NEUTRON BEAM LABORATORY
The Neutron Beam Laboratory (NBL) is one of the experimental facilities at the RSEC. Well-collimated beams of neutrons, thermalized by a D 2 0, are passed into the NBL for use in various neutron beam techniques. When the reactor core is placed next to a D 2 O tank and graphite reflector assembly near the beam port locations, thermal neutron beams become available for neutron transmission and neutron radiography measurement from two of the seven existing beam ports. In steady state operation at 1 MW, the thermal neutron flux is 1x10 13 n/cm 2 sec at the edge of the core and 3x10 13 n/cm 2 sec at the central thimble. The Penn State Breazeale Reactor (PSBR) can also pulse with the peak flux for maximum pulse ~ 6x10 16 n/cm 2 sec with a pulse width of 15 msec at half maximum.
Current Status of PSBR Beam Ports:
The PSBR has seven beam ports. The locations of the beam ports within the biological shield and elevations of the beam ports with respect to the reactor pool floor are given in Figure 1 and Figure 2. The internal diameter of the beam ports are four inches for BP #3 and BP #5; five inches for BP #1 and BP #7; and six inches for BP #2, BP #4 and BP #6. The center of BP #4 is sixty five inches from the pool floor while BP #1, BP #3, BP #5 and BP #7 sixty inches and BP #2 and BP #6 are fifty four inches from the pool floor. With the current setup of reactor-core-moderator assembly only BP #4 is at the centerline of the TRIGA core. (Active length of TRIGA fuel is 15”). BP #1, 3, 5 and 7 are five inches below the centerline of the core and BP #2 and 6 are eleven inches below the centerline of the core. The core grid assembly does not permit lowering the core more than the current arrangement. When the PSBR reactor was built MTR type fuel elements with active length of 24” were used. With the MTR fuel the beam port arrangement did not limit the maximum neutron output. In the mid 60's the PSBR was converted from MTR type to TRIGA type fuel. With TRIGA fuel, only one beam port is at the centerline of the core active area, four beam ports are five inches below the centerline and two are eleven inches below the centerline (below the active fuel region). Because of these inherited limitations only two beam ports are currently being used. BP #4 with 3 x 10 7 n/cm 2 sec flux at the aperture is used for research, primarily neutron radiography and radioscopy, and BP #7 with ~ 10 5 n/cm 2 sec neutron flux is used for service activities involving neutron transmission measurements. Since the BP #4 collimators are primarily designed and optimized for neutron radiography and radioscopy measurements, it is not possible to obtain desired results for other measurements. We are currently trying to use BP #4 for all of our research projects. Due to space limitations, we must shuffle delicate research equipment around. More importantly, each project or experimental techniques require a special or dedicated neutron beam with different collimations and neutron flux. With the current set-up and arrangement we can only perform meaningful research for neutron radiography and radioscopy.
New Beam Ports and Beam Hall Expansion:
Due to inherited design issues with the current arrangement of beam ports and reactor core-moderator assembly, the development of innovative experimental facilities utilizing neutron beams is extremely limited. Therefore, a new core-moderator location in PSBR pool and beam port geometry needs to be determined in order to build useful neutron beam facilities. A study is underway with the support of DOE-INIE funds to examine the existing beam ports for neutron output and to investigate new core and moderator designs that would be accessible by new additional beam ports. The MCNP modeling of both cases is near completion. We envision a location in the pool where reactor core would be “parked” and surrounded by a moderator (D 2 O or graphite). New beam ports would be geometrically aligned with the core-moderator assembly for optimum neutron output.
The new core-moderator and beam port arrangement requires expansion of the existing beam laboratory in order to place instrumentation, neutron guides, and beam catcher, etc. Both the new design of core-moderator/beam port arrangement and the expansion of the current beam laboratory to form a beam hall are strongly related. The new beam hall will have a total of 4,000 sq ft of experimental area (the existing area of ~1,000 sq ft plus a new additional area of ~3,000 sq ft). Research areas envisioned for RSEC's new beam port/beam hall design are as follows. Neutron Depth Profiling facility for depth vs. concentration measurements, impurity determination of He-3 and B-10 in semiconductors, metal and alloys; Cold Neutron Source and Cold Neutron Prompt Gamma Activation Analysis for neutron focusing research, materials characterization and determination of impurities in historically or technologically important material; Neutron Powder Diffraction for structural determination of materials, and a Triple Axis Diffractometer to train students on neutron diffraction and perform preliminary structural determinations of materials.
Projects utilizing the NBL during the year included the following:
• Study of a loop heat pipe using neutron radiography (see Research and Service Utilization Section, page…..). Bettis Atomic Power Laboratory used the RSEC beginning in June 2000, to evaluate the operational characteristics of an ammonia loop heat pipe. This work resulted in several presented papers and a Ph D dissertation.
• Development of a single-disk neutron chopper for time-of -flight spectroscopy at Penn State (see Research and Service Utilization Section, page…..) This work resulted in several presented papers and a M. Sc. thesis.
• Neutron depth profiling studies at the Penn State University Breazeale Nuclear Reactor (NDP description and result of preliminary NDP measurement at RSEC is given below ).
• Analyzing soft error rates in semiconductor memories and field programmable gate errays (see Research and Service Utilization Section, page…..).
• Neutron radiography measurements for water transport in an operating polymer electrolyte fuel cell (see Research and Service Utilization Section, page…..).
• Continuous frame capture analysis software project at Radiation Science and Engineering Center (see Research and Service Utilization Section, page…..).
• Modelling of existing beam-port facility at Penn State University Breazeale Nuclear Reactor by using MCNP (see Research and Service Utilization Section, page…..).
• Investigation of preferential flow of water in sand samples using real time neutron radiography. Collaborative work with Cornell University , Ward Center for Nuclear Sciences.
• Testing of
· Neutron transmission measurements and neutron radioscopy were conducted for borated metals and other borated materials for Northeast Technology Corporation, Eagle-Picher Industries, Transnuclear , NY , and Transnucleaire , France .
· Radiographic and radioscopic techniques were demonstrated as part of several student projects; including demonstration of neutron and x-ray imaging for the Governor's School students and students enrolled in the freshman seminar (NucE 001S). The students assembled plaques containing a variety of objects and predicted their neutron & x-ray attenuation characteristics. Experiments with neutron & x-ray radiography confirmed their predictions.
Figure 1. PSU Breazeale Nuclear Reactor Beam Port Layout with D 2 O tank.
Figure 2. Elevations of the PSBR beam ports with respect to the reactor pool floor.
