ML19248D417
| ML19248D417 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 07/20/1979 |
| From: | Schroeder F Office of Nuclear Reactor Regulation |
| To: | Nellis R AFFILIATION NOT ASSIGNED |
| References | |
| NUDOCS 7908150756 | |
| Download: ML19248D417 (2) | |
Text
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. Richard A. fiellis Scottsdale Ch51stian Home 3339 K."CFiTc CenteF Plaza '
i Scottsdale, Arf::ona 85251 Cear "r. Nellis:
Thank you for your 1cttcrs of ;iay 16 cnd June 18,chich s;cre referred to the !!uclear Regulatcry Ccmissien by the Library of Congress. ;le have reviewad your inquiry regarding the charact:rf stics of fuel assemblics in the Three Mile Island nuclear pcwer plant and the n,
' car character-istics of certain materials. !!e have provided our ans-
- to your questions in the enclosure.
"a are pleased to have been of service in this catter. Please let ma how if additional infc:- ation is neadcd.
Sir.cerely, Crisinal Signed by
- 7. Schreeder Frank Schrc' der, Ceputy Director Divisicn of Systas.s SFety
Enclosure:
As stated cc:
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Enclosure _
Responses to Richard A. Nellis Letters to Library of Congress Dated May 16, 1979 and June 18, 1979 The uranium dioxide fuel rods in IMI-2 are contained in fuel assemblies, which are groups of fuel rods arranged in square arrays with 203 rods per assembly.
The metallic cladding of each fuel rod is Zircaloy-4, and each rod is approximately 153 inches in length with an outside diameter of 0.430 inches.
The fuel column is lad. inches in length and is made up of sintered uranium dioxide pellets that are 0.700 inches long and 0.370 inches in diameter.
Each fuel pellet weighs approxi-mately 12.5 grams or 0.44 ounces.
In TMI-2, the core contains 177 fuel asserablies, with a total uranium dioxide weight of 204,907 pnunds.
Regarding Pe nuclear poison characteristics of Doron and beryllium, natural boron has an averaje thermal neutron absorption cross-section of 155 birns while for beryllium, the absorption is only 0.01 barns.
(The absorption cross-section, stz.ted in barns, is a measure of the effective-ness of a material as a nuclear " poison"; the higher the cross-section, the more effective is the material in controlling nuclear reactors.)
Soron-10 is the isotope responsible for the high cross-section in natural boron (-20: B-10) and by itself, has an abscrption cross-section of 3315 barns. Soron can be enriched in the 3-10 isotope in much the same way as uranium is enriched in U-235, thereby, increasing its crcss-section for special application.
Boron compounds, either as a solid form in rods or in soluticn in the primary coolant, are widely used for reactor control because of their very high neutron absorption cross-section.
Beryllium has been used in some experimental reactors as a moderator or reflector. One of the reascos for using beryllium as a reflector is its very lcw absorption.
Regarding ccmuents on nucleus stability, the absorption crcss-section of an isotope in the icw neutron energy range is largely determined by the reacticn resonance carameters and energy level location in the e cited state of the compound nucleus, i.e.,
the nucleus consisting of the absc cbing isotope plus the neutren abscrbed.
The compcund nucleus fonned frrm 3-10 plus the neutron is B-11 in which there is a reaction resenance for the change to Li-7 plus F2-4 This rescnance has a large reaction rate near thantal neutron energies, thus a large absorpticn cross-section.
For Se-10, formed from Sc-9 plus a neutron, this is not the case and thus, the cross-section for absorption is small.
a. t; C O