ML20247D583
| ML20247D583 | |
| Person / Time | |
|---|---|
| Site: | North Carolina State University |
| Issue date: | 05/07/1998 |
| From: | Monteith L North Carolina State University, RALEIGH, NC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20247D586 | List: |
| References | |
| NUDOCS 9805150100 | |
| Download: ML20247D583 (12) | |
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,. North Carchna State University is a land, Office tf the Chancellor
- Box 7001/ A Holladay Hall grant university and a constituent institution l of the University of North Carchna Raleigh, North Carohna 27695 7001 919.515 21911phonel 919 8313545(fax) 7 May 1998 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
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Subject:
Request for License Amendment - NCSU PULSTAR Research Reactor:
Modifications to Facility Technical Specifications Docket No. : 50-297 License No. : R-120
References:
NCSU PULSTAR Reactor Technical Specifications, Amendment 12, dated 30 October 1997
Dear Sir or Madam:
North Carolina State University requests a modification to the facility technical specifications to utilize beryllium reflector assemblies for core excess reactivity f management. The safety evaluation performed by our Nuclear Reactor Program staff and l the Technical Specification replacement page are included in Attachment A and B respectively. Please feel free to contact Mr. Pedro B. P6tez, Associate Director of the Nuclear Reactor Program at (919)515-4602 if you have any questions or require any additional information.
Sincerely,
/ /
4N/& ~
La[y K. Monteith ;
Chancellor l Sworn to and subscribe before me this the N day of May 1998.
~
Notary Public My commission expires b/d 140/ f l
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9805150100 990507' l PDR ADOCK 05000297 P PDR:
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1 U.S. Nuclear Regulatory Commission (2)
Document Control Desk Ref: NCSU PULSTAR Research Reactor Docket: 50-297 ;
License: R-120 )
l cc: Mr. Alexander Adams, Jr.,
U.S. Nuclear Regulatory Commission OWFN-MS: 001-B-20 Washington, DC 20555 Mr. Pedro B. Perez
, Associate Director, NRP i l NCSU Box 7909 l
Donald J. Dudz'ak, Ph.D., Head Department of Nuclear Engineering Charles W. Mayo, Ph.D., Chairperson Reactor Safety and Audit Committee j l
David DeMaster, Ph.D., Chairperson
! Radiation Protection Committee Nelson Couch, Ph.D.
Radiation Safety Officer
Attachment:
As stated l
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Attachment A l
North Carolina State University l PULSTAR Research Reactor Docket: 50-297 License No. R-120 Safety Evaluation Analysis Supporting the Utilization of Beryllium Reflector Assemblies i
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. " North Carolina State University Docket NL: 50-297 PULSTAR Research Reactor Ucense N s: R.120
1.0 INTRODUCTION
The PUIETAR reactor requires additional excess reactivity in order to continue to meet its mission of teaching, research, and service. The excess reactivity available as of the date of this report is approximately 0.9%Ak/k which is quickly reduced due to the power defect, xenon, and coolant temperature reactivity effects. The working excess reactivity at full power is barely sufficient to allow a fixed experiment of 0.250%Ak/k to run for any signiCeant duration.
Excess reactivity may be gained by changes in core material content, geometry, or a combination of the two. The PULSTAR core geometry (5x5 fuel array) is fixed under the current facility license and the only remaining options are to load fresh fuel assemblies in place of exposed assemblies and change the graphite reflectors to a better reflector such as beryllium. The PULSTAR facility currently has nine fresh fuel assemblies and has obtained five beryllium reflector assemblies through the D.O.E. fuel assistance program.
Separate experiments were performed to measure the reactivity worth of beryllium reflector assemblies. The first experiment was performed in 1993 to measure the worth of a beryllium reflector assembly in different core periphery locations. The experimental results were used to estimate the excess reactivity gain of the five beryllium reflector assemblies. The second experiment was performed in 1995 and measured the worth of five berylliuin reflector assemblies in two configurations.
The experiments met the requirements of 10 CFR 50.59 (a)(iii) and were conducted under approved PULSTAR projects and procedures which were reviewed by the Reactor Safety and Audit Committee and Radiation Protection Council.
