A Neutron Activation Analysis Code

Developed at ITER-India, Institute for Plasma Research



ACTYS is the first parent code within the project. It primarily determines the activation of any material through transmutation and decay when irradiated by neutrons. It is a point neutron nuclear activation code that solves coupled Bateman transmutation-decay ODE system using analytical linear chain solution method. The accuracy and speed of the linear solver are improved by an ‘exponential convergence ’ algorithm and a ‘chain weighing ’ termination technique that are newly developed at the Centre. The sensitivity analysis is performed using an accurate and exact analytical statement instead of approximate methods. These two methods lend ACTYS an added edge over typical linear chain solvers.

Current Uses of ACTYS +
1. Fusion related studies

The primary usage of ACTYS will be to determine activation of material irradiated by high energy neutrons within fusion facilities. Like any activation code, ACTYS basically requires neutron flux within the material irrespective of the neutron source. Accordingly, it is currently not suitable for fissile materials, although other neutron multiplying reactions such as (n,xn) etc are available.

2. Gamma source generation

Activated gammas from the irradiated material are classified into 24 or 42 groups. These can be further used to define the irradiated material as a source of gamma rays for photon transport or radiological hazard/shielding.

3. Radioisotope decay studies

Apart from material irradiation, decay chains and decay kinetics can also be studied for unstable radioisotopes. Cases such as transient and secular equilibrium are easily solved in ACTYS.

4. Waste management

ACTYS can be used for waste classification. This is done internally within the code by assessing the material activity and related parameters. Waste classification is presently done either by ANDRA or Clearance index notations.

The code at present form can provide information on inventories with detailed pathways and radiological parameters such as activity, contact dose, decay heat, gamma source spectra and other related radiological parameters. Along with the above, ACTYS also has a module to classify radiological waste. The classification can be done according to both IAEA criteria (which will be useful for fusion DEMO reactor design) as well as French criteria (used for ITER calculations). Sensitivity values for each coefficient and parameter is readily available. Uncertainty of the pathways is currently under- development.

Features +
Nuclear data library +
ACTYS primarily utilizes ENDF-6 format condensed neutron activation data files. The library files are processed using PREPRO and condensed into appropriate energy groups. Modules to utilize NJOY will be covered soon. EAF nuclear data files are also readable by ACTYS to provide a one-to-one comparison with FISPACT-2007 calculations. Presently, EAF2007, EAF2010, FENDL/A3.1 libraries are readily available with the code installation.
Validation +

ACTYS is rigorously validated. The validation tests are performed in an objective pattern starting with the fundamental decay problems. This is followed by a fusion activation solver IAEA benchmarking problem that highlights all the conditions which the code must fulfill. Further, it is tested on realistic fusion machines like ITER. The code is then used for actual ITER radiation waste analysis supplementing further validation. In all the tests, ACTYS results are also compared with a well-established code FISPACT-2007 which is at present used for ITER activation calculations widely.

The validations are chosen such that almost all fusion-neutron induced nuclear activation reactions are covered. It has been also ensured that properly pulsed long enough activation time scenarios along with proper fusion relevant materials are included in the validation process. An extensive validation exercise for various elements is also performed to remove various bugs and improve accuracy.

Some of the validations are given below. For complete list of validations, refer to the publication.

1. Decay exercise

H3 (beta- decay) He3 (stable)

Tritium beta decays to Helium-3 with a half-life 3.89105*108s. The activity predicted by ACTYS and FISPACT along with analytical values for the given decay problem are given below.

Activity for Tritium calculated using ACTYS(AACTYS) and FISPACT (AF) along with analytical (Aan) values.

2. International benchmark

IAEA in its second activation calculation benchmark comparison study identified four basic criteria for applicability of an inventory code for fusion applications. These are listed below:

1. Ability of the code to read standard libraries.
2. Accurate (within 5%) prediction of amount of nuclide in multistep pathways.
3. Ability to calculate light nuclide (H & He isotopes) production.
4. Ability to treat isometric states present in the libraries

One of the benchmark comparison involves studying irradiation of 1 kg of natural iron for 1 year with a 100 group neutron flux obtained at the first wall with neutron wall loading of 5MW/m2.

Number of Atoms calculated with ACTYS and FISPACT along with relative differences.
Material: Natural Iron, Amount of material 1 KG and irradiation time of 1 Year

3. Irradiation test

Irradiation tests are the class of validations which actually mimic a reactor scale activation scenarios. In these tests materials and irradiation time scenarios are chosen such that it represents ITER activation scenarios as close as possible. The selected materials in these tests with their relevance to ITER functionality are detailed below.

1. Stainless Steel 316 (SS316LN-IG), main structural material for ITER. IG stands for ITER Grade.
2. Copper Chromium Zirconium alloy (CuCrZr), used in cooling ducts, pipes and heat sinks for the first wall and divertor applications.
3. Inconel 718 alloy (Inc718), used as Bolts due to high strength for almost all components of ITER.
4. Tungsten (W), mainly as armor tile for frequently replaceable Divertor
5. Beryllium (Be), first wall or plasma facing component.

The irradiation scenario is chosen as per ITER SA2 guidelines 7 that have total 45 time steps. Neutron flux spectra mimicking a typical ITER first wall conditions is used as an input here.

Relative difference (%) of total activity between ACTYS and FISPACT
Example +