ML20210E787

Trip Rept of 820326 Visit to Neutron Products,Inc of Dickerson MD to Investigate Problem of Cracking in Welds in Containers of Sealed Irradiator (Cobalt) Sources & to Develop Info for AR Dept of Health

ML20210E787
Person / Time
Issue date:	04/13/1982
From:	Taboada A Office of Nuclear Reactor Regulation
To:	Serpan C Office of Nuclear Reactor Regulation
Shared Package
ML20210E645	List: ML20210E642 ML20210E648 ML20210E655 ML20210E688 ML20210E763 ML20210E787
References
SSD, NUDOCS 9907290030
Download: ML20210E787 (13)

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MEl-10RANDUM FOR: C. Z. Serpan, Jr., Chief liaterials Engineering Branch Division of Engineering Technology FROM: A. Taboada Materials Engineering Branch Division of Engineering Technology

SUBJECT:

TRIP REPORT NEUTRON PRODUCTS, INC MARCH 26, 1982 .

l At the request of State Programs, I visited Neutron Products, Inc. of Dickerson, Maryland, with Mr. Richard Brisson of the State of Maryland (DHMH)onMarch 26, 1982. The purpose of the visit was to investigate a problem of cracking in welds in containers of sealed irradiator (cobalt) sources and to develop information for the Radiological Health Section of the Arkansas Department of Health concerning the integrity of these containers.

The sealed sources are being fabricated at Neutron Products for Process Technology, Inc. of West Memphis, Arkansas, and have been licensed by the State of Arkansas (license number ARK-628-BP-6-83). Drawings numbered 200234 for the sealed source are enclosed.

Problem Microcracks were found at the root of TIG fusion welds attaching end ,

plugs to container tubes during metallographic examinations of quality l control samples for production welding of the sealed sources. These were single cracks which initiated on the inside surface between tube and end ,

plug, progressed in the axial direction with some minor variations at l the tip of the crack and appeared to be associated with the region where the weld was overlapped. The in-house neutron product specifications to ,

which these containers were fabricated permit no visible cracks on a '

cross section of the weld examined at 8X magnification. The procedure calls for'every 10th weldment to be examined. End plugs and tubing were made of Type 321 stainless steel.

fleutron Products hired Mr. Julius Heuschkel, Welding Engineering Consultant, to review the metallurgical problem and O'Donnell and Associates to analyze the potential for cracks propagation.

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,C. Z. Serpan, Jr. O 2 O APR 131982 General Observations The microcracks are of the notch extension hot tear type, a condition commonly observed in Type 321 stainless steel but also found less frequently in other grades of austenitic stainless steel weldments. Automatic inert gas shielded arc welding process with no filler metal was used for making these weldments. The welds observed were of a consistant, good quality with the exception of the root cracks. The joint designs for tb inner and outer containers, shown in the enclosed drawing, are typical joints used for tube plugging and considered by O'Donnell and Associates to be acceptable designs to minimize stresses resulting from temperature gradients and structural discontinuities. Inherent in these designs are mechanical' notches between the tube and end plug. The root cracks observed are extensions of these mechanical notches and differ only in the sharpness of the notch. There appears to be good operating experience with these designs.

O'Donnell and Associates conducted a crack propagation analysis to evaluate the potential for failure of the containers as a result of the i microcracks at the root of the weldments. They concluded that the only possible mode of failure that might be influenced by the presence of the root cracks would be crack propagation due to thermal fatigue caused by I transient thermal stresses generated when the containers are moved in or i out of a water filled storage tank. Heating results from gamma heating.

O'Donnell and Associates performed a finite element analysis of the capsule end plug-tube connection, including transient thermal analysis and structural discontinuity stress analysis. Conservative assumptions were used in the treatment of heat flow and direction of loading. They determined that the thennal stresses were approximately 9,000 psi and that more than 5,000,000 cycles would be required to propagate a crack from a depth of 25% of the tube wall to a location of 50% of the tube  ;

wall. This equates to a life of over 2,000 years when the expected i service for these containers is 39,000 cycles in 15 years. Further, the analysis showed that for this material the cracks will not reach a self propagating or critical size indicating no potential for a brittle break. As a result of this analysis, O'Donnell and Associates concluded (1) that the containers of the sealed sources will maintain their integrity for all expected service conditions; (2) that extension of cracks through the entire wall of the container is considered unlikely; and (3) that even if the container was cycled to failure, the container would leak rather than break.

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At'M 131982

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3 Conclusion The root cracking observed was due to the inherent susceptability of

, Type 321 stainless steel material to such cracking rather than improper l welding procedures or uncontrolled welding variables. Except for the

root cracking, the welds appear to be of acceptable quality. The crack

propagation analyses conducted by O'Donnell and Associates applies conventional procedures typically used for nuclear reactor application.

