ML20244E032

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Consulting Rept on Nine Mile Point Reactor Vessel
ML20244E032
Person / Time
Site: Nine Mile Point  Constellation icon.png
Issue date: 03/07/1969
From: Ed Miller, Patriarca P
OAK RIDGE NATIONAL LABORATORY
To:
Shared Package
ML17055E652 List:
References
FOIA-89-101, FOIA-89-114 NUDOCS 8904240263
Download: ML20244E032 (3)
v • d • e


Text

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h OAK RIDGE NATIONAL LABORATORY OPERATED BY UNION CARBlDE CORPORATION j NUCLEAR DIVISION tt0eMembers M POST OFFICE BOX X D OAK RfDGE, TENNESSEE 37830 3 O '

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SUBJECT:

Consulting Report on Nine Mile Point Reactor Vessel This report is limited principally to the two subjects on wMch comments were requested: (1) the acceptability of furnace-sensitized type 304 stainless steel which is present in certain locations in the reactor; and (2) the acceptability- 1 from service and specification standpoints-of the combination J groove-and- ,

fillet stainless steel field welds joining control rod drive housings to stub tubes- ,

some of these welds are repaired by weld overlay or " capping" and others have been determined not to require such weld repair.  !

The history of the performance of furnace-sensitized stainless steel in various parts of reactor vessels and core components bears out the contention that such stainless steel can operate in many reactor systems without undergoing inter-granular " stress-assisted corrosion cracking", provided specified chemical and other environmental conditions are maintained continuously throughout the i operating life of the reactor and that no accidental or operating errors occut j I

which will permit the unintended introduction of a potential corrodent or other undesired environmental factors. Corrosion technology and practice generally prefer to use construction materials with superior corrosion resistance per- '#"

mitting somewhat greater flexibility in environmental conditions, rather than e to use a more corrosion-susceptible material and attempting to maintain un-deviating, error-free control of the environment for the operating life of the v h -

vessel. llowever, this material selection practice, while preferred, is not mandatory, since other factors, technical and economic, frequently influence material selection.

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Mr. R. C. DeYoung March 7,1969

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It appears intended in the case of the NMP reactor to rely on rigid operational l'

control of the environment to prevent deterioration of the sensitized stainless steel on the assumption that this can meet the desired design objectives. As-suming this to be valid, it still appears prudent and even mandatory to require

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verification at intervals during the operating life, that the suspect critical parts are functioning as intended and.are not developing any potentially harmful j

c racking. As a minimum, periodic inspection procedures or representative i corrosion surveillance specimen programs should be established for furnace-

sensitized stainless steel parts such as the shroud support ring and the safe-

} ends to provide frequency and thoroughness of inspection as demanding as the equivalent requirements of the N-45 In-Service Inspection doctunent. It appears probable that corrosion attack, if it should develop on such parts as the shroud support ring, should be largely random and superficial. such that an appropriate in-service inspection or corrosion surveillance program should

.; - . be able to anticipate developing problems.

The second topic considered concerns the adequacy of the stainless steel field

{ welds which join the stub tubes to the control rod drive housings. According

.( ( to information available in documents and discussions at the meeting in I

liethesda on December 12th, 75 of the field welds (as of that date) had been post-hydro PT inspected and all of the field welds had been examined by a UT procedure specially developed for this joint configuration. The UT examination

{ showed a considerable number of narrow, circumferentially-oriented, but l relatively short indications of lack of fusion at the interface between the weld deposit and the CRD housing in most of these field welds. At the December 12th I meeting. it was contended that these field welds, including the approximately 60 j that required addition of weld " caps" as well as those which were not repaired j by capping, met " Code", based on tLe fact that the identified lack of fusion was detected by UT which was not a requirement of the applicable t' ode or specifi-cations. llowever, the Code does require that such welds be made by a pro-cedure which has been " qualified" in accordance with Section IX of the Code, and this includes a bend test of sufficient severity it would undoubtedly reveal

[i lack of fusion comparable to that in the production welds. It is difficult to accept the contention that a procedure which produces lack of fusion in more than half of

  • he production welds is identical with the procedure whose qualifi-cation test weld passed the severe bend test requirement of procedure qualifi-cation.

1 in those cases (about 60) where the summation of the estimated widths of thesc

.t reas of incomplete penetration reduced the total length of remaining sound weld met.d .utachment lo less than 3/4 inch. this was assumed to be insufficient

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.,n. Mr.11. C. DeYoung March 7,1969 l

and such welds were repaired by building up a weld overlay or " cap" of type 308L weld metal sufficient to meet the 3/4 inch criterion. The 3/4 inch criterion appears adequate from the standpoint of any shear stress likely to be applied to the joint, even though it is doubtful that the contention of " Code-compliance" is valid.

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l Another matter for comment pertains to the procedure used for PT examination -l

( of the welds. This involved the use of quantities of solvent in excess of the

~ amounts prescribed by the Code,. to establish the relevance or non-relevance i of certain penetrant indications; it is doubtful that this is a valid method for l' establishing rel vance, llowever, it is understood that the remaining fiehl wchls have subsequently been PT examinated by a procedure acceptable to

} Compliance, and if appropriate repairs to meet the 3/4 inch criterion are followed, it is considered that the fichi welds are adequate for the intended purpose, even though they do not necessarily meet the detailed requirements

of the Code. It should be understood that acceptance on this basis represents an approved deviation from the Code, not Code-compliance.

Yours very t ruly.

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