# Presentation: 116372

## Development of SiC Schottky Diode Detectors as an Advanced Sensor for Safeguards by Measurement of Actinide Concentrations in Molten Salt Electrolyte 

* **T.E. Blue, W. Windl*

## Overview

- Goal
- Introduction
- SiC detector background
- Methods
- TRIM simulation
- Results and Interpretation
- Radiation Damage
- Future Work

## Goal

- Develop SiC Schottky diode detectors for measurement of actinide concentrations, from alpha activities:
- In a LiCl-KCl molten salt pyroprocessing electrolyte.
- Identify greatest thickness of salt acceptable in front of the diode detector’s front face.

## Detector Photo

## Background

- Advantages of SiC semiconductor devices:
- Fast charge collection time
- Small mass
- Small size
- High break down electric field
- (2.2 MV/cm, an order of magnitude higher than that in Si or GaAs)
- High band gap
- (3.25 eV)
- Good radiation resistance

## Pyrochemical Process Fuel Cycle

***Pyrochemical Process Fuel Cycle***

## Slide 7

## Methods

- Computer Simulation
- TRIM
- Step I
- Alpha range in the salt
- Alpha range in the SiC
- Step II
- Deposited energy in the active region of SiC
- Multi-layer LiCl-KCl/SiC

## Actinides in the molten salt

- Major Contributors
- U & Pu
- U-6.4 wt%
- Pu-0.6 wt%

| 
Element |   Isotope |         
 Weight
  Percent |  Energy 
  of the  
 isotope
   (MeV) |
| --- | --- | --- | --- |
|   | U-234 | 0.458 | 4776 |
|   | U-235 | 61.99 | 4398 |
| Uranium | U-236 | 1.61 | 4494 |
|   | U-238 | 35.74 | 4197 |
|   |   |   |   |
|   | Pu-238 | 0.128 | 5499 |
|   | Pu-239 | 98.57 | 5156 |
| Plutonium | Pu-240 | 1.295 | 5168 |
|   | Pu-241 | 0.015 | 4897 |
|   | Pu-242 | 0.0001 | 4901 |

## Alpha contributors

| Element | Isotope | Activity
 (A=λn)
(dps) | Fraction of 
alpha particles
 emitted per emitted alpha particle |
| --- | --- | --- | --- |
|  | U-234 | 9.85E-03 | 2.98E-03 |
|  | U-235 | 4.64E-04 | 1.40E-04 |
| Uranium | U-236 | 3.60E-04 | 1.09E-04 |
|  | U-238 | 4.16E-05 | 1.26E-05 |
|  |  |  |  |
|  | Pu-238 | 7.11E-01 | 2.15E-01 |
|  | Pu-239 | 1.99E+00 | 6.01E-01 |
| Plutonium | Pu-240 | 9.54E-02 | 2.89E-02 |
|  | Pu-241 | 5.02E-01 | 1.52E-01 |
|  | Pu-242 | 1.28E-07 | 3.87E-08 |

## Step 1: To find the range of alpha in LiCl-KCl salt and SiC active volume

##  Simulation Methods

- Source
-  Alpha particles
- Considered to be plane
- Emitted perpendicularly into the target
- Target
- LiCl-KCl
- Density 1.6225 g/cm3
- Diameter 300 μm
- SiC active volume
- Density 3.2 g/cm3
- Diameter 300 μm

## Range of Alpha in LiCl-KCl

| Isotope | Energy of alpha (MeV) | Range of alpha in LiCl-KCl (μm) |
| --- | --- | --- |
| U-234 | 4.78 | 33.36 |
| U-235 | 4.40 | 29.66 |
| U-236 | 4.49 | 30.58 |
| U-238 | 4.2 | 27.77 |
|   |   |  |
| Pu-238 | 5.5 | 40.98 |
| Pu-239 | 5.16 | 37.28 |
| Pu-240 | 5.17 | 37.41 |
| Pu-241 | 4.9 | 34.59 |
| Pu-242 | 4.9 | 34.63 |

## Range of Alpha in SiC

| Isotope | Energy of 
alpha (MeV) | Range of alpha in SiC
(μm) |
| --- | --- | --- |
| U-234 | 4.78 | 14.92 |
| U-235 | 4.40 | 13.25 |
| U-236 | 4.49 | 13.66 |
| U-238 | 4.2 | 12.40 |
|   |   |  |
| Pu-238 | 5.5 | 18.35 |
| Pu-239 | 5.16 | 16.68 |
| Pu-240 | 5.17 | 16.74 |
| Pu-241 | 4.9 | 15.47 |
| Pu-242 | 4.9 | 15.49 |

## Step 2: Energy deposited in the active volume

## Detector Configuration

## Simulation Methods

- Multi-layer target
- Three Sub-Cases
- Sub-Case 1
- Alpha particles perpendicularly incident on 1μm molten salt layer (starts at 0 depth within the 1μm layer)
- Simulation was performed independently
- Considered 1000 alphas for each isotope
- Purpose:
- To find the maximum energy deposited by individual isotope
- Provide better understanding of the spectrum when all isotopes are blended together

## Simulation Methods

- Sub-Case 2
- Alpha particles distributed uniformly throughout the volume of the salt
- Alpha particles of appropriate energy emitted perpendicularly with respect to the detector face.
- Contribution to the spectrum weighted according to the alpha activities

## Simulation Methods

- Sub-Case 3
- Alpha particles distributed uniformly throughout the volume of the salt
- Alpha particles of appropriate energy emitted isotropically in direction space.

## Sub-Case 1:Results

| Isotope | Alpha Energy (keV) | Maximum energy deposited in SiC (keV) |
| --- | --- | --- |
| U-234 | 4776 | 4600 |
| U-235 | 4398 | 4300 |
| U-236 | 4494 | 4200 |
| U-238 | 4197 | 4000 |
|   |   |   |
| Pu-238 | 5499 | 5300 |
| Pu-239 | 5156 | 5000 |
| Pu-240 | 5168 | 5000 |
| Pu-241 | 4897 | 4700 |

## Sub-Case 1:Results

## Sub-Case 2:Results

## Sub-Case 3:Results

## Step 2: Results

## Discussion

- The peak in the spectrum is attributed to the Pu-239 isotope.
-  The Sub-Case 3 is the most accurate representation of physical reality, this alpha particle energy deposition spectrum is most important.
- The density of the LiCl-KCl molten salt that was considered for the simulation corresponds to the pure salt. In reality, the salt is not pure. The spectrum’s peak changes with change in density. Therefore, this detector can account for the change in density of the LiCl-KCl molten salt.

## Radiation Damage

## Multiscale Modeling of Radiation Effects in SiC Detectors

## Displacement damage

- PKA Spectra

- Displacement damage

- Defect density

- MCNP5

- TRIM /
- MARLOWE

- Kinetic Monte Carlo

- ab initio

- Molecular Dynamics

- Hopping rates and defect formation energies

- Very short-timedefect recombination

- PKA-target interactions

## Dose & Dose Rate Effects 

- 50 kW

- 455 kW

## Future Work

- To perform experiments for measuring the actinide concentration using the charge sensitive system.
- The simulation considered only U & Pu isotopes. In reality, there may be contributions from Am-241 and Np-237, whose effects are not known. Efforts are being made to identify how these isotopes contribute to the spectrum.
- Study by calculations and experiments the effects of temperature, dose and dose rate on the evolution of detector’s electrical properties and pulse height resolution.

## Acknowledgements

- INL,DOE,NASA
- Our project group members

## Questions