journal of ELSEVIER
nuclear materials
Journal of Nuclear Materials 233-237 (1996) 1505-1510
The impact of materials composition and irradiation modelling on the activation of ITER in-vessel components G. Cambi a
a.*,
D.G. Cepraga
b'
P. Rocco
c,
M. Zucchetti
d
Physics Department, Bologna University, 46 Via Irnerio, I-40126 Bologna, Italy b ENEA, INN-FIS-MACO, 2 Via Don Fiammelli, I-40129 Bologna, Italy c E.C., J.R.C., Safety Technology Institute, 1-21020 lspra, Italy ct Politecnico di Torino, 4 Corso Duca Degli Abruzzi, 1-10129 Torirw, Italy
Abstract
This paper presents the results of sensitivity studies aiming to assess the impact of the AISI 316 ITER structural material composition on the activation characteristics of the in-vessel components. The influence of the protective layer material, namely beryllium, carbon fibre composite, and tungsten, is also analyzed and discussed. Three neutron fluence values are considered: 0.3, l, and 3 MW y/m 2 , and the related impact on activation results in discussed. The ANITA-2 and the ASPACT-3 activation codes are used, with updated cross sections and decay data libraries based on EAF-3 evaluation files. The 1D-Sn XSDRNPM-S transport code, using the 171 group Vitamin C library based on EFF-2 data, is used to produce the flux-weighted spectrum needed for the activation calculations. The outline design of ITER defined in the fourth meeting of the Technology Advisory Committee is considered for the assessment.
1. Introduction
Neutron-induced activation data are needed for many evaluations concerning fusion reactors and, in particular, safety and environmental impact assessments. In the frame of the European Fusion Technology Program 1992-94, the safety and environment task S + E SEP! (source terms and energies) was set up to perform neutronic and activation calculations to support the ITER joint central team. According to the task objectives, the modelling should be as close as possible to evolving ITER design. The ITER TAC-4 outline design [ l ], that considers the beryllium as protective layer material for the plasma facing components PFC and a low-content (0.187%) of Mn in the AISI 3 l 6L structural material of the in-vessel components, was firstly analyzed and the results were presented in [2]. The relevant irradiation ITER characteristics considered in
'Corresponding author. Tel.: +39-51-6098297; fax: +39-516098062; e-mail:
[email protected].
that assessment were fusion power 1.5 GW, average neutron power load 1.044 and 0.735 MW /m 2 , respectively for the outboard and the inboard first wall FW, total neutron fluence on the OFW 3 MW y/m 2 , average pulse length 1000 s, dwell time 1200 s. The evolving design of ITER (October 1994) differs from the ITER TAC-4 outline design. It is based on a lower neutron fluence. Also changes in the AISI 3 l 6L composition were proposed in the mean time by ITER JCT. In this paper, the impact of the AISI 3 l 6L composition on the activation of the in-vessel components of ITER is analyzed. The optimization study to set up the s;mplified irradiation model used for activation calculations is also presented and discussed. Sensitivity studies have also been performed to assess (a) the effect on the activation of the components close to the plasma due to the adoption of different materials for the PFC protective layer, and (b) the effect of a fluence reduction on ITER materials activation from 3 to 0.3 MW y /m 2 • The corresponding results are also presented and discussed.
0022-3115/96/$15.00 Copyright© 1996 Elsevier Science B.V. All rights reserved. Pl/ 50022-3115(96)00156-0
G. Cambi et al./ Journal of Nuclear Materials 233-237 (/996) 1505-1510
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2. Methodology The assessment is based on the sequence shown in Fig. 1 that represents an integrated approach to perform neutron data processing and multigroup library production, shield-
EFF-2 DATA
AMPX PROCESSING SYSTEM
ing neutron analysis and activation evaluation in a reasonable short computer time. A one-dimensional discrete ordinate neutron flux analysis (PrS 8 approximation) in the cylindrical geometry has been chosen. Starting from the 171 energy group Vitamin C library based on EFF-2 data, the 1-D Sn code XSDRNPM-S [3] is used to generate a 100 group neutron flux-weighted spectrum in various zones of ITER, for ANITA-2 [4] and FISPACT-3 [5] activation codes. The EAF-3 activation library is used. The flux is calculated in the radial direction along the equatorial plane. The machine is described by 53 zones, from the central axis to the cryostat. The geometrical scheme for the outboard in vessel zones is shown in Fig. 2.
