Chernobyl Unit 2, November 2016 (Part I)

Please select any photo in the gallery for a larger version and descriptive caption.

This photo gallery documents the main circulation pumps and the repair/transport corridor in Unit 2 at the Chernobyl Nuclear Power Plant as they appeared in mid-November 2016.  Unit 2 operated until a fire damaged the No. 4 generator and the unit’s feedwater machinery in October of 1991, after which the unit was permanently shut down.  It is an example of the earliest variant of the RBMK plant design, following the model of the Leningrad units.  The main circulation pumps in these earlier units are aligned on an axis perpendicular to the turbines and on the +1.0m elevation, whereas in the later generation of RBMK units (e.g. ChNPP Units 3-4), the pump engines are on the +12.5m elevation and aligned parallel with the turbines so that twinned units could share the same MCP engine halls and associated cranes.  The earlier-generation units are smaller than the later generation, mainly because they lack a steam-condensing “accident localization system” beneath the reactor.

Room 114/3, the eastern main circulation pump engine room for Unit 2 at the Chernobyl Nuclear Power Plant, viewed from the +12.4m balcony at the north end of the room. Each pump motor is rated at 5.6 MWe, supplying 4.3 MW of shaft power under typical load to the pump impeller beneath the floor. Three of the four pumps are running in normal operation, and one is in standby. Also visible are the overhead service crane at the far end of the room, and the valve stems for the suction and discharge control valves on each pump. Green pipes on the wall at right carry cooling water for the pump bearings and seals.

Room 114/4, the western main circulation pump engine room in Unit 2 at the Chernobyl Nuclear Power Plant. View is to the south, showing all four MCP motors and the overhead crane for servicing them. The reactor vault is to the left. On the floor to the left of the pumps are the throttle valve controls for the main circulation circuit attached to the discharge side of each pump. In normal operation, three of the four pumps would be running and one would be on standby.

Closeup of the southernmost main circulation pump motors in Room 114/4, Unit 2, Chernobyl Nuclear Power Plant. Bearing cooling water and lubricating fluid lines to the pump can be seen.

A visitor stands next to one of the giant 6-kV main circulation pump motors in Unit 2 at Chernobyl Nuclear Power Plant, Room 114/4. Each pump motor produces about 4.3 MW shaft power under normal operating conditions.

Coolant water sampling station in Room 114/4, Chernobyl Unit 2.

Stairway in the Unit 2 reactor building at Chernobyl, lying directly beneath the steam separator compartment.

View eastward down the railroad tracks that pass beneath Units 1 and 2 at the Chernobyl plant. This repair and transportation corridor is used to move heavy equipment in and out of the plant. Above the corridor are massive panels that can be removed to facilitate the use of cranes to hoist equipment. The red door at left leads into a main circulation pump room. A radiation monitor can also be seen on the wall at left.

A Ukrainian National Guardsman stands next to the open doors of the Units 1-2 repair and transport corridor, used for moving heavy equipment in and out of the reactor buildings. View down from the +10m “gold corridor” in the deaerator building.

Locations shown in the photo gallery may be identified on the following plan of the +1m elevation in the Unit 2 reactor building, taken from plant safety documentation:

+1m elevation in Block “B” (Unit 2 reactor building), Chernobyl Nuclear Power Plant.

New life for Silkwood plant

Plutonium vault in the former Kerr-McGee Cimarron Fuel Fabrication Plant. Some 50 lb. of plutonium went unaccounted for at the Cimarron plant during the Silkwood years due to sloppy handling and accounting uncertainties.

Stigma has a long half-life.  42 years ago, a young woman named Karen Silkwood was found dead in her wrecked car on the side of Oklahoma State Highway 74.  She had been a laboratory worker at the nearby Kerr-McGee Cimarron Fuel Fabrication Plant as well as an OCAW union officer, and at the time of her death she was on a journey south to Oklahoma City, purportedly carrying evidence of unsafe work conditions and nuclear material diversion to a meeting with union representatives and the press.  After Silkwood’s death, the alleged smoking-gun documents were nowhere to be found.  Conspiracy theories blossomed in the absence of conclusive understanding into the circumstances of her death.  The idea that Kerr-McGee management had her “bumped off” gained a major following, despite no evidence underpinning this suggestion and a competing toxicology finding of methaqualone in Karen’s blood.  Two years later, in 1976, the Cimarron plant shut down in ignominy.

