Effects of S{sub N} method numerics on pressure vessel neutron fluence calculations

Journal Article · Thu Feb 01 04:00:00 EST 1996 · Nuclear Science and Engineering

DOI:https://doi.org/10.13182/NSE96-3· OSTI ID:218501

Petrovic, B G; Haghighat, A ^[1]

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1. Pennsylvania State Univ., University Park, PA (United States). Nuclear Engineering Dept.

An accurate prediction of the reactor pressure vessel (PV) fast neutron fluence is necessary to ensure PV integrity over the design lifetime. The discrete ordinates method (S{sub N} method) is the method of choice to treat such problems, and the DORT S{sub N} code is widely used as a standard tool for PV fluence calculations. The S{sub N} numerics and the corresponding DORT numerical options and features offer alternative choices that increase flexibility but also impact results. The effects of S{sub N} numerics based on PV fluence calculations for two pressurized water reactors are examined. The differencing schemes [linear, zero-weighted (ZW), and {Theta}-weighted (TW)] and their interactions with spatial and angular discretization are also examined. The linear and TW ({Theta} = 0.9) schemes introduce unphysical flux oscillations that for certain groups and positions may exceed 10%. The ZW scheme produces smooth results; however, its results differ from the other two schemes. A good compromise for PV fluence calculations is a TW scheme with a small {Theta} value (i.e., {Theta} = 0.3), which reduces the uncertainty to {approximately}3%. Angular discretization and spatial mesh size employed in typical calculations introduce another {approximately}3 and {approximately}2% uncertainty, respectively. The analysis further shows that the fixup is not necessary for the negative scattering source. The pointwise convergence criterion is also not a critical issue in the fast energy range because of a relatively fast convergence rate. Similarly, acceleration parameters impact mainly the execution time and only marginally the results. The root-mean-square combined uncertainty for standard PV fluence calculations due to the options analyzed is {approximately}5%.

• Sponsoring Organization: USDOE
• OSTI ID: 218501
• Journal Information: Nuclear Science and Engineering, Journal Name: Nuclear Science and Engineering Journal Issue: 2 Vol. 122; ISSN NSENAO; ISSN 0029-5639
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
DATA COVARIANCES
DISCRETE ORDINATE METHOD
NEUTRON FLUENCE
NEUTRON FLUX
NEUTRON TRANSPORT THEORY
PRESSURE VESSELS
PWR TYPE REACTORS
RELIABILITY