This report summarizes the experimental results of the two experiments and presents the safety evaluation for utilizing berylluim reflector assemblies at the NCSU PULSTAR research reactor facility.
i 2.0 DISCUSSION OF EXPERIMENTS l
l 2.1 General Overview l
The excess reactivity assessment required an assembly flux profile measurement of the i current Reflected Core 5x5 No. 3. The results of the measurements were used to !
i establish the reference core from which to determine the worth and impact on assembly power peaking of beryllium reflector assemblies.
2.2 Beiyllium Reflector Assembly Measurements One beryllium reflector assembly was used as a fixed experiment to measure the reactivity worth in place of a graphite reflector block at three reflector grid locations.
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. . North Carolina State University Docket Ns: 50 297 I PULSTAR Research Reactor License No.: R.120 l
l The reactor was started with Reflected Core 5x5 No.3 and the actual critical position I (ACP) was recorded and the reactor shutdown. The graphite reflector blocks in grid position positions 1-A,4-A, and 6-C were successively replaced with the beryllium reflector assembly and the reactor was re-started to establish the new ACP. The difference in ACP between the reference core and the experimental core provided the worth of the beryllium reflector assembly at the given location.
l 2.3 Assembly Flux Measurements {
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Flux measurements were made in the adjacent fuel assembly to the beryllium reflector assembly to establish the impact on axial distribution and assembly average power.
i 3.0 EXPERIMENTAL RESULTS 3.1 Beryllium Reflector Assembly Reactivity Worth Measurements The reactivity worth of one beryllium reflector assembly was measured at three core grid positions on 15 March 1993. The measured worths were 0.088%Ak/k at position 1-A, 0.181%Ak/k at position 4-A, and 0.217%Ak/k at position 6-C.
The excess reactivity gain with five beryllium reflector assemblies loaded in core grid j locations 1-A through 5-A was estimated to be 0.80 0.20%Ak/k. The second experiment conducted on 24 May 1995 established the worth of five beryllium reflectors l
as 0.80%Ak/k in configuration shown in Figure 1 and 0.82%Ak/k for the configuration l in Figure 2.
3.2 Assembly Flux Distribution Assembly axial flux etribution and power density measurements were performed in assemblies next to the oeryllium reflector assembly. The results showed minor increases in the axial peaking ratio and power.
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l 4.0 SAFETY EVALUATION l
4.1 Background on Beryllium f Beryllium is an anisotropic light metal with many important classical properties such as excellent thermal conductivity, high melting point, and is non-magnetic. It is extensively used in manufacturing springs, electrical contacts, and non-sparking tools. In addition, 1 i
beryllium has been used in reactors as a neutron moderatcr and reflector for many years.
l The element is desirable for reactor applications because of its high neutron-scattering cross-section and low neutron-absorbing cross-section. The first reactor applications I involved reflecting zero-power critical facilities. Research and test reactors currently using beryllium as reflectors range in thermal power from 2 MW to 250 MW. The 2
' orth Carolina State University N Docket N:.: 50-297 PUISTAR Research Reactor License N:.: R.120 performance of this light-metal under high neutron and gamma fluences is well documented and is summarized in this section.
The PULSTAR beryllium reflector assemblies were purchased for NCSU by the U.S.
Department of Energy through the fuel assistance program. The reflector blocks were manufactured by the Imral American Beryllium Company to specifications set for reactor grade beryllium utilized in test reactors [1]. The quality assurance tests were performed l in accordance to the requirements of Reference 1 by Brush Wellman, Inc. The material 1 certification document is included in this report as Appendix A.
4.2 Chemical Toxicity of Beryllium Beryllium is classified as highly toxic attacking the respiratory system. MSDA sheets (Appendix B) warn about breathing beryllium dust or fumes specifically during l machining or fires respectively. The metal as a solid is less of a hazard if protective l clothing such as lab coats and gloves are used to avoid contact with the skin.
4.3 Radiation Damage The mechanisms by which neutron irradiation damages beryllium metal are fast-neutron induced atomic displacement in the crystal lattices and by transmutation reactions. The atomic displacement damage is not significant in comparison to the damage from transmutation reaction which lead to helium and tritium in the metal. The specific l reactions of interest are the following: l
'Be (n,2n) 2 'He
'Be (n,a) 'He -+ R - *Li The first reaction produces helium directly and has a threshold energy of 1.85 MeV.
