Request ID | 99 | Type of the request | High Priority request | ||
---|---|---|---|---|---|
Target | Reaction and process | Incident Energy | Secondary energy or angle | Target uncertainty | Covariance |
94-PU-239 | (n,f) nubar | Thermal-5 eV | 1 | Y | |
Field | Subfield | Created date | Accepted date | Ongoing action | Archived Date |
Fission | 23-MAR-18 | 12-APR-18 | Y |
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Requester: Dr Roberto CAPOTE NOY at IAEA, AUT
Email: roberto.capotenoy@iaea.org
Project (context):
Impact: Cf. Ref. [1,2]. A similar, but stronger than in U-235, resonance nubar effect is expected for Pu-239 due to the 1/2 GS spin.
Accuracy: Accuracy below 1% is required on the evaluated data. New measurements must strive to achieve a relative uncertainty below about 1% on the ratio to Cf-252(sf) nubar, as done in the best past experiments [3]. Statistical precision below about 1% at the resonances is required in order to unambiguously identify resonant fluctuations.
Justification document: A new evaluation of the PFNS [4] in the thermal energy range has determined a lower value of the average neutron energy than that reported in the existing evaluated nuclear data libraries. This value is in agreement with Rising et al and Neudecker independent evaluations. However, a number of thermal-solution benchmarks has shown that the combined use of the new Thermal Neutron Constants and a softer prompt fission neutron spectrum at thermal energy yields k-eff values that are larger than measurements by a margin that increases as the above-thermal-leakage fraction (ATLF) increases (see Ref. [5]). Therefore a reduced criticality is needed for high-leakages solutions. Such reduced criticality may arises due to the (n,gf) process in Pu-239 resonance nubar. Unfortunately, only measurements from the 70s and 80s are available, a critical region below 5 eV needs to be remeasured with higher incident-energy resolution and higher accuracy and precision to improve existing evaluated data files. References
Comment from requester: Additionally to changes in nubar changes in resonance parameters may be required. We cannot split those effects on studied criticality benchmarks.
Review comment:
Entry Status:
Main recent references: Experiments Theory/Evaluation
Work in progress (as of SG-C review of May 2018)
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