ML20132E731

Application for Amends to Licenses DPR-39 & DPR-48 Re Proposed Changes to Specimen Capsule Withdrawal Schedule. Forwards WCAP-10902, Plant-Specific Neutron Fluence Evaluation for Zion Units 1 & 2

ML20132E731
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	09/13/1985
From:	Leblond P COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20132E735	List: ML20132E731 ML20132E758
References
0590K, 590K, NUDOCS 8510010155
Download: ML20132E731 (9)

Text

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t [1 Commonwealth Edison *

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O Address Reply to. Post Office Box 767 Chicago. Illinois 60690 l

l September 13, 1985

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Mr. Harold R.-Denton, Oltector~- -~~

l Office of Nuclear Reactor Regulation l U.S. Nuclear Regulatory Commission Washington, DC 20555 l

Subject:

Zion Nuclear Power Station Units 1 and 2 Proposed Amendment to Facility Operating '

License Nos. OPR-39 and DPR-48 Specimen Capsules NRC Docket Nos. 50-295 and 50-304

Reference:

August 19, 1985 letter from P. C. LeBlond to H. R. Denton.

Dear Mr. Denton:

The referenced letter transmitted a proposed change to Zion's specimen capsule withdrawal schedule. This change is largely based upon WCAP-10902, " Plant Specific Neutron Fluence Evaluation for Zion Units 1 and 2." 11 copies of this report are included with this letter for your review.

Examination of Figures II.1-1 and 11.2.-2 in WCAP 10902 clearly show that the 4 'V W, Z) will not attain the projected EOL inner wall fluencecapsules of 1.8 x 10 (S,19,n/cm2 until approximately 22 EFPY' of reactor operating time has elapsed. However, the 40 capsules will attain the same fluence level after only 8.5 EFPY of operation. Since the Unit 2 X capsule is the only remaining uncommitted 400 capsule, it must be retained so_that the material properties of Zion's vessels can.be measured at fluences beyond 1.8 x 1019 n/cm2, This would be required if Commonwealth Edison should decide to justif 19 n/cm2.y Note reactorthatoperation the Unit 2beyond X capsule an inner wall would fluence provide theofneeded 1.8 x- 10 information approximately 13.5 EFPY sooner than any of the 40 capsules. This additional operating time could be used to devise and implement additional flux reduction i programs, if they should be required.

Mr. B. J. Elliot of your office has expressed a concern regarding the accuracy of fluence projections subsequent to the implementation of Low Leakage core loading patterns. Tables II.2-6 and II.2-12 of WCAP 10902 -

demonstrate the excellent historical agreement between the fluence projections for conventional core patterns and the measured flunces obtained from the installed dosimetry. Future confirmation of this~ agreeiaent will be obtained from the scheduled withdrawal of the Y capsule from each unit, the-potential withdrawal of the Unit 2 X capsule, and the results of Zion's 4 g

excore dosimetry program. Q\

B510010155 850913 l"'

PDR ADOCK 05000295 P PDR t

H. R. Denton September 13, 1985 Zion's excore dosimetry program is described in the attachment. The Cycle 9 exposures on each of the units will be compared against the predicted fluences to provide reassurance of the validity of the neutron transport analyses.

As provided by 10 CFR 50.91, the State of Illinois is being notified of this amendment request by transmittal of a copy of this letter and the attachment.

If you have any further questions regarding this matter, please direct them to this office.

Three (3) signed originals and thirty-seven (37) copies of _ this letter and its attachment are hereby provided for your review.

Very truly yours, h

P. C. LeBlond Nuclear Licensing Administrator 1m Attachment cc: Resident Inspector - Z w/o Enc.

J. A. Norris - NRR M. C. Parker - State of Ill.

SUBSCRI AND S 'OR to day before(se {his of L !LtM/r7,/ni ,1985 i

. Ash Notary Public 1

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ATTACHMENT REACTOR CAVITY NEUTRON DOSIMETRY ZION UNITS 1 and 2 BACKGROUND The purpose of this measurement program is to establish, for the beltline region of the Zion Units 1 and 2 reactor pressure vessels, the azimuthal and axial gradients of fast neutron fluence (E3Pl.0 MeV) and dpa (displacements per atom) that will be accrued during Cycle 9; and to provide the capability for long term monitoring of the fast neutron exposure that

-will occur during subsequent fuel cycles. These measurements will also provice a vehicle for the verification of the ability of neutron transport analyses to predict through wall embrittlement gradients.

The Cycle 9 measurements will be accomplished by installing passive neutron cosimeters in the reactor cavity annulus located between the pressure vessel and the primary biological shielo. These dosimeter packages will remain in place for the entire fuel cycle and will provide neutron spectral coverage sufficient to allow the determination of exposure parameters in terms of both neutron fluence (E?l.0 MeV) and dpa. Following analysis at the conclusion of Cycle 9, the measured data will be used in conjunction with the results of neutron transport calculations to project exposure gradients through the vessel wall.

