ML20212L301
| ML20212L301 | |
| Person / Time | |
|---|---|
| Site: | National Bureau of Standards Reactor |
| Issue date: | 02/27/1987 |
| From: | Rozier Carter NATIONAL INSTITUTE OF STANDARDS & TECHNOLOGY (FORMERL |
| To: | Dosa J Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8703100340 | |
| Download: ML20212L301 (11) | |
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UNITED STATES DEPARTMe nfT OF COMMERCM! -
National Ea,ce neu of Stenciarsim '. L-k%/ Garthe,rsburg. Maryland 20090 s
Please Note: New Telephone Numbers F
(301) 975-6210 '
- FTS 879-6210
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February 27, 1987 -
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s Mr. John J. Dosa, Project Manager
- Standardization and Special e Projects Directorate
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Division of PWR Licensing-D -
Office of Nuclear Reactor Regulation .
U.S. Nuclear Regulatory Commis6 ton
- Washington, D.C. 20555 , ,
Dear Mr. Dosa Subjoot . Additional Information. Dookot No. 5018'll 2 -
Enclosed is the additional information you r sy'Josted in your lett,ec dt December 30, 1986. .
Sincerely, ,
OfW b-Robert S. Carter hw '
Chief, Reactor Radiation Divis'0n ,
Enclosure
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Docket No. 50-184 Unique Purpose Exemption Request Response to Request for Additional Information
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Question 1.
An important justification for a unique purpose exemption is that the reactor profram contributes significantly to the national interest and cannot be accomplished without the use of HEU fuel. In 1984, a Major O Materials Facility Committee of the National Research Council of the
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Navicnal Academy,of Sciences reviewed major neutron research facilities in the United Staten. Please identify and discuss any comments or
- f. recommendations'pf this Committee, or any comparable group, with respect jq to your facility. that may establish your reactor program's contribution a - + to the national interest.
,. l l l v Ansaert o In Novektier.1983 the President's Office of Solence and Technology Policy asked thd Nattoral Research Council to assist in establishing priorities
' for major facilities for e.aterials research. The committee was co-chaired
/~ by Frodor(cs Seitz, a past president of the National Academy of Sciences, and Dean Motmann of IBM.
The Committee recommanded priorities for the development and construction of fao111 ties during thd next doende and included two categories:
o Major new facilities, and o New Capabilities at existing facilities The comtritteo concluded that "both _ categories are essential for_t_h,o_
effootin evolut in the United Stat n ik *M tiexi,londecade of science and advanood and beyond."_ _ technologyis (The underlining that of the CromitteW a
in tnejr report).
- i. The Comrlt:.et f ound as follows for new capabilities at existing i facilitteM i
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"Rectnt developments make it both practical and cost effective "
! N to' adapt oortain existing user facilities to now purposos by
! > adding experimental .hsils. Instruments, and modified sources.
These addit ions provide an opportunity for new frontier notences they are not simply extensions of existing work.
"The Commir, toe's recommendations in order of priority for the addition of these new capabilities at existing user f acilities are "1. Centers for Cold Neutron Resenroh. Guide halls and
, instrumentation for explotting the only cold neutron sources in
/ ths U.S. located at the Brookhaven National Laboratory and at
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- the National Bureau of Standards should be developed in an p- , , orderly fashion.
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"There is no cold neutron guide hall in the United States, and such f acilities are urgently needed to address the rapid expansion.of neutron applications in materials science, chemistry, and biology. Many central. problems in these sciences can only be s solved using new instruments with cold neutron beams. These centers will enable U.S. scientists to be e competitive in cold neutron research during the next decade;
'and they will provide,new instrumentation concepts for developing future neutron scattering sources."'
In partial support of the committee's recommendation that their number one priority for the development of ne,w capabilities at existing facilities is the development .of Centers for cold -neutron research, they then take note of the development of neutron scattering facilities overseas. They note:
i "An important key to the European success,L especially at the
/ Institut Laue Langevin (ILL), has been' the development and use of cold neutron sources and associated guide halls to create instruments for ultra high-resolution and high-Sensitivity
, ,- spectroscopy. These currentlyi provide energy resolutions as much as five orders of magnitude better than those available in the United States; they also enable studies of small-angle and medium-resolution dif f raction and other new scientific applications. As already noted, there is only one cold neutron reactor source in the United States, at BNL, and another under development, at NBS.
