ML20213B074
| ML20213B074 | |
| Person / Time | |
|---|---|
| Site: | 07102027 |
| Issue date: | 07/29/2020 |
| From: | Daher-TLI, Transport Logistics International |
| To: | Office of Nuclear Material Safety and Safeguards |
| NJDevaser NMSS/DFM/STL 415.5196 | |
| Shared Package | |
| ML20213B073 | List: |
| References | |
| Download: ML20213B074 (32) | |
Text
(B)-B Thermal Analysis B.1 Outline The thermal conditions for type A fissile package are set forth as follows.
In performing a thermal test, the thermal conditions applicable as those for the special test shall be set taking into consideration of the general test conditions as provided in the rules for a fissile package, as well as the amount of cumulative deformation caused by successive falls as required under said special test conditions.
In this analysis, based on a transport on dry conditions, considerations are made mainly of the following points.
(1) As for the general test conditions, assumption is made of the heat-input from solar radiation.
(2) With regard to the special test conditions, these shall be set so as to satisfy the requirements of the rules for a fissile package.
B.1.1 Thermal design of package The package is composed of an inner container, structured with double stainless steel walls filled with thermal insulator in between, and an outer container made of stainless steel frames and stainless steel plates with shock absorbers such as balsa and paper honeycomb fixed inside.
The thermal design characteristics of the package are as follows.
(1) The contents are unused fuel assemblies, whose decay heat is negligible small.
(2) The thermal insulator of the inner container has the thermal insulation capability required at times of fire under the special test conditions.
(3) As practically no decay heat is expected from the contents, the package has no specific, supplementary system of cooling etc. added to it.
(4) In order to prevent increase of internal pressure at times of fire as under special test conditions, fuse-plugs are installed each two at the outer container main body and at its lid. Also with the inner container, 4 at its main body, 2 at its lid, and 1 at its end lid.
(5) Fuel rods, representing the containment boundary of the package, are protected by the effect of thermal insulator from the heat input due to fire as under the special test conditions.
(B)B-1
B.1.2 Conditions of Analysis (1) Thermal conditions under the general test conditions In order for the evaluation of the package to be on the safer side, the following thermal conditions are applied in evaluating the thermal safety of the package.
The temperature of the package shall be a temperature of which the heat input from solar radiation is taken into consideration.
(2) Thermal conditions under the special test conditions Thermal conditions for the type A fissile packages.
i) Packages are to be subject to the conditions of successive drop provided in the general and special test conditions regarding fissile packages.
ii) Successively to i) above, packages shall be placed in 38 environment until surface temperature becomes equilibrate and then, shall be placed under 800 environment for 30 minutes under the condition of solar radiant heat and under the design condition that the internal heat is produced in the maximum rate in the package.
iii) Cooling shall be made under the condition of the solar radiant heat and under the design condition that the internal heat is produced in the maximum rate in the package even while packages are in the cooling process, provided where no artificial cooling is allowed.
The evaluation of this package is conducted using the results of the prototype tests, which have been performed to replace the fuel rods as the contents to the fuel assembly.
Incidentally, as it was difficult at the time of prototype test to cool the package while under the loading of solar radiation, the thermal safety of package is evaluated on the safer side applying a correction temperature obtained from adding to the resultant temperature of prototype tests, the differences of temperature found between the package in its maximum value and the environment as under the general test conditions.
B.2 Thermal properties of component material The thermal properties of main component material are shown Table (B)-B.1.
(B)B-2
Table (B)-B.1 Thermal properties of main component material Specific Thermal Density Material Temp. heat conductivity (g/cm3)
(J/kgK) (W/mK)
(1) Outer containers 27°C 7.92 4.99 x 102 1.6 x 101 Stainless steel (SUS304)
(2) Inner container Stainless steel (SUS304) 27°C 7.92 4.99 x 102 1.6 x 101 Thermal insulator 20°C 0.26 1.05 x 103 2.15 x 10-1 (alumina)
B.3 Specifications of components The material specifications and operation temperature limits for the main components, whose properties are affected by conditions of operational temperatures, are set forth as follows.
