1: have a clear life-cycle cost advantage over other energy sources; Economics-2: have a level of financial risk comparable to other energy projects Safety and reliability-1: excel in safety and reliability Safety and reliability-2: have a very low likelihood and degree of reactor core damage Advanced Research Designs Generation IV Reactors Molten salt reactor ( 熔鹽式反應器 )( 熱 ) Supercritical water reactor ( 超臨界水反應器 )( 熱 ) Very high temperature reactor ( 超高溫氣冷反應器 ) ( 熱 ) Gas cooled fast reactor ( 氣冷式快滋生反應器 )( 快 ) Lead cooled fast reactor ( 鉛冷卻快滋生反應器 )( 快 ) Sodium-cooled fast reactor( 鈉冷卻快滋生反應器 )( 快 ) GOALS FOR GENERATION IV 第四代反應爐有以下優點 : - 核廢料仍有放射性, 但半衰期已從數百萬年降至數百年 - 使用新式設計, 同樣數量的核燃料多產出 100 至 300 倍的能量 - 可利用消耗現有核廢料產電 - 大幅改善運轉安全性一種無法預測的問題是當操作員對新式反應爐運作不熟悉時, 可能會有較高風險核工程師大衛洛克博姆認為大部份的核事故都是這樣造成的, 他說 : 我們無法模擬操作員會犯怎樣的錯誤美國某研究實驗室主任說 : 生產建造維護新式核電廠會面臨新的學習問題, 也許技術證明可行, 但人類卻會犯錯 (Wiki) 15

16 Very-High-Temperature Reactor Very-High-Temperature Reactor (VHTR)- utilizing a graphitemoderated core. This reactor design envisions an outlet temperature of 1,000 C. The reactor core can be either a prismatic-block or a pebble bed reactor design. The high temperatures enable applications such as process heat or hydrogen production via the thermochemical iodine-sulfur process. 超高溫反應爐 (VHTR) 的設計概念是運用石墨作為減速劑氦氣或熔鹽作為冷卻劑此設計設想出水口溫度可達 1000 C, 爐心則可採燃料束或球床式反應爐高溫可用於產熱或產氫製程 (Wiki) 美國已選定其為下一世代核反應器, 而第一部示範機組預定於 2021 年開始商轉 ( 李敏, 科學月刊, 2011) 第一個實驗性 VHTR 在南非建成 ( 南非球床模組反應爐 ), 但已於 2010 年 2 月停止挹注資金成本提高與難以突破的技術困難, 使投資人與消費者躊躇不前 (Wiki) Supercritical-Water-Cooled Reactor Supercritical-Water-Cooled Reactor (SCWR)- using supercritical water as the working fluid. SCWRs are basically light water reactors (LWR) operating at higher pressure. As most commonly envisioned, it would operate on a direct cycle, much like a Boiling Water Reactor (BWR), but since it uses supercritical water as the working fluid, would have only one phase present, like the Pressurized Water Reactor (PWR). It could operate at much higher temperatures than both current PWRs and BWRs. 超臨界水反應爐 (SCWR) 使用超臨界水作為工作流體 SCWR 是以輕水反應爐 (LWR) 為基礎, 運作於高溫高壓環境, 採取直接一次性循環最初的設想是 : 採取如同沸水反應爐 (BWR) 的直接循環但在改用超臨界水作為工作流體後, 水便為單一相態, 類似壓水反應爐 (PWR) SCWR 的可運作溫度比 BWR 與 PWR 還高由於 SCWR 具有較高的熱效率與簡單的設計結構, 成為倍受關注的新式核反應爐系統目前 SCWR 主要目標是降低發電成本 SCWR 是以兩種科技為基礎進一步發展而成 : 輕水反應爐與超臨界蒸氣鍋爐前者是世界上大部分商轉中的反應爐類型 ; 後者也是常用的蒸汽鍋爐類別 (Wiki) Molten Salt Reactor Molten Salt Reactor (MSR) - is a type of nuclear reactor where the coolant is a molten salt. 熔鹽反應爐 (MSR) 是一種反應爐類型, 其冷卻劑甚至是燃料本身皆是熔鹽混和物這有許多不同細部設計的延伸型, 目前也已建造了幾個實驗原型爐最初和目前廣泛採用的概念, 是核燃料溶於氟化物中形成金屬鹽類, 如 : 四氟化鈾 (UF 4 ) 和四氟化釷 (ThF 4 ) 當燃料熔鹽流體流入以石墨減速的爐心內時, 會達到臨界質量現行大部分設計是將熔鹽燃料均勻分散在石墨基體中, 提供低壓高溫的冷卻方式 (Wiki) 熔鹽式反應器的燃料為液態, 鈾溶解於氟化物中, 於管路中循環, 當流體流入石墨構成的爐心時, 滿足臨界的條件, 發生核分裂反應, 也會產生新的可裂物質液態燃料可以流入再處理裝置, 將分裂產物與可裂核種移除熔鹽式反應器可以用來消耗使用過的核燃料中半衰期極長的超鈾原素其實, 熔鹽式反應器並非新的設計, 美國早在核反應器發展的初期, 即曾嘗試將此反應器用於航空器的推動, 亦曾建構兩個示範機組 ( 李敏,2011) 鈉鉛金屬冷卻快滋生反應器鈉金屬冷卻快滋生反應器與鉛金屬冷卻快滋生反應器並非新的設計, 世界第一座產生電力的反應器即為鈉冷滋生反應器, 目前日本中國均有示範型之鈉冷反應器, 蘇俄已有發電之鈉冷反應器機組, 將此型機組列入四代核反應器的概念發展有宣示性的意味, 而鉛冷卻快滋生反應器早已在蘇俄的潛艇上使用四代核反應器中的鉛冷反應器的設計, 是將反應器相關組件封在一個盒子內, 能連續使用數十年不用換燃料, 在反應器內的可裂核種逐漸消耗的同時, 亦產生新的可裂核種, 以維持臨界, 待反應器已無法達臨界時, 再將整個反應器運走, 使用者將沒有機會接觸到核燃料, 大幅降低核武器材料擴散的可能性快滋生反應器除了可以滋生可裂核種外, 亦可燒掉使用過核燃料中的半衰期極長的超鈾原素, 縮短理論上高階核廢料需要照管的時間 ( 李敏,2011) 16

