Summary and Concluding Remarks

In the framework of the LWR-PROTEUS Phase II programme, the reactivity worth of UO2

fuel rod segments with a PWR irradiation history of up to 7 cycles, and of MOX samples with a history of up to 3 cycles, are being measured in various neutron spectra. The chemical assays of the burnt fuel samples provide the isotopic concentrations of 9 major actinide nuclides, 8 minor actinide nuclides and 29 fission products. The strength of the programme lies in the fact that highly burnt fuel discharged from a nuclear power plant is measured for reactivity effects in PROTEUS and analyzed physically and chemically, in parallel, as part of the same programme. Measurements carried out during the approach-to-critical and commissioning period of the reference Phase II configuration in PROTEUS have provided confirmatory

evidence for the design of the experiments and of the high accuracies to be expected in the programme.

The current extension of the available validation base for reactor physics codes to very high burnup is essential for regulatory acceptance of future burnup increases. Furthermore, the PROTEUS experiments could provide valuable evidence to justify a significant reduction of the degree of conservatism in present-day PWR core designs. Finally, the experiments will also be important for the validation of codes used to predict the reactivity of spent fuel in storage and transport configurations, i.e. will provide a new extended basis for burnup credit evaluations.

ACKNOWLEDGEMENTS

The LWR-PROTEUS programme is being conducted jointly by PSI and the Swiss Nuclear Utilities with specific contributions from Elektrizitäts-Gesellschaft Laufenburg (EGL) and Aare-Tessin AG für Elektrizität (ATEL). We are particularly grateful to H. Achermann (EGL), H. Fuchs (ATEL), G. Straub (KKM) and W. Kröger (PSI) for their strong support of the experiments. Also thanked are G. Bart, Z. Kopajtic, B. Wernli, I. Guenther-Leopold and S.-G. Jahn for their important contributions to the planning work, as well as D. Kuster, R.

Schwarz and H. Schweikert for the preparation of samples. Thanks are also due to P.

Bourquin, M. Fassbind and M. Berweger for excellent reactor operation and maintenance, as well as to J. Ulrich, J. Kohout and K. Kohlik of PSI’s Logistics and Marketing Department (LOG) for their valuable engineering support.

REFERENCES

[1] WILLIAMS, T., et al., “LWR-PROTEUS - New Experiments at a Zero-Power Facility Using Power Reactor Fuel”, Proc. Int. Conf. on the Physics of Nuclear Science and Technology, Long Island, NY, Oct. 5-8, 1998, Vol. 1, pp. 720-727.

[2] JONEJA, O.P., et al., “Validation of an MCNP4B Whole-Reactor Model for LWR-PROTEUS Using ENDF/B-V, ENDF/B-VI and JEF-2.2 Cross-Section Libraries”, Annals of Nuclear Energy, 28, pp. 701-713 (2001).

[3] MEISTER, A., GRIMM, P., CHAWLA, R., “Neutronics Design of LWR-PROTEUS Phase II High-Burnup Fuel Reactivity Measurements”, Trans. Am. Nucl. Soc., 85, pp.268-269 (2001).

[4] BASSELIER, J., LIPPONS, M., ABELOUS, C., “A Detailed Investigation of the Source Terms Devoted to UO2 and MOX High-Burnup LWR Fuel through the ARIANE International Programme”, KTG-Fachtagung Brennelement-Technik, Kernauslegung und Reaktorbetrieb, Karlsruhe, Germany, February 3-4, 1998.

[5] KASEMEYER, U., et al., “Feasibility of Partial LWR Core Loadings with Inert Matrix Fuel”, Proc. ARWIF 2001, October 22-24, 2001, Chester (UK).

Experimental measurement of the isotopic composition of high enrichment and high burnup fuel

C. Alejano, J.M. Conde,

Consejo de Seguridad Nuclear, Spain J.A. Gago,

Empresa Nacional de Residuos (ENRESA), Spain M. Quecedo, J.M. Alonso

ENUSA Industrias Avanzadas, Spain

Abstract. Within the frame of the fuel safety and reliability research activities in Spain, a project has been initiated in 2002 to measure the isotopic composition of PWR fuel with a high initial enrichment at high local burnup levels. The fuel to be measured was included in an irradiation demonstration program carried out at the Vandellós 2 NPP, and was fully characterised before irradiation. Poolside inspections were performed at each and every reload. After irradiation, the fuel has been included in several research programs:

• Ramp testing and PIE examinations

• Reactivity insertion accidents research in the CABRI program

• Measurement of the mechanical properties of the cladding in the PROMETRA program

• High burnup fuel safety research program of JAERI (ALPS program)

The isotopic composition measurement program will complete and enhance the outcome of these programs, and will serve as a base for the validation of burnup credit analysis methods to be applied to transport casks in the future. The program will include the measurement of six samples obtained form two rods, with burnup values ranging from 40 to 70 MWd/kgU. The isotopes to be measured have been decided on the basis of their importance for criticality, shielding and residual heat calculations. The preliminary results should be obtained before the end of 2002.

1. BACKGROUND

The participation of Spain in high burnup fuel research activities has been increasing steadily during the last decade. The national activities carried out by the fuel supplier (ENUSA), basically consisting of fuel demonstration and irradiation programs up to high burnup values, are complemented by the participation of different Spanish organizations in a number of international research efforts. Some of those are the CABRI Water Loop Program, the NRC high burnup fuel program, the Halden Reactor Project, the Robust Fuel Program managed by EPRI and the ALPS program of JAERI.

One of the high burnup fuel research fields in which different Spanish organizations are interested is that of the isotopic fuel composition at high discharge burnup values. Isotopic composition data is needed to validate fuel burnup codes, this being an issue specially important for the implementation of burnup credit in criticality safety analysis of both storage and transport systems. However, none of the programs mentioned above are providing isotopic composition data representative of current fuel designs, and with an initial enrichment and irradiation history similar to those now used.

The lack of data in this field has prompted the startup of a co-operative effort to independently measure the isotopic composition of PWR fuel with a high initial enrichment at high discharge burnup values. The program will use fuel irradiated in the so-called irradiation extension program (described in the next paragraph), and the participant organizations are the Consejo de Seguridad Nuclear, ENRESA (responsible in Spain for waste management),

ENUSA (Spanish fuel vendor), ENDESA (Spanish utility), Kansai and Mitsubishi Heavy Industries.