"The United States has no guide halls to improve the versatility and flexibility of cold or thermal neutron instruments. In contrast, 60 percent of the neutron scattering instruments at the ILL (reference 7) are located in a large guide hall, and a new guide hall and cold source are to be completed over the next two years. Also, there are major efforts at ILL to develop and construct focusing monochromators, polarizing devices, reflecting supermirrors, environmental control systems, dedicated instruments for diffraction surveys using neutron cameras, and more. Besides the ILL program, there is a new reactor center, called Orphee.
at Saclay near Paris,. with two hydrogen cold sources, which will ultimately commission over twenty new instruments for neutron scattering and fundamental physics research. Expanded guide halls with many new instruments are also under construction at the KFA Research Reactor in Julich and at the Berlin reactor. Finally, the Japanese geirernment has approved funding for the complete modernization of the JAERI III Reactor at a cost of $150 million, including a replacement of the vessel, and upgraded fuel and beam tube arrangement, and installation of a large cold source and guide hall.
"The total current operating expenditures for neutron scattering at research reactors in Western Europe is about $80 million per year, in FY 83 dollars, including associated reactor operation costs, roughly triple the U.S. effort. An order of magnitude difference emerges when one compares capital investment for new spectrometer development and construction 2
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efforts. The consequences of this investment gap over the past decade'between European and U.S. research reactors are being felt increasingly in our inability to compete in many areas of new science involving such techniques as high-resolution
' neutron spectroscopy, small- and medium-angle diffraction, and
-diffuse scattering."
In their more fulsome conclusion that centers for cold neutron research is
-their number one priority for.the addition of new capabilities at existing facilities they state:
" Guide halls and instrumentation for exploiting the only cold neutron sources in the U.S., located at the Brookhaven National Laboratory and the National Bureau of Standards- (underlining added) facilities, should be developed in an orderly fashion.
"These facilities are urgently needed to address the rapid expansion of neutron applications in materials science, chemistry, and biology; many central problems in those fields can only be solved using new instruments with cold neutron beams. These centers will provide a diverse, flexible array of cold neutron instruments, matching current capabilities in other industrialized nations. Further, by using advanced techniques for beam focusing and polarization, such facilities would exceed existing worldwide capabilities, in areas such as
.high resolution spectroscopy of catalysts and polymer systems and in studies of impuritien and inhomogenettles in bulk materials.
"Research using cold neutron facilities has received inadequate support.in U.S. during the last decade, a period of major investments in cold neutron research in other countries. The Western European investment alone is at least ten times that of the United States. There are only two cold neutron reactor sources in the United States one at Brookhaven and one being developed at the National Bureau of Standards (underlining added). Guide halls, which improve the versatility and flexibility of cold or thermal neutron instruments, do not exist in the United States while there are six fully instrumented cold neutron guide halls either completed or under development in Western Europe. Implementing this priority will enable U.S. scientists to be competitive in cold neutron research during the next decade and will provide new instrumentation concepts for developing future neutron scattering facilities."
It is clear from the above that a prestigious committee (chaired by a past president of the National Academy of Sciences) at the request of the President's Office of Science and Technology Policy has determined that the development of Centers for Cold Neutron Research is a top priority of U.S. Science. Furthermore, they have pointed out that only NBS and BNL
. are currently in a position to implement their top priority, and strongly recommend that they do so.
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Because of the fact that the NBSR is.the only reactor.in the U.S. that can accommodate a cold source large enough to provide .enough cold neutron beams to permit the development of a complete set of advanced instruments in a large guide hall, NBS has been chosen as the first facility to implement the recommendations of the "Seitz Report." At the time of the original NBS request for an exemption, it was noted that the President's 1987 budget. presented to Congress included a request for funds to implement the recommendation of the "Seitz report". This funding has now been approved by Congress, and NBS is moving ahead rapidly to construct a large guide. hall (110' x 200') and a carefully selected set of instruments.
The recommendations of the Seitz-Eastman committee, the budget requests of OMB, and the final approval of Congress all demonstrate the National need to develop a center for cold neutron research at NBS. It is not in the national interest to degrade such a facility by the use of LEU fuel.
This response so far has only addressed the new capabilities at NBS, a subject only mentioned as a possibility in the original NBS submittal.
However, this new facility development will approximately double the reactor capability to contribute to the Nation's Scientific and technological needs, and so is worthy of the evaluation given it above.