(a) Shock absorber (paper honeycomb)
Density approx. 0.049 g/cm3 Thermal conductivity 0.326 W/mK Operational temperature limits -185°C to 107°C (b) Thermal insulator (Alumina)
Density approx. 0.25g/cm3 Thermal conductivity 0.215 W/mK Operational temperature limits to 1,300°C (c) Gaskets (natural rubber)
Density approx. 1.14 g/cm3 Operational temperature limits -50°C to 120°C B.4 General test conditions The contents of the package are unused fuel rods, whose decay heat is negligibly small. Furthermore, the transport for road is tied down in a freight container for international trade. there is no possibilities of long and direct exposure to solar radiation. In a ship the condition is same as that by road, and the package temperature is expected to be about the same as that of the environment. However, in order to be on the safer side, it has been taken that the conservative stand in confirming the integrity of package as under the following conditions.
(B)B-3
The higher temperature side:
In order to be on the safer side, evaluate the thermal safety of package, assuming the package to be subject to the solar radiation conditions as provided in the separate note No. 4 (the general test conditions regarding BM type packages) of the "Notice specifying the details etc. of technical standards regarding transport of nuclear fuel material etc. outside of factories or offices" (hereinafter called "the notice").
The lower temperature side:
In order to be on the safer side, the ambient temperature is set to be -40°C B.4.1 Thermal analysis model B.4.1.1 Analysis model (1) The maximum temperature As the maximum temperature of package, it was taken that the steady state temperatures of its surface material and components, assuming where the environmental temperature as 38°C and heat-inputs from solar radiation as 800 W/m2 and 200 W/m2 on the ceiling surface and the wall surfaces of outer container as shown in the Figure (B)-B.1.
(2) Maximum internal pressure Maximum internal pressure of the inner container is obtained from the maximum temperature derived in above by the Boyle Charles Law.
(B)B-4
Solar heat 800W/m2 Outer container ceiling surface Outer container wall surface 720mm 200W/m2 200W/m2 Solar heat Solar heat 642mm Floor surface Bolster Figure (B)-B.1 Thermal analysis model under solar radiation (B)B-5
B.4.1.2 Test model This is not applicable.
B.4.2 Maximum temperature (1) Specifically set conditions It is attempted to obtain the maximum temperature of the package surfaces as under the environmental temperature of 38°C as follows.
The surface temperatures of package raised from solar heat transfer are separately calculated on the ceiling surface and on the wall surfaces of the outer container, and the higher one is taken as the maximum surface temperature of the package.
Test conditions specifically set are as follows.
(a) Environment temperature to = 38°C (b) Heat transfer of outer container ceiling surface qH = 800W/m2 (c) Heat transfer of outer container wall surfaces qv = 200 W/m2 (d) Boundary surface layer temperature tB = 54°C (the medium value of temperatures between environment and outer surfaces of package)
In the above specifically set condition, the equation obtaining an answer to the surface temperature t of outer container is q
t = + t 0 ***************************************************************************(1)
Where, q: heat transfer on surfaces of outer container W/m2
- heat transfer coefficient on surfaces of outer container W/m2K to: environment temperature 38°C The heat transfer coefficient H of the ceiling surface of outer container is given by H = H1 + H2 ********************************************************************(2)
Where, H1: natural convection heat transfer coefficient W/m2K H2: radiation heat transfer coefficient W/m2K (B)B-6
The heat transfer coefficient V of the wall surface of outer container is given by V = V1 + V2 ********************************************************************(3)
Where, V1: natural convection heat transfer coefficient of the wall surfaces of outer container W/m2K V2: radiation heat transfer coefficient of the wall surfaces of outer container W/m2K Basing on the basic equations (1) through (3), the values of heat transfer coefficient and heat transfer, catch for the ceiling surface and wall surfaces of outer container and the surface temperature t of outer container are given as follows.
