Comparison to CALVIN

The Used Fuel Disposition Campaign developed a Transportation-Logistics Simulation (TSL) tool that uses the legacy Civilian Radioactive Waste Management System (CRWMS) Analysis and Logistics Visually Interactive model (CALVIN). TSL-CALVIN simulates the logistics and costs of managing SNF across reactors, storage facilities, and disposal facilities. It has the capability to track discharges from a reactor site to a disposal facility and calculate the various costs associated with onsite storage, transportation, interim storage (offsite), and emplacement. The model also provides logistic information relative to the waste stream movement and system resources required to accomplish that movement.

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A reference scenario was required to test the compatibility between CALVIN and the TVM. The reference scenario contained the eight reactors and ten pools as described in the previous section. The BWR reactors only used a canister with a nine-assembly capacity and the PWR reactors only used a canister with a four-assembly capacity. The reference scenario only used one canister per reactor type to allow an easier transition between the two models. The two canisters were the smallest for each canister’s respective reactor type. Since the TVM implements a limit for the number of canisters leaving a reactor, small canisters require the model to run the simulation longer. The limits for the reference scenario for the TVM were 100 canisters per year, with a maximum of 25 canisters removed annually from a single shutdown reactor and 15 canisters removed annually from an operating reactor. CALVIN had a yearly CISF acceptance limit of 162 MTHM in order to match the 100 canisters shipped per year. CALVIN does not use reactor limits. Table 22 shows the model input comparison for CALVIN and the TVM.

Table 22: Model input comparison

Model PWR Canister ID BWR Canister ID CISF Acceptance Limit Operating Reactor Limit Shutdown Reactor Limit

TVM 1 2 100 Canister 15 Canisters 25 Canisters

CALVIN 1 2 162 MTHM N/A N/A

CALVIN differs from the TVM in that CALVIN uses metric tons of heavy metal (MTHM) as the unit for establishing acceptance rates and throughput while the TVM uses number of canisters as the baseline unit for acceptance rates and throughput. Canisters contain assemblies, which have masses in MTHM, but not all assemblies have the same mass; similarly, the canister capacity will vary by fuel type. This is illustrated in Table 23. The more realistic limit for throughput will be number of canisters instead of mass, because the number fixed time to load

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and unload a canister is a heavier burden on the system than the variable cost of loading assemblies into a canister.

Table 23: Comparing the can size, average assembly weight, and average canister weight used in the example scenario for different reactor types

BWR/PWR Ref. Can Size Avg. Weight/Assembly Avg. Weight/Canister

BWR 9 0.0106 MTHM 0.0957 MTHM

PWR 4 0.0491 MTHM 0.1963 MTHM

Since the assembly weights are not uniform between BWR and PWR types (resulting in possible different canister weights), the comparison to analyze the yearly limit for CALVIN used trial and error. The goal was to allow CALVIN to remove 100 canisters in a year in the same way as the TVM. Allocating 162 MTHM per year allowed Calvin to ship around 100 canisters in a year.

A comparison of the different models for the reference scenario is in the Tables 24 and 25 below. Table 24 removes 100 canisters in a year, while Table 25 removes 45 canisters in a year.

Removing 100 canisters a year in this OFF allocation strategy totals one more shutdown reactor year for the TVM than CALVIN. The biggest discrepancy is in reactor 1 where the TVM unloads all the SNF six years earlier than CALVIN. The difference in the CALVIN and the TVM most likely stems from the way canisters are loaded from the allocation strategy. The TVM does not allow semi-loaded canisters to be removed. Instead of shipping a semi-loaded canister, the TVM loads it completely and ships it. The next allocation for that reactor is not affected by the previous reactor removal. Since CALVIN is using MTHM, the next allocation for a reactor site could be affected by a previous removal. Another difference in the TVM and CALVIN is which assemblies get loaded. CALVIN attempts to load the youngest fuel first (hottest) and the TVM

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Table 24: Comparing the dates of reactor shutdown between the TVM and CALVIN using OFF and a limit of 100 canisters per year

Reactor TVM CALVIN 1 2068 2074 4 2076 2076 6 2036 2037 7 2081 2080 9 2076 2073 12 2077 2076 14 2081 2079 16 2081 2080 Total 278 277

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Table 25: Comparing the dates of reactor shutdown between the TVM and CALVIN using OFF and a limit of 45 canisters per year

Reactor TVM CALVIN 1 2133 2133 4 2139 2137 6 2052 2053 7 2148 2147 9 2131 2133 12 2137 2138 14 2145 2145 16 2146 2145 Total 733 733

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loads the coldest fuel first at each respective reactor. Utilities may attempt to remove the YFF, but for the purpose of this study, a coldest fuel first loading strategy is a conservative view.

Removing 45 canisters per year in this OFF allocation strategy totals an equal number of shutdown reactor year for the TVM and CALVIN. At most, the last pickup date for a reactor differs by two years.

Constraining the number of canisters that can be removed in a year greatly increases the number of shutdown reactor years. It also provides more of an opportunity to optimize the allocation strategy. The less SNF removed in a year, the more sensitive the allocation strategy becomes. As the yearly limit increases to the sum of the reactor limits, the optimization impact gets smaller until it reaches zero. In order for an optimized allocation strategy exist, the inequality expressed in equation 6.1.1 must be true, i.e., yearly limit must be less than the minimal sum of all reactor limits in a year.

𝒀𝒆𝒂𝒓𝒍𝒚𝑳𝒊𝒎𝒊𝒕 < 𝒎𝒊𝒏 ∑ 𝑹𝒆𝒂𝒄𝒕𝒐𝒓_𝑳𝒊𝒎𝒊𝒕𝒔 (6.1.1)