In 1983, Meryl Streep played Karen Silkwood to critical acclaim in a major motion picture that served to cement the murder theory in the popular imagination.  While the basic plausibility of the alleged murder conspiracy fades with each passing year, it endures as fact in the folk wisdom of numerous anti-corporate and anti-nuclear advocates.  As for the Kerr-McGee plutonium fuel plant, it too endures; and after decades of vacancy, is poised to rise from the ashes of its scandal-ridden nuclear past as a manufacturing facility for aircraft parts.  This is particularly remarkable, as very few former nuclear facilities survive cleanup intact, and few structures survive decades of neglect to the elements.  (Some of the surrounding lands, however, remain under NRC license and are still being remediated for contaminants.)  I visited the site in the fall of 2016, and would like to thank Jeff Lux, project manager and engineer, for his generosity and willingness to take me around this landmark in the cultural history of nuclear technology in the USA.

Facade of the Kerr-McGee Cimarron plutonium fuel fabrication facility of Karen Silkwood fame, seen in the fall of 2016. The structure has been gutted, meticulously cleaned, sold for $6000 at auction, and is now being outfitted for manufacturing avionics.

Front office of the former Kerr-McGee plutonium fuel fabrication facility in Oklahoma. The building is being reused by an aviation company.

This vast open room in the southeastern quadrant of the plutonium plant was once a warren of analytical laboratories, and the workplace of Karen Silkwood within the Kerr-McGee plutonium fuel fabrication facility. The room is being outfitted now as a machine shop by the new owner.

Finished fuel storage room and shipping/receiving bay. Some original signage from the operating days remains on the wall. Also on the wall are grid lines used for conducting contamination surveys.

A sign still on the wall from the operational days of the Kerr-McGee plutonium fuel plant, when finished fuel elements were stored in this room.

This wall shows grid markings and radiation survey measurements (presumably in units of disintegrations per minute per 100 sq. cm.).

Fuel element fabrication area. Notice grid lines on the walls for radioactive contamination surveys.

Pu fuel pellet fabrication area, showing sand-blasted and removed non-structural walls from plutonium cleanup efforts.

Looking north across the Cimarron River floodplain, dotted with groundwater sampling wells behind the Pu facility.

The most contaminated water on the former Kerr-McGee site is found in this area toward the northeast. We can see a lot of sampling well head covers in this photo looking north toward the Cimarron River.

Fire-suppression reservoir that was part of the original plant works. The fishing is said to be great here, but the NRC won’t allow it.

Corner marker for an underground radioactive waste disposal area on the former Kerr-McGee plant property.

The Kerr-McGee Cimarron Fuel Fabrication Facility plutonium plant seen from the east in 2016. The companion uranium facility was to the left, but no longer stands on the site.

Sampling wells with color-coded caps that denote their depth. These wells lie near a solid radioactive waste burial area on site.

Manhattan Project National Historical Park, Part I: B Reactor

B Reactor from the east, looking towards the reactor discharge face and the irradiated fuel pool and loading dock.

The charge face of B Reactor, the centerpiece of public tours.

In November 2015, the US National Park Service and Department of Energy came to an agreement outlining a new national park, one that would focus on the history of the American effort in World War II to develop nuclear energy for warfare (the “Manhattan Project”).  B Reactor at Hanford is already open with scheduled tours managed under this arrangement.  It was the world’s first plutonium production reactor, designed and built under truly remarkable wartime circumstances, and it operated from 1943 to 1968.

By special arrangement with Colleen French, the DOE’s park coordinator at B Reactor, I was able to visit the reactor at my own pace with a small group of nuclear enthusiasts in March.  Geiger counters, scintillators, and gamma spectrometers also came along, although there was some official resistance to their presence.  And this brings me to the two questions I hoped to answer in visiting this place: firstly, how are the NPS and DOE handling the interpretive challenges inherent in opening a radiation facility to the general public of all ages; and secondly, will hardcore “nukeheads” like me find a sufficiently authentic and engaging experience given the constraints imposed by preparing the site for the public.  My experience at B Reactor was heartening.  The reactor remains an interesting radiation environment (see photo galleries below), and its staff have made rational choices in seeking balance between public safety and respect for the authentic realities of the place.  For nerds with the right instrumentation, the radiation signatures in various parts of the building tell little stories about what happened there.  Reactor equipment has been lovingly left intact throughout–down to the decommissioning tags from 1968.

