Effective Pu-238 and Np-237 neutron absorption cross sections in N and K Reactors
The efficiency of producing Pu-238 from Np-238 depends on the relative absorption cross sections of the target, Np-237, and the product, Pu-238. A lowering of the Pu-238/Np-237 cross section ratio reduces the destruction of Pu-238 formed during reactor operation. The absorption cross sections of both these isotopes are strongly neutron energy dependent; the absorption cross section of Pu-238 decreases more rapidly with thermal neutron temperature increases than the conventional v{sup {minus}1} dependency and exhibits negligible resonance absorption. On the other hand, Np-237 is a very nearly v{sup {minus}1} thermal neutron absorber and has dominant low level resonance cross sections. Thus, for higher thermal neutron temperatures and a more epithermal neutron spectrum, depletion of the Pu-238 product is reduced relative to Np-237 burnout. The relative absorption cross sections of these two isotopes were calculated for the K and N Reactors as a function of graphite temperature for two linear densitie of neptunium in the target elements for each.reactor type. The method of calculation was as follows: The HAMMER integral transport code was used to obtain region and cell averaged four-group cross sections for both the fuel and target cells. These cross sections were then used in the HFN diffusion theory code to obtain reactor-effective cross sections.
- Research Organization:
- Douglas United Nuclear, Inc., Richland, WA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 93766
- Report Number(s):
- DUN--4349; ON: DE95012600
- Country of Publication:
- United States
- Language:
- English
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