17 快中子反應爐 Gas-Cooled Fast Reactor (GFR)- features a fast-neutron spectrum and closed fuel cycle for efficient conversion of fertile uranium and management of actinides. The reactor is helium-cooled, with an outlet temperature of 850 C and using a direct Brayton cycle gas turbine for high thermal efficiency. Sodium-Cooled Fast Reactor (SFR)- cooling by liquid sodium and fueled by a metallic alloy of uranium and plutonium. The fuel is contained in steel cladding with liquid sodium filling in the space between the fuel and the cladding. Nuclear Power Pro and Con Lead-Cooled Fast Reactor (LFR)- featuring a fast-neutron-spectrum lead or lead/bismuth eutectic (LBE) liquid-metal-cooled reactor with a closed fuel cycle. The LFR is cooled by natural convection with a reactor outlet coolant temperature of 550 C, possibly ranging up to 800 C with advanced materials. The higher temperature enables the production of hydrogen by thermochemical processes. Disadvantages of Nuclear Power Possibly disastrous accidents Nuclear waste dangerous for thousands of years unless reprocessed Risk of nuclear proliferation associated with some designs High capital costs Long construction periods largely due to regulatory delays High maintenance costs High cost of decommissioning plants Designs of current plants are all large-scale Advantages of Nuclear Power Substantial base load energy producing capability No greenhouse gas emissions during operation Does not produce air pollutants The quantity of waste produced is small Small number of major accidents only 2 (TMI & Fukushima) in types of plants in common use Low fuel costs; Large fuel reserves Ease of transport and stockpiling of fuel Future designs may be small and modular 17

圖二. 壓水式輕水反應堆核電站示意圖如圖一所示, 當可裂變的鈾 -235 核吸收一個中子, 核裂變就發生了裂變將鈾 -235 核分為兩個具有動能的較小的核 ( 如鍶 -90 和氙 -143)

圖二. 壓水式輕水反應堆核電站示意圖如圖一所示, 當可裂變的鈾 -235 核吸收一個中子, 核裂變就發生了裂變將鈾 -235 核分為兩個具有動能的較小的核 ( 如鍶 -90 和氙 -143) 福島核危機背後的科學繆謙 ( 香港中文大學化學系 ) 翻譯自 Science behind the Fukushima Nuclear Accident by W. H. Chan, Department of Chemistry, Hong Kong Baptist University, 原英文本已上載於 IYC2011 Forum 引言