The radiation signatures at B Reactor were thrilling to me, like little ghosts of the past jumping out to whisper their secrets, but of course, radiation is sometimes feared and loathed.  I empathize with administrators who worry that the crackle of a Geiger counter might repulse or anger some visitors.  My own view is that all kinds of genuine reactions, ranging from enthusiasm to fear, are valid, and all should be tolerated.  Scientifically-informed judgement should guide how safety is established at such sites, but it is still possible to be welcoming and accommodating toward visitors expressing a broad spectrum of reactions, including both the occasional phobia and the occasional super-demanding “nukehead” (e.g., me).  The sites in the nascent Manhattan Project National Historical Park belong to all of us–the enthusiastic and the timid, the plant operators and the “downwinders,” the bombers and the bombed.  Uniting us all is interest in the history, and I am encouraged by the respect for history I witnessed at B Reactor this year.  Best wishes to the other Manhattan Project park sites as they open doors to the public.

Now what you probably came here for: captioned photo galleries!

Reactor operating position and safety systems

B Reactor offers a window into the minds of reactor designers who had never before worked at the power scale envisioned for plutonium production, but who still thought of a surprisingly comprehensive suite of instrumentation, controls, and safety systems, many of which have analogous descendants in modern reactors.  Notable are multiple ranges of power measurement instruments, flux profiling and distribution control in the core, gravity-dropped safety rods, a backup gravity-operated shutdown system in case the core sustained mechanical damage, emergency core cooling tanks in case of a water delivery failure, electrical and hydraulic redundancy in the horizontal control rod system, seismometer SCRAM in case of earthquake or war; and individual fuel channel pressure measurements.

Control console at B Reactor.

Control rod adjustments on the B Reactor console. Rods 2, 4, 5, 6, 7, 8, and 9 were hydraulically operated and referred to as “shim” rods. They were adjusted infrequently, using the shim pumps as sources of hydraulic power. “A” rod and “B” rod were electrically controlled and used for fine power adjustment.

Vertical safety rod (VSR) motor switches at the B Reactor console. The horizontal control rods (HCRs) were just that: control rods, whereas the VSRs were intended to provide shutdown automatically in a power outage, aided by gravity.

Ball-drop scram at B Reactor. Activating this switch would send millions of pea-sized boron carbide balls pouring into the reactor from above. The system was designed to provide safety even if thermal-mechanical damage to the core prevented the vertical safety rods from entering to effect shutdown.

Process tube pressure measurement station in the B Reactor control room. Each process tube passing through the reactor core was linked to this station with a thin pipe, and operators could valve each of them independently onto the large gauges visible here.

Triply-redundant seismometers in B Reactor would trip the reactor in case of earthquakes (or bombings).

Horizontal control rods

Horizontal control rods were used to regulate the reactor power and adjust the flux distribution in the core.  Some of the rods were hydraulically driven, others electrically driven.  The “inner rod room” lies directly above the control room and is still quite radioactive and off limits (even to me).  This is where withdrawn rods would actually reside after exiting the core.  Their drive mechanisms are on the other side of a heavily-shielded wall, the “outer rod room” (shown in most of these photos).  Radiation is detectable in the outer rod room, and particularly in a floor drain under it.  The radiation here mostly comes from cobalt-60, a product of neutron activation of steel.

Entrance to the Rod Room housing horizontal control rods (HCRs) at B Reactor. The original signage is charming, instructing employees to, please, not pull out control rods without permission. Accidentally starting the reactor was understood to be a bad thing, even back then!

Drive mechanisms for the nine horizontal control rods (HCRs) at B Reactor. Seven were hydraulically driven and two were electrically driven to provide precision adjustment. The bottom and middle trestles shown here contain only hydraulic rods. The two electric ones are on the top trestle.

The holiest-of-holies, the Inner Rod Room at B Reactor, is through the door and the concrete maze shown here. It’s still quite radioactive, as one would expect of a place where things were inserted into and removed from a nuclear reactor core on a regular basis. The black contraption on the wall in the center of the photo is a periscope used to observe the Inner Rod Room during operation. At left are hydraulic drives for the horizontal control rods.

View from the Rod Room out onto the trestle, north toward the Columbia River in the distance. The trestle was used to aid in handling the very long horizontal control rods.

