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Neutron reference measurements for environmental protection

Objective

Specific Objectives
-To continue the study, in a systematic manner, the interaction of neutrons with matter and thereby to provide the basic knowledge needed for the establishment of a complete neutron database;
-To perform measurements of neutron cross sections and related parameters needed for the feasibility study of the proposed incineration of long lived radioactive isotopes and minor actinides;
-To provide experimental data for the improved neutron data-base which is required for the detailed safety assessment of possible incineration facilities;
-To perform the high-resolution neutron cross section measurements needed for shielding applications;
-To perform measurements which provide the basic input data to model calculations used in nuclear data evaluation.
Planned Deliverables

Feasibility Studies of Waste Incineration Projects OECD, JEFF file and Nuclear Industry Needed for studies of nuclear waste transmutation.
-99Tc(n,T), (n,ƒ×) cross sections: Finalise the analysis of the completed measurements including the resonance parameters from the simultaneous fit. The data will be will be submitted to the NEA databank.
-237Np(n,T), (n,ƒ×) cross sections: Complete a feasibility study for measurements of average resonance capture data on a purified 237Np sample. If the study is successful the 237Np cross-sections will be measured and analysed, and the data will be sent to the NEA databank.
-129I(n,T), (n,ƒ×) cross sections: Following the proper characterisation of the sample the ongoing transmission and capture measurements will be finalised. A PhD thesis will result on the transmission measurements with a resonance analysis up to 4keV. A simultaneous resonance analysis will be started, to be completed in 2003.

Data for accelerator driven systems (ADS) OECD, JEFF file and Nuclear Industry These data are needed for the feasibility studies of waste incineration projects and accelerator driven systems.

-99Tc(n,p) and (n,Ą) cross sections: Publication of the experimental results.
Compilation of the data in EXFOR format and submission to the NEA databank from where they will be distributed to the relevant centres in the USA, JAPAN and IAEA. Evaluated curves will be compiled in ENDF format and submitted to the JEFF project (OECD) and NNDC (USA) and other interested centres.

-Activation cross sections leading to long-lived products: Results for the
94Mo
(n,p)94Nb and 204Pb(n,p)204Tl reactions will be published. Measurement data will be compiled in EXFOR format and submitted to the NEA databank from where they will be distributed to the relevant centres in the USA, JAPAN and IAEA.
Evaluated curves will be compiled in ENDF format and submitted to the JEFF project (OECD) and NNDC (USA) and other interested centres.

-Collaboration with CERN for development of TOF facility: Further support will be provided to the CERN nTOF development activity as requested from the members of the nTOF construction group.

Data for shielding and structural materials OECD & Nuclear Industry These measurements are needed for reactor criticality safety considerations and radiation shielding calculations.

-52Cr(n,n) and 58Ni(n,n) cross sections

Measurements will be completed with the (n,ng) technique at the 200 m flight path station of GELINA using two HPGe detectors at 90 and 125 degree. The results will be finalised in 2002 and sent to the NEA databank. A publication will be prepared.

Summary of deliverables made by: 31/12/2001

Feasibility Studies of Waste Incineration Projects OECD, JEFF file and Nuclear Industry Needed for studies of nuclear waste transmutation.

- ) cross sections: Simultaneous R-Matrix analysis of the capture and total cross-section measurements were completed up to 100keV for 600 resonance's. Analysis of the cross sections in terms of average parameters was also done up to 100keV.
(99Tc(n,T), (n) cross sections: Re-analysis of transmission data with improved resolution function(237Np(n,T), (n, -decay daughter 233Pa were investigated. For diagnostics of the efficiency of the separation, the sensitivity of a HPGe detector for the determination of the 233Pa to 237Np ratio is presently being investigated.
-activity. Methods for purifying 237Np from its (commenced and a feasibility study of a capture measurement on a purified 237Np sample was obtained by the separation of 233Pa which contributes most of the) cross sections: Low-energy transmission of 127I was measured on a very thin sample made of a LiI solution. Low-energy capture and transmission measurements of 129I were also carried out on other samples. Low energy transmission runs covering the range up to 1keV and using two different sample thicknesses for both 127I and 129I isotopes were completed. Analysis is in progress using the REFIT code to include the resolution function calculated by Coceva et al. Similar low energy runs have been performed for capture and analysis is in progress. The resonance analysis of 5 samples of 127I and 129I was completed up to 1 keV. The uncertainty on the content of these two isotopes was too large ((129I(n,T), (n,>5%). Preliminary results were compared to those of Macklin (ORELA) with discrepancies of the order of 10%.

Data for accelerator driven systems (ADS) OECD, JEFF file and Nuclear Industry These data are needed for the feasibility studies of waste incineration projects and accelerator driven systems.

-99mTc reaction were determined using the T(p,n) and T(d,n) reactions at the IRMM Van De Graaff and using the D(d,n) neutron source at FZ-Jülich. The important spectrum corrections were applied and the spectrum correction method for the D(d,n) source was scrutinised by inspecting the activation of four standard cross sections with different reaction thresholds.

() data were finalised and cross sections for the 99Tc(n,n'() cross sections: (n,p) and (n,(99Tc(n,p) and (n,Lo )47Sc reaction was completed and published.