(2) Ceiling surface temperature of outer container (i) Heat transfer coefficient of ceiling surface of outer container H The natural convection heat transfer coefficient H1 is given by Nu H1 = **********************************************************************(4)
Where, Nu: Nusselt number no dimension
- thermal conductivity of air [1]
0.0281 W/m2K l: width of ceiling surface of Please refer on page 7 of Attachment outer container 0.720 m 3 Next, it was attempted to obtain the Grashof number required in calculating the Nusselt number Nu. As the natural convection heat transfer, as regards the ceiling surface of outer container occurs to its horizontal surface, the Grashof number Gr is given by (B)B-7
g 3 (t1 t 0 )
Gr = **********************************************************(5) 2
- Where, g: gravitational acceleration 9.81 m/s2
- expansion coefficient of air (54°C) 3.058 x 103°C-1 t1: surface temp. of ceiling surface of outer container assumed as 70°C
- coefficient of kinematic viscosity 1.857 x 10-5m2/s Therefore, the Grashof number is calculated as Gr = 1.039 x 109 Where, as the Prandtl number Pr of air (54°C) is 0.719[1], the following equation is obtained. Please refer on page 3,7 and 10 of Attachment 3 8
GrPr = 7.47 x 10 In case when GrPr is greater than 2 x 107 in the natural convection of air as on the horizontal surface, the air flow may be called a turbulence, and the Nusselt number Nu is obtainable from the following equation.[1]
Nu = 0.13(GrPr)1/3 **************************************************************(6)
117.96 Please refer on page 5 of Attachment 3 By assigning this Nusselt number into equation (4), the natural convection heat transfer coefficient H1 of the ceiling surface of outer container is calculated as Hl = 4.60 W/m2K While, the radiant heat transfer coefficient H2 of ceiling surface of outer container is given[1] by H2
(
t1 4 t 0 4 ) ***********************************************************(7) t1 t 0 Where, Please refer on page 5 of Attachment 3
- emissivity of ceiling surface (stainless steel) of outer container 0.1
- Stefan Boltzmanns constant 5.67 x 10 W/m K
-8 2 t1: surface temp. (assumed as 70°C) of ceiling surface of outer container 343 K t0: environmental temp. (38°C) 311 K (B)B-8
Therefore, the radiant heat transfer coefficient H2 of the ceiling surface of outer container is expressed as H2 = 0.79 W/m2K Accordingly, the heat transfer coefficient H of the ceiling surface of outer container is derived from equation (2) as H = H1 + H2
= 5.39 W/m2K (ii) Amount of the heat transfer q of ceiling surface of outer container The absorption coefficient of solar radiation heat on the ceiling surface of outer container is set as 0.3. This represents an assumption sufficiently on the safer side, considering the emissivity of stainless steel (SUS 304) to be within a level of about 0.1.
q = 0.3 x 800 = 240W (iii) Ceiling surface temperature t of outer container From H and q as obtained by equations respectively of (i) and (ii) above, along with from equation (1), t is obtained as follows.
q 240 t= + + 38 H 5.39
= 82.5°C In calculating H, assumption was made of the surface temperature as 70°C. In factors of H, the one most dependent of temperature is its internal term of radiant heat (H2). The resultant temperature t obtained as above is however, 82.5°C, which is higher than the 70°C applied in calculating H2. In this study of radiant heat transfer, the temperature of container is higher than that of the environment, therefore, in releasing heat, the heat quantity becomes greater as the container temperature is higher.
In calculating the value of H2, the assumption of a lower container temperature means estimating the heat quantity released to environment smaller than actual, with the result that the container temperature is calculated higher than it actually is. Therefore, the surface temperature of 70°C represents a safer side assumption.
