Proceedings of the 19th Annual Meeting of Particle Accelerator Society of Japan
October 18 - 21, 2022, Online (Kyushu University)

PASJ2022 TUP006

AVAILABILITY ANALYSIS FOR THE 30-MW PROTON LINAC OF THE
JAEA-ADS PROJECT
B. Yee-Rendon∗ , Y. Kondo, J. Tamura, K. Nakano, F. Maekawa and S. Meigo
Japan Atomic Energy Agency (JAEA), Tokai, Japan
Abstract
Japan Atomic Energy Agency (JAEA) is designing a 30MW proton linear accelerator (linac) as one of the fundamental components for its accelerator-driven subcritical system (ADS) proposal. ADS accelerators demand extremely
high reliability and availability to avoid thermal stress in thesubcritical reactor structures. Thus, reliability and availability assessments of the accelerator are mandatory to detect
weakness in the lattice designed and evaluate redundancy
configurations to fulfill the demanded operation. This study
applied the Reliability Block Diagrams (RBD) method to
calculate the Medium Time Between Failures (MTBF) for
different linac configurations: all the linac’s elements in aseries configuration and a combination of hot-standby forthe low-energy section of the linac and k-out-of-n redundancy for the high-energy part. The estimation considered
the detailed arrangement of the cavities and magnets thatcompose the linac lattice. In this report, we describe thereliability model of the JAEA-ADS linac, report the MTBF
results, and point out the potential route toward operatingwith the required availability.

INTRODUCTION
The Japan Atomic Energy Agency (JAEA) is working
on the design of a 30-MW CW proton linear accelerator(linac) for the accelerator-driven subcritical system (ADS)
proposal [1]. Figure 1 displays a simple schematic of theJAEA-ADS facility. Support systems are all the infrastructure required to operate the linac: electrical power grids
and cryogenic plant, among others. The JAEA-ADS linac
will accelerate a 20 mA proton beam to a final energy of
1.5 GeV. Then, the beam transport to the target (BTT) will
carry from the end of the linac to the spallation target inside
the 800-MWth thermal power subcritical reactor.

Table 1 summarizes the most relevant parameters of theJAEA-ADS linac. Reliability is the priority requirement for
the ADS to avoid thermal stress in the subcritical reactor
structures due to beam trips. The beam trip analysis for
the JAEA-ADS facility estimates the Medium time between
failure (MTBF) is about 172 h, based on beam trips longer
than 5 minutes [2]. Such reliability is beyond the current
linac performance; thus, the JAEA-ADS linac adopted areliability-oriented design [3].
Table 1: Main Characteristics of the JAEA-ADS Accelerator
Parameter
Particle
Beam current (mA )Beam energy (GeV)
Duty factor (%)
MTBF (h)Proton20
1.5100 (cw)>172

Figure 2 shows the JAEA-ADS linac baseline. It is composed of a normal conducting part and a superconducting
section. Most of the energy gain is provided by the superconducting region that comprises three different types ofSRF cavities operating at different frequencies: Half-WaveResonator (HWR) operates at 162 MHz, Single Spoke Resonator (SSR), at 324 MHz, and five-cell Elliptical Resonator(EllipR), at 648 MHz. Additionally, the SSR and EllipR sections have two different SRF cavity models, each of them
optimized at a different geometrical beta 𝛽𝑔 to achieve highacceleration [4].
After obtaining a robust beam optics design, we implemented fast beam recovery schemes based in hot standby
and local compensation based on k-out-of-n to reduce thebeamdown time due to the beam trips [5]. This scheme is
known as fault-tolerance configuration.
This work assessed the reliability of the full JAEA-ADS
facility. Furthermore, it showed that the fault-tolerance
schemes for the linac satisfied the requirements of MTBF
for the JAEA-ADS proposal.

