Light Water

H₂O

Moderators & Coolants

Density: 0.998 g/cm³

Light water at room temperature (~20°C). Primary moderator and coolant in PWRs and BWRs.

Composition

Nuclide / Element	Fraction
H-1	0.666667
O-16	0.333333

S(α,β) required: lwtr

Code output

MCNP

c Light Water (H2O)
c Density: 0.998 g/cm3 (use -0.998 on cell card)
m16    1001.80c  0.666667  $ H-1
       8016.80c  0.333333  $ O-16
mt16  lwtr.20t

Notes

Density at 20°C and 1 atm. Adjust density for operating temperature: ~0.72 g/cm³ at 300°C (PWR hot leg), ~0.74 g/cm³ at 286°C (BWR).

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