171-GROUP VITAMIN-C LIBRARY '-----------------------------------·
---------------------------------
BONAMI-S (Self-shielding Bondarenko treatment)
XSDRNPM-S (Sn transport calculation) (angular flux distribution) (multigroup flux weighted spectrum)
ACOUPLE
a)
formaifiili"conversfoid'rom !
..~l'.l:':ll~P{)~.f.{)..~C.f.iyllt.i{)_ll.l'.~~f!S.J
b) r~~~~f.~~;::~;,~f~~1~~;~s;~~~\t~::: ---- -- ---- - --- ----- ----· --- -- --- -- - -. -- ---- . - ---· ----- --- . -- .- ··-·· - -.- -----, ( Multigroup EAF ACTIVATION LIBRARIES i -
'.
_______________________________________ ---------------------------------------"'
ANITA-2
FISPACT-3
3. First wall and shield blanket main features The blanket-shield design consists of FW /SB outboard and inboard sectors of 316 stainless steel jointly cooled by low temperature and low pressure water (Toutlet = 160°C, p = 2.1 MPa) acting also as shielding material. The FW panel is a bonded composite of 316 SS ( 1 mm) and Cu-!Zr-lCr (5 mm). A thermal power of 575 MW is removed in normal operation. The TAC-4 AISI 316 L structural material ( p = 7960 kg/m 3 ) wt% composition (in the following referred as 'SS316-old') is V 0.17, Cr 17.39, Ni 13.16, Mo 1.44, Mn 0.187, Si 1.30, Nb 308 ppm, Ta 60 ppm, W 61 ppm, N 411 ppm, P 370 ppm, C 2840 ppm, S 175 ppm, Fe balance. The 'SS316-old' composition has only laboratory relevance, due to the high manufacturing costs. Therefore, a more standardized composition for structural materials has been proposed. From a neutronic point of view, it mainly differs from the previous one by the Mn and the Co content. The updated AISI 316 LN structural material (same density) wt% composition (in the following referred as 'SS316-new') is Cr 17.4, Ni 12.3, Mo 2.5, Mn 1.8, Si 0.46, Co 0.17, Cu 0.20, Ta 60 ppm, N 600 ppm, P 270 ppm, C 240 ppm, S 20 ppm, Nb 300 ppm, Bi 10 ppm, Fe balance. The beryllium (the reference material for the PFC protective layer) is 100% natural Be ( p = 1500 kg/m 3 ). The carbon fibre composite CFC and the tungsten materials considered as alternative options as PFC protective layer have the following compositions: CFC ( p = 1800 kg/m 3 ) carbon (C-12 isotope) contains the following impurities, in ppm: Fe 15, Ca 2, Ni I, Cu I, Zn I, Mg I, Cr I, K 5, Na I, Al 3, P 8, Ti 3; W ( p = 19300 kg/m 3 ) natural tungsten (W-180, W-182, W-183, W-184, W-186 isotopes) without impurities.
4. Irradiation modelling Fig. I. Neutron transport and activation calculation methodology flow sheet.
The nominal irradiation scenario for ITER-EDA would imply, if exactly represented, an activation model with
G. Cambi et al./ Journal ofNuclear Materials 233-237 (1996) 1505-1510
1507
p L
~~-
A~~im!~l'm~lllm!illll!!llillillmlll~
s
M ~---~It'/' A Fig. 2. Geometric zone scheme of the in-vessel outboard regions of ITER-EDA outline design.
more than 1000 pulses and pauses. This calculation must be repeated for each zone in which the reactor is divided, and for each material. Such an analysis would require unacceptable long computer times. However, the irradiation history of the machine cannot be effectively represented by a single continuous irradiation period, or a few of them. A sensitivity calculation has been carried out [6) as follows. A steel with a simplified composition has been irradiated in the outboard first wall. The initial irradiation model has followed almost exactly the nominal agenda, and it has been taken as reference result. Then, other models have been used for the same material and flux, with increasing degree of simplicity. An optimum model has been chosen, as the simplest (quickest) model with satisfying agreement with the reference model. The central node is short- and medium-term activation, which is affected by a too simple model of the pulsed irradiation. Long-term activation is estimated in the same way by a pulsed model or by its continuous equivalent. In conclusion, an optimized pulsed model with less than 100 pulses in total has been adopted for the calculations. This optimization reduces the computer time remarkably (up to a factor four smaller than the original model), while short-term activation results remain always within 5% with respect to the complete model.