Assumptions used are conservative. In view of the low stresses and extremely slow crack growth rate resulting, it would appear that a very low probability exists that the sealed soruces would fail and leak as a result of the microseracks observed in the root of the tube-to-end plug wel ds. Also, the double containment design and lower thermal stress expected on the inner container further lower the likelihood that the sealed sources would leak, i

A. Taboada Materials Engineering Branch Division of Engineering Technology

Enclosure:

As stated cc: J. O. Lubenau, SP l

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RADIOACTIVE MATERIAL LICENSE Supplementary Sheet License Number ARK-628-BP-6-83 AMENDMENT NO. 4 Process Technology, Inc.

North Airport Road Post Office Box 2265 West Memphis, Arkansas 72301 In accordance with amendment request dated April 2,1982, Arkansas Radioactive Material Lictnse ARK-628-BP-6-83 is amended as follows:

Item 20 changed to read:

"Except as specifically provided otherwise by this license, the licensee shall possess and use radioactive material described in Items 6, 8, and 9 of this license in accor-dancetwith statements, representations, and procedures contained in:

A. Application dated November 11, 1980, signed by Martin A. Welt, Ph.D.

B. Drawings submitted October 20, 1980 C.

Letter with enclosures dated November 19, 1980, signed by Robert Buckley D. Letter with enclosures dated April 23, 1981, signed by Robert Buckley E. Letter with enclosures dated May 18, 1981, signed by Charles M. Thomas F. Letter dated June 1,1981 signed by Robert Buckley G. Letter dated June 11, 1981, signed by Robert Buckley H. Letter dated July 2,1981, signed by Martin A. Welt, Ph.D.

I. Letter dated April 2, 1982, signed by Martin A. Welt, Ph.D.

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1. kHlKEXAWWNUX' Bernar;l Bevill Chief of Licensing and Compliance

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Radiol::gical Health RADIOACTIVE MATERIAL LICENSE ARK-628-BP-6-83 License Number Supplementary Sheet AMENDMENT NO. 3 1

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Process Technology, Inc.

N;rth Airport Road P:st office Box 2265 West Memphis, Arkansas 72301 In accordance with amendment request dated September 3, 1981, Arkansas Rad Material Lienese ARK-628-BP-6-83 is amended as follows:

Item 8 is changed to reads t

Sealed Sources A. AECL Model C-188

.B. Neutron Products Inc. Model 12-5-3 C. Neutron Products, Inc. Model 12-C-3 D. Neutron Products, Inc. Model 10-S-3 E. Neutron Products, Inc. Model 10-C-3 F. Neutron Products Inc. Model 12-CC-5 G. Neutron Products, Inc. Model 24-CC-5 H.' General Electric Model CEP-916

1. Neutron Products, Inc. Drawing Number A200234-D Item 9 is chansed to read: ,

2,250,000 curies total.

No single source to exceed 22,000 euries.

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108 LAKE DENM ARK ROAD, ROCKAWA N. J. 07866 (201) 627 2900 P. O. BOX 185 yt-8400 Ai.;ria. 2,4bd Mr. Bernard Bevill, Chief Licensing and Compliance Radiological Health Section State of Arkansas Department of Health 4815 West. Markham Street Little Rock, Arkansar Re: ' ARK - 628 - BP 83

Dear fir. Bevill:

I.would like to take this opportunity to formally request that o be ame,ur-nded Radioactive to permit the Source Material receipt of License 7/ ARK-626-BP-6-83 approximately 1.2 Uci of special cobalt-60 sources prepared by Neutron Frouucts Inc. of Dickerson, Maryland. These sources have been encapsulated in 321 stainless steel and it'is our intention to have them reencapsulated in 304 series stainless steel within one year from the date of receipt. The vendor, Neutron Products, has had detailed analyses performed on the 321 stainless steel sources and it may be safely concluded that the integrity of the sources will not be compromised within the year's passage; in fact, the conservative analysis prepared by O'Donnel & Associates reveals a life expectancy in excess of 2000 years.

This source material is urgently required for a nuclear reactor component test irradiation scheduled to begin April 19 Prior dosimetry must be performed, which presents us with a very tight schedule. Your prompt review and approval would be appreciated.

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12 0 RADI ATION RESEARCll & PROCESSING FOR INDt!S'IRY SINCl. IW

. y, , p n Radiation ' ik ch nology, Inc.

Process Technology Inc. will increase the frequency of its pool water monitoring program from a quarterly to a monthly basis and will institute daily surveys of the pool water ion exchange system. Both increased frequency procedures will be of a precautionary nature and will take place until all of the ~321 elements are replaced by 304 material.

We trust that.these procedures will be sufficient and thadt you again for your assistance in this matter, l

Very truly yours, Radiatio nol y, Inc.

