The power obtained in a reactor using U-235 disintegration is 1000 kW. The mass decay of U-235 per hour is:

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1. **Identify Given Values:**
   - Power ($P$) = $1000 	ext{ kW} = 1000 	imes 10^3 	ext{ W} = 10^6 	ext{ J/s}$.
   - Time ($t$) = 1 hour = $3600 	ext{ s}$.
   - Speed of light ($c$) $\approx 3 	imes 10^8 	ext{ m/s}$ .
2. **Calculate Total Energy ($E$):**
   - Energy produced in 1 hour = Power $	imes$ Time.
   - $E = 10^6 	ext{ J/s} 	imes 3600 	ext{ s} = 3.6 	imes 10^9 	ext{ J}$.
   - Alternatively, using conversion factors: $1 	ext{ kWh} = 3.6 	imes 10^6 	ext{ J}$ . Energy = $1000 	ext{ kWh} = 1000 	imes 3.6 	imes 10^6 	ext{ J} = 3.6 	imes 10^9 	ext{ J}$.
3. **Apply Mass-Energy Equivalence:**
   - According to Einstein's equation, $E = \Delta m c^2$.
   - Mass decayed ($\Delta m$) = $E / c^2$.
   - $\Delta m = \frac{3.6 	imes 10^9 	ext{ J}}{(3 	imes 10^8 	ext{ m/s})^2} = \frac{3.6 	imes 10^9}{9 	imes 10^{16}} 	ext{ kg}$.
   - $\Delta m = 0.4 	imes 10^{-7} 	ext{ kg}$.
4. **Convert to Micrograms:**
   - $1 	ext{ kg} = 10^9 	ext{ micrograms} (\mu	ext{g})$.
   - $\Delta m = 0.4 	imes 10^{-7} 	imes 10^9 \mu	ext{g} = 0.4 	imes 100 \mu	ext{g} = 40 \mu	ext{g}$.

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