United States Nuclear Regulatory Commission - Protecting People and the Environment

RELAP5/MOD3 Assessment for Calculation of Safety and Relief Valve Discharge Piping Hydrodynamic Loads (NUREG/IA-0093)

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Publication Information

Date Published: February 1994

Prepared by:
E. J. Stubbe, L. VanHoenacker, R. Otero

TRACTEBEL
Avenue Ariane 7
B-1200 Brussels
Belgium

Prepared as part of:
The Agreement on Research Participation and Technical Exchange
under the International Thermal-Hydraulic Code Assessment
and Application Program (ICAP)

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

This report presents an assessment study for the use of the code RELAP 5/MOD3/5M5 in the calculation of transient hydrodynamic loads on safety and relief discharge pipes. Its predecessor, RELAP 5/MOD1, was found adequate for this kind of calculations by EPRI. The hydrodynamic loads are very important for the discharge piping design because of the fast opening of the valves and the presence of liquid in the upstream loop seals.

The code results are compared to experimental load measurements performed at the Combustion Engineering Laboratory in Windsor (U.S.A.). Those measurements were part of the PWR Valve Test Program undertaken by EPRI after the TMI-2 accident.

This particular kind of transients challenges the applicability of the following code models

  - Two-phase choked discharge
  - Interphase drag in conditions with large density gradients
  - Heat transfer to metalic stuctures in fast changing conditions
  - Two-phase flow at abrupt expansions

The code applicability to this kind of transients is investigated. Some sensitivity analyses to different code and model options are performed. Finally, the suitability of the code and some modeling guidelines are discussed.

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