The attachment fixtures to be used to position the Cycle 9 dosimetry will remain in place following irradiation. Therefore, cosimeters designed for long term monitoring of the pressure vessel could be reinstalled to establish the capability to follow and verify the effects of any changes in fuel management strategy on pressure vessel exposure.

DESCRIPTION OF DOSIMETRY The passive neutron detectors used in this program will incluoe six advanced dosimeter capsules containing radiometric monitors and solid state track recorders to provide spectral coverage at selected locations in the beltline region. In addition, stainless steel gradient wires will be used to complete the determination of the azimuthal and axial exposure gradients.

Since the reactors are intended to exhibit 1/8 core symmetry, the six spectral sets will be concentrated to provide a neutron spectrum map within a single 45o azimuthal sector. Axial coverage will encompass 16 feet relative to the core midplane.

The locations of all dosimetry within the reactor cavity are shown schematically in Figures 1 and 2. In Figure 1, the azimuthal locations of four strings of dosimeters are depicted relative to the primary loop layout.

The axial locations of dosimeter packages within the reactor cavity annulus are depicted in Figure 2. Placement of the six multiple foil advanced

l dosimeter sets will be such that spectra determinations can be made at four locations on the midplane of the active core with the intent to measure changes in spectra caused by varying amounts of water located between the outer core boundary and the pressure wall. Due to the irregular shape of the reactor core, water thickness varies significantly as a function of azimuthal angle within a given octant. . The remaining two multiple foil sensor sets will be positioned opposite the top and bottom of the active core at the azimuthal angle corresponding to the maximum neutron flux. Here the intent is to measu.re axial variations in neutron spectra over the core height, particularly:near the top of the fuel where backscattering of neutrons from primary loop nozzles and vessel support structures could produce significant pertubations.

At each of the four azimuthal locations selected for core midplane spectra measurements stainless steel gradients wires will extend over the full twelve foot height of.the active fuel. Following irradiation, these wires will' be segmented to provide neutron flux information at 6 inch intervals for each traverse. The data obtained from these gradient wires will be correlated . directed with iron, nickel, and ' cobalt foil measurements obtained from the multiple. foil sensor sets.

The multiole foil sensor sets used during the first irradiation cycle to characterize-the neutron spectra within the reactor cavity and.

ouring subsequent cycles to provide long term monitoring of vessel exposure are retained within 3.5" x 1.0" x 0.5" reactangular aluminum 60611 capsules.

A description of these individual sensor set holders is shown in Figure 3.'

These capsules are designed to accoitmodate radiometric foils and solid. state track recorders within holes drilled in the aluminum block. .The dosimeter materials will be retained within the aluminum block by a cover plate held in place by eight small screws.

Aluminum 6061 was selected for the irradiation capsules in order to minimum neutron flux perturbations at the sensor set locations as well as- to limit the radiation levels associated with shipping and handling of the capsules ~following irradiation. Each capsule represents an aluminum mass of approximately 60 grams.- Thus, each set of six capsules will result in an increase in the aluminum inventroy in the containment building of only 360 grams (S O.8 lb.). An increase of this mhgnitude should be insignificant relative to the total aluminum inventory already present in the containment.

The contents of the dosimeter capsules to be used during the Cycle 9 irradiations are illustrated on Figure 4. Solid state track recorders containing ~ deposits of fissionable isotopes of U-235, U-238, Np-237, and Pu-239 in minute q'uantities'(S 10-9 grams) are included in all irradiation cycles for the cavity dosimetry programs. There are several advantages to the use of SSTR's in a long term monitoring situation. The minute deposits of fissionable material required for the radiator not only minimize the inventory of nuclear material, but also eliminate paperwork associated with E

the shipping and handling of larger quantities of fissible and fissionable isotopes. Since the track recorder readout is actually accomlished with the mica cover, the deposits themselves are not destroyed and may be reused from

cycle to cycle. Furthermore, the mica recorders serve as a permanent record of the neutron exposure incurred during the irradiation.

ATTACHMENT IN THE REACTOR CAVITY The four dosimeter strings described in the preceding sections will be attached to 0.040 inch diamter type 304 stainless steel wire that will in turn be secured to and suspended from the pressure vessel mirror insulation near the elevation of the primary loop nozzles and will extend down to the j elevation of permanent scaffolding located in the sump area below the reactor

pressure vessel.

Attachment at the nozzle elevation will be via the insertion of 1 inch stainless steel sheet metal screws into the mirror insulation. One i

screw will be sufficient to hold each dosimeter string. Attachment in the sump area will be accomplished by tying the stainless steel wire directly to the permanent scaffolding located below the pressure vessel.

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