[en] This document serves as a user's manual and theoretical manual for the CRUNCH1D computer program. CRUNCH1D is a numerical integration code designed to analyze the HTGR core for seismic excitation. The core is represented as a one-dimensional horizontal strip of blocks constrained within the PCRV. Each block of the CRUNCH model represents one or more columns of the actual core. One additional block is provided to model the core support floor. Seismic excitation is provided by defining the motion of the PCRV. CRUNCH has two types of mathematical models for collisions; the standard spring-damper model, and an impulse-momentum model