This standard specifies the nuclear criticality control criteria for handling, processing and treating plutonium-natural uranium mixtures and certain subcritical limits for isolated geometrically simple plutonium-natural uranium mixtures. This standard applies to handling, processing and treating plutonium-natural uranium mixtures outside the reactor. This standard does not apply to assembling these materials under controlled conditions (such as criticality experiments). GB 15146.5-1994 Nuclear criticality safety of fissile materials outside the reactor Nuclear criticality control criteria and subcritical limits for plutonium-natural uranium mixtures GB15146.5-1994 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Nuclear criticality safety for fissile materialsoutside reactors
-Nuclear criticality control criteria and subcriticallimits for plutonium-natural uranium mixtures1 Content and scope of application
GB15146.5—94
This standard specifies the nuclear criticality control criteria for the operation, processing and treatment of plutonium-natural uranium mixtures and certain subcritical limits of isolated units of plutonium-natural uranium mixtures with simple geometric shapes. This standard is applicable to the operation, processing and treatment of plutonium-natural uranium mixtures outside reactors. This standard is not applicable to the assembly of these materials under controlled conditions (such as criticality experiments). 2 Reference standards
GB15146.1 Nuclear criticality safety of fissile materials outside reactors Nuclear criticality safety administrative regulations GB15146.2 Nuclear criticality safety of fissile materials outside reactors Basic technical criteria and subcritical limits for the operation, processing and treatment of fissile materials
3 Terms
3.1 Controlled parameter
A parameter required to be kept within the specified limit. 3.2 Subcritical limit (limit)
A limiting value specified for a controlled parameter that can make a system definitely in a subcritical state under specified conditions. This limit has left a margin for the uncertainty of the calculation and experimental data used to derive the limit, but no margin for unexpected events (such as double batches or inaccurate analysis results, etc.).
3.3 Surface density
The mass of fissile material projected vertically on a unit area of ​​a plane. For a uniform plate of infinite width, the surface density is the product of the thickness of the plate and the concentration of fissile material in the plate.
3.4 ​​Natural uranium
Natural uranium as referred to in this standard refers to uranium with an isotopic enrichment of uranium-235 equal to or less than 0.71% (by weight). 4 Nuclear criticality control criteria
4.1 Administrative management criteria
Approved by the State Administration of Technical Supervision on July 7, 1994 and implemented on January 1, 1995
GB 15146.5-94
The administrative management of nuclear criticality safety in the operation, processing and handling of ring-natural uranium mixtures must comply with the provisions of GB15146.1. 4.2 Basic technical criteria
4.2.1 The basic technical criteria for nuclear criticality control in the operation, processing and handling of ring-natural uranium mixtures must comply with the provisions of GB15146.2. 4.2.2 The operation, processing and handling of ring-natural uranium mixtures must consider the homogeneity control of the ring-natural uranium mixture itself, that is, it is required to keep the mixture completely uniformly mixed and consider whether the ring is likely to be separated from the uranium. 4.2.3 When formulating process specifications, the controlled parameters must retain a certain margin based on the subcritical limit to cope with the uncertainty of process parameters and the accidental exceeding of the limit.
5 Subcritical limits (limits)
5.1 Basic conditions for the application of limits
Clause 5.2 to 5.5 give some subcritical limits for ring-natural uranium mixtures. These limits can only be used if the following basic conditions are met:
a. The reflection effect of the neutron reflector and other nearby fissile materials of the ring-natural uranium mixture unit is not greater than the reflection effect of the equivalent infinitely thick water reflection layer that surrounds the unit; b. The ring-natural uranium mixture remains completely uniformly mixed, and the ring is not separated from the uranium; c. The uranium in the mixture must be natural uranium.
5.2 Limits for homogeneous systems of water-natural uranium oxide mixtures For homogeneous systems of water-natural uranium oxide mixtures with PuO weight percentages of 3%, 8%, 15% and 30% in (PuO2+UO2), the mass, volume, cylinder diameter, plate thickness, concentration and surface density limits are listed in Table 1. The limits listed in the table for each PuO2 weight percentage are given for three different cyclic isotopic compositions. When applying these limits, any 238Pu and 242Pu present must be ignored in the calculation of the cyclic isotopic composition. For a homogeneous system of cyclic-natural uranium oxide mixture in water with PuO. weight percentage in (PuOz+UO2) varying between 3 and 30%, the relationship between the mass, cylinder diameter, plate thickness and surface density limits and the PuO2 weight percentage is shown in Figures 1 to 5. The limits shown in each figure are given for three different cyclic isotopic compositions. When applying these limits, any 238Pu and 242Pu present must also be ignored in the calculation of the cyclic isotopic composition. It is required that the cyclic-natural material particles in the homogeneous mixture (or slurry) are uniformly distributed and the particle diameter is not greater than 127um, that is, it can pass through a 120-mesh sieve.
