Used Fuel Disposition Campaign

International Collaboration in Disposal Research: Potential HotBENT Collaboration Jens Birkholzer Lawrence Berkeley National Laboratory FCT UFD Working Group Meeting “International Session” UNLV, Las Vegas, NV 06/9/2016

Used Fuel Disposition

HotBENT - Studying the effects of high temperatures on clay buffers/nearfield

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A planned collaboration project, led by NAGRA, to conduct a joint GTS experiment integrated with lab and modeling studies to evaluate buffer

behavior at 150oC to 200oC

Other potential partners: NUMO, RWM, SURAO, GRS (plus SKB?)

Used Fuel Disposition

Due to the high temperature it is expected that the following physico-chemical effects will occur:

– cementation possibly affecting mechanical properties – illitization (under certain conditions, e.g. high potassium concentrations) affecting

mechanical properties

Due to the strong thermal gradients: – complex moisture transport process, including convection of vapor – delayed saturation – heterogeneous, time-dependent density distribution (differential swelling)

What to expect in the buffer for T > 150oC?

Numerical models developed, or being under development, can be used to simulate the thermal period of a repository, but database for T > 150 °C limited (laboratory) or non-existent (large scale)

Pellet- based buffer

Used Fuel Disposition

NAGRA’s Interest in the Experiment

A part of the bentonite buffer is exposed to temperatures higher than 100oC in the current NAGRA designs

Higher design temperature can achieve significant cost reductions NAGRA’s PA argumentation is that at least half of the bentonite needs to remain

intact. Ensuring that the largest part of the buffer remains intact adds additional robustness as construction related voids might be present reducing overall buffer related performance (e.g., overall swelling pressure).

The higher and the more homogeneous the swelling pressure the lower the chance of microbial impacts at the canister surface the easier the argumentation related to the canister lifetime.

NAGRA’s interest in HotBENT is to: – Increase database of bentonite performance at temperatures higher than 150oC *

– Understand processes that can only be captured at the large scale, address the up-scaling effects (at scales relevant to the repository design)

* complement/underpin results from lab studies, HE-E, FE

Used Fuel Disposition

DOE’s Interest in the Experiment: Direct Disposal of DPCs

5 Hardin, E.L., Repository Engineering

Largest capacity: Magnastor DPC system (37-PWR or equiv.)

Thermal limits: 35.5 kW storage/24 kW transport

Fuel cool time >4 yr OoR depending on burnup

Pictures and data from NAC International website 31Mar2012

Used Fuel Disposition

Potential Experiment in FEBEX Tunnel at Grimsel Test Site

Old/former FEBEX-DP tunnel (70m, well characterized, multiple boreholes,…) 40 “Big Bags” and 10 pallets of bentonite blocks MX80 (FE-experiment) Auger machine (to be adjusted), currently at FMT

Used Fuel Disposition

FEBEX Tunnel Dismantling

Used Fuel Disposition

HotBENT Modular Design and Schedule

Timeline: – NAGRA/LBNL joint paper on high-temperature field

experiment at IHLRWM conference 2015 – First multi-institutional HotBENT planning meeting in Baden,

Switzerland, February 12, 2016 – Second multi-institutional HotBENT planning meeting in

Ittingen, Switzerland, May 3-4, 2016 – HotBENT concept to be proposed to all GTS partners at 14th

ISCO meeting June 8-9, 2016 – Detailed design planning and cost estimates by Fall 2016

(additional planning meetings September and December?) – Launch project in 2017/2018