ML20147B368

Requests Amend of Lic SNM-123 to Allow Use of one-curie Pu(239)-beryllium Source at Locations Other than Univ Park, Pa.W/Encl Rept on Wachter Boron Poison Measuring Equip

ML20147B368
Person / Time
Site:	07000144
Issue date:	11/27/1978
From:	Cunningham R PENNSYLVANIA STATE UNIV., UNIVERSITY PARK, PA
To:	Rouse L NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
References
NUDOCS 7812150250
Download: ML20147B368 (13)

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THE PENNSYLVANI A STATE UNIVERSITY 207 OLD MAIN BUILDISO gyg UNIVERSITY PARK. PENNSYLVANIA 16802 vice President for 27 November 1978 "q3 DEC 4 f.7.10 l E Area Code 814 Research and Graduate Studies 865-6332 g,r

• 3, 01 rector for Nuclear Material Safety and Safeguards

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U.S. Nuclear Regulatory Commission Wastington, D. C.

20555 Att:

Leland Rouse Docket 7.0 1.44

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Gentlemen:

The Pennsylvania State University requests the amendment of spec Itf? lear material license SNM-123 to allow the use of a one curie plutonium (239)-bery111um source at locations other than University Park, Pennsylvania. The Nuclear Engineer-ing Department at the University in cooperation with Wachter Associates of Pittsburgh, Pennsylvania is developing a device to test for the presence of the proper amount of neutron absorber material in spent fuel storage racks tanks.

Testing involves the measurement of the neutron attenuation through the poison curtains of the storage racks. The neutrons are produced by a radioisotope neutron The final design of the device will utilize an americium (241)-bery11ium source.

source in each of the four fuel channels surrounding a channel conthining a neutron detector.

An amendment to our byproduct material license 37-18--4 is being filed to cover the use of the Am-Bo sources.

However, the manufacturer cannot make delivery of the Am-Be sources until late January 1979.

We would like to start testing the device the first week of January 1979, prior to the installation of new storage racks at the Watts Bar nuclear power plant. We propose to use one of our existing one curie Pu-Be sources for these initial tests.

Attachment A of this application briefly describes the testing device and the procedure for use of the neutron source. Minor modifications will be required to accomodate the single Pu-Be source, Use of the source must be approved by the University Isotopes Committee and follow the rules for the use of radioisotope neutron sources as given in section 18 of " Rules and Procedures for the Use of Radioactive Material at The Pennsylvania State University", supplement B of our application dated 21 April 78 for renewal of license SNM-123. The use of the source will be by or under the direct supervision of a University employee at the testing site.

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""*"TY"dW-Rg55ffi~ng po'rhissibn N Mii= Gidde other. spent duct storage: pool sites; and at-manufacturing facilities. for' spent fuel h=#

storage racksithrou'ght. the United States, in order to accomodate any otheftists which.may he possible; prior to receipt of the Am-Be sources.

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e Transportation will be by common carrier or by University vehicle in a i

The University DOT-7A container to be built and tested at the University.

has previously built and tested DOT-7A containers for up to 3 curies of Am-Be and has experience in transporting material as a private carrier under DOT regulations.

Because of the testing timetable noted above, your prompt consideration of this request would be greatly appreciated.

Any questions may be directed to this office or to R. W. Granlund, University Health Physicist, 814/863-3459.

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NUCLEAR REGULATORY COMMISSIONI ATTACHMENT A-

.26 November 78 4

Wachter Boron Poison' Measuring Equip ent' Introduction As more and more fuel elements are discharged from nuclear power A

plants, the problem of' local storage of these elements becomes acute.

temporary solution is to outfit or retrofit existing storage pools with new high density storage racks that permit the safe storage of a large number of fuel elements in a given space. To achieve a high density or a 1arge packing. factor in the. pool,. some of the racks currently being

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installed.contain strips of boroflex, a silicone rubber-like compound that has a high boron-10 concentration.

Boron-10 has a large thermal neutron absorption cross section and its presence in given amounts and.

t geometry enables the pool to ts loaded with a large number of fuel elements without any criticality hazard.

The high density racks currently being manufactured by Wachter Asso-ciates of Glenshaw, Pa. take a form similar to that shown in figure 1.

Here a large number of stainless steel storage bins (typically 160 in a Each bin has two 10 x 16 array) are welded together to form a module.

slot-like sections into which may b.e inserted boroflex strips that are encapsulated by a welded stainless steel sheath. The poison containing subassemblics are sealed external to the 'oin structure and are then in-1

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the neutrons end to create a highly effective flux trap.

l Because the rubber-like strips of poison are now encapsulated in Also, con-stainless steel, the presence of the poison cannot be seen.

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.siderabic amounts of handling of thousands of poison strips are involved i

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before the rack is finally installed in a reactor site pool, and a small' probability of error, such as not escapsulating the poison, is postulated.

To eliminate such errors, NRC requires that final on-site measurements be made to assure that each bin has the proper neutron attenuation character-istics. This report describes the measuring device that has been developed.

System Description

The apparatus operates on the principle of measuring the neutron attenuation between a neutron source and a neutron detector that are separated by a rack wall.

