The ILL20-23 programme and its long shutdown activities

The most critical project during the past 14 months has been the replacement of the H1-H2 beam tube and in-pile neutron guides that allow the extraction and transport of thermal and cold neutrons to the instruments in the ILL7 guide hall.

To replace the H1-H2 beam tube, a huge amount of work had to be done in the reactor building, including the dismantling of 330 meters of guides in pile and in level C casemate up to the reactor containment double wall to make way for the work. The operation also gave us the opportunity to replace all the other pool guides, which must be changed every 10 years because the glass they are made of deteriorates over time due to their exposure to radiation from the reactor core.

A huge operation in itself, which gave the opportunity to modernise and renew infrastructure such as the H1-H2 pool at level C, which provides biological shielding for beam extraction, and the guide system for crossing the containment double wall (C5 guide system) which feeds through the outer reactor wall. The latter new design improved the reactor safety regarding exceptional seismic event with its possible associated major flood to ensure compliance with the highest safety standards and guarantee the longevity of our key

neutron delivery infrastructure. This works implied the complete replacement of an additional 50 meters of neutron guides. This project was successfully completed on time, while following the quality procedures agreed with the ASN control.

In early 2022, much of the ILL7 guide hall had been excavated down to the river bed of the Grenoble valley to prepare for the future new double guide H24 and triple guide H15 and their associated nine new or refurbished instruments.

Reconstruction began promptly with extensive concrete landscaping ready to accept the new guide and instrument suites for both the H24 and H15 projects.  Civil engineering work has been carried out in phases, beginning with the new D10+ zone and the H24 dual guide and working further roughly in instrument order along the Chartreuse side of the guide hall toward Xtrem’D, IN13+, and the future area for FIPPS.

A similar situation could be seen on the Vercors side of the guide hall with the dismantling of the old H1 casemate to prepare for civil engineering work required for the H15 triple guide and its instruments suite: D007, D11+, SHARP+ and SAM.

As critical prerequisite for restarting the user programme in ILL7, namely the construction of the new cold guide casemate(H1 casemate), was a critical challenge, which has again been successfully completed on time by the end of 2022. This 300m² structure made of concrete, lead and steel had been specially designed to accommodate for the three additional future branches of the guide H15, which will supply neutrons to the new H15 instruments. The construction of this casemate was vital to ensure the safe distribution of neutrons to users of the existing cold guides: it is now a done deal.

During the spring and into the summer of 2022, installation of the first instrument components began, such as the primary spectrometer shielding for D10+ and XtremeD along with the instrument zone separation walls. By the beginning of the summer, work on the new H1 steel casemate roof could begin and the new foundation pillars for the D11 detector tank could be poured.

By the end of the summer, work began on reinstalling the IN13 and CT2 instruments while the new floors for FIPPS and SHARP+ were prepared at the ends of the H24 and H15 beamlines, respectively.

Through the autumn and into winter 2022-23, instrument mounting had quickly progressed with D10+, IN13, XtremeD and CT2: all beginning to look like finished neutron instruments and ready to start their Cold Commissioning. At the same time, the D11 detector tube was moved into its new position and the SHARP+ flight chamber was delicately ‘air-lifted’ though the roof of ILL7 into its new position at the end of the guide hall on its Vercors side.

Meanwhile, following the successful replacement of the H1-H2 beam tube in the reactor building, the great puzzle of the 350-meter long guides started to be reassembled by the end of autumn 2022. Realigning the whole neutron distribution feeding ILL7 guide hall with a positioning accuracy of the order of a few hundredths of a mm in just two months, that was the challenge that we had to face up to enable the reinstallation of the eleven H1H2 safety valves, the prerequisite authorising fuel element loading, final tests and reactor start-up. It started by the flight of the so-called “Pink Housing” across the level C to reach the reactor core: a very delicate handling of such mechanical piece of 700Kg loaded with 35 meters of fragile glass guides, which will give birth to the ILL7 neutron delivery system. In early December, the following guides units could be reinstalled within the narrow space of the level C pool (about 15m² for 60m of guides), and connected over during the following weeks to the last sections already installed across the reactor containment double wall.

On the Chartreuse side of ILL7, the new suite of H24 instruments will begin commissioning with the restart of the reactor in February 2023. We are expecting gains of an order of magnitude on the new D10+ single crystal diffractometer with respect to the old D10 instrument thanks to the new detector and increased divergence, guide and monochromator size. Gains in intensity are expected on IN13+, primarily due to the performance of the new H24 guide, coupled with a new temperature-gradient monochromator. New capabilities and capacity will be available with the new CRG powder and single crystal diffractometer XtremeD, while the end of the new H24 guide will make way for the future relocation of the fission fragment spectrometer FIPPS, giving the instrument more space, reduced background and most importantly a stable and intense neutron beam.