5. Results and discussion The study considers various parameters that impact PFC material activation, decay heat, and contact dose: the
FW /SB structural material (AISI 316 L) composition, the protective layer material, and the total neutron fluence.
5.1. AlSl 316 L manganese content impact on PFC materials activation In order to provide indications of the Mn impact on the activation parameters (namely the specific activity and the decay heat) of the irradiated ITER in-vessel materials, a sensitivity analysis has been performed using the ANITA-2 activation code. Five different values of the Mn content into the SS3 l 6-old have 1:Jeen considered: 0.187% (the original T AC-4 value), 0.5%, 1.0%, 1.5%, 2%. The activation calculations for the different Mn contents have been performed for three different regions, namely zone 31 (outboard first wall steel panel, OFW2), zone 32 (inner region of the outboard shielding blanket, OSB5. l), and zone 42 (outer region of the outboard shielding blanket, OSB 1). The main results related to zone 31 are summarized in Table 1, for various cooling times after the plasma end. More detailed results are given in Ref. [7]. The results analysis shows that, in the Mn% range investigated, the OFW2 steel specific activity increases linearly with Mn content (about 14% for one percent Mn increase) at plasma shut down while it is not affected for a cooling time longer than 1 day. The decay heat only increases more significantly at plasma shut down (about 35% for one percent Mn increase). A similar trend has been found for steel of the OSB5. l and OSB I zones, but the increases are much higher, particularly for the OSB 1 steel (zone 42).
Table I Activation characteristic versus Mn content for different cooling times (outboard first wall steel panel OFW2-zone 31) Mn%
Specific activity (Bq/cm 3 ) 1d
0 0.187 0.5 l 1.5 2
1.46E + 1.52E + 1.63E + 1.72E + 1.82E+
Specific decay heat (W /cm 3 )
12 12 12 12 12
8.70E + 8.73E + 8.79E + 8.80E + 8.86E +
50 yr 11 11 11 11 11
2.41E 2.41E 2.41E 2.36E 2.36E
+ + + + +
09 09 09 09 09
0
Id
50 yr
2.22E - 01 2.47E - 01 2.87E - 01 3.23E- 01 3.62E- 01
2.60E- 02 2.65E- 02 2.73E- 02 2.80E- 02 2.88E- 02
l.02E- 05 1.02E- 05 1.02E - 05 1.00E - 05 1.00E- 05
G. Cambi et al./ Journal of Nuclear Materials 233-237 (1996) 1505-1510
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Table 2 Specific activity (Bq/cm 3 ) of various zones at different cooling times: comparisons between 'old' and ·new' AISI 3 l 6L composition results Zone
31 32 42
AISI 316L 'old'
AISI 316L 'new'
0
Id
50 yr
0
Id
50 yr
l.46E + 12 1.47E + 12 3.39E + 09
8.70E + 11 8.69E + 11 2.07E + 09
2.41E + 09 4.22E + 09 1.49E + 07
l.87E+ 12 2.13E+ 12 6.35E + 09
9.21E+ II 9.35E + 11 2.22E + 09
2.28E + 09 3.95E + 09 l.24E + 07
5.2. A/SI 316 L composition impact on PFC materials activation
5.3. Impact of the protective layer material on PFC materials activation
A comparison of the activation characteristics between the two steel compositions, 'old' and 'new', is given in Table 2 for some outboard in-vessel ITER zones. The results show that the low Mn content (0.187 wt%) stainless steel has lower activation values till about 50 years after the end of the irradiation time with respect to the higher Mn content (1.8 wt%) stainless steel, whereas for a longer cooling time the situation is more favorable for 'SS316-new'. The details of the activation results for the two AISI 3 l 6L are given in [8]. The analysis of the results related to 'SS316-old' indicates: The isotopes that give the highest % contribution to the specific activity (for the OFW2-zone 31) are: at plasma shut down: Fe-55 (29), Mn-56 (21), Cr-51 (16), V-52 (8), Co-58 (6), Co-58ml (6), Co-57 (5), Al-28 (3); 1 year of cooling: Fe-55 (86), Co-57 (7), Mn-54 (4). The analysis of the results related to 'SS316-new' indicates: The isotopes that give the highest % contribution to the specific activity (for the OFW2-zone 31) are: at plasma shut down: Mn-56 (32), Fe-55 (22), Cr-51 (13), V-52 (5), Co-58 (5), Co-58ml (5), Co-60m (5), Co-57 (3); 1 year of cooling: Fe-55 (79), Co-60 (8), Co-57 (5).