Although a prestigous committee of the National Academy has not recently reviewed our existing programs and proclaimed them as vital to the National interest, NBS would not have been recommended. for the new center for cold neutron work, if its current programs were not already a national resource. As stated much more fully in the original NBS submittal, the current programs are'also very important to the Nation's technological foundation as demonstrated by the quality and relevance of the programs and the large number of. industrial and university scientists who participate in them. The national value of the current programs are demonstrated by the comments of the Secretary of Commerce whose major goal is to strengthe1. She U.S. cou:petitiveness in world trade. In a letter to Chairman Zech ne states:
"I am very concerned that any reduction in the capabilities of the reactor will seriously diminish its intended mission."
and "The research at the reactor serves a national need not only in scientific research, but to provide fundamental information on materials to assist United States industry in developing new materials and maintaining an internationally competitive position."
He concludes his letter with:
"Therefore, I strongly urge you to grant the NBS request for an.
exemption so that this important contribution to the Nation's economic and scientific health is not compromised."
-Thus, it has been well documented that the programs at the NBSR contribute significantly to the national interest and should not be diminished in any way.
-Question 2.
Provide a quantitive discussion which demonstrates that your reactor core is of special design and could not perform its intended function without using HEU fuel. ~ Include the bases for this determination.
Answer:
The NBSR was ' designed to give as high a thermal neutron flux (for its power) over as large a region as practical with a minimum of fast neutron and Y-ray background. This was achieved by using heavy water for both the coolant and reflector. The thermal neutron absorption cross section for D2 0 is more than 1000 times smaller than the H 2O cross section so that a high thermal flux is maintained far out into the reflector. In the NBSR, the thermal neutron flux in the reflector is still only reduced by a factor of two at 30 cm from the core. This is of particular value for the installation of a large cold source, the center of which must be some distance from the core.
The use of D 0 also allows the fuel elements to be spread out in the core.
2 This not only provides space within the core for irradiation facilities, but decreased the concentration of fast neutrons and Y-rays that originate in the fuel elements. As a result, the thermal to fast neutron ratio for such a D20 core is typically twice that of an H O core 2
of the typical MTR design. In the NBSR, however, the fast neutron and Y-radiation background in the beam tubes is further reduced by the use of the split core design.
This is a design, unique to the NBSR in which the core is split in the horizontal plane resulting in two closely coupled cores but separated vertically by 18 cm. The radial beam tubes "look" at this gap and consequently do not directly "see" the fast neutrons or Y-rays produced in the fuel. Thus, the core has been carefully designed to maximize thermal neutron intensity by minimizing any unnecessary absorbing material and to reduce fast neutron and Y-ray background to a minimum. An important element in achieving this optimization was the use of HEU fuel so the unproductive neutron absorption in U-238 would not decrease the available thermal neutron flux.
In addition to the basic design features incorporated to optimize thermal flux, the reactor is operated in such a way that the control rods (shim arms) control a minimum of reactivity. This is achieved by a systematic rotation of fuel elements that permits the reactor to operate on a four week fual cycle with the replacement of only four of thirty fuel elements each cycle. Every element is moved during each refueling in such a way that the loading in any one fuel position never changes by more than 10-15 g, and the four elements removed average close to 70% burnup. The small reactivity that must be controlled, means that the shim arms operate in the reflector region above the core resulting in a minimum of neutron absorbtion or flux perturbation in the central region of the core that serves the beam tubes.
And finally, the regulating rod which is located in the center of the cors remote from the beam tubes is designed of low absorbing material (aluminum) so that it is relatively large and controls as much by fast 5
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neutron leakage as by neutron absorbtion, further minimizing parasitic ebsorbtion.
Thus, a great deal of thought, expense (heavy water), and effort-has gone into building and operating the reactor in such a way as to get as many thermal neutrons per megawatt as possible for the many reactor facilities designed into the reactor and at the same time minimize the background.
Although even the most sophisticated calculations are limited in their ability to calculate beam tube currents and details of spectral distributions as a function of position in a heterogeneous core such as the NBSR, more limited two group, two dimensional calculations have been made that indicate the available thermal flux would drop about 7 to 10%
while the epithermal flux would rise a few percent resulting in a at least 10% decrease in the signal to noi.7e ratio. The computer codes used do not account for resonance absorbtion und similar higher energy phenomena, nor do they provide direct information on the intensity of the high energy neutrons that are most important in background considerations. If these could be taken into account, a greater reduction in the thermal flux would be demonstrated.
