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Engineering Services and Support of QA: Enhancement of TRACE Model for NPP Gösgen Extension of the TRACE Model for NPP Gösgen for partial load states


  • Employer:
    Gösgen Nuclear Power Plant
  • Implementation period:
    july 2016 – january 2019


Gösgen NPP (Kernkraftwerk Gösgen, KKG) is located in the municipality of Däniken, in the canton of Solothurn, Switzerland on the banks of the river Aar. Gösgen NPP is operated by the company Kernkraftwerk Gösgen-Däniken AG.

The KKG has a pressurized water reactor designed by the German Kraftwerk Union AG, a then subsidiary of Siemens AG, then Areva NP and now part of Framatom. It contains 177 fuel assemblies, 48 of which are equipped with control elements. Each fuel assembly can hold up to 225 rods, but only 205 (204 for the MOX ones) are occupied by the fuel rods. The remaining 20 channels are reserved to the control rods. Rated parameters of the reactor installation are 324 ⁰C and 153 bars. The thermal power is 3002 MW (3062 MW for 104 % power).

The reactor installation has three primary side loops. The three steam generators of vertical type transfer the heat to the secondary coolant loop at 65 bar and 280 ⁰C. The turbine is composed of a high-pressure and three low-pressure units. It generates a net electric power of 970 MW that is delivered to the 400 kV power grid.


The project covers changes in the reactor installation model (developed with TRACE program) to enhance the model for simulations of low power states (85 % of operation and 61,5 % with 2-loop in operation). The model is validated against results from the KKG full-scope simulator. 

The scope of the activities foreseen in the contract can be summarized as follows:

  • Development of model for 85 % power level 
  • Development of model for 61,5 % power 61,5 % with 2-loop in operation
  • Performance of scenarios for model validation and analysis of the results.

The scenarios that have been used for validation are Loos-of Offsite Power (LOOP) and LOCA from Primary to Secondary side (SGTR). 

The main goal of the project is to demonstrate capability of the model to simulate accident scenarios at low power levels.


The KKG model for design and beyond design (without core melt) basis accidents is developed with TRACE program and as for the purposes of this project the power control is changed for simulation of low power states (85 % of operation and 61,5 % with 2-loop in operation). 

Four accident scenarios have been run in the frame of the project covering Loos-of Offsite Power (LOOP) and LOCA from Primary to Secondary side (SGTR) initiating events. The SGTR scenarios are performed only with the 2-loop model i.e., 61,5 % power. 

The results are compared against results from the KKG full-scope simulator. 

As a result of the comparison, it can be concluded that the developmental TRACE_KKG model is capable to accurately represent the LOOP and the SGTR initiating events that are based on partial load initial conditions.