B Reactor’s designers had a simple solution for maintaining hydraulic pressure to the horizontal control rod drives in a loss of power situation: pressurize the hydraulics with giant pistons full of river gravel. Who said nuclear technology had to be complicated?

I hold the scintillation spectrometer next to a large “U” trap in plumbing under the Rod Room at B Reactor. Even in this photo, one may observe the twin peaks of the Co-60 spectrum.

The drain contains only Co-60 according to its gamma spectrum. This is most frequently produced by neutron activation of steel. Its presence in a drain trap suggests that it was mobilized by condensation, washing, or some other process involving water.

Reactor discharge face

Irradiated nuclear fuel slugs would be pushed out the back of B Reactor into a water-filled trough.  This is a truly exciting part of B Reactor, since the radiation levels are bordering on high even today.  The gamma spectra reveal the activation nuclide europium-152, which we know accumulated in the cooling water system (see below) but could also be formed in the pile graphite and shielding concrete; and long-lived fission product cesium-137.  The Cs-137 was formed in fuel and subsequently escaped through ruptures and leaks in the fuel cladding.

The dirty backside of B Reactor, off-limits to public visitors, is shown here. This is where irradiated fuel slugs would be discharged from the core by pushing them out the backs of the process tubes. They would fall into a water trough below and await collection by crews in the irradiated fuel basin. Occasionally, fuel slugs would get caught in the plumbing instead of falling like they were supposed to. One solution to this problem was to dislodge them with a high-pressure water jet. Occasionally, human beings had to run in carrying makeshift tools and manually help the errant slugs find their way down. Today, the discharge face remains deliciously radioactive with contributions from activation nuclide Eu-152 and fission product nuclide Cs-137.

At the discharge face of B Reactor, the dominant gamma radiations come from fission product Cs-137 (released from damaged fuel slugs) and activation product Eu-152 (produced in high yield from neutron capture in natural europium, which could be in the water pipes, the shielding concrete, or the graphite in the pile).

“Hot tool” storage at B Reactor. This room is located just outside the concrete maze leading to the reactor discharge face, and it is where various rudimentary sticks and hooks were kept for those occasions requiring someone to run behind the reactor and knock loose a wayward spent fuel slug!

A remote-controlled robot was designed to handle stuck fuel slugs at the discharge face, eliminating the need for human beings and high-pressure water hoses.

Irradiated fuel storage pool

After being irradiated, short-lived radioactivity in the fuel was allowed to decay for several months before chemical processing to recover the plutonium was undertaken (typically, unless one was doing a “green run,” in which case you would process it right away).  In common with the reactor discharge face area, radiation levels in the fuel storage pool at B Reactor remain a little too high for public access.  However, the wooden decking over the pool can be viewed through a window.  The cause for the high residual radioactivity is none other than our old friend, cesium-137, which escaped from damaged fuel.

The storage basin contents were not limited to irradiated uranium for plutonium production. As the board here shows, sometimes other material, such as thoria (Row 26), were irradiated at B Reactor.

Jake Hecla smiles as his scintillator roars. This door leads into the garage where rail cars were loaded with irradiated fuel from B Reactor. And it’s hot, still sizzling with Cs-137 from damaged fuel slugs.

Irradiated fuel basin at B Reactor. The wooden floors cover the pool, which is about three meters deep and holds buckets of irradiated fuel shielded by water. This area is quite radioactive still, and off-limits to the public.

Only one peak in this spectrum: Cs-137 from damaged fuel slugs.

Above and below the reactor

At the “pile top” we find the gravity-aided vertical safety rod (VSR) mechanisms, as well as hoppers full of boron carbide balls–a last-ditch shutdown feature in case the VSR guide tubes warped from thermal-mechanical damage in the core.  Below the reactor is a small basement (the “Beckman room”) where reactor flux measuring instruments were located.  Today, the basement contains an impressive stash of radioactive tools and fuel handling equipment, probably left in position from shutdown in 1968.

Top of the pile at B Reactor, with discharge side to the right. Winches high above control the vertical safety rods (VSRs), now fully inserted into the pile. Around each VSR penetration are hoppers filled with boron carbide balls as a last resort for shutting down the reactor.

Hoppers full of pea-sized boron carbide balls surround each VSR penetration. A switch in the control room would drop these balls into the reactor core in the event of trouble getting the VSRs to fall.