5.3 Mass limits for dry and moist natural uranium oxide mixtures For homogeneous mixtures of dry and moist natural uranium oxide, i.e., homogeneous mixtures of slightly moderated cyclopentadiene-natural oxide, the mass limits for Pu and (PuO2 + UO2,) are given in Table 2. These limits apply to such mixtures where the 240Pu isotopic composition is greater than the 241Pu isotopic composition.
5.4 Weight percentage limits for cyclopentadiene in unlimited quantities of cyclopentadiene-natural uranium oxide mixtures and nitrate mixtures For unlimited quantities of [PuO2 + UO2,] mixtures and [Pu(NO) + UO2(NO2,),] mixtures, the weight percentage limits for cyclopentadiene are given in Table 3. These limits apply to such mixtures where the 2Pu isotopic composition is greater than the 241Pu isotopic composition. These limits do not apply to mixtures of elemental cyclopentadiene with elemental uranium.
5.5 Limits for heterogeneous systems of cyclic-natural uranium oxide mixtures in water The relationship between the mass, volume, cylindrical diameter and plate thickness limits for heterogeneous systems of cyclic-natural uranium oxide mixtures in water and the weight percentage of PuO2 in the oxide mixture is shown in Figures 6 to 9. The limits shown in each figure are given for three different cyclic isotopic compositions. When applying the limits given in the figures, it is not necessary to consider the size and shape of the mixture blocks, nor the degree of moderation of the water in the system, but any 238Pu and 242Pu present must be ignored when calculating the cyclic isotopic composition. Note: The curves in Figures 7, 8 and 9 applicable to cyclic isotopic compositions of 24°Pu ≥ 25% (weight) and 21Pu ≤ 15% (weight) shall not be extrapolated to the limit line for PuO2 percentage exceeding 18% (weight). 164
GB 15146.5—94
Table 1 Subcritical limits of homogeneous systems of ring-natural uranium oxide mixtures in water (except for the atomic ratio which is the lower limit, all other values ​​are upper limits) PuO2 in (PuO2+U,), %
(weight)
Ring isotopic composition1
Ring (Pu) mass, kg
Oxide (PuO2+UO,) mass, kg
Diameter of infinitely long cylinder, cm
Thickness of infinitely wide plate, cm
Volume, L
Ring (Pu) concentration, g/1www.bzxz.net
Oxide (PuO2+UO2) concentration, g/L
H: Pu atomic ratio
Ring (Pu) surface density, g/cm2
Oxide (PuO,+UO,) surface density
Note: 1) Isotopic composition:
_240Pu>241Pu:
24.330.834.8
11.014.9 17.4
23.544.863.4
37803203
10. 214. 4
I——240Pu≥15% (weight) and 241Pu≤6% (weight); —240Pu≥25% (weight) and 241Pu≤15% (weight). 8.2
26.530.735.2
37803253
2) When the weight percentage of PuO, in (PuO,+UO,) is 30%, the scale and volume limits cannot be used for isotopic compositions I and 1, unless the oxide concentration is less than 5700g/L (for isotopic composition I), or the oxide concentration is less than 4500g/L (for isotopic composition I). 3) This concentration limit does not apply to oxide mixtures with a PuO/(PuOz+UO) ratio of less than 3% by weight, because the relative importance of 235U increases in materials containing a large amount of uranium.) Mixture materials, the percentage of rings in the mixture can be found in Table 3.
Table 2 Subcritical limits for isolated units of slightly moderated ring-natural uranium oxide mixtures (applicable to ring isotopic compositions of 240Pu>241Pu) (PuO＋UO,)
PuO2,% (weight)
Density is theoretical density of dry
Mixed oxide
Pu massPuO,+UOzPu mass
(PuO,+UO,Pu mass (PuO,+UO,)Pu massPu，+UO,)mass, kg
Mass, kg
Mass, kg
Mass, kg
Any quantity
(PuO,+U0,)density≤11
Pseudo-subcritical
H: (Pu+U)-0
Density is the theoretical density of wet
mixed oxide
(PuO,＋UO,)density≤
9.4 g/cm3
0
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