METHODOLOGY

Figure 1: JAEA-ADS design.
∗ byee@post.j-parc.jp

This analysis was based on the reliability engineering
works [6–8] and high-intensity linac reliability studies [9–12]. The calculations concentrated on evaluating the facility’s reliability during the useful life period of the system.
Figure 3 shows the common failure rate evolution of the system, the so-called bath-tub curve. At the useful life period,the failure rate (𝜆) is constant.
𝜆 is expressed as:- 286 -Proceedings of the 19th Annual Meeting of Particle Accelerator Society of Japan
October 18 - 21, 2022, Online (Kyushu University)

PASJ2022 TUP006

Figure 2: JAEA-ADS linac configuration.

Figure 3: Failure rate evolution of a system.

1.
(1)
MTBF
Availability (A) is the common figure of merit to evaluate
the reliability of the linacs. A is the probability that a system
is properly operating when it is required, and it has thefollowing simple steady-state representation:

Figure 4: System connections: series (a), hot standby (b),and k-out-of-n (c).

𝜆=MTBF,(2)MTBF+MTTR
where MTTR is the medium time to repair.
Reliability analysis was performed using reliability block
diagrams (RBD). The RBD approach divides a system into
individual blocks where reliability parameters are estimated.
Figure 4 shows the different configurations of the elementsthat were considered for the JAEA-ADS linac. In seriesconnect: if one of the sections fails, the full system is down.
For the hot standby, part of the system is duplicated, with onepart the principal operator and the other as offline-powered
equipment ready to operate in case of a failure in the major
structure. The k-out-of-n configuration states that a systemcomposed of n elements needs at least k of its components
to operate.
For each of the connections, the equations to compute theMTBF and 𝐴 for repairable systems are provided.

Series:MTBFSeries =1,∑𝑖 𝜆𝑖ASeries = ∏ A𝑖 ,

𝐴=(3)
(4)

where 𝜆𝑖 and A𝑖 are the failure rate and availability of the 𝑖element, respectively.
Hot standby:
3𝜆 + 𝜇,2𝜆2(5)

2𝐵 + 𝐵2,
1 + 2𝐵 + 𝐵2
where the 𝐵 = MTBF/MTTR.
k-out-of-n:(6)

MTBFhot standby =where 𝜇 = 1/MTTR.

- 287 -Ahot standby =MTBF𝑘−𝑜𝑢𝑡−𝑜𝑓 −𝑛 =(𝑘 − 1)!𝜇𝑛−𝑘.
𝑛!𝜆𝑛−𝑘+1(7)Proceedings of the 19th Annual Meeting of Particle Accelerator Society of JapanOctober 18 - 21, 2022, Online (Kyushu University)

PASJ2022 TUP006𝑛𝑛!
A𝑘−𝑜𝑢𝑡−𝑜𝑓 −𝑛 = ∑𝐴𝑖 (1 − 𝐴)𝑛−𝑖 ,𝑖!(𝑛− 𝑖)!
𝑖=𝑘(8)

where the 𝑛 elements have the same availability A.
This study assumed that each element is completely independent, except for the relationship indicated in the RBD.
The calculations were done by implementing the formulas
in a python [13] script, which results had a good agreementwith a free reliability software [14] and other reliability studies [9, 10] .

RESULTS

Table 3: Configuration of the beam transport lines for theJAEA-ADS design. The notation for representing the elements is B = Buncher cavity, D = Dipole, S = Solenoid, andQ = Quadrupole.
SectionQSDBMEBTHSBT A (series)
HSBT B (series)
HSBT A (fault-tolerance)
HSBT B (fault-tolerance)
BTT

60076
11001000000102200120

The MTBF of the JAEA-ADS facility was computed as aseries connection of the support systems, JAEA-ADS linac,and BTT, as shown in Fig. 1. This was done to evaluate
different configurations applied to the linac. Table 2 shows
the data input used in this analysis. The values are based onavailability studies on high-intensity linac facilities [9–12].
Table 2 has two types of SRF cavity packages: low-𝛽 andhigh-𝛽. low-𝛽 value was obtained from the PIP-II analysis
for the HWR cavities [10]. In our study, the low-𝛽 arealso used for SSRs cavities. The high-𝛽 corresponds tothe elliptical cavities and uses the data from SNS [11]. Inaddition, two types of quadrupoles were employed: one tooperate in the normal environment of the linac and the otherto operate in a high radiation environment, BTT.
Table 2: Reliability Values of the Components Use for theRBD Calculations

Figure 5: Block diagram for the JAEA-ADS linac and BTT.