(B)B-9
(3) Temperature of outer container wall surfaces (i) Heat transfer coefficient of outer container wall surfaces: V The equation to obtain the natural convection heat transfer coefficient of outer container wall surfaces V1 is, Nu V 1 = m *********************************************************************(8)
Where, Num: average Nusselt number with no dimension
- thermal conductivity of air (44°C) 0.0274 W/mK (assuming the surface temperature as 50°C) l: height of outer container wall surfaces 0.642 m Next, the Grashof number required in calculating the Nusselt number Num is to be obtained. Under a uniform heat transfer surface heat flux and a uniform ambient fluid temperature, the natural convection heat transfer is effected on the vertical surfaces of outer container wall surfaces, and the equations to obtain the Grashof number is, 4 g qV Gr1 = ***************************************************************(9) 2 Where, Gr1: Grashof number at the uppermost part no dimension (l = 0.642m) of outer container wall surfaces g: gravitational acceleration 9.81 m/s2
- expansion coefficient of air (44°C) -3 3.155 x 10 °C-1
- coefficient of kinematic viscosity 1.756 x 10-5 m2/s
- thermal conductivity of air (44°C) 0.0274 W/mK qv: heat transfer on outer container wall surface 200 x 0.3 W/m2 (Absorption coefficient being 0.3)
Accordingly, the Grashof number is, Gr1 = 3.74 x 1010 As where, the Prandtl number Pr of air (44°C) being 0.719, therefore, Gr1Pr = 2.69 x 1010 Now when natural convection of the air occurs on a vertical surface, whose heat transfer surface heat flux and the ambient fluid temperature are uniform, and the value of Gr1Pr is also found to be smaller than 1012, the convection may be called a laminar air flow, and the average Nusselt number Num is obtainable from the following equation, (B)B-10
Num = K(Gr1Pr)1/5 ************************************************************* (10) provided where, 1/ 5 Pr K =
4 + 9 Pr + 10 Pr 1/ 2 Accordingly, the average Nusselt number is, Num = 63.4 By assigning this Num into equation (8), the natural convection heat transfer coefficient V1 of outer container wall surfaces is obtained.
V1 = 2.70 W/m2K While, the equation to obtain the heat transfer coefficient of outer container wall surfaces V2 is,[1]
V 2 =
(
t14 t0 4 ) ********************************************************** (11) t1 t0 Where,
- radiation rate of outer container wall surfaces (SUS 304) 0.1
- the Stefan Boltzmanns constant 5.67 x 10 W/m K
-8 2 4 t1: the surface temp. (Assumed as 50°C) of outer container wall surfaces 323 K t0: environmental temp. (38°C) 311 K Accordingly, the radiant heat transfer coefficient of outer container wall surface is, V2 = 0.72 W/m2K Therefore, the heat transfer coefficient V of outer container wall surfaces is derived from equation (3) as follows.
V = V1 + V2
= 3.42 W/m2K (ii) Heat transfer amount q of outer container wall surfaces The solar radiant heat absorption coefficient as on outer container wall surfaces is set as 0.3, which represents a sufficiently conservative assumption considering the emissivity of stainless steel (SUS 304) remaining on the level of about 0.1.
The amount is, q = 0.3 x 200
= 60W (iii) Temperature t of outer container wall surface From V and q in para. (i) and (ii) above, and also from the equation (1) t is obtainable as follows.
(B)B-11
q 60 t= + t0 = + 38 V 3.42
= 55.5°C In calculating V above, assumption was made of the surface temperature as 50°C. Among the factors of V, the one most dependent on temperatures is its internal term, radiant heat (V2). While, the resultant temperature t obtained is 55.5°C which is higher than the 50°C used in calculating the above V2. And, in this study of radiant heat transfer, the temperature of container is higher than that of environment, therefore, when releasing heat, the heat quantity becomes greater as the container temperature gets higher. In calculating the value V2 of making assumption of a lower container temperature means estimating the heat quantity released to environment smaller than actual, with the effect that the container temperature is calculated higher than it actually is.
Therefore, to have taken the surface temperature as 50°C represents an assumption on the safer side.
(4) Maximum temperature As the equations (2) and (3) above, the ceiling surface temperature becomes the highest of all the surface temperatures of outer container, with the resultant value of 82.5°C83°C. Also, the heat release from the contents is negligibly small. Therefore, under the general test conditions, the temperatures of the package never exceed 83°C.