This neutron-sensitive ion chamber at the top of B Reactor is among the earliest reactor instrumentation still surviving. Its converter material is probably natural boron. It is moderated with several inches of beeswax!

A platform on B Reactor’s south side accesses a number of ports used for experimental irradiations.

The “Beckman Room” in the basement of B Reactor. This is where ion chambers were inserted against the graphite pile to measure neutron flux (equivalently, reactor power level). The weak current signals were read by Beckman electrometers and relayed to the control room.

Radioactive tools in the basement of B Reactor, probably in the same place they were left in when the reactor shut down in 1968. On the shelves at right are some cooling water nozzles for fuel channels. Hanging above is a Frisbee, probably used as an ad-hoc tray for small parts!

Cooling water systems

B Reactor employed a once-through cooling circuit: water was drawn from the Columbia River, treated, pumped through the reactor’s process tubes, allowed to “cool down,” both thermally and radiologically, in an outdoor basin, and then discharged back into the river.  The discharge water sampling station in B Reactor allowed chemists to monitor their effluent, alerting them to damaged fuel or water treatment problems.  Today, the sampling station remains a bit radioactive, with the rare-earth activation nuclide europium-152 being wholly responsible for the measured gamma radiation there.

“Valve pit” where treated cooling water from the Columbia River enters B Reactor. The flanges in the pipes are disassembled as part of an arms-control agreement with Russia, illustrating the reactor’s decommissioned and inoperable status.

Discharge water piping from B Reactor is hidden in a shielded duct. During operation, this water would become neutron activated passing through the core. Although most activation nuclides are short-lived, some long-lived ones like Eu-152 remain to this day.

Taylor Wilson operates the scintillation spectrometer next to water sampling equipment at B Reactor. We found a lot of Eu-152 in this area.

Deactivation tags from 1968–B Reactor’s end of service–are still intact in the water sampling room.

Gamma energy spectrum of the water sampling station, showing the many energies emitted by activation product Eu-152.

Reactor grounds

The back yard of B Reactor has some interesting stuff, like pallets full of channelized reactor graphite and drums full of unused boron carbide shutdown balls.  Several railroad cars used to transport irradiated fuel are now permanently displayed on the grounds, and these are sizzlin’, producing peak gamma exposure readings in excess of 5 mR/h, all due to residual Cs-137.

The south side of B Reactor, seen from near where one of the emergency cooling water towers once stood.

The north face of B Reactor seen by most visitors. The large trestle at left allows exchange of control rod components from the rod room just in front of it. At right is the charge side of the reactor, at left is the discharge side.

Spare reactor graphite sits abandoned on pallets behind B Reactor at Hanford.

Drums of pea-sized boron carbide balls used as an emergency reactor shutdown measure at B Reactor and the other Hanford plutonium production reactors. These drums are currently outside B Reactor, presumably awaiting disposal.

Rail cars used to transport irradiated nuclear fuel slugs from B Reactor under water. Their destination: the “canyons,” where plutonium would be extracted.

A survey meter with an energy-compensated Geiger probe measures about 6 mR/h next to a rail car at B Reactor once used to transport irradiated nuclear fuel. The radiation comes from residues of Cs-137 leaked from the fuel.

2015 Photos from Chernobyl

I have been extremely slothful in attending to my blog, and if anyone still reads it, I apologize and thank you for your patience!  I’m attempting to catch up for the last few years in my spare time, posting the content and photos I’ve intended to publish more punctually but somehow haven’t found the time to do yet.  The following images were taken at Chernobyl Nuclear Power Plant in September of 2015 (with a couple from 2013, another trip I somehow managed not to document on my blog).  Amazing progress has been made on the New Safe Confinement.

Condition of the Unit 4 control room at Chernobyl in late 2015. A Desk (reactor control point) where I am standing; P Desk (balance of plant) in the middle; and T Desk (turbogenerator controls) at the far side of the photo.

My hand points to the location of the AZ-5 shutdown switch on the A Desk in Unit 4 control room. On April 26, 1986, this position was occupied by an operator named Leonid Toptunov. The operation of the AZ-5 switch following a turbine test set in motion the reactor’s destruction.

Reactor core cartogram in the Unit 4 control room. Numerous lamp covers are missing now, probably taken as souvenirs by visitors and workers over the years.