The 10% or more reduction in the signal to noise ratio is particularly severe on the most advanced, frontier type measurements. These measurements, typically, have very small signal to noise ratios, and the reduction in the signal combined with the increase in background would increase the difficulty of performing these experiments by 15 to 20%.
Furthermore, the change to LEU fuel would change the neutron spectrum in the reactor. This would adversely affect many of the standards type programs at the NBSR. Many staff-years have gone into characterizing the many reference standards facilities at the NBSR. If the NBSR were to switch to LEU fuel, many more staff-years would be required to recharacterize these facilities and the Nation would be without these valuable reference standards for at least one to two years.
Thus, the NBSR could not perform its intended function without the use of HEU fuel.
Question 3 Research projects which are based on neutron flux levels or spectra attainable only with HEU fuel can be considered as a basis for a unique purpose exemption. Identify and provide quantitative estimates, and the bases therefore, of the impact on each of the programs discussed in your September 19, 1986 submittal, that would result from the changes in neutron flux densities, fluences, neutron spectra, and background noise if LEU fuel were substituted for HEU fuel in your facility.
Answer:
The following is a listing of major programs that would be affected as a result of the conversion.
Hydrogen in Metals The NBS has the best capability in the world for studying the behavior of hydrogen in metals and alloys. Typically, these are very difficult 6
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measurements. because the signal is so lo'w with a signal to background ratio. of 1 or less. Under these conditions, the estimated 7% decrease in thermal neutron flux. and 35 increase in background would increase the
_ required time for each experiment by at least 15%. The instrument used for this'research is booked solid 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> a day, seven days a week so the time cannot be made up. Consequently, many important experiments must be postponed or lef t undone. The most important experiments, those that are -
pushing the frontiers of1 science are, of course, the most difficult.
otherwise they would have been done already. In these cases, the background is often three or more times larger than the signal resulting in very long running times. The use of LEU would extend the already long times by-18 to 20 percent. The difficulty 'is compounded by the need to maintain stable sample conditions (some samples deteriorate with time) and electronic stability over longer periods of time.
Catalysis The NBS program in this. area is the leading one in the United States. 'It involves . probing the motion of critical molecular species which are of ten present as only a small fraction of the catalyst material. Thus, again, the measurements involve very low signals and long running times similar to the Hydrogen in Metals program discussed above, and the use. of LEU would decrease the productivity of this industrially oriented program by 15 to 20 percent.
Electronic Materials This program provides fundamental information on electronic materials important to'U.S. technology as discussed in the previous NBS submittal.
Although the signal to noise ratio is not as big a problem in these measurements as some, they involve the collection of a great deal of data for a single measurement. Thus, the measurements are long and complicated. The instruments used for this work are fully utilized with considerable back log so the 7 to 10~ percent increase in experiment length causes an equivalent loss in productivity.
Biomolecular Structure The- NBS facility is only one of three in the world for the study of the structure of biomolecules. Because of the complex structure of the dif fraction pattern from these molecules and the thousands of reflections that must be measured, the highest possible spatial resolution and intensity is required. Even with the present intensities and background, each structure requires many weeks to complete. The use of LEU would increase this time by 10% on the average (7% decrease in flux and 3%
increase in background), making a very difficult measurement more difficult. Furthermore, some of the biological samples deteriorate with
~ time making the need for maximum intensities even.more urgent.
Ceramics The development of improved ceramic materials is one of the exciting new emerging technologies vital to our Nation's international competitiveness.
A variety of neutron scattering instruments at the NBSR are used in characterizing new ceramics, and measuring structural change and defect 7
t-formation as a result.of. materials processing. To remain internationally competitive'in.this vital technological field requires the highest
- possible neutron flux and low background. Again, some of the most critical experiments are marginal because of low signal-to-noise ratio.
The increased measurement time of 15 to 20 percent resulting from the use of LEU and the difficulties. resulting from even lower signal-to-noise ratios would mean that many marginal but important experiments would not be done.