Two alternatives for beryllium as first wall protective layer have been assessed from the neutronic point of view, namely CFC and tungsten. Both the inboard and the outboard beryllium protective layer IPL and OPL have been replaced by CFC or W. For the stainless steel(' SS316-old') of the zones OFW2, OSB5. l and OSB 1, the specific activity and the specific decay heat are higher for the reference design (Be as protective layer material). For the two alternative options, the percentage differences with respect to the reference design are shown in Table 3 for various cooling times. For the protective layer itself, the higher activation data are those related to the tungsten and the lower ones (several orders of magnitudes) are those referred to the CFC, both for the inboard and the outboard side. More detailed results are presented in [9]. 5.4. Impact of the neutron fluence on PFC materials activation
An analysis aiming to verify the impact of the neutron fluence on various in-vessel materials of ITER has been performed by considering as the reference structural material the 'SS316-new' composition. Beryllium is considered as protective layer material.
Table 3 Specific activity and decay heat of AISI 316L of various zones: percentage difference between the alternative protective layer options and the reference design Cooling time
Activation parameter Specific activity (Bq/cm
Decay heat (W /cm 3 )
3
)
0 1d 1 yr 50 yr 0 Id I yr 50 yr
OFW2 (zone 31)
OSB5.l (zone 32)
OSB I (zone 42)
CFC
w
CFC
w
CFC
w
-17% -18% -21% -3% -17% -15% -17% -8%
-4% -4% -2% -17% -5% -5% -4% -13%
-14% -15% -18% -5% -15% -13% -16% -7%
-3% -3% -2% -7% -4% -3% -3% -7%
-12% -12% -13% -11% -12% -12% -12% -11%
-1% -0.5% -1% -1% -1% -!% -1% -1%
G. Cambi et al./ Journal of Nuclear Materials 233-237 (1996) 1505-1510
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Three multistep irradiation scenarios have been considered, resulting in total neutron fluences of 0.3 MW y /m 2 (scenario A), I MW y /m 2 (scenario B), and 3 MW y /m 2 (scenario C). Table 4 shows the results for some inboard zones of ITER in-vessel components, at plasma shut down and for various cooling times. Based on comparison of the results, the following conclusions can be outlined: The activation parameters related to the materials of the different in-vessel regions of ITER are dependent from the total neutron fluence. More precisely, as expected, they increase with fluence. The activation parameters percentage increase is dependent on the cooling time. The analysis of the activation parameters for all the three fluence scenarios points out that: The isotopes that give the highest contribution to the OFW2 specific activity are: at plasma ending: Mn-56 (30 to 40%), Fe-55 ( 10 to 25%), Cr-51 (IO to 20%); I year of cooling: Fe-55 (70 to 80%), Co-57 (about 10%), Co-60 (about 10%); 50 years of cooling: Ni-63 (> 90%). The isotopes that give the highest contribution to the OFW2 decay heat are: at plasma ending: Mn-56 (70 to 75%), V-52 (11 %), Co-58 (about 4%), Co-60 (about 4%); I year of cooling: Co-60 (50 to 75%), Mn-54 (15 to 35%); 50 years of cooling: Co-60 (75 to 90%), Ni-63 (IO to 20%). More details on the isotope % contribution to the activation parameters are given in [8).
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The results of the two activation codes ANITA-2 [4] and FISPACT-3 [5) have been compared, starting from the same 1-D Sn neutron transport calculation results. The 'SS3 l 6-old' composition has been considered as reference structural material and beryllium is considered as protective layer material. Table 5 shows the specific activity and the decay heat of some in-vessel zones of ITER, namely the zones 31, 32 and 42, obtained with ANITA-2 and with FISPACT-3. The calculations refer to a total neutron fluence of 3 MW y /m 2 . More detailed FISPACT-3 results are given in [6). The analysis of the results shows a small inconsistency (about 15%) between the two codes. A more detailed analysis pointed out an error in the FISP ACT code in performing the evaluation of the internal transition decays (I' activity). Once the FISPACT-3 code is modified, the
1510
G. Cambi et al./ Journal of Nuclear Materials 233-237 (1996) 1505-1510
Table 5 Specific activity and decay heat of AISI 3 l6L of various outboard zones: ANITA-2 and FISPACT-3 codes result comparison Zone
Cooling time
Specific activity (Bq/cm 3 ) ANITA-2 FISPACT-3
Decay heat (W /cm 3 ) ANITA-2
FISPACT-3
31
Ih I yr 50 yr 1h I yr 50 yr Ih I yr 50 yr
1.18E + 3.76E + 2.41E + l.17E + 3.42E + 4.22E + 2.74E + 5.97E + 1.49E +
1.21E - OJ 5.42E- 03 l.02E - 05 l.19E - 01 4.86E- 03 l.48E - 05 2.55E- 04 8.92E- 06 4.55E- 08
l.03E - OJ 5.76E- 03 9.95E- 06 l.OOE- 01 5.19E- 03 l.37E - 05 2.IOE - 04 8.42E- 06 4.46E- 08
32
42
12 11 09 12 11 09 09 08 07
l.08E+ 12 3.41E + 11 2.17E + 09 l.08E+ 12 3.14E + 11 3.68E + 09 2.56E + 09 5.65E + 08 l.45E + 07
discrepancy in the activation results between ANITA-2 and FISPACT-3 code are lower than 5%.
