|SIG - Cross section
|Threshold - 20 MeV
|Latest review date
Dr Edward T. CHENG at GA, USAProject (context)
Structural material for fusion power reactorsImpact
SiC is a potential very low activation structural material for a fusion power reactor. Al-27 produced from neutron irradiation of Si generates Al-26 via the Al-27(n,2n) reaction. Al-26 is a long-lived radionuclide with a half life of 720,000 years emitting high energy gammas. The concentration of Al-26 in SiC determines whether the decommissioned fusion blanket qualifies for recycling.Accuracy
The request for 20% accuracy is based on what seemed feasible for the nuclear data community to achieve and probably would be sufficient for applications as well. It is not based on any sensitivity calculations.Justification document
The estimates consider waste generated by four full power years at 5 MW/m2 neutron wall load and are based on a particular scenario for waste handling using evaluations for Si-28(n,x)Al-27 provided by ENDF/B-VI and ADL-3 which are adopted in FENDL/A-2.0. Estimated concentration limits for Si are a factor 10 higher than earlier estimates, so that SiC would qualify as a truly low-activation material. The request asks for experimental data to validate these estimates and a subsequent re-evaluation. No direct experimental data exist.
Reference 1: E.T.Cheng, Jour. Nucl. Mat.,258-263(1998)1767
Reference 2: E.T. Cheng, Proc. of the Int. Conf. on Nuclear Data for Science and Technology, eds. G. Reffo, A. Ventura and C. Grandi, SIF, Bologna, 1158 (1997)
Two methods to measure this reaction cross section have been suggested by Herbert Vonach and others. These include (1) Measurement of Na24 activity with high-purity Si samples and intense neutron sources, and (2) Measurement of total production in Si and then subtracting the well known (n,p) cross sections to obtain the (n,n'p) values. An attempt to measure this cross section data at 14 MeV a few years ago failed due to the contamination of the Si samples with the impurity Al. The request for 20% accuracy is based on what seemed feasible for the nuclear data community to achieve and probably would be sufficient for applications as well. It is not based on any sensitivity calculations.Review comment
The accuracy is not known. Estimates from present and earlier evaluations differ by a factor of ten.
The request appears to imply application to post-ITER fusion reactors in view of the high neutron dose required to generate relevant quantities of Al-26. Reference  refers primarily to the Si-28(n,np) reaction, whereas the production of Al-27 from Si-28 is important. This therefore also implies the (n,d) reaction since the respective thresholds are 12 and 9.7 MeV. Quantitative information is supplied that seems to suggest directly that 20% accuracy is of interest to the application. Stoichiometric SiC has 70 wt% of Si, whereas the scenario assumed for the estimates of Ref.  results in an upper limit of 85 wt% Si for recycling. This request qualifies as a General request primarily since the project end time is unspecified.Entry status
Completed (as of SG-C review of May 2018) - Development in state-of-the-art nuclear reaction codes such as TALYS and EMPIRE allowed to fulfil this request. The uncertainties in the main evaluated files (ENDF/B-VIII.0, JEFF-3.3, TENDL-2015) are all consistent above the threshold reaction and vary within a 15-25% band between 13 MeV and 20 MeV.Main recent references
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