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301/349-5001 TWX: 710-828-0542 April 2, 1982 Mr. Bernard Bevill State of Arkansas Department of Ilealth 4815 West Markham Street Littic Rock, Arkansas 72201

Dear Mr. Bev111:

Thisletterwillconfirmourvarioustelephoneconversations15thecourseof which I outlined for you our reasons for suspending production, and stopping the shipment of sources to Radiation Technology during the last week in Febru-ary; and our reasons for resuming production last week, and being satisfied that these sources are appropriate for shipment and use.

1. Our quality assurance plan for the production of all sources requires that every tenth weld be sectioned, polished, and etched and examined critically under a microscope to confirm that the welding process is under control.

2. One of the criteria set for proceeding with production is that no cracks be observed in the metallographic sections at a magnification of 8X.

3. One of the reasons for this criterion is that it is very difficult in the abstract to define a procedure for evaluating cracks if any are found. -

4. In the course of examining metallographic sections from the second batch of sources that were being produced for Radiation Technology, we assigned the responsibility for preparing the metallographic sections to a trainee who etched the specimens more heavily than had previously been our practice (the specification calls for a light etch) .

5. When examining the more heavily etched specimens under high magnification (50X) we observed microcracks in a significant fraction of the samples.

We were unable to explain the phenomenon at the time, and as a result we stopped the shipment of the sources which had been previously prepared, and suspended production of the sources that were in process pending further evaluation.

6. In the intervening period, we have experimented with different welding con-figurations in the belief that the microcracks could have been attributed in some way to the eccentricity of the end caps. We determined experimentally that similar microcracks were observed in more ideal configurations, and that l this h>70 thesis was not valid.

7. We also produced some 304 L Type SS weldments in the same configuration as y

Radiation Technology sources. We observed a crack in only one of the sec-tions taken from those twelve welds.

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< ~ o o i , Mr. Bernard Bevill l April 2, 1982 Page Two

8. We recovered our archive samples of weldments previously made using SS 321 and submitted them to the heavy etched that hat, been used in Radiation Technology samples. Similar microcracks were observed.

9. We reviewed all of the archive samples prepared for metallographic pur-poses for Radiation Technology, and determined that the process used was reproducible throughout, and under control.

10. We subsequently confirmed, as a result of consultations with welding ex-perts, that the type of microcracks we were observing was typically experi-enced in the welding of Type 321 SS.

11. We noted that in all of the specimens, microcracks began at the notch that inherently exists between the outer wall of the end cap and the inner wall of the tube, inboard of the weld zone, and extends along the axis of the tube into the weld zone. The microcracks do not exhibit a tendency to turn toward the outside of the weld, and in no case did we observe any microcrack to reach a point within 75% of the distance to the surface of the weld.

12. Based on a preliminary stress analysis, we tentatively determined that the microcracks are unlikely to be under any stress that could cause them to propagate to the surface, and we subsequently arranged for O'Donnell G Associates, of Pittsburgh, to perform a detailed stress analysis and advise us as to the likelihood that these sources would perform their intended func-tion for their intended lifetime. The resv e ' of their analysis, which con-servatively forecast a life of 2,000 yes e' has been forwarded to you under separate cover.

13. Last September, we encapsulated a group of sources from Type 321 SS for our own use and since that time they have experienced in excess of 1100 cycles in our irradiator here at Dickerson. Upon heavy etching the metallographic samples from these sources exhibit microcrack structure similar to that ob-served in the Radiation Technology samples.

14. As a result of these various considerations it is clear to us that while those microcracks represent a literal deviation from our written specifica-tion, they are not indicative of any flaws in the sealing of these sources; and there is no reason to believe that their presence will have any material impact on the safety or usefulness of these sources. The warranty on these sources is valid, and we are prepared to furnish our customers an extended warranty, if he so chooses, at the same price that is normally charged for such extensions.

Very truly yours, NELTTRON PRODUCTS, INC.

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Marvin M. Turkanis Vice President BHT /mbn NEUTRON 3RODUCTS inc

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301/349-5001 TWX: 710-828-0542 April 1, 1982 Mr. Bernard Bevill State of Arkansas Department of Ilealth 4815 West Markham Street Little Rock, Arkansas 72201 Re: Sources for Radiation Technology

Dear Mr. Bevill:

Enclosed is the report from O'Donnel 6 Associates, Inc., which we received by telecopier late this afternoon.

A cover. letter formally requesting approval of these sources for Radiation Technology will be transmitted to you by telecopier tomorrow. We received O'Donnell's report too late to retransmit by telecopier to you today, and would have missed Federal Express if cover letter was prepared today.

We would appreciate your immediate initiation of review of our request to amend previous submission to accept the microcracks we observed in the metallo-graphic production control sampics as an acceptable deviation to our specifica-tions in the Source and Device Catalogue.

Sincerely, NEUTRON PRODUCTS, INC.

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j Marvin M. Turkanis Vice President Mir/mbn ,

Enclosure cc: A1 Toboada, NRC Richard Brisson, DIMI, St. of Md.

Robert Buckley, Radiation Technology Ted Russen, Radiation Technology Joel 0. Lubenau

_ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _