Comparison of Gamma and Neutron Dose Rate Variations with Time for Cast Iron and Metal–Concrete Casks Used for RBMK-1500 Spent Fuel Storage
Abstract
:1. Introduction
2. Containers Used for RBMK-1500 Spent Fuel Storage
3. Methodology
- Stage No. 1: RBMK-1500 spent fuel characteristics are modeled using the TRITON code of the SCALE 6 computer code system [18]
- Stage No. 2: the obtained spent fuel characteristics are used as input data for the MAVRIC code [19] of the SCALE 6 code system that performs gamma and neutron transport modeling and calculates resulting dose rates.
- The gamma and neutron sources were defined as homogeneous cylinders containing 102 spent FB and the 32M basket structures. Secondary gamma emissions due to (n, γ) reactions and bremsstrahlung, and emissions from neutron-activated steel components of SF assemblies were not taken into account. Neutron activation of the container components was deemed insignificant [20].
- In order to evaluate the impact of certain energy gamma or neutron emissions from the spent fuel on the resulting gamma or neutron dose rates, separate inputs for individual energy groups (19 energy groups for gamma and 27 groups for neutrons) were created. Neutron and gamma energy groups and their energy boundaries are presented in Table 1.
- The minimum cooling period for RBMK-1500 spent fuel after which the spent fuel is allowed to be loaded into the dry storage container is 5 years. Dose rate distributions and variations were analyzed for a storage period from 5 to 300 years. The 5 year period indicated in the figures below means that the container has only just been loaded with spent fuel.
- It was assumed that aging mechanisms do not change the shielding properties of the container components.
- Three dose rate calculation points (at the center of the container’s top/bottom and side walls) were located on the outer container surface.
4. Results and Discussion
5. Conclusions
- Approximately 97–99% of the gamma dose rate on the side wall of a cast iron or metal–concrete container is caused by photons that are emitted from spent fuel and have energies within 7–12 gamma energy groups. The influence of the remaining 13 gamma energy groups on the gamma dose rate is insignificant. For longer storage periods (50, 300 years) the major contributors to the gamma dose rates on the side wall of both containers are Group No. 7 (0.6–0.8 MeV) photons.
- About 99% of the neutron dose on the side wall of the analyzed containers is determined by neutrons that have energies within 21–27 neutron energy groups. The contributions of the remaining 20 neutron energy groups on the neutron dose rate are negligible. Unlike the contributions of gamma energy groups, the neutron dose rate for all storage periods is determined by the same dominant neutron energy groups.
- Steel lids at the top of the containers provide effective shielding against gamma photons. Therefore, neutron dose rates are dominant at the top of both containers. The CASTOR® RBMK-1500 container side and bottom walls are made of ductile cast iron that provides better shielding against gamma photons, whereas the metal–concrete structures of CONSTOR® RBMK-1500 are better shielding materials against neutrons. For extended storage periods, the total dose rates are mainly determined by neutrons for both containers.
- The total dose rates on the surface of the metal–concrete container are less than those of a cast iron container. The smallest difference between dose rate values occurs at the top of the containers, and this difference is constant during the whole storage period. More significant differences in the dose rate values occur at the side and bottom walls of the containers. The differences vary with storage time, i.e., the total dose rates range from 2–7 times for storage periods up to 50 years, whereas, for extended storage periods, the difference grows to 60 times.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Group No. | Neutron Energies, MeV | Group No. | Gamma Energies, MeV |
---|---|---|---|
1 | 1.00 × 10−11–1.00 × 10−8 | 1 | 1.00 × 10−2–4.50 × 10−2 |
2 | 1.00 × 10−8–3.00 × 10−8 | 2 | 4.50 × 10−2–0.1 |
3 | 3.00 × 10−8–5.00 × 10−8 | 3 | 0.1–0.2 |
4 | 5.00 × 10−8–1.00 × 10−7 | 4 | 0.2–0.3 |
5 | 1.00 × 10−7–2.25 × 10−7 | 5 | 0.3–0.4 |
6 | 2.25 × 10−7–3.25 × 10−7 | 6 | 0.4–0.6 |
7 | 3.25 × 10−7–4.14 × 10−7 | 7 | 0.6–0.8 |
8 | 4.14 × 10−7–8.00 × 10−7 | 8 | 0.8–1.00 |
9 | 8.00 × 10−7–1.00 × 10−6 | 9 | 1.00–1.33 |
10 | 1.00 × 10−6–1.13 × 10−6 | 10 | 1.33–1.66 |
11 | 1.13 × 10−6–1.30 × 10−6 | 11 | 1.66–2.00 |
12 | 1.30 × 10−6–1.86 × 10−6 | 12 | 2.00–2.50 |
13 | 1.86 × 10−6–3.06 × 10−6 | 13 | 2.50–3.00 |
14 | 3.06 × 10−6–1.07 × 10−5 | 14 | 3.00–4.00 |
15 | 1.07 × 10−5–2.90 × 10−5 | 15 | 4.00–5.00 |
16 | 2.90 × 10−5–1.01 × 10−4 | 16 | 5.00–6.50 |
17 | 1.01 × 10−4–5.83 × 10−4 | 17 | 6.50–8.00 |
18 | 5.83 × 10−4–3.04 × 10−3 | 18 | 8.00–10.0 |
19 | 3.04 × 10−3–1.50 × 10−2 | 19 | 10.0–20.0 |
20 | 1.50 × 10−2–1.11 × 10−1 | ||
21 | 1.11 × 10−1–4.08 × 10−1 | ||
22 | 4.08 × 10−1–9.07 × 10−1 | ||
23 | 9.07 × 10−1–1.42 | ||
24 | 1.42–1.83 | ||
25 | 1.83–3.01 | ||
26 | 3.01–6.38 | ||
27 | 6.38–20.0 |
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Smaizys, A.; Narkunas, E.; Poskas, G.; Poskas, P. Comparison of Gamma and Neutron Dose Rate Variations with Time for Cast Iron and Metal–Concrete Casks Used for RBMK-1500 Spent Fuel Storage. Appl. Sci. 2021, 11, 7362. https://doi.org/10.3390/app11167362
Smaizys A, Narkunas E, Poskas G, Poskas P. Comparison of Gamma and Neutron Dose Rate Variations with Time for Cast Iron and Metal–Concrete Casks Used for RBMK-1500 Spent Fuel Storage. Applied Sciences. 2021; 11(16):7362. https://doi.org/10.3390/app11167362
Chicago/Turabian StyleSmaizys, Arturas, Ernestas Narkunas, Gintautas Poskas, and Povilas Poskas. 2021. "Comparison of Gamma and Neutron Dose Rate Variations with Time for Cast Iron and Metal–Concrete Casks Used for RBMK-1500 Spent Fuel Storage" Applied Sciences 11, no. 16: 7362. https://doi.org/10.3390/app11167362
APA StyleSmaizys, A., Narkunas, E., Poskas, G., & Poskas, P. (2021). Comparison of Gamma and Neutron Dose Rate Variations with Time for Cast Iron and Metal–Concrete Casks Used for RBMK-1500 Spent Fuel Storage. Applied Sciences, 11(16), 7362. https://doi.org/10.3390/app11167362