ML20064F513

Responds to 940125 Request for Addl Info Re Conversion of Gtrr from High to low-enriched U Fuel

ML20064F513
Person / Time
Site:	Neely Research Reactor
Issue date:	03/02/1994
From:	Karam R Neely Research Reactor, ATLANTA, GA
To:	Mendonca M Office of Nuclear Reactor Regulation
References
NUDOCS 9403150342
Download: ML20064F513 (5)

Text

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g' i Georgia Institute of Technology NEELY NUCLEAR RESEARCH CENTER L, ,- 900 ATLANTIC DRIVE ATLANTA, GEORGIA 30332-0425 gga (404) ss4-a000 March 2, 1994 Mr. Marvin M. Mendonca, Senior Project Manager Non-Power Reactors and Decommissioning Project Directorate Division of Operating Reactor Support Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D. C. 20555

Dear Mr. Mendonca:

This is our response to the request received January 25, 1994 from you for additional information concerning the conversion of the GTRR from High to Lov-enriched uranium fuel.

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. Question 1:

In your January 21, 1993 cover letter, you proposed to possess, but not use,'up to 5.1 Kg of HEU (93 percent-enrichment) until it can be removed from your facility.

Provide planned inventories and associated proposed license limits for possession of irradiated HEU fuel, and provide similar inventories and limits for unirradiated HEU fuel, as applicable. Requirements for unirradiated HEU fuel limits is provided in the attached order. Also, provide your plans for removal of all HEU fuel from your facility.

Answer:

Currently our total U23s inventory is -4550 grams. We have in the core 17 fuel' elements. Eight elements have been irradiated and are in storage. The'17 fuel elements in the core and the eight elements in storage- have all been irradiated to approximately the same fluence. In addition, .we have one element that has never been irradiated and two partial elements- with 10 plates each for experimental purposes. (A normal element has 16 plates of The-limit for HEU on hand should not exceed 4550 grams fuel. ) 23s, of-U The plan for the inventory of HEU we currently have after we convert, is to store it in the storage pool and not use it until-we are able-to ship it to DOE. The plan for shipping the HEU to DOE requires ~that wo:have a licensed cask, a DOE place to ship it' to, and a -license from NRC to ship. I Furthermore, we will write a procedure for preparing the fuel for shipment from the Neely Nuclear Research. Center and obtain approval for this procedure from the Nuclear Safeguards Committee. -

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Tr* a: 642507 GTRIOCAATL PDR Far 404-853 9325 (Venty 404 894 3600) :

s 1 AUnit of the Universrty System of Georoia An Eaual Education ac,d Emotovment Opportunity institution

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Mr. Marvin Mendonca March 2, 1994 Page 2 Our license limit for U235 is currently 13.5 Kg of U 235 (See License Amendment #6). After conversion to LEU we do not foresee that our inventory of LEU will exceed 25 elements.

The amount of Us 23 in one LEU element is 225 grams.

Consequently, we do not anticig35 ate our LEU inventory to exceed 25 x 225 = 5625 grams of-U However, to be safe, we recommend that our limit on LEU fuel on hand be limited to- two complete cores. i.e., 2 cores x 19 elements x 225 arams U23s ,

core element 8850 grams.

Question #2:

Section 5.4 of Attachment 1 of the application for conversion, dated January 21, 1993, states that a 14 element core will be analyzed for thermal-hydraulic safety margins because it is the n.inimum-sized core to be used at the Georgia Tech Research Reactor (GTRR). This implies that the safety margins for the 14 element core would envelope those for larger sized cores.

Larger sized cores would be the norm for routine reactor operations and are allowed. Therefore, provide verification that all larger sized cores, which are allowed by your license and technical specifications, are not more limiting. Include assessment for total flow conditions, onset of flow instability, onset of nucleate boiling, and departure from nuclear boiling (e.g., Tables 9 and 10, and Figure 10 of the referenced attachment).

Answer:

The calculations in Tables 9 and 10 of referenced attachment have been repeated for a 17 element core. The calculations were performed by Dr. William Woodruff of Argonne National Laboratory. The results are attached. Note that by going from 17- to 14-element core the flow rate is decreased by 18%

and the power per element is also decreased by 18%. The power peaking factor is slightly higher for the 17 element core because of the asymmetry of the core (see Fig. 6 of referenced attachment). The difference is, however, very small and within the uncertainty associated with the calculation. For a nineteen element core, we ' have symmetry again and the decrease in power per element is the same as the decrease in flow rate per element. Consequently, the onset of flow instability and/or departure from nucleate boiling are virtually the same for 14, 17 or 19 elements core (see attached data).