Power indicator for the No. 8 turbogenerator in Unit 4 control room at Chernobyl. This turbogenerator was being “run down” on the night of the accident, as engineers were testing the ability of plant equipment to continue operating from this inertial energy source. The test itself was successful, but the attempt to shut down the reactor afterward led to disaster.

Control rod servo-indicator in the Unit 4 control room at Chernobyl. This is the rod indicator for Channel 40-37, reading in 0-8 meters insertion depth. This control rod, like most, descended from above the core. (A small fraction were inserted from below.) The reading is meaningless now, the servo-indicator having been decoupled from the drive mechanism in the reactor hall. However, on the night of the accident, it probably last read between 1 and 2 meters insertion when the explosion happened. The further entry of the rods was blocked by thermal-mechanical damage as the core overheated.

The hottest spot we found in the Unit 4 control room at Chernobyl was on the south wall of the Deaerator Building behind the panels, where we measured about 30 mR/hr (35000 CPM) from gamma radiation with an energy-compensated Geiger probe. The red marker pinpoints our location on north-south axis 51 (near the west end of the old control room).

My group on the +10m stairwell landing at the west end of the Deaerator Building, preparing to enter the Unit 4 control room.

The south Main Circulation Pump engine hall in Reactor 3 at Chernobyl. A replacement bearing assembly is in the foreground.

This Ludlum 26 Geiger counter is reading its maximum value from loose contamination on a valve housing in the Units 3-4 ventilation building. Significant particulate contamination is present throughout even nominally “clean” areas in the power station today.

The Unit 2 control room at Chernobyl. This reactor also met its end in an accident; a generator fire in October 1991 destroyed TG-4 and caused damage to all main and backup feedwater pumps. The reactor was shut down and cooled with the aid of fire pumps, and it has been offline ever since.

Corridor 418 at axis “I”, looking north toward the Khodemchuk memorial. The concrete wall on the left here blocks a small entrance into the destroyed Unit 4 reactor building.

State of the New Safe Confinement at Chernobyl in September of 2015. The massive arch will slide over Units 3 and 4 at the power plant, seen in the background.

September 2015 view of the east side of the New Safe Confinement arch.

Dump truck on the New Safe Confinement construction site.

Workers underneath the vast arch of the New Safe Confinement at Chernobyl look toward the power plant. The striped ventilation chimney over Units 3 and 4 is not the original, but a much smaller temporary replacement. The remains of the original are being stored in the turbine hall.

An engineer explains the hydraulic traction system that will lift and move the New Safe Confinement arch structure into place over Units 3-4 at the Chernobyl Nuclear Power Plant.

Fire Station No. 2 at the Chernobyl Nuclear Power Plant, 2015. This fire station’s crew was first on the scene of the 1986 accident–and many of the firemen died. The station remains staffed and in service, although the hose tower is too contaminated for use and the apron in front of the garage has been repaved to cover contaminated surfaces.

A Ukrainian fireman and an American fireman stand beside a Soviet-era fire truck remaining in service at Fire Station No. 2, Chernobyl Nuclear Power Plant.

Main Circulation Pump engine hall in Unit 5, Chernobyl. The pumps were never installed, and gaping holes remain in the floor where they were to be placed.

A fortuitous late-afternoon beam of sunlight illuminates the dark interior of the Reactor 5 Central Hall, Chernobyl Nuclear Power Plant. Units 5 and 6 were close to completion at the time of the Unit 4 accident in 1986, but were scrapped afterward. The abandoned structure is dark and very dangerous inside.

Herb Anderson’s “Live Block” of the Chicago Pile

 

They don’t give out spent nuclear fuel as a memento anymore.  But on the tenth anniversary of the first nuclear reactor (the Chicago Pile) going critical, pile physicist Herbert L. Anderson was presented with this handsome “live block” of graphite and uranium metal fuel, piping hot and right out of the reactor core.  With an estimated two millicuries of Cs-137 then distinguishing it from the natural uranium whence it was made, the unique artifact spent the next sixty years as part of Anderson’s home decor, a reminder of his pivotal role in one of the 20th century’s greatest triumphs in physics.  Herb’s wife Betsy kindly gave it to me in 2014 with the hope that new understanding and appreciation would follow.

