Reliability Modeling of an ADS Accelerator SNS-ORNL/Myrrha Linac

(MAX project)

EuCARD2, GENEVA (20-21 March 2014 )

CERN

Step 1. SNS Linac modeling (MAX Task 4.2)

– Input Data

– Methodology

– SNS Fault Tree

– Reliability Analysis

– Modeling results evaluation; SNS Logbook Data

– Conclusions

Step 2. Myrrha Linac modeling (MAX Task 4.4)

– Model Assumptions

– Fault tree; Quantification data

– Control System; Fault tolerance

SNS Linac reliability analysis

- feedback on SNS Linac reliability performance

- modeling tool for Myrrha Linac (Task 4.4).

Draft preliminary conclusions and recommendations:

- Maximize the reliability/availability and the safety of the MYRRHA accelerator

- Guidance for designing MYRRHA accelerator.

MAX Task 4.2 - Existing accelerator reliability modeling (methodology currently applied for NPPs – modeling with Risk Spectrum)

The Spallation Neutron Source (SNS – ORNL) Linac was selected

1. SNS Linac Modeling (MAX Task 4.2)

SNS Linac Modeling – Input Data

SNS Design (Systems and Functions)

System functions and interfaces

Components No. (by type)

Degree of redundancy

Data Source:

SNS public info; SNS Design Control Documents (DCDs)

Reliability Data (Quantifying model )

Failure - MTTF and repair times – MTTR

Data Source:

SNS Operation team (SNS BlockSim model – George Dodson, John Galambos)

SNS Operating Data

Component failures modes - cause, type of component, time to repair, etc

Failures causing acc. trips: cause, component and system concerned, duration of trip (Availability data)

Data Source:

SNS Operation Data collection (http://status.sns.ornl.gov/beam.jsp)

SNS BlockSim Model

SNS Linac Modeling – Input Data

http://status.sns.ornl.gov/beam.jsp

The Results from modeling - evaluated with respect to the SNS Logbook operational data - accelerator trip failures and overall availability - recorded during the period October 2011 – June 2012.

General Assumptions

Not modeled – SNS Ring - RTBT, stripper foil, etc. (not relevant for Max project purposes)

Risk Spectrum Type 1 reliability model – Repairable (continuously monitored) – for all SNS Linac components

• Failure/Repair processes – exponential distributions; failure/repair rates ct.

• It is assumed q=0

¨Mean Unavailability¨ type of calculation (unavailability values for the basic events):

Q=λ/(λ+µ

(Long-term average unavailability Q is calculated for each basic event)

SNS Linac Modeling – Methodology

SNS Module 1- first modeling step: RFQ + MEBT + DTL

Gradual development of the SNS Linac model

In-depth understanding of the SNS design and functioning for an accurate model.

SNS Fault Tree (complete model) - graphical representation of the SNS systems functional structure describing undesired events (“ system failures") and their causes.

SNS Linac Modeling – Model development

SNS Linac Fault Tree – main level

SNS Linac Modeling – Fault Tree

DTL RF Fault Tree Structure

SNS Linac Modeling – Fault Tree

1. SNS Linac Modeling

Analysis Case – Results Q = 2.60E-01 = 0.26; Q = 26 %

A = 1 - Q = 73 % (Mean Availability)

Minimal cut set (MCS) analysis - generate minimal cut sets of the fault tree and perform a point-estimate quantification of the top event.

SNS Linac Modeling – Reliability Analysis

SNS Linac Modeling – Analysis Results

In line with the conclusions from the SNS RS Model runs:

RF system and electrical system failures - most frequent

Electrical systems failures - most contributing to accelerator downtime

Accelerator trip failures frequency (by system)

SNS Linac Modeling – Results evaluation; SNS Logbook data (Accelerator trip failures)

Accelerator downtime contribution (by system)

RF System failures (no. & duration-hours)

In accordance with the SCL RS analysis: Most affected subsystems of the SNS Linac (by failures leading to accelerator trips):

SCL-HPRF (Superconducting Linac - High Power Radiofrequency) - short failures frequency

HVCM (High Voltage Converter Modulator - duration of trips

SNS Linac Modeling – Results evaluation; SNS Logbook data (Accelerator trip failures)

The reliability results show that the most affected SNS Linac parts/systems are:

SCL, Front-End systems (IS, LEBT, MEBT), Diagnostics & Controls RF systems (especially the SCL RF system) Power Supplies and PS Controllers

These results are in line with the records in the SNS Logbook

Reliability issue that most needs to be enforced in the linac design is the redundancy of systems, subsystems and components most affected by failures

Need for intelligent fail-over redundancy implementation in controllers, for compensation purposes

Enough diagnostics have to be implemented to allow reliable functioning of the redundant solutions and to ensure the compensation function.

SNS Linac Modeling – Conclusions

1. SNS Linac Modeling

Activities Design & reliability data base (Sources: SNS, Max team, suppliers, conservative assumptions / reliability targets)

Myrrha Linac model - based on the SNS RS Model; considering the SNS reliability analysis results and conclusions.

Iterative process – Myrrha Linac Model updating during design work

Myrrha Linac Risk Spectrum fault tree – 95% completed; preliminary results in line with previous

Reliability analysis to be performed, with due consideration of reliability challenges

Special attention - design of advanced Diagnostics and Control systems

Overall approach

Fault Tree, based on SNS model + Max design

Basic Events: Component / Function failures

Undeveloped Events/Systems: Reliability targets

Reliability model: Availability / Failure frequency (Linac shutdown)

Reliability Analysis: Design Optimization

Myrrha linac - Reliability challenges:

Injector Switch

Fault tolerance/compensation function

SSAs (Solid State Amplifiers) reliability

2. Myrrha Linac Modeling (MAX Task 4.4)

1. SNS Linac Modeling

Myrrha Linac Modeling – General Assumptions

Modeling Assumptions

- RF System: considered SNS (except Klystrons, modulators, & related) SSAs

(spec. RFQ: Myrrha 4-rod (176MHz) vs. SNS RFQ (4-vane))- AUX syst SNS, modified for Myrrha (current design)

- Missing Reliability data

Assumptions

(Equipment overall Reliability data from manufacturer available? (IS ECR, RFQ, SSAs)

Targets

(to be further considered)

/// (detailed design developing the fault trees (rel. data?)

1. SNS Linac Modeling

Myrrha Linac Modeling (Fault tree; quantification data)

Missing Data:

- No significant impact expected - (Comps/Assemblies level of details) - Undeveloped Events

- Relevant impact (INJ switch-magnet, Fault tolerance/Comp. syst., Control syst) – Assumptions/Targets

1. SNS Linac Modeling

Myrrha Linac Modeling (Control Syst.; Fault tolerance)

CTRL System modeling

- Fault tree development (Myrrha control philosophy)

- Rel. Targets to be assigned for: Diagnostics, Data Acquisition & Processing, C-C signals transm., local Control modules, etc.)

- Defined Diagnostics are currently being included in the general CTRL syst. fault tree

1. SNS Linac Modeling

ACKNOWLEDGMENTWe would like to thank G. Dodson and J. Galambos (SNS) for their help in completing the SNS Reliability Study.

Thank you

A.E. PITIGOI – EA (aph@empre.es)

P. FERNANDEZ RAMOS – EA (pfr@empre.es)