Uncertainty assessment for accelerator-driven systems
- Argonne National Laboratory, 9700 S. Cass Avenue, Bldg, 208 Argonne, IL 60439 (United States)
- CEA Cadarache, F.13108 Saint Paul Les Durance Cedex (France)
The concept of a subcritical system driven by an external source of neutrons provided by an accelerator ADS (Accelerator Driver System) has been recently revived and is becoming more popular in the world technical community with active programs in Europe, Russia, Japan, and the U.S. A general consensus has been reached in adopting for the subcritical component a fast spectrum liquid metal cooled configuration. Both a lead-bismuth eutectic, sodium and gas are being considered as a coolant; each has advantages and disadvantages. The major expected advantage is that subcriticality avoids reactivity induced transients. The potentially large subcriticality margin also should allow for the introduction of very significant quantities of waste products (minor Actinides and Fission Products) which negatively impact the safety characteristics of standard cores. In the U.S.A. these arguments are the basis for the development of the Accelerator Transmutation of Waste (ATW)L,which has significant potential in reducing nuclear waste levels. Up to now, neutronic calculations have not attached uncertainties on the values of the main nuclear integral parameters that characterize the system. Many of these parameters (e.g., degree of subcriticality) are crucial to demonstrate the validity and feasibility of this concept. In this paper we will consider uncertainties related to nuclear data only. The present knowledge of the cross sections of many isotopes that are not usually utilized in existing reactors (like Bi, Pb-207, Pb-208, and also Minor Actinides and Fission Products) suggests that uncertainties in the integral parameters will be significantly larger than for conventional reactor systems, and this raises concerns on the neutronic performance of those systems. As an example, the multiplication factor in many designs of subcritical systems are envisioned to be around 0.98 because of the need to massively multiply the spallation source. If uncertainties on cross section lead to a significant variation of this value a modification in the planned core layout or additional margin in the acceleration size will be required. Predictions of reactivity variations during operation are also crucial and significant uncertainty on this value is expected for the ATW, which can create problems on fuel inventory, safety issues, control requirements, and accelerator dimensioning. The power distribution in such a system is quite different from that in the standard reactor situation because of the presence of the external source that tends to peak the power toward the source region. A partial flattening is obtained through inward shuffling of irradiated fuel and the use of lead, which also serves as a reflector. The objectives of this paper are 1) to assess the effect of nuclear data uncertainties on the ADS performance and 2) to define the major contributors to these uncertainties. An uncertainty analysis of the impact of cross section data knowledge on the main neutronic integral parameters has been performed for an ATW type system. Uncertainties larger than those calculated for reactor systems are obtained. This can be attributed to uncertainties of lead and bismuth and transuranic dominated fuel compositions. Cross sections for the (n, 2n) reactions do not seem to play a major role in the uncertainty assessment. Similarly to what has been done in the past for reactors, an experimental program on a zero-power mock-up facility, like the MUSE experiments in MASURCA, should contribute to significantly reduce uncertainties on integral parameters to values that will be acceptable for an efficient neutronic design of an ADS system. Finally, the recent availability of neutronic cross section data files up to 150 MeV motivates a sensitivity study to data over the 20 MeV energy threshold to assess the importance of correctly calculating the neutron flux distribution in this energy range and the high energy neutron damage for an ADS system. Similar studies in the future, as the ones carried out in this paper, will be performed for transmutation dedicated ADSS presently under consideration in France.
- Research Organization:
- American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
- OSTI ID:
- 23142216
- Resource Relation:
- Conference: Global'99: International Conference on Future Nuclear Systems - Nuclear Technology - Bridging the Millennia, Las Vegas, NV (United States), 29 Aug - 3 Sep 1999; Other Information: Country of input: France; 13 refs.; available from American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 (US)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
ACTINIDES
BISMUTH
CRITICALITY
CROSS SECTIONS
DESIGN
FISSION PRODUCTS
LEAD-BISMUTH EUTECTIC
LIQUID METALS
MASURCA REACTOR
MEV RANGE
MULTIPLICATION FACTORS
NEUTRON FLUX
NEUTRONS
RADIOACTIVE WASTES
SODIUM
SPENT FUELS
SUBCRITICAL ASSEMBLIES