The cold neutron instruments on the Vercors side of ILL7 are also now ready to restart, with the exception of the H15 instruments. The work on H15 has been planned in such a way as to allow the construction of the out-of-casemate H15 guide and instruments to continue during reactor operation in 2023. The next long shutdown at the beginning of 2024 will allow the final in-casemate installation of the new H15 guides, connecting the new guide at last to its new instrument suite ready for commissioning and user operation during the second half of 2024. We expect huge gains in performance from instruments such as D007 and SHARP+ (CRG) due to the new high-performance H15 guide, dedicated focussing guide and beam optics, and improved or larger detectors. D11 should regain its theoretical brilliance to match that of D22 and D33, as should the new CRG SANS instrument SAM. 

Several other instrument projects will also begin commissioning and enter the user programme in 2023. The neutron imaging instrument NeXT is a fully rebuilt instrument with two measurement stations allowing state-of-the-art N-imaging with advanced contrast techniques, high spatial resolution, intense neutron flux and combined X-ray imaging. The cold neutron diffractometer and wide-angle scattering instrument D16 now has a fully renewed secondary spectrometer, including a new position- sensitive detector covering four times the solid angle of the previous detector, allowing for more rapid measurements over an extended q-range. Although already commissioned in 2020, the thermal time-of-flight spectrometer PANTHER willfurther increase its performance thanks to its new cascade of five background choppers. SuperSUN will finally produce its first ultra-cold neutrons after an extended and complex instrument project and commissioning. We have also been able to launch several new instrument upgrade projects, including a new banana detector for the D20 powder diffractometer due to be installed in 2024. The MARMOT project will provide multiplexed energy and angle analysis on the cold neutron TAS instrument Thales, while the wide-angle spin-echo instrument WASP will receive its full complement of detectors.

Over the last few months, the ILL has had to satisfy many commitments vis-à-vis the French nuclear safety authority, the ASN, as well as carrying out mandatory maintenance work.

The long reactor shutdown was due to last 16 months: 14 months of nominal work and 2 months provision to cover risks. Most of major milestones were completed on time thanks to the high motivation of ILL staff. Some activities could be realised smoothly, but we had to face some unexpected technical difficulties and also cope with delays in procurement of raw materials. Nevertheless, we were able to contain the unexpected setbacks within the scheduled 2-month margin and stick to the initially planned total duration of 16 months.

The many activities carried out within the Reactor Division included the following major operations:

- the replacement of the H1H2 Beam tube – the most complex beam tube ever made, which extract the cold and thermal neutrons feeding all instruments of the main ILL experimental hall : one of the most difficult and critical operation of the long shutdown, perfectly achieved without delay.

- the replacement of the reactor core chimney – a highly critical part which not only houses the fuel element in the core but also channels its cooling: one of the most important milestones in the schedule, successfully achieved earlier than planned.

- the reinforcement of the Fresh Air Intake: to avoid risk of damaging the reactor containment in the event of an earthquake, the old concrete building has been demolished and replaced by a lighter structure

- the testing of the CRU (emergency core reflood system) safeguard system for an even safer installation, which ensures that the fuel element remains under water even in the worst-case scenario

- the testing of the leaktightness of the reactor building containment – which must be tested every 5 years, in accordance with the regulations. The containment comprises an outer metal dome and an inner concrete wall, which are separated by an air space known as the annular space, which is maintained at an overpressure. No leak detected: a successfull containment capability giving  a green light for the forthcoming years
- the cleaning of the ILL’s old detritiation facility. The aim of this operation, which involves most of the services in the Reactor Division, is to remove the tritiated gas currently still present in the detritiation building by 2025. The idea is to design a new process for the catalytic recombination of tritiated deuterium gas with oxygen in order to produce heavy water for the primary circuit.

Beside the intensive work during the shutdown, the ILL activity on the fuel cycle continues with its participation in the HERACLES programme with the aim of using low enriched Uranium (LEU) within the next ten years. Work towards a feasibility study review at the end of 2023 is ongoing.

As has been the case for the last two years, the ILL’s relations with the ASN continue to be good, as shown by the confidence expressed by the regulator at the annual review in March 2022. Feedback received from the 2022 inspections has been positive overall.

The ASN has issued its final decision on the ten-year safety review, validating the list of the safety modifications to be carried out and authorising the ILL to continue to operate until the next safety review in 2027.