[en] The Namelist-variable IELV = 1 option inputs ELEV cell-centered elevations for one-dimensional (1D) hydraulic and HTSTR components. TRAC-P then internally evaluates interface-centered GRAVs. TRAC-P checks that GRAVs evaluated from input ELEVs for the HTSTR component and GRAVs input directly under the Namelist-variable IELV = 0 option for 1D hydraulic and HTSTR components lie within the range of -1.0 to 1.0. TRAC-P, however, does not check that GRAVs evaluated from ELEVs input for 1D hydraulic components lie in this range. Knolls Atomic Power Laboratory requested that TRAC-P Version 5.4.28 be programmed to perform this GRAV value check. Update FXGRAV checks that GRAVs evaluated from input ELEVs for one-dimensional hydraulic components lie in the value range of -1.0 to 1.0