(Activation cross sections leading to long-lived products: Summing corrections were analysed for these reactions. The 204Pb(n,p) activity determinations were finalised and the activity determination of 94Nb was completed. Final 204TI spectra were received from FZ Juelich and analysis of neutron fluencies and related corrections is ongoing. Activity determinations of 204Tl were carried out and work is ongoing on the cross sections for 204Pb(n,p)204Tl. For the study of the 14N(n,p)14C reaction, a postdoc contract was approved. The study of the 51V(n,n'Lo Collaboration with CERN for development of TOF facility: The collaboration agreement with n-TOF was finalised. The n-TOF facility became operational in April 2001, and neutron flux measurements immediately started in order to fulfil the requirements for the commissioning phase of the facility. The detectors used for these tests needed to be calibrated against 10B ionisation chambers. After this test phase, which lasted two weeks, various preliminary measurements were started at the 184 m flight path station. However the background was exceedingly high so the facility was shutdown on 11th June 2001. Calibration measurements of the CERN BC702 neutron detector were performed in July. The 60 m flight path was used. The detector was placed in the beam, which was well collimated (1.5 cm). The neutron flux was measured using one of the IRMM boron chambers. Two days at 800 Hz, a few hours at 100 Hz allowed going down to about 1eV neutron energy and the data are of good quality with sufficient statistics. The precise calibration of the BC702 will now allow to extract the flux at n-TOF.

Data for shielding and structural materials OECD & Nuclear Industry These measurements are needed for reactor criticality safety considerations and radiation shielding calculations.
Lo 52Cr(n,n') and 58Ni(n,n') cross sections OECD & Nuclear Industry The mechanical set-up for mounting detectors at the 200 m station was finalised by the workshop and installed at the flight path. The flux distribution was measured at the 100 m station with 2 available fission chambers for comparison and tests started with a Ge and BaF2. Two 52CrO2 samples were prepared and delivered them for use. The characterisation of the data acquisition system was carried out and detector set-ups were maximised. The first test runs were made with the 58Ni sample. Basic count rates were determined from which the minimum measurement time with an HPGe was established to be 2 months. Sample-out background was 2/3 of the sample-in yields in the energy range of interest. This led to the decision to significantly improve shielding against prompt background. Beam profile measurements showed homogeneity of the beam within 3% over the area of collimation with small halo effects. Flux normalisation with a fission chamber at 100 m was tested. Chamber window thickness were minimised, data analysis was set up and the first results on 58Ni can be expected in January 2002.

Output Indicators and Impact

Output indicators:
- Experimental (point-wise) data delivered in EXFOR format to the OECD-NEA databank;
- Resonance parameters (obtained by R-matrix fits to the experimental data) delivered to the OECD-NEA databank;
- Evaluated data submitted to JEFF and NNDC;
- Publications in refereed journals;
- Internal reports, JEFF reports, contributions to WPEC;
- PhD theses.
Impact:
- Use of IRMM data in evaluation projects;
- Citation of IRMM experimental work in publications;
- Requests for measurement campaigns at GELINA and the Van de Graaff accelerator;
- Collaborations with external research groups.
Summary of the project

This research project is focused on the transmutation of nuclear wastes obtained via neutron capture or fission reactions by exposing the concerned materials to high neutron fluxes. More specifically, one needs to burn up the so-called long-lived fission products (LLFP) (e.g. isotopes with half-lives longer than 105 years) and minor actinides (MA) such as Np, Am, and Cm isotopes. It has also been proposed that the actual burning should take place in Accelerator Driven Systems (ADS), e.g. hybrid systems consisting of a high-energy proton accelerator, a spallation source, and a sub critical assembly.
The task of the present project is to contribute to the production of a nuclear database for these studies. In particular, transmutation applications require the knowledge of capture and fission cross sections of the concerned isotopes as a function of the neutron energy. These data are largely unknown both because they attracted little interest in the past, and because the radioactive samples to be used in the measurements are very difficult to obtain. The ADS systems also require a lot of new data because some components used in these systems are different from those of conventional reactors and the neutron energies involved are much higher. It should be noted, however, that the neutron sources present at IRMM allow measurements only up to 20MeV.

Rationale

A satisfactory solution to the problem of nuclear waste disposal is a necessary pre-condition for the public acceptance of nuclear energy in the European Union. Also, in case of decline or even a stop (unlikely) of the electricity production by nuclear energy, the need still exists to safely dispose of or destroy the nuclear wastes accumulated so far. For these reasons the problem of wastes has recently attracted increased attention from politicians and the scientific community in general.
The IRMM's Neutron Physics Unit has a unique obligation under the Treaty of Rome for the measurement of neutron data. This requires highly specialised equipment. IRMM hosts a 150MeV electron linear accelerator (GELINA) and a 7 MV Van de Graaff accelerator as well as specifically dedicated laboratories. The GELINA time-of-flight facility has the best energy resolution worldwide. This makes the IRMM the only European laboratory (and one out of 2 or 3 in the world) that is capable of producing these data over an energy range of a few meV to about 20MeV. IRMM has a long-standing expertise in this field and has attained worldwide recognition for producing top-level neutron data measurements.

Coordinator

Institute for Reference Materials and Measurements
Address
Retieseweg
B-2440 Geel
Belgium