ML19246B493
| ML19246B493 | |
| Person / Time | |
|---|---|
| Issue date: | 06/18/1979 |
| From: | Carbon M Advisory Committee on Reactor Safeguards |
| To: | Gilinsky V NRC COMMISSION (OCM) |
| References | |
| NUDOCS 7907160068 | |
| Download: ML19246B493 (2) | |
Text
s o
UNITED STATES
! }]W* m
- y. gr NUCLEAR REGULATORY COMMISSION T
e ADVISORY COMMITTEE ON REACTCR SAFEGUARDS
-'o
[
WASHINGTON, D. C. 20555
-r w
June 18, 1979 Honorable Victor Gilinsky Comissioner U. S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
SUMMARY
COMPA" SON OF STAINLESS STEEL AND 2IRCALOY FUEL ROD CIADDDJG
Dear Dr. Gilinsky:
This is in response to your memorandum of May 8,1979 concerning the relative cerits of stainless steel and ircaloy fuel rod cladding.
S e following dis-cusses cladding perforrance of these two materials under both normal operating and accident conditions.
Early cladding developnent programs (1950's to mid-1960's) studied both stain-less steel and zircaloy cladding extensively.
Both :naterials have been used in power reactors.
A consensus was eventually reached that zircaloy is the more desirable of the two materials, and by the mid-1960's, zircaloy was predominant.
Safety aspects of both types of clad raterial were reviewed by the ACRS.
- Today, only two U.S. co=nercial nuclear power plants (Conn. Yankee - PhR, and Lacrosse -
BhR) use stainless steel clae fuel rods.
There are prirarily three factors which enter the grison of the two materials for normal operation:
1.
Stainless steel cladding is susceptible to stress corrosion cracking in a BhR environme t during norral operation whereas zircaloy is not. Con-secuently, stainless steel clad rods experienced much hieher defect levels in SWRs.
For PWRs, stress corrosion cracking cf this nature has not been a problem.
2.
There is a large neutron economy advantage in the use of zircaloy as op-posed to stainless steel because zircaloy has a: much lower neutron capture crcss-section. m is translates into lower uranium ore and enrichment requirements.
3.
Of the critium generated in the fuel by fission, much more is chemically trapped by zircaloy than by stainless steel.
'mus, use of circaloy sig-nificantly reduces environmental releases of tritium and problems associated with this nuclide at nuclear power plants.
364 25F 7907160067
Honorable Victor Gilinsky June 18, 1979 In regard to accident conditions, as indicated in your memorandum, stainless steel has an advantage over zircaloy in rcleasing only approximately 16% as much heat on being oxidized by steam.
However, during this reaction the two alloys will generate comparable amounts of hydrogen.
Other properties that are important in accident sequences are rate of oxidation and melting tenper-ature. The rate of oxidatian is reasonably low fgr both materials up to about 1650 F.
For temperatures between 1650 F and 2000 F, stainless steel has a some-what lower rate.
In the temperature range of most importance for accident con-ditions, greater than 2000 F, zircaloy has a slower rate of oxidation although this aspect is complicated bg the higher heat of reaction. Also, zircaloy has a higher melting point (3360 F vs. 2550 F) than stainless steel.
For an act:ident such as occurred at TMI-2, there is no reason to believe stain-less steel wc 1d have had any performance advantage over zircaloy.
Sincerely,
/
Pax W. Caroon Qairman ec:
Q airman Hendrie Comissioner Kennedy Comissionel Bradford Commissioner Ahearne Office of the Secretary ACRS Members 364 56
.