ML19208D460

Notifies of Leakage of Air from aluminum-clad Fuel Elements Utilized in Reactor Assembly

ML19208D460
Person / Time
Site:	05000356
Issue date:	05/07/1975
From:	Beck G ILLINOIS, UNIV. OF, URBANA, IL
To:	US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML19208D457	List: ML19208D456 ML19208D460 ML19208D462
References
NUDOCS 7909280449
Download: ML19208D460 (4)

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UNIVERSITY OF ILLINOIS MQ 211 Nudra - Enginanng Laborator liil""a, Illi 'en 61 sol NUCLEAR ENGINEERING PROGRAM Q V l

AT URBANA-CHAMPAIGN g; ,,y, ccs,2. 7 333 2295 Flay 7, 1975

Director Division of Reactor Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20555

SUBJECT:

Leakage of Air from Aluminum-Clad TRIGA Type i Fuel Elements Utilized in LOPRA Reactor Assembly.

License No. R-117, Docket No. 50-356.

t Incident During the annual surveillance check on the LOPRA fuel elements,

, it was noted that as several of the fuel elements were lifted out of the grid plate, air bubbles were coming from the low portion of the element.

On a check of 11 elements on April 23, the last one that was removed gave indications of air being released from the lower portion. This element was removed from the core matrix and placed in a rack at the side of the bulk shielding tank. The checks on the elements were continued on April 29 when 4 more elements indicated leakage out of 17 that were checked.

In all cases the leakage appeared to come from the lower part of the element.

One of the elements was removed on April 30 to inspect the lower part where the end fixture was attached to the cladding. This check showed that the leakage was coming from the welded portion. Some corrosion in this area was evident, but the cause of same has not been fully determined.

There was no detectable release of radioactive effluents from the fuel elements. A N5!C Continuous Air Particulate Monitor showed no gcrease in the counting rate - this instrument has a sensitivity of about 10 uCi/ml.

A 200 cc water sample was taken from the bulk shielding tank (location of the fuel elements) and evaporated for a radioactivity check with a flow counter.

The counting rate that was obtained was essentially background. For the size of sample that was used gnd the counting time utilized, the sensitivity for this check was about 10~' uCi/cc.

Information on Fuel Elements lhe fuel elements involved were received from AfRRI in May, 1965 fo r use in suberitical experiments. With the exception of 6 standard elenents and 4 thermocouple elements, the remainder had either damaged end fixtures or had exceed the 100 mil limitation on growth. The tebing on the TC elements had been cut about 0-inches above the top fixture in order to fit in the shipping cask. Af te r recei pt of the elements , the end fixtures were repaired by securing the elements in a lead fuel cask and then bending the fixture back into place. A cap was welded on the 1C elements with a ring at the top to allow movement under wate r.

The six standard elements, which were within damage specifications, were used in the Mark II TRIGA assembly for brief periods of time in 1967-6S. These were used as additional fuel for making reactivity measurements with the B-ring fuel elements removed.

After the LOPRA license was received in December, 1971, the elements have been used for the operation of this facility. To extend measurements being made in the area of " Reactor Coupling," an instrumented element that had 7 909280 Vd jusu ,

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Page 2 been retained when the Mark II fuel elements were transferred to Michigan State was repaired to obtain temperature information. In September, 1974, during the movement of fuel elements fo. a sub-critical experiment, air bubbles were seen coming from the upper portion of the TC elements that had been obtained from AFRRI. The suspected elements were placed in the racks at the side of the tank for later checks. In January, 1975, repairs were made on the upper portion of these elements.  !!owever, two of the threc elements that were resealed at that time were found to be Icaking during the checks on April 23 and April 29.

, on April 1,1975, the Mark II instrumented fuel element was found to have a severe bend in the thermocouple extension tube. The element was removed and a crack was found in the extension tube where the bend was located.

Since the crack was below the area where the tube is filled with epoxy, it was surmised that some water had leaked into the fuel portion. Be fo re repairs were initiated on this element, the cladding was heated and the moisture in the element was collected in a balloon to check on any activity that might be released in this process. Data on this is given in the following section.

Radiation lla:ards The fuel elements in question have a dose rate of 20-100 mr/hr/M, which indicates a total activity of about 0.2 - 1.0 curies per fuel element. The fractional portion of this activity that one would

-6 expect to,ge released from the fuel meat is estimated to be from 2 x 10 to 2 x 10 . (

Reference:

Pages XIV-16 to XIV-22 of the Safety Analysis Report for the Illinois Advanced TRIGA, August, 1967.)