Furthermore, among the package components, the one having the lowest heat resistance is foam polyethylene, whose temperature limit is 90°C. Accordingly, the integrity of the packaging is to be maintained as long as it is kept under 83°C.
(B)B-12
B.4.3 Minimum temperature Assuming the temperature of environment to be -40°C with no solar radiation, the temperature of package becomes minimum, reaching -40°C the value same as that of the environment.
As the main component material used in the package comprises stainless steel, paper honeycomb, alumina insulator, natural rubber, and foam polyurethane, no functional property deterioration will be seen of the material by -40°C.
B.4.4 Maximum internal pressure Assuming 83°C the maximum temperature of the package available from the solar radiation heat transfer at paragraph B.4.2, as the temperature of nuclear fuel assemblies comprising the contents, calculation is made of the max. internal pressure with the fuel rods.
The equation for internal pressure of the fuel rods is, T
P = P0 T0 Where, P: internal pressure of fuel rod generated at maximum temperature MPa P0: initial internal pressure of STACY fuel rod 0.5 MPa (absolute pressure)
T: maximum temperature of fuel rods 356 K T0: initial temperature of fuel rods 293 K Wherefrom, the maximum internal pressure generated at the maximum temperature of the fuel rods is obtainable as follows.
356 P= x 0 .5 293
= 0.61 MPa (absolute pressure) = 0.51 MPa (gage pressure)
(B)B-13
B.4.5 Maximum thermal stress The evaluation is made of cladding tubes under the general test conditions. The analysis units concerning the cladding tubes are as shown in Table (B)-B.2.
Table (B)-B.2 Analysis units of cladding tube Items Dimensions Max. inner diameter of cladding tube (mm) 8.39 Min. wall thickness of cladding tube * (mm) 0.54 The cladding tube material is zirconium alloys, with the following circumferential mechanical properties. [2]
Tensile strength 270 MPa (20°C) 150 MPa (380°C)
Yield strength (0.2%) 210 MPa (20°C) 130 MPa (380°C)
Elongation 28 % (20°C) 33 % (380°C)
As the tensile strength and the yield strength tend to linearly decrease within the temperature range from 20°C to 343°C, the evaluation values at the maximum temperature of contents is obtainable by interpolating the data both at 20°C and at 343°C.
(Evaluation) = 1
( X X 0 ) (T T ) + X (T1 T0 ) 0 0 Where, X: evaluation value of tensile or yield strength MPa X0: value at 20°C MPa X1: value at 380°C MPa T: maximum temperature, 83°C T0: 20°C T1: 380°C Evaluation values of the tensile strength and yield strength at 83°C are shown in Table (B)-B.3.
(B)B-14
Table (B)-B.3 Mechanical properties at maximum temperature Items Mechanical properties Tensile strength 249 MPa Yield strength (0.2%) 196 MPa The radial stress a of the cladding tube under the general test conditions is to be obtained as follows.
Pd
=
2t Where,
- radial stress of cladding tube MIPa d: maximum inner diameter of cladding tube m t: minimum wall thickness of cladding tube m P: maximum internal pressure MPa (gage)
Accordingly, the radial stress a of 9x9-type cladding tube is, through applying d = 8.39mm
=8.39 x 10.3 m t = 0.54 mm
= 0.54 x 10.3 m P = 0.51 MPa (gage) obtainable as follows.
0.51 x 8.39 x 10 3
=
2 x 0.54 x 10 3
= 3.97 MPa The radial stress of the cladding tube is found to be sufficiently below the yield strength (196MPa), and therefore the integrity of said cladding tubes is maintained.
B.4.6 Summary and evaluation of results (1) Under the environment temperature of 38°C and under a long duration of exposure to solar radiation conditions where equilibrium state is reached between the heat input and heat release from natural convection as well as from radiation, the maximum temperature of the package become 83°C. And by this temperature, no material property deterioration takes place of the components of the package. Therefore, the integrity of package is maintained, with no fear of cracks and damages caused to it.