System/package

The analysis focussed on the reliability of the JAEA-ADS
linac. Figure 6 depicts the two schemes for the JAEA-ADS
facility considered in this analysis: series and fault-tolerance.
The fault-tolerance scheme was developed from fast beam
recovery studies for the JAEA-ADS linac to achieve highreliability [5]. Fault-tolerance consisted of the use of hotstandby redundancy from the ECR to the HWR section, theso-called injector, and local compensation based on k-out-ofn redundancies for the rest of the linac, i.e., from the SSR1
section to the end of the linac.

Support systems
ECR package
LEBT package
Buncher package
Low-𝛽 SRF cavity package
High-𝛽 SRF cavity package
Solenoid package
Quadrupole package
Quadrupole package in BTT
Dipole package in BTT
Vacuum system
Steering system
Control system
Local cryogenic system

MTBF (h)MTTR (h)1.8 ×103
1 ×103
6.7 ×103
1.3 ×104
2.9 ×104
1.2 ×104
8.3 ×104
3.1 ×104
7.1 ×104
7.1 ×104
4 ×104
8.3 ×104
5 ×104
5 ×105

462
5.4
97.7
5.6
67.8
2.4
44.6
24
42
1.22Table 4: Summary of the MTBF and Availability of theSupport Systems and the BTT for the JAEA-ADS Facility

For support systems, Tables 2 and 4 reported the MTBF,MTTR, and availability were used in this analysis. The reliability for the BTT was computed as a series configuration ofthe elements that composed it. Table 3 presents informationon the configuration of BTT [15, 16]. The BTT section wasmodeled using the configuration presented in Fig. 5. Eachtransport line contains one auxiliary system and does nothave local cryogenics. The MTBF and availability werecomputed by using input data of Table 2, and their values
are reported in Table 4.

Section

MTBF(h)steady stateavailability (%)

Support systems
BTT

1881.2
5100

97.6
99.1

This study compared the MTBF for series against fault tolerance schemes for the JAEA-ADS linac to evaluate which
configuration is most suitable for the ADS project. The
MTBF of the section will be the contribution of the RF
cavities, magnets, auxiliary systems per period, and local
cryogenics connected in series, shown in Fig. 5. It is noteworthy that the RF cavity and magnet packages considered- 288 -Proceedings of the 19th Annual Meeting of Particle Accelerator Society of Japan
October 18 - 21, 2022, Online (Kyushu University)

PASJ2022 TUP006

that the SSR1 section could operate if 64-out-of-66 cavities
were operational. Similar to the solenoids, 32-out-of-33 wasrequired to work.
Table 6: MTBF for the Different Section of the JAEA-ADS
Linac Baseline
SectionInjector
HSBT B
SRR1
SSR2EllipR1
EllipR2
Whole linac
Figure 6: Diagram for the JAEA-ADS accelerator facility.
Subplot (a) shows the a series connection configuration. Subplot (b) is the the fault-tolerance configuration which consist
in hot-standby in the injector part and k-out-of-n redundancy
configuration for the main linac.
the entire assembly, such as power supplies and instrumentation. Tables 3 and 5 show the configuration of each sectionthat composes the JAEA-ADS linac.
Table 5: Lattice configuration in the superconducting
linac. The notation used for the layout is C = SRF cavity, S = Solenoid, and Q = Quadrupole.
SectionLayout

