ML20128B603
| ML20128B603 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 05/15/1985 |
| From: | Vassallo D Office of Nuclear Reactor Regulation |
| To: | Parker M ILLINOIS, STATE OF |
| References | |
| NUDOCS 8505240597 | |
| Download: ML20128B603 (2) | |
Text
i, May 15, 1985 DISTRIBUTION Mr. Michael C.' Parker, Chief
! Docket Files! NRC PDR Division of Nuclear Engineering Local PDR ORB #2 Rdg Department of Nuclear Safety HThompson OELD 1035 Outer Park Drive SNorris RBevan Springfield, Illinois 62704 ELJordan BGrimes JPartlow ACRS (10)
Dear Mr. Parker:
Gray File This is in regard to your letter of March 13, 1985 to Mr. Harold Denton concerning the use of hafnium in control rod blades in Quad Cities, Units 1 and 2.
You are correct with regard to the large disparity in the cross-section for
. elemental hafnium and boron. However, this disparity is accounted for in
.the computation of the relative worths of the two control rod designs from which the conclusion was reached that the two worths were essentially equal. The following discussion provides qualitative arguments to explain this equality.
Both the boron carbide and hafnium rodlets are " black" to incoming neutrons. That is, a thermal neutron incident upon either rodlet is absorbed. The total number of neutrons absorbed by each rodlet is dependent chiefly upon the size of the rodlet which is the same for both rods.
Although hafnium is used.in control rods in its full density elemental form, the boron is used as a compvind, boron carbide, which is compacted to approximately 70 percent of its theoretical density. Thus the effective density of the boron is only about 60 percent of its elemental value.
In addition to thermal absorption, resonance energy neutron absorption plays a significant role in determining the total control rod worth.
In this regard hafnium has a somewhat higher resonance absorption than boron.
Hafnium has a long history of use as a control rod material in the Naval Reactors program and has been approved by the NRC for use in numerous
-comercial reactors.
I hope the foregoing discussion adequately responds to your concern.
Sincerely, Original signed by/
l Domenic B. Vassallo, Chief 0 rating Reactors Branch #2 ivision of Licensing DL:0RBf2 DL:0RB#Rg.))
.0RB#2 DVass llo l
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ti Mr.' Dennis L. Farrar Commonwealth Edison Company Ouad Cities' Nuclear Power Station, Units 1 and 2 cc:
'Mr. B. C. O'Brien James G. Keppler President Regional Administrator Iowa-Illinois Gas and Region III Office Electric Company U. S. Nuclear Regulatory Commission 206 East Second Avenue 799 Roosevelt Road Davenport, Iowa 52801 Glen Ellyn, Illinois 60137 Robert G. Fitzgibbons, Jr.
Susan N. Sekuler Isham,' Lincoln & Beale Assistant Attorney General Three First National Plaza Environmental Control Division Suite 5200 188 W. Randolph Street Chicago, Illinois 60602 Suite 2315 Chicago, Illinois 60601
'Mr. Nick Kalivianakis Plant Superintendent The Honorable Tom Corcoran Quad Cities Nuclear Power Station United States House of 22710 - 206th Avenue - North Representatives Cordova, Illinois 61242 Washington, D. C.
20515 Resident Inspector Mr. Gary N. Wright U. S. Nuclear Regulatory Commission Nuclear Facility Safety 22712 206th Avenue North Illircis Department of Cordova, Illinois 61242 Nuclear Safety 1035 Outer Park Drive, 5th Floor Chairman Springfield, Illinois 62704 Rock Island County Board of Supervisors Rock Island County Court House Rock Island, Illinois 61201 l.
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