RELAP5 Nuclear Reactor Thermal-Hydraulics (.i, .inp, .r5)

@modelscript/relap5 (languages/relap5) provides high-fidelity 80-column card deck parsing, non-equilibrium two-phase hydrodynamic modeling, 6-group delayed neutron point kinetics solving, DAE lowering, and Modelica 3.x projection for INL RELAP5-3D nuclear reactor systems, thermal-hydraulic loops, and safety margin evaluations.

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Supported Extensions & Standards

Extension	Format	Description
.i / .inp	RELAP5 Input Card Deck	Fixed-column card deck specifying hydrodynamic volumes, junctions, heat structures, trips, and kinetics
.r5	RELAP5-3D System Deck	Multi-loop PWR/BWR coolant systems, steam generators, emergency core cooling systems (ECCS)

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Key Capabilities

1. Two-Phase Non-Equilibrium Hydrodynamics

• Employs a full 6-equation two-fluid formulation with separate mass, momentum, and energy conservation equations for liquid and vapor phases:
  • Phase Mass Conservation:$$\frac{\partial }{\partial t}({\alpha }_k{\rho }_k)+\frac{1}{A}\frac{\partial }{\partial x}({\alpha }_k{\rho }_k{v}_{k}A)={\mathrm{\Gamma }}_k(k\in \{l,v\})$$
  • Phase Momentum Conservation:$${\alpha }_k{\rho }_k\frac{\partial v_k}{\partial t}+{\alpha }_k{\rho }_k{v}_k\frac{\partial v_k}{\partial x}=-{\alpha }_k\frac{\partial P}{\partial x}+{\alpha }_k{\rho }_{k}g\cos \theta -F_{\text{wall},k}-F_{\text{inter},k}+{\mathrm{\Gamma }}_k(v_{ki}-v_k)$$
  • Phase Energy Conservation:$$\frac{\partial }{\partial t}({\alpha }_k{\rho }_k{u}_k)+\frac{1}{A}\frac{\partial }{\partial x}({\alpha }_k{\rho }_k{u}_k{v}_{k}A)=-P[\frac{\partial {\alpha }_k}{\partial t}+\frac{1}{A}\frac{\partial }{\partial x}({\alpha }_k{v}_{k}A)]+Q_{\text{wall},k}+Q_{\text{inter},k}+{\mathrm{\Gamma }}_k{h}_{ki}$$
• Tracks interphase friction, bubbly/slug/annular flow regime transitions, and subcooled boiling.

2. 6-Group Delayed Neutron Point Kinetics & Reactivity Feedback

• Solves the stiff differential equations of reactor core power during transients and reactor SCRAM:$$\frac{dP}{dt}=\frac{\rho (t)-\beta }{\mathrm{\Lambda }}P(t)+\sum _{i=1}^6{\lambda }_i{C}_i(t)$$$$\frac{d{C}_i}{dt}=\frac{{\beta }_i}{\mathrm{\Lambda }}P(t)-{\lambda }_i{C}_i(t)(i=1,\dots ,6)$$where $P$ is normalized thermal power, $\mathrm{\Lambda }$ is prompt neutron generation time, and $\beta =\sum {\beta }_i$ is delayed neutron fraction.
• Incorporates dynamic physical reactivity feedback:$$\rho (t)={\rho }_{\text{control}}(t)+{\alpha }_{\text{Doppler}}(\sqrt{T_{\text{fuel}}}-\sqrt{T_{\text{fuel},0}})+{\alpha }_{\text{density}}({\rho }_{\text{mod}}-{\rho }_{\text{mod},0})$$ensuring negative Doppler fuel temperature feedback stabilizes reactor transients.

3. Direct DAE Lowering

• Compiles hydrodynamic volumes, inter-volume junctions, and heat structures into @modelscript/runtime's DAEBuilder linear memory arena.
• Enables co-simulation between nuclear primary coolant loops, secondary steam turbine power plants, and electrical generator controls (@modelscript/psse).

4. Bidirectional Modelica 3.x Projection

• Projects RELAP5 primary loops and core volumes into Modelica.Fluid two-phase thermal hydraulic circuits and nuclear reactor models.

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Pre-Flight Diagnostics

The RELAP5 parser and validator enforce card syntax, hydrodynamic connectivity, and trip cutset safety:

10 rules8 error2 warning Run with msx relap5 lint

Code	Rule	Severity	Message
M8601	dangling-volume-connection	error	Junction '<junctionId>' specifies undefined <end>-volume '<volId>'.
M8602	unclosed-trip-logic-cutset	error	Trip logic '<parentTripId>' references undefined child trip ID '<childTripId>'.
M8603	negative-heat-capacity	error	Heat structure '<hsId>' specifies non-positive conductivity (<k> W/m-K) or capacity (<cp> J/m³-K).
M8604	sonic-choked-flow-singularity	warning	Junction '<junctionId>' flagged for critical sonic choked flow transition.
M8605	missing-kinetics-delayed-groups	error	Point kinetics model specifies <count> delayed groups; standard reactor kinetics requires 6 precursor groups.
M8606	negative-prompt-neutron-lifetime	error	Prompt neutron generation time '<lambda>' s must be strictly positive.
M8607	adverse-volume-elevation	warning	Volume '<volId>' elevation change dz (<dz> m) exceeds physical volume length (<length> m).
M8608	negative-junction-loss-coefficient	error	Junction '<junctionId>' specifies negative form loss coefficient (K_forw=<kForw>, K_rev=<kRev>).
M8609	invalid-time-step-bounds	error	Minimum time step (<minDt> s) exceeds maximum time step (<maxDt> s).
M8610	negative-pressure-state	error	Volume '<volId>' specifies non-positive thermodynamic pressure (<p> Pa).

Generated from languages/relap5/src/errors.ts. All languages →

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CLI Usage

# Inspect hydrodynamic volumes, junctions, and core kinetics cards
msx relap5 inspect PwrPrimaryLoop.i

# Run pre-flight card validation and trip logic cutset analysis
msx relap5 lint PwrPrimaryLoop.i

# Simulate 6-group delayed neutron point kinetics during rod drop / SCRAM
msx relap5 kinetics PwrPrimaryLoop.i --duration=10.0

# Lower two-phase volumes and kinetics into ModelScript linear DAE arena
msx relap5 to-dae PwrPrimaryLoop.i

# Project into Modelica 3.x two-phase nuclear thermal-hydraulics model
msx relap5 to-modelica PwrPrimaryLoop.i -o NuclearLoop.mo