Now, having had nearly two years to get to know this artifact, I can share some preliminary findings about it–and a few lingering questions as well.  I am grateful for ongoing partnerships with the University of Missouri and the Vinca Institute of Nuclear Sciences that are bringing new details to light about its metallurgy and history, and I am grateful for past assistance from the University of New Mexico here in Albuquerque.  I am actively searching for ways to bring this piece of the first reactor to an appreciative public audience.  So, dear reader, if you have suggestions or information that will help with either the technical understanding of the artifact, or its accommodation in a museum for the upcoming 75th anniversary of the Manhattan Project, please get in touch.

Part I: Basic physical description

This is a “live block” (meaning a piece of graphite with nuclear fuel installed in it), distinguished from the “dead blocks” of pure graphite that were interspersed or used as reflectors in the Chicago Pile.  Several museums possess “dead blocks”; to my knowledge, these include the American Museum of Science and Energy (Oak Ridge), the Bradbury Science Museum (Los Alamos), the National Atomic Testing Museum (Las Vegas), and the National Museum of Nuclear Science and History (Albuquerque).  My friend Kelly Michaels has an excellent photo set of these artifacts.  Pieces of Chicago Pile fuel also survive independently;  most notably, this piece once belonging to Alvin Weinberg.  However, the Herb Anderson “live block” is unique, to my knowledge, in that it contains fuel and moderator together.  The block’s measured dimensions, including fuel dimensions and those of the decorative housing, are available in a SolidWorks model to interested parties (please contact me).

The “T01” lot stamp appearing on the right face of the graphite block indicates that the graphite is AGOT made by the National Carbon Company, one of at least six types of graphite used to build the Pile.  AGOT had the lowest neutron absorption of all of these types, so was preferred for the pile’s core region.  About 2/3 of the CP-1 pile consisted of AGOT.  This grade of nuclear graphite went on to be used in the Graphite Reactor at Oak Ridge and the plutonium production reactors at Hanford.

The fuel is unclad uranium metal in cylindrical elements that bear identifying stamp marks on the front faces.  When I replaced the original cracked acrylic housing around the artifact, I was able to weigh the fuel elements directly.  The left element weighed 2.564 kg, and the right one, 2.553 kg.  The left element stamp reads “M230/L101/P2” while the right one reads “M170/L79/P1”.  The significance of these marks remains unknown to me.  I believe that if someone is able to assist in their interpretation, we might learn which of the three recorded contributing manufacturers of U metal produced this fuel.  It should be noted that metal fuel was a small minority of the Chicago Pile fuel, amounting to just 5.4 metric tons; the vast majority of the fuel was pressed-oxide “pseudosphere” elements.  Metal was made variously by Westinghouse, Metal Hydrides Corp., or the Ames Process.

Another question raised by this artifact is that it contains cylindrical metal fuel placed into chamfered recesses in the graphite designed for receiving “pseudosphere” oxide fuel.  As such, the cylinders cannot remain centered or upright in the recesses without the assistance of some acrylic supports that may be seen in the x-ray image.  I am quite sure that acrylic was not part of the original pile construction!  One is tempted to question, then, whether this fuel-and-stringer combination is original.  It could be that most graphite live blocks were machined for pseudosphere fuel, but when metal became available, the pseudosphere live blocks were used anyway (perhaps with graphite inserts serving the mechanical function of the acrylic supports, which begs the question of why the artifact contains acrylic instead; or perhaps without any supports, the fuel cylinders simply being dropped awkwardly into the recesses).  A lack of detailed photos from the construction of CP-1 makes the question hard to answer.

Part II: Gamma spectrometric estimate of fuel burnup

Mentioned earlier is the fact that this fuel contains cesium-137.  In fact, the external radiation signatures are dominated by this long-lived fission product.  Without a doubt, then, the fuel has been significantly exposed to reactor operation.  By comparing count rates in the Pa-234m gamma peaks to that in the Cs-137 peak at 662 keV, we can determine the quantity of Cs-137 remaining in the fuel under the assumption that the Pa-234m is in equilibrium with its U-238 parent.  This will motivate the estimation of fuel burnup range under various assumptions about the artifact’s history.  I performed the requisite experiments with my PGT germanium detector and obtained the spectrum shown above, leading to an estimated activity of 540 microcuries of Cs-137 distributed throughout the total fuel at the time of measurement.  Here are a few historical scenarios and the fuel burnup roughly corresponding to them:

