Basis and Safety Case of Spent Fuel Storage

Transcription

1 Basis and Safety Case of Spent Fuel Storage T. Saegusa, K. Shirai, M. Wataru, H. Takeda, K. Namba CRIEPI, Japan May 2014 IAEA Work Shop on DPC Safety Case May 19-21, 2014 CRIEPI 1/37

2 Safety Case of Spent Fuel Storage CRIEPI Concept of safety case in GSR Part 5; The safety case is a collection of arguments and evidence in support of the safety of a facility or activity. The safety case will normally include the findings of a safety assessment, and will typically include information (including supporting evidence and reasoning) on the robustness and reliability of the safety assessment and the assumptions made therein. ERC CRIEPI 2/37

3 1. Spent Fuel Characteristics and Need for Storage 2. Safety Regulations, Code and Standard 3. Metal Cask Storage 4. Concrete Cask Storage 5. Vault Storage 6. Spent Fuel Integrity 7. Others Contents 2.1 New Regulatory Requirements 3.1 Design Concepts and Economy 3.2 Heat Removal 3.3 Containment 3.4 Sub-Criticality 3.5 Structural Integrity 3.6 Seismic Performance 3.7 Severe Accident Performance 3.8 Interaction between Transport and Storage CRIEPI 3/37

4 2.5 Safety Regulations, Code and Standard -Four Safety Functions 1. Confinement of the radioactive material 3. Criticality Prevention 2. Shielding (control of external radiation level) 4. Heat Removal (prevention of damage caused by heat) CRIEPI 4/37

5 2.1 New Regulatory Requirements after Fukushima Air in CRIEPI 5/37

6 2.1(1) Other Safety Measures Consideration of Natural Phenomena Safety shall not be lost by earthquake, tsunami, etc. If the storage building were collapsed by the natural phenomena, the basic safety functions shall not be affected. With appropriate measures and period, the shielding and heat removal functions shall be recovered. Multiple initiating events occurring simultaneously shall be considered. CRIEPI 6/37

7 2.1(2) Other Safety Measures Consideration of External Event Safety shall not be lost by accidental external man-made disaster. Spent fuel storage facilities shall be designed to protect airplane crash with a probability more than 10-7 /year. Spent fuel storage facilities shall be designed by appropriate measures to protect illegal access of outsiders. CRIEPI 7/37

8 2.1(3)Comparison with International Regulations The new regulations includes requirements of IAEA GSR Part 5 Predisposal Management of Radioactive Waste and SSG-15 Storage of Spent Nuclear Fuel. The new regulations added a heat removal requirement referring German Safety Guidelines for dry Interim Storage of Irradiated Fuel Assemblies in Storage Casks. CRIEPI 8/37

9 3.2(1) Heat Removal -Cask building with chimney- Open or Closed Inlet 排気スタ Outlet ック開閉部 Scale: 1/5 Fan Cask model 模 7700 擬 Unit : mm キ Video of an experiment on natural cooling (Thermal Hydraulic Phenomena). CRIEPI 9/37

10 3.2(1) Results of Heat Removal Test 1) The ceiling height hardly influences the heat removal characteristics. 2) The ceiling temp. is seriously affected by ceiling height. Therefore, the ceiling height should be determined considering the temp. restriction of concrete and electrical parts. 3) There are two kinds of flow in the storage area, e.g., an upward flow induced by buoyant force on the cask surface and a horizontal flow induced by chimney effect. These two flows contribute to cool the casks. 4) The chimney (stack) height directly influences the heat removal characteristic. CRIEPI 10/37

11 Leak 漏洩率 Rate (Pa (Pa-m3/s) m 3 /s) Residual 残留反発力 repulsion force (N/mm) (N/mm) Leak 漏洩率 Rate (Pa (Pa-m3/s) m 3 /s) 3.3 Containment -(1) Long-term containment of metal gasket 基準漏洩率 Standard Leak Rate (Pa-m3/s) 平 Ave. 均 標準偏差 σs 経過時間 ( 年 ) 基準漏洩率 Standard Leak Rate (Pa-m3/s) 平 Ave. 均 標準偏差 σs Elapsed year Ⅰ 型モデル Ⅱ 型モデル Elapsed 経過時間 ( year 年 ) Type I model Type II model Type II model Type I model 試験の温度条件 Temperature is (139 C 一定 constant. ) での解析結果使用済燃料の発熱低下を考慮した条 Initial temp. was 139 C and 件での解析結果 decreases with ( time. 初期温度 139 ) Critical repulsion force to loose containment (12 N/mm) 密封喪失限界残留反発力 (12N/mm) Storage 時間 period (year) (year) Analytical result of containment due to stress relaxation of metal gasket (Type I) CRIEPI 11/37