Four sources of equal activity and one detector are used in the configuration shown -in figure 2 in order to check more than one. wall at a.

time. These sources (30-100 mci) each have neutron emissions of about 4

5 7.5x10 to 2.5x10 n/sg principally at energies above 1.5 mev. The sources l

and/or the detector are surrounded by a polyethylene moderator that is used to thermalize the neutrons and make the measurement more efficient.

The sources and the detector are tied together at the end of~ a long probe like structure, shown in figure 3, such that the assembly may be inserted into the rack for a distance up to six feet. The measurement is a "go--no go" type, with absolute attenuation measurements being made at any desired insertion point in the rack.

The. electronics associated with the.nobe head are conventional and are shown in the block diagram of figure 4.

Here the pulses from a high

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.1 this meter is fed into the "Y" terminal of an X-Y recorder and a direct measurement of neutron level at the detector is obtained.

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pen is indexed along as the probe 1s-moved from bin to bin providing a record on standard graph paper. A count rate is first obtained with the probe retracted into its housing out of the rack, but at its adjacent edge. The probe is then inserted a given distance into the rack and the count rate drops drastically.

In the event that one wall lacks its required poison or the poison assembly is in any.way defective, a higher signal level is it.M: e.ed on the recorder.

As each n.easurement is made, a limit switch is closed on the probe assembly and this switch contact is used.to activate an electronic counter circuit that feeds the "X" input to the recorder and steps the pen along 1

to a new horizontal position. The probe is then extracted, and should

.l give its former minimum attenuation signal, thus providing a check that-the system is operative.

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Stepping signal In order to actuate the X-Y recorder horiz'ontal indexing, an analog Each voltage is required that can be divided up into 16 equal steps.

step is then cdded to the preceding.one to create an input signal to the recorder.

The direct approach would be to use a 16 position stepping relay whose contacts received their-signals from a resistance network that l

provided 16 taps from a voltage divider.

A cheaper, more reliable approach can be used employing a hybrid integrated circuit counter network l

I and an elemental D to A converter. The block-schematic diagram is shown l

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Description of Probe Assembly The detector-source probe (figure 3) consists of five thin-walled aluminum tubes that are attached at one end by two plates. The four sources and/or the detector are surrounded by clinders of polyethylene moderator. The sources are aligned axially to 1e opposite the center of the sensitive region of the detector.

Each source is retained in a holder and the holder is then secured in the moderator block or source holder by means of a threaded plug.

Each of the aluminum tubes are three inches in diameter with a nominal wall thickness of.083 inches, and are approximately 7 ft long.

A sag of about.040 inches would be anticipated at the end of this length of tubing if the tubes were rigidly mounted at one enc'.

As a consequence, adjustment; is provided at the rear plates to spring the-tubes slightly inward to pro-vide a good centering grip when the probe is inserted into the rack bins.

A tapered centering block is mounted at the ~ rack side of the supporting plates which will furnish a two point support for the fully inserted assembly and keep it centered.

Shielding protection during operation is provided by distance.

Broad red lines will be painted on the tubing a meter away from the sources.

Administrative procedures will require that the assembly not be grasped For a bare at a point closer than the one meter distance from the sources.

6 one curie Am-Be (2.5x10 n/s) source at one meter the neutron dose equivalent

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total of'5.1. mrem /hr'.

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will usually be 2 meters or more and the sources will be shielded inside the poison curtain most of the time. This should reduce the average dose equivalent rate to 1 css than 1 mrem /hr.

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To operate the equipment, the operators move to the rear of the assembly, grab the tubing beyond the red line, and insert the probe as far as.it will go. -At the end of the inward travel, a microswitch is activated which indexes the recorder to the next measuring position.

The probe is then fully retracted and inserted into the next bin position.

Measurements will be made in successive bins along a given row by merely All moving over one bin and repeating.the insertion-extraction process.

output data:is automatically recorded. The only. manual operation required at the electronics end of the equipment is to reset the vertical index at the end of eachL row measurement. When the probe is not in.use at the test site, it will be stored _.in a. locked, external shielded box.. Sources are to ti stored in a locked shield'when not in the testing apparatus at.

sites other than University Park.

1 Source Handling The sourcos are enclosed.in a. marked, thin-walled, source holder with a threaded hole at one end. The. source is removed from the storage shield or shipping container by threading,the transfer tool into the hole in the source holder and lifting it from the shield. The source in the holder is then inserted into the source cavity in the probe, the transfer tool l

l removed, and the plug for the source cavity in the probe screwed into place.

The operati6n is reversed to transfer the source from the probe to the storage shield or shipping container. The source is only to be handled awm...,

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Sources are only to be used by or under the direct supervision of Pennsylvania State University Employees and in accordance with'the conditions-f-

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of the Authorization to Use Radioactive Material issued by the University Isotopes Committee. All personnel using the-probe or handling the sources are to wear neutron and gamma sensitive personnel monitoring devices.

Before transfer of the sources to a site not under University control, the user will provide the Health Physics Office with a written notice from a responsible authority at the site granting permission to use the sources.

Transportation may be by common carrier or by University personnel in a University vehicle. The arrangements and packaging must be approved by the Health Physics Office, which will provide the shipper certification for hazardous material. anct determine the labeling and placarding required. Any emergencies or unusual conditions involving the use or transport of the sources are to be reported immediately to the Health Physics Office, e

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