Information provided by Brigadier Naeem Salik:-
"For instance, a 50-megawatt plutonium production reactor working at 100 percent capacity can produce 18.25 kilograms of plutonium per year. However, these plants normally run at a much lower capacity, and most calculations use a baseline of between 60 percent and 70 percent capacity. Running at this capacity, a 50-megawatt plant will produce around 11 to 13 kilograms per year, assuming that it can maintain the same efficiency through the entire 365 days. In practice, however, the plants may run as low as 40 percent to 50 percent capacity, producing up to 7 to 9 kilograms per year. Moreover, the reactors cannot run 365 days per year. Reactors shut down for refueling and routinely face technical snags, which are not accounted for in existing calculations." - Brigadier Naeem Salik
Breakdown of provided information:-
50 MW = 18.25 kg (100% capacity)
50 MW = 13 kg (70% capacity)
50 MW = 11 kg (60% capacity)
50 MW = 9 kg (50% capacity)
50 MW = 7 kg (40% capacity)
At 100% capacity:-
Khushab 1 =
50 MW
Khushab 2 = 60 MW
Khushab 3 = 80 MW
Khushab 4 =
100 MW
Total =
290 MW
We take
50 MW = 18.25 kg in this case.
Khushab 1 =
18.25 kg
Khushab 2 = 21.9 kg
Khushab 3 = 29.2 kg
Khushab 4 =
36.5 kg
Cumulative plutonium output =
105.85 kg
At 60% capacity:-
Khushab 1 =
30 MW
Khushab 2 = 36 MW
Khushab 3 = 48 MW
Khushab 4 =
60 MW
Total =
174 MW
We take
50 MW = 11 kg in this case.
Khushab 1 =
6.6 kg
Khushab 2 = 7.92 kg
Khushab 3 = 10. 56 kg
Khushab 4 =
13.2 kg
Cumulative plutonium output =
38.28 kg
"Currently, Pakistan has four operational plutonium production reactors at its Khushab complex. Assuming the reactors run at 60 percent capacity, each would produce slightly less than two weapons’ worth of plutonium per year, toward a total output of around 36 kilograms of plutonium—six warheads at 6 kilograms per warhead—per year. This suggests that Pakistan could produce up to 60 plutonium warheads over the next decade." - Brigadier Naeem Salik
NOTE: My calculation is very close to that of Brigadier Naeem Malik, considering 60% capacity.
At 40% capacity:-
Khushab 1 =
20 MW
Khushab 2 = 24 MW
Khushab 3 = 32 MW
Khushab 4 =
40 MW
Total =
116 MW
We take
50 MW = 7 kg in this case.
Khushab 1 =
2.8 kg
Khushab 2 = 3.36 kg
Khushab 3 = 4.48 kg
Khushab 4 =
5.6 kg
Cumulative plutonium output =
16.24 kg
@Mrc
FYI
With your approach, you will get
63.51 kg of plutonium from the 4 reactors while operating at 60% of their cumulative capacity, which is wrong:
"Currently, Pakistan has four operational plutonium production reactors at its Khushab complex. Assuming the reactors run at 60 percent capacity, each would produce slightly less than two weapons’ worth of plutonium per year, toward a total output of around 36 kilograms of plutonium—six warheads at 6 kilograms per warhead—per year. This suggests that Pakistan could produce up to 60 plutonium warheads over the next decade." - Brigadier Naeem Salik
My calculation is very close to his on the other hand.
Your mistake is to consider 18.25 kg plutonium production rate as a
constant while you re-adjust 'operational capacity' of the reactors from 100% to 40%. Plutonium production rate of each reactor drops
alongside its 'operational capacity' in reality, it doesn't stay the same (see provided information).