Approximately 10 cc of water was collected fron heating the Mark II instrumented element. This water was evaporated and an activity of 0.01 uCi was measured with a flow counter. An atter.pt was made to possible identify the .sotopes with a 4000 channel analyser, however the background in the laboratory was found to overshadow a source of this strength.

This element has a dose rate of 20 mr/hr/M.

With proper precautions, work can be done on the elements with only a moderate amount of exposure to the individual. The mechanic, who repaired the three AFRRI fuel elements, received a total dose of about 270 mrem.

It should be noted that the LOPRA has not been operated above 2 watts since March 25, 1975 so that there would be essentially no short half-life fission products involved. Since the license was received in December, 1971, the total operat ion has been 39 kilowatt-hours or less than 1.0 kilowatt-hours per element. The last operation above 10 kilewatts (licensed power for LOPRA) occur red in February,1963 at which time they were removed from the AFRRI facility.

Review The inst rumented fuel elements described above had defects in the aluminum extension tube that is used for the thermoccuple wires. The actual cladding was not involved as is the case for the standard fuel elements.

Region III, Directorate of Regulatory Operations was noti fied by phone of the difficulties with the AFRRI instrument elements in September, 1974 It was agreed that this would not be a reportable incident, but that the elements should not be utili:ed in the facility until the expected leakage was corrected.

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. . s Page 3 Region III, Office and Inspection and Enforcement, USNRC was notified by phone on April 30, 1975 concerning the difficulties with the standard fuel elements. It was concluded that a report to the Division of React,r Licensing, USNRC, Washington, D.C. should be filed giving the present situation as well as any conclusions concerning possible repair of the elements with the defects near the cladding.

The personnel, in charge of the TRIGA facilities at General Atomic Company, San Diego, California, have been notified. The impression obtained from the GA personnel was that although difficulties should be expected in i

re-welding the end plug to the cladding, an individual experienced in aluminum welding could very likely obtain a good seal at this juncture. Drawings of the original AFRRI clements have been obtained, and before any welding is attempted, communications will be made to the personnel at General Atomic who perform these duties.

An approval of a basic procedure to be utili cd has been approved by the Nuclear Reactor Committee at a meeting on May 1, 1975. This approval is contingent on the notification of the Division of Reactor Licensing of the plans. One of the fuel elements was inspected by two staff members from the Mining and Metallurgy Department at the University of Illinois. Their general conclusions were that the openings could be due to a combinations of a slight defect in the original weld and later stresses placed at this j uncture . The appearance of corrosion then results from possible impurities in the weld defect. These individuals will also check on other possibilities of sealing the plug to the cladding other than by aluminum weluing.

Conclusions At the present time it is planned to attempt to repair the fuel elements following the basic procedure given below. It should be noted that this procedure is based on the fact that the activity is of a nature that can easily be handled with some precautions. The procedure will be tried on a single element anl may be altered on future elements depending on the results.

Steps: 1. Remove approximately 1/16 inch of the plug-cladding interface.

This should remove the present weld and allow the plug to be removed from the fuel element.

2. Check inside portion of cladding and outer portion of the plug for any evidence of corrosion or possible damage.

3. Place fuel element in furnace and heat to about 150 C to remove any moisture that may have gotten into this area. During this process, the moisture will either be collected or air p articulate will be used to check on any activity that is released. In either case, the NMC Air Particulate Monitor will be in operation to check on any gaseous effluents released.

4. Clean out inner portion of the cladding and the outer portion of the plug.

5. Re-weld the aluminum plug to the cladding. Check element for any Icaks.

Note: Shielding will be placed around the fuel section of the element during any inspection, cleaning, and welding. Personnel monitoring will. be done with a self-reading dosimeter and a film badge for those individuals doing the work.

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page 4 Of major consideration is the fact that these fuel elements will be used i.n the LOPRA, which has a power limitation of 10 kW and an excess reactivity limitation of 60 cents. 'the maximum fuel temperature at 10 kW is about 15-20 C. above the water temperature, and there is essentially no change in the temperature next to the cladding. Later damage to these fuel elements is far more likely to occur from moving the elements in and i out of the core than from reactor operation.

I Yours truly,

- ,L L a b *7i. )#&

. 7 Gdrald P- Beck, Reactor Supervisor Nuclear Reactor Laboratory University of Illinois Urbana, Illinois 61801 Copy: Region III, Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 799 Roosevelt Rd.

Glen Ellym, Ill. 60137 1 ~. " 7 iLsJ .'