• The fuel operates in CP-1 only (December 1942-February 1943):  163 kWd/MTU
• The fuel operates in CP-1 and its reconstruction in the Red Gate Woods (CP-2), and is removed from the operating reactor before being presented to Herb Anderson in November 1952 at the Tenth Anniversary celebration in Chicago: 132 kWd/MTU
• The fuel was removed from the pile (CP-2) when it was decommissioned in 1954, and somehow was then integrated into the artifact: 127 kWd/MTU

There are challenges with all three potential histories.  The first is very unrealistic, given the known operating conditions of CP-1 in the brief months it was in use.  Intermittently critical, with a peak power of ~200 W achieved on one day only, the burnup in the fuel attested by these calculations is many thousands of times greater than what is possible according to the conventional history of that Pile.  The second scenario is supported by both the burnup calculation (even though I am aware of no formal operating records from CP-2) and the description given by Mrs. Anderson of how Herb got the item, but it leads to two big puzzles, firstly concerning how the fuel was removed from the reactor while the reactor was still in service, as the pile was not designed to be easily disassembled in the CP-2 instantiation; and secondly concerning the high activity levels of the discharged fuel when it must have been released from government custody to Anderson.  The third explanation avoids the issue of taking apart the reactor just to obtain a souvenir as the reactor was disassembled during decommissioning; however, it is historically inconsistent with the story told by Mrs. Anderson.  So what this gamma spectrometry measurement allows us to say with certainty is that the fuel was used in CP-2 (as well as the original pile, presumably).  Beyond that, plenty of thought-provoking questions remain.

Part III: Neutron multiplication properties

It would seem there is no greater aspiration for a piece of the world’s first nuclear reactor than to return, momentarily, to the task originally undertaken with so much fanfare: multiplying neutrons in fission chain reactions.  These three photos above show some multichannel-scaling apparatus to look at fission in the CP-1 block (set up in my kitchen, because this is a “cooking” project of sorts).  We are going to examine the time correlation between neutron counts in a bank of two He-3 proportional counters next to our specimen.  Both counter tubes and the specimen are reflected by polyethylene blocks to trap neutrons in the system as best we can.  Highly-correlated counts point to fission “chains”, in which a fission event causatively leads to successive ones on a time scale controlled by the neutron transport properties of the specimen and surroundings.  I’ll measure correlation by way of excess variance, or the Feynman Y-statistic: the difference between the measured variance-to-mean ratio of counts accumulated in a certain time window interval and unity (which corresponds to idealized, uncorrelated, Poisson-distributed counts).  We’ll look at the CP-1 live block by itself and with a small additional neutron source present.  We will also look at the neutron source alone, a lead brick, and the empty polyethylene cavity.  Results and commentary below.

So what the fuck does this mean?  Firstly, the CP-1 block by itself produces strongly time-correlated neutrons (purple data) on a measurement scale of about a millisecond or greater, while the little homemade AmBe neutron source is pretty much stochastic (red data).  (Note, though, that the AmBe source is about five times stronger a neutron source than the block.)  Putting the block in with the AmBe source slightly reduces the neutron count (~12%) versus the source alone, but produces excess correlation of nearly 30% of the block by itself, indicating the presence of induced fission.  The high correlation in the block itself may be attributed to spontaneous fission (SF) as a minor decay mode of U-238, as well as a smaller contribution of spallation and fission induced by secondary cosmic rays.  These neutron sources each produce a burst of neutrons, and are also closely coupled to successive induced fissions.  The AmBe source, by contrast, is driven by radioactive decay: alpha particles slam into beryllium.  Notice the curvature of the data in all cases: it rises as we lengthen the counting window.  That is to say, there is more neutron correlation as the window gets longer.  Neutrons take their time moving through materials, scattering, slowing down, and finally reaching the detector, and neutrons produced in coincidence will not register as such unless the window is long enough to account for their random meanderings through material.  Finally, just to illustrate fission and other fission-like reactions in something other than uranium, I put a 20-pound lead brick in the counter.  Now you may believe that lead is not a fissionable material, but under the right conditions–such as when a 500-MeV electron in the secondary cosmic ray spectrum hits it–the lead nucleus can split up by fission or by a somewhat similar process called spallation, cooking off a distribution of neutrons.  And that is why we see highly-correlated neutrons (green data) being emitted by lead.  Again note the upper right graph, though: lead is a very weak source of neutrons even though the ones that are emitted are highly time-correlated.