HWR
SRR1
SSR2
EllipR1
EllipR2

S-C
S-C2
S-C3
Q2 -C3Q2 -C5Baseline
Cavities/
Periods/
Magnets Cryomodules
25/25
66/33
72/24
60/42
70/28

SeriesMTBF (h)fault-tolerance

2.3×1028.3×104
2.4×102
2.6×102
1.4×102
1.4×102
3.8×101

3.4×103
4.2×103
6.7×1029.2×102
1.1×103
1.6×1032.1×102

Table 6 summarizes the MTBF for series and faulttolerance configurations for the baseline design of the JAEAADS linac. MTBF is greater for the fault-tolerance casethan the series one, except for the HSBT B section. However, this is because the HSBT B for series configuration
comprised only one solenoid, as shown in Table 3. In seriesconfiguration, the MTBF was decreased when the number ofelements increased. In the case of fault tolerance, the MTBF
mainly depended on the number of elements that were compensated simultaneously: as the number of compensatedcomponents increased, the MTBF increased. The MTBFof only the JAEA-ADS linac is 38 and 210 h for series andfault-tolerance, respectively.
Table 7: Summary of the MTBF and Availability of theJAEA-ADS Facility for the Different Configurations

25/3
33/33
24/24
21/21
14/14

Table 3 presents two beam transport line designs fromthe HWR to the SSR1 section, HSBT. In addition, HSBTis divided into two regions: HSBT A and B. HSBT A is
the part of the transport line that is duplicated when the hotstandby scheme is applied. On the contrary, HSBT B is
the part that is common for both injectors. When a seriesconfiguration is considered, HSBT is only HSBT B thatis composed of one solenoid, as reported in the referencedesign [4]. Fast beam recovery studies showed we could
simultaneously compensate for the failure of all the SRF
cavities or magnets that composed a period from the SSR1
to EllipR2 sections. The k-out-of-n redundancy is only applied to the RF cavity and magnet packages. For example,
in SSR1, a period comprises one solenoid and two SSR cavities. The total amount of solenoids and cavities is 33 and66, respectively. Thus, the k-out-of-n redundancy indicatedConfiguration

MTBF
steady state(h)availability (%)

SeriesFault-tolerance

36.9
184.1

82.695.9

Table 7 reports the MTBF and steady-state availability
for the JAEA-ADS installation, considering the contributionof the support systems, the JAEA-ADS linac, and the BTT.
The MTBF for the series scheme was about 37 h, but thefault tolerance was 184 h, which is higher than the requiredMTBF.

CONCLUSIONSThis work assessed the MTBF and the steady state availability of the JAEA-ADS facility, for its useful life period,by using the reliability block diagram method. The analysis separated the contributions into three parts: supportsystems, JAEA-ADS linac, and beam transport to the target.
This study focussed on the contribution of the JAEA-ADS
linac baseline design considering two configurations: series
and fault-tolerance, which comprise hot standby by the injector part and k-out-of-n redundancy for the main linac. The- 289 -Proceedings of the 19th Annual Meeting of Particle Accelerator Society of Japan
October 18 - 21, 2022, Online (Kyushu University)

PASJ2022 TUP006

calculations used data from other high-intensity accelerator
facilities and a detailed configuration of the elements thatcomposed the JAEA-ADS linac lattice.
Fault-tolerance scheme exhibited high-reliability performance by increasing the MTBF almost six times regarding
the value achieved by the series configuration. As a result,the MTBF of 184 h satisfies the requirement over 172 h. This
result shows that fast beam recovery schemes for the linac
allowed to fulfill the requirements of MTBF for the JAEAADS design. In future work, a more robust model will be
developed to provide a more accurate assessment of thereliability.

ACKNOWLEDGMENTS
The authors would like to thank to the members of theJAEA-ADS and J-PARC linac groups for their commentsand suggestions. This work was supported by the Subsidy
for Research and Development on Nuclear Transmutation
Technology.

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