ML20196D471
| ML20196D471 | |
| Person / Time | |
|---|---|
| Site: | North Carolina State University |
| Issue date: | 11/30/1998 |
| From: | Perez P North Carolina State University, RALEIGH, NC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20196D474 | List: |
| References | |
| TAC-MA1936, NUDOCS 9812020251 | |
| Download: ML20196D471 (9) | |
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- g North Carolina State University is a land-N: clear Reactor Program grant university and a constituent institution i
of The University of North Carolina
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STATE i JN M FN I Y Department of Nuclear Engineering Campus Box 7909 Raleigh, NC 27695-7909 919.515.2321 919.515.5115 (fax) 30 November 1998 l
U.S. Nuclear Regulatory Commission Document Control Desk Washington DC 20555 j
Subject:
Response to Request for Additional Information (TAC No. MA 1936)
References:
Request for License Amendment - NCSU PULSTAR Research Reactor:
Modification to Facility Technical Specifications,7 May 1998 Request for Additional Information (TAC No. MA 1936), A. Adams, Jr.
U.S.N.R.C. to P.B. Perez, NCSU, September 28 1998.
Dear Sir or Madam:
The responses to the reference Request for Additional Information (RAI) is included in the attachment to this letter. Our response includes two proposed revisions to the Technical Specifications and the affected pages are included in the attachment. Please contact me at (919) 515-4602 if you have any questions regarding this response or our request for a license amendment.
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Pedro B. Perez Associate Director, Nuclear Reactor Program Attachments: As stated cc: A. Adams, Jr., USNRC Sworn to and subscribe before me this the 80dof November 1998.
Mro N Y y
Notary Public My commission expiresN/r.
Ii98 9812020251 981130I PDR ADOCK 05000297 P
PDR_
t U.S. Nuclear Regulatory Commission (2)
Document Control Desk j
Ref.
NCSU PULSTAR Research Reactor Docket 50-297 l
License R-120 i
Distribution
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i A. Adams, Jr., USNRC
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R.O. Scattergood, Ph.D., Chairman, RSAC C.W. Mayo, Ph.D., Director, Nuclear Reactor Program
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North Carolina State University PULSTAR Research Reactor License No. R-120 Docket No. 50-297 Response to Request for Additional Information (TAC NO.1936) 30 November 1998 i
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North Carolina State University IJcense,R-120 '
Response to Request for Additional Information Docket 50-297 (TAC No. MA 1936)
Istaduction The staff of the PULSTAR reactor has prepared the following responses to the Request for Additional Information.
Question 1 i
In addition to the requested change in the Technical Specifcations (TSs) allowing beryllium refectors, you have proposed deleting the requirement in TS 3.1.a. for "a fve by fve army confguration"in the fuel element geometry. However, you have provided no discussion or l
justifcation for this change. Ifyou want to make this change to the TSs, please provide a safety analysis including impacts on reactor operations and on reactor safety including accident analysis.
1 Response 1 North Carolina State University requests deleting the TS 3.1.a. requirement for a square core configuration in order to enhance the neutron fluence at experimental facilities as l
required for teaching and research applications. The PULSTAR reactor was designed with this ficxibility and includes a six by six core grid plate and movable control assemblies to
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accommodate different core configurations. The flexibility in core configuration geometry is limited to core performance results which are bound by the Updated Safety Analysis Report [1].'
The staff of the PULSTAR reactor reviewed the facility Updated Safety Analysis Report and found any geometrical configuration of a twenty-five assembly core is bounded by the USAR analyses when the following core performance limits or specifications are met.
(a).
Number of assemblies is twenty-five (TS 3.1(a) USAR Appendix 3-B)
The number of assemblies in the core is a basic initial condition for various safety analyses documented in the USAR. As an example, USAR 13.2.1.1 and Appendix B,Section IV document the "IAss of Primary Flow" analysis.
The primary consideration in the analysis was Departure from Nucleate Boiling (DNB) ratios and related fuel temperatures. These values are cooling channel specific and calculated from average fuel channel models and applying hot channel factors. Geometrical configurations with the same number of assemblies will not change the average channel power.
Core configuration changes involving the fuel and/or reflector assemblies may affect the total nuclear peaking factor. As a result, the PULSTAR staff performs axial and Page 2 of 7
l North Carolina State University License R-120 Response to Request for Additional Information Docket 50-297 (TAC No. MA 1936) l l
radial peaking factors and other measurements following new five-by-five core configurations. The same will be performed for any geometric configuration.
j Operating the reactor with twenty-five assemblies and removing the specification for a five-by-five geometrical configuration does not invalidate the assumptions or results of the Loss of Primary Flow analysis provided other core performance limits are met.
Specifically, total hot channel peaking factor, core inlet temperature, total scram worth, reactivity insertion rate, scram circuitry delay time, low flow scram circuitry delay, and core thermal power. A change in geometry will only affect the total peaking factor.
(b).
Total peaking factor limit of 2.92 (USAR 3.2.4.2 and Appendix 3-A)
As stated in (a) above, the total peaking factor may change with core configuration changes and is measured by the PULSTAR staff for all new core configurations.