(B)B-15
(2) At the minimum temperature (-40) assumed on the safer side, there are no low temperature brittleness nor any decrease of strength expected of the main component material. Accordingly, the integrity of packaging is to be maintained, with no cracks and damages caused thereto.
(3) When the fuel assemblies, the contents, reach the maximum temperature 83, the maximum internal pressure of fuel rods becomes 0.61MPa (absolute). The radial stress caused by this internal pressure to the cladding tube is found to be sufficiently below the yield strength of zirconium alloys. Accordingly, the integrity of fuel rods are to be maintained, without any crack or damage caused thereto.
B.5 Special test conditions Evaluation of the integrity of contents (fuel assembly) is made by means of a thermal test performed under the conditions as provided in the special test conditions for the fissile package. The thermal conditions for the fissile package are as follows.
i) Packages are to be subject to the conditions of successive drop provided in the general and special test conditions regarding fissile packages.
ii) In succession to I) above, packages shall be placed in 38 environment until surface temperature becomes equilibrate and then, shall be placed under 800 environment for 30 minutes under the condition of solar radiant heat and under the design condition that the internal heat is produced in the maximum rate in the package.
iii) Cooling shall be made under the condition of the solar radiant heat and under the design condition that the internal heat is produced in the maximum rate in the package even while packages are in the cooling process, provided wherein no artificial cooling is allowed.
B.5.1 Thermal analysis model B.5.1.1 Analysis model Thermal analysis as under the special test conditions were performed basing on those of prototype tests, therefore no analysis model is applicable.
B.5.1.2 Test model The thermal test was performed on a full scale (1/1) test package simulated the package, which was subject to drop tests and then successively to a thermal test.
The photograph of the test package is shown in Photo. (B)-B.1.
(B)B-16
The specifications of the test package used are as follows.
(1) Reduction scale: 1/1 (full scale)
(2) Dimensions: 720 mm W x 722 mm H x 5,068 mm L (3) Contents: an inner container, a dummy fuel bundle and a dummy weight (4) Weight: gross weigh, approx. 1.5 tons (5) Instrumentation: thermocouples in 25 locations (The installation locations are as shown in Figure (B)-B.2 to Figure (B)-B.4)
The specifications of test facilities are as follows.
(1) Type of heating furnace: combustion gas convection type, with the burner on both sides and with 2 traversal platform cars (2) Types and units of burners:
HS 40 type high-speed burner (400,000 kcal/h) x 8 units (3) Effective internal dimension of furnace:
3,000mm W x 200mm H x 7,000mm L (4) Accuracy of effective heating zone temperature: +/- 20°C Photo (B)-B.1 Test package (B)B-17
(1) For temperature measurement inside furnace atmosphere (on outside outer container)
(Upward direction)
Top view (Upward direction)
Side view (2) For temperature measurement inside outer container (on inside of outer container)
(Upward direction)
Top view (Upward direction)
Side view Figure (B)-B.2 Installation locations of thermocouples on outer container (B)B-18
(1) For temperature measurement outside the inner container (on outside inner container)
(Upward direction)
Top view Lid (Upward direction)
Side view (2) For temperature measurement inside the inner container (on inside of inner container)
(Upward direction)
Top view Lid (Upward direction)
Side view Figure (B)-B.3 Installation locations of thermocouples on inner container (B)B-19
(Upward direction)
Dummy Dummy fuel weight assembly A - A cross section Dummy Dummy fuel weight assembly B - B cross section Dummy Dummy fuel weight assembly C - C cross section Dummy weight Dummy fuel assembly Top view Figure (B)-B.4 Installation locations of thermocouples on contents (B)B-20
B.5.2 Evaluation conditions of package The conditions of thermal test as follows.
Where, the test package was left for 30 min. under an atmospheric environment of 800 in accordance with the prescribed rules of test conditions. Incidentally, the test package was placed, horizontally on the blocks used for the thermal testing. After placing the test package equipped with thermocouples onto the blocks of platform cars above by means of mobile crane, the test package was put into the furnace, and the test started.