Mr. Marvin Mendonca March 2, 1994 Page 3 Question #3 Section 8.4.2 of the 1967 GTRR Safety Analysis Report discusses a postulated fuel-loading accident scenario. This .

postulated accident, although very unlikely, was not '

considered for the LEU fuel conversion. Discuss the bases for not including this scenario in the conversion application. l Include comparisons of the safety margin to loss of fuel- ,

integrity or associated parameters for the proposed LEU fuel for the accident scenario.

Answer:

In order for any fuel element to be added to the GTRR when the reactor is critical or nearly critical, the upper shield plug ,

and the lower shield plug must be removed individually and i separately. The reactor must have been checked out, and the  !

control rods must have been withdrawn to criticality position i before one can add anything. This is never done at the GTRR.

It is simply not credible. What we analyzed is a scenario in which a step reactivity of 1.5% 8k/k is inserted. The magnitude of the step (i.e. 1.5% 6k/k) was set equal to the  ;

sum of the magnitudes of all the static reactivity worths of '

all the unsecured experiments which are allowed under our l Technical Specifications. The purpose of the analysis was to show that there is a sufficient margin of safety between the  ;'

maximum allowable reactivity worth and the maximum step reactivity insertion that can be tolerated without fuel damage, assuming failure of reactor scram systems.

Under the above scenario, the analysis showed that fuel melting would not occur until the step reactivity is greater than 2.2% Sk/k. The margin of at least 0.7% 8k/k (2.2-1.5) above the maximum allowed reactivity for a single experiment is sufficient to ensure that the facility is safe even under the verv 'nJ.ike.kr conditions that a maximum step reactivity is inserted and the scram system failed to function.

We appreciate the opportunity to respond to the questions you raised. Should you have additional questions, please let me know.

Sincerely,

@. /9

• MA, R.A. Karam, Ph.D., Director Neely Nuclear Research Center RAK/ccg cc: Gary W. Poeblein

4 i e a

A Comparison of 14 and 17 Element Cores The following tables provide a comparison of GTRR cores with 14 and 17 elements:

Table 1: Reactor Power Limits for a Maximum Inlet Temperature of 123 F Based on DNB and FI.

Reactor Coolant GTRR- ANL-LEU ANL-LEU Flowrate, HEU 14 17 gpm Reactor Power Level (MW) for DNB 760 5.5 5.3 4.9 1625 11.5 10.8 10.7 Reactor Power Level (MW) for F1 l 760 5.3 5.0 4.7 1625 10.6 10.6 10.4 l

Table 2: Thermal hydraulie Data with a Minimum Coolant Flow of 1625 gpm and a Maximum Inlet Temperature of 123"F. ,

GTRR- ANL-LEU ANL-LEU IIEU 14 17 l 1

Coolant Velocity, m/s 2.44 2.61 2.15 Friction Pressure Drop, kPa 10.9 15.0 10.5 Power / Plate, kW 21.2 18.8 15.5 Outlet Temperature ofIlottest Channel, F 157 156 157 Peak Clad Surface Temperature, F 219 224 224

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Minimum DNBR 2.29 2.17 2.14 Limiting Power Based on Min. DN11R, MW 11.5 10.8 10.7 Flow Instability Ratio (FIR) 2.12 2,11 2.07 Limiting Power Based on FIR, MW 10.6 10.6 10.4 These tables correspond to expanded versions of Tables 9 and 10 in the reference document. The l

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17 element LEU core can be compared to the 14 element LEU core. The flowrate is decreased by l about 18% while the power / clement is also decreased by about 18% in going from 14 to 17 ele-  !

ments. The peaking factors for the two cores are slightly different with 1.58 for the 14 element l core (see Fig. 8 of reference document) and with 1.62 for the 17 element core (see Fig. 9 of the reference document). Since the 17 element core is no longer symmetric, the power is slightly skewed and hence the higher peaking factor. The 17 element core at 1625 gpm using the same peaking factor as that for the 14 element case gives limiting powers of 11.0 MW based on DNBR l (2.19) and 10.6 MW based on FIR (2.13) or values that are slightly higher than those for the 14 el-ement core. The limiting values shown in Tables 1 and 2 are not significantly different for the two cases, and a 17 element core raises no new safety issues. j 1

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Reference:

J. E. Matos, S. C. Mo and W. L. Woodmff, " Analysis for Conversion of the Georgia Tech Re-search Reactor from IIEU to LEU Fuel," Sept.1992 l I

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