The lithium produced in the second reaction is transformed to helium and tritium by thermal neutron absorption. The threshold energy for this reaction is 0.71 MeV [1].
Atomic dispersion of helium and tritium reduce the ductility of the metal and may lead to cracking of the beryllium reflectors. However, the damage is clearly fast-neutron induced and the effects are not noticeable until total fluences of approximately 6.0 (10")
n/cm' (> 1 MeV) [2].
l 4.4 Safety Analysis - Irradiation Damage l
The PULSTAR integrated fast fluence rate (> 1 MeV) can be conservatively assumed to be 10" n/cm 2/sec at full power at the core periphery. Material damage would not be expected until about 10' seconds or 31 years of continuous full power operation.
Damage of the beryllium due to neutron-induced embrittlement is not expected at the PULSTAR facility. Nevertheless, the beryllium reflector assemblies will be visually inspected at the same interval as the graphite block reflector elements.
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, ' North Carolina State Udversity Docket N:.: 50 297 PULSTAR Research Reactor l License No.: R 120
5.0 CONCLUSION
S The experimental results show approximately 0.8%Ak/k increase in excess reactivity with five beryllium reflector assemblies replacing graphite reflector assemblies. An excess reactivity increase of this magnitude would extend the PULSTAR core-life by l approximately 7,500 MWhrs (Figure 3). l
6.0 REFERENCES
- 1. Material Specification Beryllium Pressing and Components for Nuclear Reactors and Reactor Systems, EG&G Idaho, Inc., ANC-8005G Revision H, June 20,1991.
- 2. The Effects of Neutron irradiation on Beryllium Metal, B.S. Hickman, Conference on the Metallurgy of Beryllium, The Institute of Metals, London England,18 October 1961.
- 3. Stress and Deformation Analysis ofIrradiation Induced Swelling, B.V.
Winkle, Aerojet Nuclear Company, ASME Publication,74-PVP-44,28 June 1974.
- 4. Properties of Irradiated Beryllium: Statistical Evaluation, J.M. Beeston, Idaho National Engineering Laboratory, TREE-1063, October 1976. l 1
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, ' North Carolina State University Docket No.: 50-297 PULSTAR Research Reactor Ucesse No.: R-120 l
l Figure 1 I
i NCSU PULSTAR Reactar Reflected Core 5X5 No. 5 Grid Map l 1 2 3 4 5 6 l BF1)
G-7 BE2, G-8 Bs3 G-4 A F-23 F-14 F-10 F-11 F-6 B3 B l
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F-12 F-13 ,
F-9 G-5 E l
F-24 F-22 F-18 F-19 F-25 O F 5
i
' North Carolina State Uxlversity Docket No.: 50-297
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PULSTAR Research Reactor Uce re No.: R-120 ;
Figure 2 1
NCSU PULSTAR Reactor l Reflected Core 5X5 No. 6 Grid Map l
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F-26 F-17 F-12 F-13 F-9 G-5 E F-24 F-22 F-18 F-19 F-25 O F 6
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Attachment B North Carolina State University PULSTAR Research Reactor Docket: 50-297 License No. R-120 Technical Specification Synopsis of Modifications and Replacement Page 1
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l NCSU PULSTAR Reactor Facility l , Docket: 50-297 License: R-120 Synopsis of Technical Specification Modifications Technical Specification Section 3.1 " Limiting Conditions for Operation - Reactor Core Configuration":
o item (a) changed "A maximum of twenty-five fuel assemblies in a five-by-five array configuration" to "A maximum of twenty-five fuel assemblies".
The change allows for other than square configurations to be utilized.
O item (b) changed "A maximum of ten graphite reflectors located on the core periphery" to "A maximum of ten reflector assemblies of either graphite or beryllium or a combination of these located on the core periphery".
The change allows for the use of beryllium and graphite reflector assemblies to be used for reactivity management.
These proposed changes for Amendment 13 are shown on the next page where striked-out text represents deletions and red-lined text represents additions. Following that presentation, the Technical Specification replacement page is enclosed.
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