(1) Posture of package at the thermal testing: horizontal state (2) Atmosphere temperature : 800 or above (3) Duration of heating : 30 min. or more (4) Heating pattern of furnace : as shown in Figure (B)-B.5 The furnace and platform cars of the thermal test facility had been preheated to 700 when the door was opened and the test package was brought into the furnace by moving the platform cars. At this time, although the intra-furnace temperature temporarily fell in the meantime, the furnace was heated until the intra-furnace temperature reached 800. And its condition was kept until the outer surface temperature of package reached 800, and thereafter it was kept heating to 800 or above for 30min. or more, until being brought out of the furnace by opening the door. Confirmation was made of the test package having been heated to 800 or above for 30min. or more by means of the thermocouples equipped to outside the test package (the ones shown as TQ1 to TQ6 in Figure (B)-B.2), whose results are shown in Figure (B)-B.6.
B.5.3 Temperature of package The temperature changes during test for each part of the test package as at the thermal testing are shown in Figure (B)-B.6~(B)-B.10. Also, the maximum temperature for each part of the package are shown in Table(B)-B.4.
(B)B-21
Table (B)-B.4 Maximum temperature for each part of test package as under the special test conditions Position of Location of Maximum Time passed 1) measurement thermocouple temperature (min.) 3)
() 2)
Outer container outside TQ-3 876.7 59[5]
Outer container inside TW-3 820.9 84[30]
Inner container outside TM-3 808.9 85[31]
Inner container inside TN-3 400.2 89[35]
Contents TF-3 270.7 112[58]
- 1) The signs correspond to the thermocouple locations as in Figure (B)-B.2~B.4.
- 2) The maximum temperature are obtained from periods limited to those after start of the thermal testing.
- 3) The times passed represent the time-period spent after start of measurement.
The starting time of testing designates the time when all the thermocouple temperature as at outside of the outer container are found to exceed 800degree-C, which is translatable in terms of duration of so much time after measurement start to 54 mm.
Also, the figures shown in [ ] represent the duration of time when the starting time of testing is set as 0 min.
In this evaluation, the object is contents (fuel rods) and from the test results the contents show the temperature of a fuel assembly. The maximum temperature of the inner container inside, 401degree-Cis assumed as the maximum temperature of fuel rods conservatively. Furthermore, in consideration of conditions under the special test conditions (load of the solar radiant heat stipulated in the Separate Statement No.4-1 of the Notification), the maximum temperature of the contents obtained by the thermal test is to be set conservatively adding some temperature to the maximum temperature Note) which is considered to be increased by loading of the solar radiant heat.
Judging from the several fact that the combustion of paper honeycomb and so on was observed and the continuation of the burning inside test unit was observed when taken out from the heating reactor, its calorific value was considered to become the highest and due to natural cooling, it was considered to satisfy the condition under the special test conditions (in consideration of inner generation stipulated in the Separate Statement No.5-2 of the Notification).
Note) The temperature difference (45) between the maximum temperature (83) obtained by loading of insulation under the general test conditions and (B)B-22
environmental temperature (38)
The maximum temperature of contents = 401 + 45 = 446 Incidentally, after the thermal testing, it was observable that a part of the fuel assembly packaging material, polyethylene separators etc., had partially melted down and stuck to fuel rods. It is assumed that polyethylene bags etc. partially melt down and stick to fuel rods in a protection case of this package.
(B)B-23
minute Preheating of furnace Temperature (B)B-24 Setting of test package Time Fig. (B)-B.5 Heating pattern of furnace (conceptual figure)
Temperature (B)B-25 Time (Minute)
Fig. (B)-B.6 Temperature changes during thermal test (outside of outer container)
Temperature (B)B-26 Time (Minute)
Fig. (B)-B.7 Temperature changes during thermal test (inside of outer container)
Temperature (B)B-27 Time (Minute)
Fig. (B)-B.8 Temperature changes during thermal test (outside of inner container)
Temperature (B)B-28 Time (Minute)
Fig. (B)-B.9 Temperature changes during thermal test (inside of inner container)
Temperature (B)B-29 Time (Minute)
Fig. (B)-B.10 Temperature changes during thermal test (contents)
B.5.4 Maximum internal pressure It is attempted to obtain the max. internal pressure each for 8x8-type and 9x9-type fuel rods as under special test conditions. The equations for above are as follows.