Magnetic Materials The value. cf this. program to industry and defense was demonstrated in the previous NBS submission. Again the signal-to-noise ratio is a major concern for many of these experiments and _ the use of LEU would extend measurement times by 15 to 20 percent as discussed above. Furthermore, many new "in-situ" types of experiments involve time dependent phenomena, when the phenomena under study decay with time, making maximum available fluxes and minimum counting times essential.
Nuclear Methods of Chemical Analysis This program, as demonstrated in the earlier NBS submittal, is vital to the characterization of standard Reference Materials, and its neutron depth profiling f acility is the premier national facility. The previous submittal' addressed.in some detail the degradation of the program's effectiveness caused by the use of LEU. Briefly, the productivity of all parts of the program will be reduced by 7 to 10% because of the 7%
reduction in thermal flux and the 3% increase in background. But, of even greater concern is the change in the neutron spectrum that could result from the switch from HEU to LEU fuel. The problem is not that the experiments could not- be done almost equally well with _the new spectrum; it is the fact that the new spectrum must be characterized accurately that
. presents a problem. More than two staff-years would be required to recharacterize the in-core irradiation f acilities so that the accurate measurements done by this group can be maintained. During the change over to the LEU fuel which would take about one year, the spectrum would be constantly changing so a meaningful attempt at recharacterization could not be started in less than a year. Thus an important part of the standards capability would be adversely affected for a period of more than one year.
Polymers The demands of polymer research on neutron methods (particularly small angle neutron scattering) push these methods to the limit of their capabilities. Because many of these measurements have very low signal-to-noise ratios, they are adversely affected by the switch to LEU by 15 to 20 percent. Real-time measurements are just starting now. Because of the short time available for each measurement as the polymer chains relax, the easiest real-time measurements are marginal. The reduction in flux and signal-to-noise ratio resulting from the use of LEU would be sufficient to terminate this new effort.
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Neutron Fields and Dosimetry Standards The NBS maintains the national standards for radiation dosimetry and radiation measurement. Several reactor facilities are vital components of this standards program. The reactor facilities have been carefully characterized over a period of years. The change in the neutron spectrum resulting from the use of LEU, even if small, would require the extensive recharacterization of the facilities. Thus, the conversion to LEU would make this vital standards f acilities unavailable for 1 1/2 to 2 years while the transition to LEU and recharacterization was going on.
Fundamental Physics Fundamental physics measurements always require the best available conditions. The important signals are usually much less than background, and months of painstaking measurement are required. In the previous NBS submittal, an example of such a measurement was described. The decrease of flux and the signal-to-noise ratio caused by conversion to LEU would have increased the time required for that experiment by 20% and further buried the critical signal in the background. It is probable that this experiment would not have been attempted under LEU conditions.
Neutron Radiography Most aspects of the small neutron radiography program at the NBS would not be too severely affected by the 7 to 10 percent additional time required to expose a radiograph. However, one program involves the exposure of rare works of art. To minimize possible radiation damage to these objects, extensive steps have been taken to reduce fast neutron and Y-ray background. The museum paintings studied in this program are of particular concern. The conversion to LEU would increase the radiation damage to the paintings by 10 percent - a highly unattractive result.
Cold Neutron Research Congress has now authorized the construction of a $24,000,000 facility including a 110' x 200' guide hall and associated instruments (see answer to question 1). It is not practical to address the hundreds of experiments that will be done each year at this national user facility. It should be sufficient to point out that each of the 15 or more instruments installed in the guide hall will be the very latest state-of-the-art. The majority of the instruments will be unique in the United States. Clearly this facility is intended for frontier research that can't be done anywhere else in the United States. As pointed out throughout this answer to question number 3, it is this frontier research requiring the most difficult measurements, that suffers most from a reduction in signal-to-noise ratio. Therefore, the whole cold neutron research project, the number one priority of the Seitz-Eastman report and the only such facility in the United States, would suffer a productivity loss of 15-20% if the NBSR were required to convert to LEU. This is clearly not in the interest of the Nation which is trying to improve its competitive position relative to Europe and Japan which already have such facilities operating at their full potential.
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Summary Conversion of 'the NBSR to LEU. fuel, would reduce its thermal neutron flux about seven percent and increase fast flux by about three percent. This would reduce the productivity of the many programs at the NBSR from seven to twenty percent, including a fifteen to twenty porcent reduction in .the future productivity of the Nations only fully competitive cold neutron research facility. -Several standards related. facilities would be of limited value during a one to two year period while they were being recharacterized.
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