• M. Jandel et al., New Precision Measurements of the 235U(n,g) Cross Section, PRL 109 (2012) 202506, EXFOR 14149
• A. Wallner et al., Novel Method to Study Neutron Capture of 235U and 238U Simultaneously at keV Energies, Phys. Rev. Lett. 112 (2014) 192501, EXFOR 23170
• J. Balibrea et al., Measurement of the neutron capture cross section of the fissile isotope 235U with the CERN n_TOF Total Absorption Calorimeter and a fission tagging based on Micromegas detectors, NDS 119 (2014) 10
• Y. Danon, et al., Simultaneous measurement of 235U fission and capture cross sections from 0.01 eV to 3 keV using a gamma multiplicity detector, Nucl. Sci. and Eng. 187 (2017) 191
• J. Balibrea et al., Measurement of the neutron capture cross section of the fissile isotope 235U with the CERN n TOF total absorption calorimeter and a fission tagging based on micromegas detectors, EPJ Conferences 146 (2017) 11021

Theory/Evaluation

• R. Capote et al., IAEA CIELO Evaluation of Neutron-induced Reactions on 235U and 238U Targets, NDS 148 (2018) 254

Validation

• O. Iwamoto et al., Uranium-235 Capture Cross-section in the keV to MeV Energy Region, International evaluation cooperation, Report NEA/WPEC-29, OECD NEA (2011)
• M. Salvatores, et al., Methods and Issues for the Combined Use of Integral Experiments and Covariance Data: Results of a NEA International Collaborative Study, Nuclear Data Sheets 118 (2014) 38
• G. Palmiotti, et al., Combined Use of Integral Experiments and Covariance Data, Nuclear Data Sheets 118 (2014) 596

Additional file attached:SG26-report.html
Additional file attached:

Request ID	36		Type of the request	High Priority request
Target	Reaction and process	Incident Energy	Secondary energy or angle	Target uncertainty	Covariance
92-U-238	(n,g) SIG	20 eV-25 keV		See details	Y
Field	Subfield	Date Request created	Date Request accepted	Ongoing action
Fission	Fast and Thermal Reactors	15-SEP-08	15-SEP-08

Requester: Prof. Massimo SALVATORES at CADARACHE, FR
Email:

Project (context): CEA Cadarache

Impact:
Design phases of selected reactor and fuel cycle concepts require improved data and methods in order to reduce margins for both economical and safety reasons. A first indicative nuclear data target accuracy assessment was made within WPEC Subgroup 26 (SG-26). The assessment indicated a list of nuclear data priorities for each of the systems considered (ABTR, SFR, EPR, GFR, LFR, ADMAB, VHTR, EPR). These nuclear data priorities should all be addressed to meet target accuracy requirements for the integral parameters characterizing those systems (see the accompanying requests originating from SG-26).

Accuracy:
Target accuracies are specified per system and per energy group when they are not met by the BOLNA estimate of the current (initial) uncertainties. The weighting factor λ is explained in detail in the accompanying document. Changes from the reference value of λ=1 show the the possible allowance for other target uncertainties. Two cases (A and B) are distinguished for λ≠1 (see Table 24 of the report).

Energy Range	Initial versus target uncertainties (%)
	Initial	ABTR			SFR			EFR		GFR		LFR		VHTR		EPR
		λ=1	λ≠1,a	λ≠1,b	λ=1	λ≠1,a	λ≠1,b	λ=1	λ≠1,a	λ=1	λ≠1,a	λ=1	λ≠1,a	λ=1	λ≠1,a	λ=1	λ≠1,a
9.12 - 24.8 keV	9	3	2	2	4	3	3	3	2	2	1	2	2			5	4
2.03 - 9.12 keV	3									1	1
22.6 - 454 eV	2													1	1	1	1

Justification document:
1. OECD/NEA WPEC Subgroup 26 Final Report: "Uncertainty and Target Accuracy Assessment for Innovative Systems Using Recent Covariance Data Evaluations" (link to WPEC Subgroup 26 Report in PDF format, 6 Mb).
2. OECD/NEA WPEC Subgroup 7 (SG-7) Final Report: "Nuclear data standards" (link to WPEC Subgroup 7 Report in PDF format, 450kb).

Comment from requester:
Given the present state of knowledge the above target accuracies are very tight. However, any attempt that significantly contributes to reducing the present accuracy for this quantity is strongly encouraged. Any such attempt will significantly enhance the accuracy with which reactor integral parameters may be estimated and will therefore impact economic and safety margins.

Review comment:
In this particular case high accuracy is required throughout the energy range. Only the groups shown above have initial uncertainties larger than the target uncertainties. The low initial uncertainty is a result of the standards evaluation (see SG-7 report above). Concerns have been raised that despite the excellent efforts of this subgroup an independent check is in order to verify the present view on required corrections to experimental work for the unresolved resonance range.

Entry Status:
Completed (as of SG-C review of May 2018) - New time-of-flight measurements have been performed worldwide, e.g., at LANSCE [Ullmann:2014], JRC-Geel [Kim:2016] and n_TOF [Mingrone:2017;Wright:2017]. These experimental data have been used in the CIELO evaluation [Sirakov:2017,Capote:2018] and for the evaluation of the standards [Carlson:2018]. The CIELO evaluated data have been adopted in ENDF/B-VIII.0 and JEFF-3.3; the evaluated uncertainties match the requested accuracy.

Main references:
Please report any missing information to hprlinfo@oecd-nea.org

Experiments