Student internship: Calculation of Residual Decay Heat and its Effects on Reactor, Storage and Disposal Applications

Residual decay heat (DH) plays an important role during reactor operation, transients or accident scenarios and is one of the limiting parameters regarding design and operation of spent fuel storage facilities or a final geological repository. Especially in the latter case it attracted a lot of attention recently and new DH measurements are being sought worldwide and in particular in one of the Swiss NPPs (with ETH involvement).

The calculation of decay heat follows straight forward differential equations for isotopic build up through various reactions of the nuclei with neutrons, and for their decay chains in combination with the specific heat release of the individual decay processes. Even when sophisticated codes like ORIGEN or SNF enable high accuracy calculations, the uncertainty lies typically in the range of 5 % and can be as high as 10 %. For this reason, different standards for deriving conservative calculations have been developed in the U.S.A, Germany and Japan.

As part of a student internship, the numerical calculation of DH for the variety of fuel assembly designs in Swiss NPPs will be carried out. The focus is on coding the international standards DIN 25463, ANS-5.1, and JAERI-M-91-034 to enable the calculation of DH according to fuel assembly type and operation history. For the operation history, a parametric study should be performed to assess the impact of the simplification on the reactor, storage and disposal applications. Optional work packages include:

• Performance of the DH calculations in ORIGEN and comparison of the results with the standards
• implementation of the DH results in the existing FEM model of a storage cask
• performance of uncertainty analyses using the storage cask model
• adaption of the cask model to other cask types

The candidate requires basic knowledge of reactor technology and numerical skills in one of the current programming languages and environments. This work can be performed as part of an internship at ENSI lasting at least 2 months or as normal semester thesis with partial attendance at ENSI in addition to regular lecture participation. German is not required, but an active attitude towards acquiring or further developing German language skills is expected. If you have any questions, please contact Mr. J. Dus ([email protected]).

Eidgenössisches Nuklearsicherheitsinspektorat ENSI
Industriestrasse 19
5201 Brugg
+41 56 460 86 30
[email protected]