6. Conclusions
The irradiation of the Plasma Facing Components of the ITER-EDA fusion machine has been assessed, with reference to the outline design defined at the T AC-4 meeting. The impact of various parameters, like the AISI 316 L structural material composition, the plasma facing component protective layer material and the neutron fluence, on the activation results is assessed and discussed. A one-dimensional discrete ordinate neutron flux analysis (P3-S 8 approximation) in the cylindrical geometry has been chosen. The 171 energy group Vitamin C library based on EFF-2 data has been used with the 1-D Sn code XSDRNPM-S to generate a 100 group neutron fluxweighted spectrum in various zones of ITER for ANITA-2 and FISPACT-3 activation codes. The EAF-3 activation library is used for the activation calculations and the results given by the two codes are compared. The irradiation model used for the activation calculations is presented and discussed. The following conclusions can be outlined: For the manganese wt% range investigated (from 0.187 to 2%), the in-vessel steel specific activity increases linearly with Mn content (about 0.14/Mno/o) at plasma shut down while it is not affected for a cooling time higher than 1 day. The decay heat only increases more significantly at plasma shut down (about 0.35 / Mn%). For the stainless steel of the in-vessel zones the specific activity and the decay heat result to be higher for the reference design (beryllium as protective layer material) with respect to the two alternative options that consider CFC and W. For the protective layer itself, the higher activation data are those related to the tungsten and the lower ones (several orders of magnitudes) are those referred to the CFC, both for the inboard and the outboard side.
The activation parameters related to the materials of the different in-vessel regions of ITER are dependent on the total neutron fluence and they increase with fluence. The two activation codes used for the assessment give results in good agreement, the differences being lower than a few percent.
References [I] P. Rebut, Detail of the ITER Outline Design Report - Summary and Overall Physics Issues, Fourth Meeting of the Technology Advisory Committee, S. Diego Joint Work Site, 10-12 January, 1994. [2] G. Cambi et al., ITER Environmental Source Terms evaluated with the European Multi-Code Approach: activated corrosion products contribution, 18th Syrup. Fus. Technol., Karlsruhe, Germany, 22-26 August, 1994 (Elsevier, Amsterdam), to appear. [3] N.M. Green and L.M. Petrie, XSDRNPM-S - A one-dimensional discrete ordinate code for transport analysis, ORNL/NUREG /CSD-2/V2/R4. [4] D.G. Cepraga, S. Boeriu and I. Maganzani, ANITA-2, an updated version of the activation code ANITA, ENEA-FUS technical report, to appear. [5] R.A. Forrest and J.Ch. Sublet, FISPACT-3-User Manual, AEA/FUS 227, April 1993. [6] M. Zucchetti et al., Activation calculation for ITER EDA, DENER Dipartimento di Energetica Politecnico di Torino, PT DE 358 /IN, June 1994; ENEA FUS S + E TR 7 /94, June 1994. [7] D.G. Cepraga et al., ITER EDA: Neutronic and activation calculations-Sensitivity analyses. Part I (ANITA-2 activation code), ENEA, Addendum to FUS S + E TR 3 /94, September 1994. [8] G. Cambi and D.G. Cepraga, ITER-EDA Outline Design neutronic and activation calculations: The impact of the neutron fluence (ANIT A-2 activation code), FUSS+ E TR 19/94, December 1994. [9] D.G. Cepraga et al., ITER EDA: Neutronic and activation calculations - The impact of the protective layer material (ANITA-2 activation code), FUS S+E TR 16/94, October 1994.