12 L.M.P. Evaluation Tim e (year) Tem perature of 2nd Lid( ) 3.3(1) Evaluation of the Long-term Sealability InitialTem p.150 InitialTem p.140 InitialTem p.130 InitialTem p.120 M easured Tem p.(typeⅠ) M easured Tem p.(typeⅡ) The trends of the gasket temperature depends on the cask design Year TypeⅠ TypeⅡ Temp. of 2nd Lid (Type Ⅰ) Initial Temp. 140 Initial Temp. 135 Initial Temp. 130 Initial Temp. 120 Temp. of 2nd Lid (Type Ⅱ) Year InitialTem p.of 2nd Lid( ) CRIEPI 12/37

13 3.3 (1) Containment- Summary Two kinds of cask lid structure models are being tested for more than 19 years at constant temperature. The very reliable containment performance has been demonstrated. By applying the Larson-Miller parameter, the results indicate a longer period of sealing performance taking account of the decay heat of the spent nuclear fuel. After finishing the test, all of the lids were opened. The degradation data of the gaskets were obtained. CRIEPI 13/37

14 3.5 Structural Integrity -(1)Drop test of ductile cast iron cask- CRIEPI 14/37

15 3.5(2) Heavy Weight Drop Tests onto Cask by Building Collapse CRIEPI 15/37

16 3.5 Structural Integrity -(3)Instantaneous leak in cask drop test- Background Conventionally, leakage tests are performed before and after drop tests of the package. On the other hand, it has been known that packages may leak momentarily at the moment of the mechanical impact. However, such momentary leakage has not been measured quantitatively. Purpose To quantitatively measure momentary leak from a full-scale metal cask without impact limiters in a full scale drop test. CRIEPI 16/37

17 1m 1m 3.5(3) Test Conditions Horizontal drop test Rotational impact test The cask was dropped The cask was rotated around horizontally from 1 m high. an axis of a lower trunnion. Height 1m 1m 12.6 trunnion gasket Concrete floor Concrete floor The front trunnion attacked the concrete floor, directly. Both the cask corner and the front trunnion attacked the concrete floor, directly. CRIEPI 17/37

18 Depth(cm) 3.5(3) Concrete floor after Horizontal Drop Test Lid A 0 A Length(cm) Floor Level A-A Section The Center of Trunnion Lid Direction The depth of penetration to the concrete floor of the trunnion was about 10 cm. CRIEPI 18/37

19 3.5(3) Leak Rate from the Primary & the Secondary Lids at Horizontal Drop Test Leak rate(pa m 3 /s) Leak rate(pa m 3 /s) Secondary Lid Primary Lid He:4atm Cask Body Helium leak Detector 2 Helium leak Detector The total amount of helium gas leakage from the primary and secondary lids was Pa m 3. This value is about 10-8 % of the initially filled helium gas. The amount of leakage was insignificant Time(min) Time(min) CRIEPI 19/37

20 Depth(cm) 3.5(2) Concrete floor after Rotational Drop Test Lid Cask corner Trunni on Length(cm) Trunnion Cask corner Floor Level The depth of penetration to the concrete floor of the trunnion was about 5 cm. CRIEPI 20/37

21 Leak rate(pa m 3 /s) Leak rate(pa m 3 /s) 3.5(2) Leak Rate from the Primary and the Secondary lid at Rotational Drop Test Secondary Lid Primary Lid He:4atm Cask Body Helium leak Detector 2 Helium leak Detector The total amount of leakage from lids was Pa m Time(min) This value is about 10-7 % of the initially filled helium gas. This value was larger than that of the horizontal drop test. Nevertheless, the amount of leakage was also insignificant Time(min) CRIEPI 21/37

22 3.5(3) Summary of Momentary Leak from Metal Cask w/o Impact Limiters Momentary leak rates were quantitatively measured at the drop tests of a full scale metal cask simulating drop accidents in a storage facility. Negligible helium leak was observed in both cases. At the rotational impact test, the amount of leakage was larger than that of the horizontal drop test. However, the amount of leakage was insignificant. CRIEPI 22/37

23 3.6 Seismic Performance -Cask tipping over- CRIEPI 23/37

24 3.7 Severe Accident Performance -(1)Cask burial in concrete debris- Stainless/ Pb/Stainless Cask CRIEPI 24/37

25 3.7(1) Test cases in building collapse I : Debris covered lower part of the vertical cask. II : Debris covered upper part of the vertical cask. III : Debris covered upper part of the horizontal cask. IV : Debris fully covered the horizontal cask. I II II I IV CRIEPI 25/37