The assumption of 2.92 in various calculations in the USAR is obtained from USAR Appendix 3-B,Section III, Table III by multiplying the radial and axial peaking factors. This total peaking factor is often referred to as the total " nuclear " peaking factor.
As stated in (a), core configuration changes involving the fuel and/or reflector assemblies may affect peaking factors. As a result, the PULSTAR staff performs axial (F,) and radial (F,y) peaking factors and other measurements following new five-by-five core configurations. The total nuclear peaking factor obtained from multiplying F,, and F, (F,y
- F,) is compared to the limit of 2.92 during start-up physics testing.
The start-up physics test procedures will be performed for any geometric configuration. However, it is noted that the peaking factor limit is the only nuclear limit applied in the SAR for various safety analyses which is not a TS. The staff of the PULSTAR reactor proposes on the attached affected TS page to make the 2.92 a TS. This will ensure all parameters used as assumptions in the safety analyses are given as a TS.
(c).
Core flow rate of 500 gpm (TS Figure 2.1.1, USAR Appendix 3-A & 3-B)
The mass flow through the core is an important parameter in many safety analyses.
The primary flow rate is not impacted by the geometrical configuration of a twenty-l Page 3 of 7
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North Carolina State University Ucense,R-120 Response to Request for Additior.at Information Docket 50-297 (TAC No. MA 1936) five assembly core. In addition, TSs 3.1(c) specifies that all locations in the grid plate l
which are not occupied by a reflector or fuel assembly must have a plug to prevent flovi by-pass.
(d).
li el assembly reactivity worth limit of 1590 pcm (TS 3.1(c), USAR 13.2.2.1)
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l This limit on fuel assembly worth is based on a twenty-five fuel assembly PULSTAR core being capable of absorbing a step input of reactivity of more than 1590 pcm without failure of fuel pin cladding.
Any core configuration changes involving the fuel ard/or reflector assemblies may affect fuel assembly worth. As a result, the PULSTAR staff performs assembly worth measurements following new five-by-five configurations. The same will be performed l
for any geometric configuration.
(e).
Core excess reactivity limit of 3970 pcm (TS 3.2(b) and USAR 3.1.2.1)
Any core configuration changes involving the fuel and/or reflector assemblies may l
affect core excess reactivity. As a result, the PULSTAR staff performs excess l
reactivity measurements following new five-by-five configurations. The same will be
. performed for any geometric configuration.
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(f).
Minimum shutdown margin limit of 400 pcm (TS 3.2(a) and USAR 3.1.2.1)
Core configuration changes involving the fuel and/or reflector assemblies may affect l
the shutdown margin. As a result, the PULSTAR staff performs shutdown margin measurements following new five-by-five core configurations. The same will be performed for any geometric configuration.
1 The basis for these limits are found in the PULSTAR facility USAR and the Nuclear Regulatory Commission's Safety Evaluation Report related to the renewal of the facility operating license [2].
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North Carolina State University l
IJcense,R-120 Response to Request for Additional Information Docket 50-297 (TAC No. MA 1936)
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Question 2 j
in the discussion ofpossible mdiation damage to the proposed beryllium reflectors, it is stated that they will be visually inspected on the same schedule as the graphite reflectors. However,
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because the TSs do not requite such inspections, please provide information on the current basis l
for the gmphite reflector inspection, including the schedule and the criteria for acceptable performance.
l Response 2 i
t The reflector assemblies inspection is performed in conjunction with the biennial fuel inspection procedure.
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He scope of the reflector inspection program is to verify the reflector assembly is in i
iacchanically acceptable condition for continued use as a neutron reflector. The reflector block holder, or assembly cage, is inspected for missing machine screws and overall
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i-mechanical appearance. In addition, the reflector block is visually inspected for mechanical bowing which would decrease the effectiveness of the reflector due to increasing the water F
gap between the core and reflector block. This increases absorption in the moderator and i
decreases the reflector block effectiveness as a neutron reflector.
i Conclusion The PULSTAR reactor. staff find the Technical Specifications as proposed and the USAR analyses support our request to remove the five-by-five array configuration specification.
The proposed modification to our TS to specify the nuclear peaking factor limit of 2.92 as a Limiting Condition for Operation is consistent with other TSs which originated from the USAR analysis assumptions.
References 1.
North Carclina State University PULSTAR Research Reactor Updated Safety l
- Analysis Report, Amendment 12,30 October 1997.
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NUREG-1572, Safety Evaluation Report related to the renewal of the operating license for the research reactor at North Carolina State University, April 1997.
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North Carolina State University License, R-120 Response to Request for Additional Information Docket 50-297 (TAC No. MA 1936)
J North Carolina State University PULSTAR Research Reactor License No. R-120 Docket No. 50-297 Response to Request for Additional Information (TAC NO.1936)
Affected Technical Specification Pages 30 November 1998 Page 6 of 7
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North Carolina State University Ucense, R-120 Response to Request for Additional Information l
Docket 50-297 (TAC No. MA 1936) l Change Synopsis The following replacement pages to the facility Technical Specifications are part of 'the response to the Request for Additional Information.
Page 5 Added a definition for Total Nuclear Peaking Factor i14 Section 1 and renumbered affected definitions.
Page 12 Added to Section 3 a new specification for the total nuclear peaking factor 1
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