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.

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.

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.

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.