The equation to obtain the internal pressure for 9x9-type fuel rods is T
P = P0 T0 Where, P: internal pressure of fuel rod generated at maximum temperature MPa P0: initial internal pressure of STACY fuel rod 0.5 MPa (absolute pressure)
T: maximum temperature of fuel rods 719 K T0: initial temperature of fuel rods 293 K Therefore, the internal pressure generated at the maximum temperature in 9x9-type fuel rods is obtainable as follows.
719 P= x 0.5 293
= 1.23 MPa (absolute pressure)
= 1.13 MPa (gage pressure)
B5.5 Maximum thermal stress The evaluation is made of cladding tube under the special test conditions. Analysis units concerning the cladding tube are as shown in Table (B)-B.5.
Table (B)-B.5 Analysis units of cladding tube Items Dimensions Max. inner diameter of cladding tube (mm) 8.39 Min. wall thickness of cladding tube * (mm) 0.54 The material of cladding tube is zirconium alloys, with the following circumferential mechanical properties. [2]
(B)B-30
Tensile strength 270 MPa (20°C) 150 MPa (380°C)
Yield strength (0.2%) 210 MPa (20°C) 130 MPa (380°C)
Elongation 28% (20°C) 33% (380°C)
As zirconium alloys tend to lineally decrease their tensile strength and yield strength as the temperature range from 20°C to 380°C, the acceptance criteria at maximum temperature of the content are assumed by extrapolation.
The radial stress of the cladding tube as under special test conditions is obtainable as follows.
pd
=
2t Where,
- Radial stress of cladding tube MPa d: Maximum inner diameter of STACY cladding tube 8.39x 10.3 m t: Minimum wall thickness of the cladding tube 0.54 x 10.3 m P: Maximum internal pressure of the cladding tube 1.13 MPa (gage pressure)
Accordingly, the radial stress of the cladding tube is, 1.13 x 8.39 x 10 3
=
2 x 0.54 x 10 3
= 8.78 MPa The radial stress of cladding tube above is found to be sufficiently below the tensile strength (115 MPa) of zirconium alloys as at 446°C, and therefore, no damage due to thermal stress is expected of the fuel rods.
B.5.6 Summary and evaluation of results (1) Thermal testing was done using a full-scale (1/1) test package.
(2) The maximum temperature of contents as at thermal testing was 401°C (actual measurement).
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(3) The evaluation purpose maximum temperature of contents was set as 446°C, which is the addition of the actual value (2) above (401°C) with the temperature difference between the maximum temperature (83°C) and the environment temperature (38°C) as under general test conditions.
(4) The max. internal pressure of the fuel rods at 446°C is 1.13 MPa (gage pressure).
(5) The radial stress generated in the cladding tube (excluding the liner thickness from the strength factors) by the maximum pressure at 446°C is 8.78 MPa, which is below the tensile strength of zirconium alloys (at 446°C) 115 MPa.
Accordingly, there is no possibility of fuel rod damages due from thermal influences as under special test conditions.
(6) As after the thermal test, melting down phenomenon was observed among the packing material of fuel assemblies and the cushioning material of inner container, consideration is to be made of this melting down phenomenon with the packing material and cushioning material of inner containers, when performing a critical analysis on the damaged packages.
B.6 Attached documents B.6.1 Attached documents - 1 Reference
[Appendix document - 1] Reference (1) Compiled by the Japan Mechanical Society Data on Thermal Conduction Technology (Rev. 4th edition)
(2) Issued by Nikkan-Kogyo Shinbun-sha Nuclear Reactor Material Handbook (1st edition)
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