26 3.7(1) Results of thermal performance tests & analyses at various building collapses Temp. ( ) at various cases of coverage with debris Cask component I II III IV Design criteria on max. allowable temp. Spent fuel Lead in cask body Gasket in primary lid month 248-2months month Gasket 2nd lid in NA CRIEPI 26/37

27 3.7 Severe Accident Performance -(2)Airplane crash on cask- Objective : To evaluate integrity of a metal cask under a hypothetical airplane crash accident. Key Issue : Cask Lid Sliding & Opening Leak tightness of the metallic gasket is very sensitive to lid movements Animation Video CRIEPI 27/37

28 3.7(2) Cases for Airplane Crash Tests Case 1 Reduced Model Cask (2/5) Full Scale Model of Cask Lid Case 2 Simulated Engine Simulated Engine Horizontal Crash Test of 2/5 Reduced Cask Model Crashed by a Simulated Engine Vertical Crash Test of Full Scale Model of Cask Lid Crashed by a Simulated Engine CRIEPI 28/37

29 3.7(2) Crash Test Result (measurement) The measured leak rate was within the permissible value for transport casks. widen narrow CRIEPI 29/37

30 3.8 Interaction between Transport & Storage -(1)Vibration in transport impacts containment in storage- Background and Objective Transport casks receive mechanical vibration in transport. The containment performance of metal gaskets is influenced by large external load or displacement. Quantitative influence of such vibration in transport on the containment performance of the metal gasket has not been known, but is crucial information particularly if the cask is stored as it is after the transport. CRIEPI 30/37

31 Leak rate (Pa m 3 /s) Radial Direction Displacement (mm) 3.8 (1) Measurements of Leak Rate and Radial Displacement with Time under Cyclic Loading If the amplitude exceeded 0.02mm, the leak rate did not recover. Leak rate Rad. dispmt amplitu de 230 cycles Time (s) CRIEPI 31/37

32 3.8 (1) Vibration in Transport Impacts Containment in Storage- Summary 1. Mechanical vibration in transport would influence the containment performance of the metal gasket for storage if the amount of sliding exceeded a threshold value. 2.The threshold values in the model were: 0.1~3 mm of static displacement, or ±0.02 mm of cyclic displacement. CRIEPI 32/37

33 acceleration (m/s 2 ) 3.8 Interaction between Transport & Storage -(2)Ageing in storage impacts containment in transport- Dynamic Analysis for Cask Lid (1/3) To evaluate influence of vibration force during transportation on sealing performance of the aged gasket Calculated opening disp. of the metal gaskets perpendicular to the flange surface With acceleration measured during actual sea transportation vertical horizontal Analytical model axial -30 axial vertical horizontal time (s) Time history of acceleration

34 Opening Disp. at 1st Lid (mm) Opening Disp. at 2nd Lid (mm) 3.8 -(2)Ageing in storage impacts containment in transport- Dynamic Analysis for Cask Lid 2/3 Opening disp. evaluated by the dynamic analysis Primary lid : maximum value was smaller than mm. Secondary lid : maximum value was smaller than mm. Each opening disp. << r u (spring back distance) of the gasket used for 60 years. The sealing performance will be maintained in good condition (Primary lid) widen (Secondary lid) widen Time (sec) narrow 180 0deg 45deg 90deg 135deg 180deg 225deg 270deg 315deg Time (sec) Time history of opening displacement narrow 0deg 45deg 90deg 135deg 180deg 225deg 270deg 315deg CRIEPI 34/37 180

35 3.8-(2)Ageing in storage impacts containment Summary 3/3 Numerical methodology of sealing performance of metal gasket after long term usage was proposed. Spring back distance r u of the gasket used for 60 years : 0.09 mm Opening disp. by dynamic analysis with the accelerations measured during actual sea transportation was evaluated. Opening disp. of the primary lid and the secondary lid : smaller than mm. Opening disp. << spring back distance r u The sealing performance will not be lost by lid opening during the sea transportation within the acceleration measured.

36 Conclusion CRIEPI published a book of safety case for spent fuel storage. The book includes experiments and analyses supporting evidence and reasoning on the robustness and reliability of the DPC. These information will become a basis for further development by advanced techniques on experiments, analyses, lessons learned, etc., in the future. CRIEPI 36/37

37 Acknowledgement Parts of the researches in this book were carried out by contracts from the Japanese governments, i.e., Agency for Natural Resources and Energy of Ministry of Economy, Trade and Industry (METI). Nuclear and Industrial Safety Agency of METI (now, Nuclear Regulatory Authority) CRIEPI 37/37