1. Preliminary Hazard Analysis of Bunker
Overview
Manorma Kumar
(Christine Marklund and Alf Nilsson, Lloyd’s Register)
16 October 2018

2. Requirements (1) Risk Matrix Hazard identification
ESS risk matrix from GSO is used for Radiation safety (ESS rev 5) and conventional safety risk matrix (ESS Risk Matrix for Conventional Safety Risks).
Hazard identification
Both operation and maintenance hazards are considered. Installation hazards are also addressed but not in great detail.
Integration (PSS requirements)
PSS information is used as far as possible.

3. Requirements (2) Completeness Passing the results Seismic events
Hazard analysis is made as complete as possible due to time constraints. Not part of a global hazard analysis, still just the bunker.
Passing the results
Not a case now
Seismic events
The Bunker is designed to withstand the requirements in the ESS Global Seismic Strategy, together with the Seismic Ground Motion Hazard Assessment. The H4 seismic requirement has been removed from the bunker requirements.
Others
Partly addressed

4. Scope Bunker Structural Support System (BSSS) Bunker Wall System (BWS)
Bunker Roof System (BRS)
Bunker Access Safety System (BASS) including the Bunker PSS (Personal Safety System)

5. Hazard analysis of Bunker System (BS)
Internal events BS
Internal events emanating outside the BS but on ESS site
External events emanating outside the ESS site
Component failures
Events with multiple failures

6. Methodology Choose the system or area to be analyzed
Define initial conditions.
Identify Hazards, PIEs and Top events and assign Event classes to the PIEs.
Analysis - sequence of events
Analysis – radiological impact
Analysis - non-radiological (conventional) impact
Identify impact on other systems & areas

7. Risk Matrices (Radiological risks)
Notation
Description
Definition
Frequency per year H1
Normal Operations
All the operating conditions that are planned - H2
Anticipated events
Events and circumstances which can be expected during the facility’s lifetime
> 10-2 H3
Unanticipated events
Events and circumstances which are not expected to occur during the facility’s lifetime
10-4 – 10-2
H4A
Improbable events
Events and circumstances which are not expected to occur
10-6 – 10-4
H4B
Events with multiple failures
Events and circumstances in the frequency range greater than 10-4 per year analysed in combination with common cause failure instead of a single failure
> 10-4 H5
Highly improbable events
Events and circumstances that can potentially lead to a significant radioactive emission to the surroundings; highly improbable events postulated independently of the occurrence frequency
10-7 – 10-6 R
Residual risk
< 10-7

8. Risk Matrices (Conventional risks)
Likelihood
Notation
Description
Frequency per year 1 H2
Frequent
> 10-2 2
H3A
Occasional
10-3 – 10-2 3
H3B
Remote
10-4 – 10-3 4 H4
Improbable
10-6 – 10-4 5 H5
Highly improbable
< 10-6

9. Postulated Initiating Event (PIE)
A postulated initiating event (PIE) is “an event identified during design as capable of leading to anticipated operational occurrences or accident conditions. The primary causes of postulated initiating events may be credible equipment failures and operator errors (both within and external to the facility) or human induced or natural events.” [IAEA Safety Glossary, 2007]

10. Identification of PIEs (1)
Internal Events BS
After maintenace, personnel gets trapped inside bunker, H3
Start-up of proton beam with open BS or with people inside BS, H3
Flooding, H3
Fire, H3
Leaving instruments, tools or other items inside BS, H3
Environmental conditions (temperature, humidity etc.), H3
High radiation level, H4
Stacked roof sections fall during maintenance, H3

11. Identification of PIEs (2)
Internal events emanating outside the BS but on ESS site
Beam turns on during maintenance, H3
Drop of heavy load (> 1000 kg), H4
Drop of lighter load (≤ 1000 kg), H3
Accidental removal of parts of the roof blocks, H3
Collision between crane and bunker, H3
Improper installation of Bunker roof blocks after maintenance, H3
Flooding, H3
Fire, H3
Transportation impact on BS, H3

12. Identification of PIEs (3)
External events emanating outside the ESS site
Seismic events, H5
Loss of external power, H2
Strong wind including tornado, H4
Heavy snow load, H4
Extreme temperatures, H4
Fire, H4
Impact from industrial and transportation accidents, H4
Airplane crash, R

13. Identification of PIEs (4)
Component failures
Failures in the PSS instrumentation degrading the PSS for BS, H3
Other instrument failure, H3
Failures in beam shutters, H3
Events with multiple failures
Multiple failures in the PSS instrumentation severely degrading the PSS for BS, H4B
Multiple failures in several beam shutters, H4B

14. Hazard analysis (1) Radiation Fire Flooding
Structural Integrity – Seismic/Earthquake
Drop loads

15. Hazard analysis (2)

16. Conclusions and recommendations
The issue of ventilation or no ventilation in the bunker should be resolved and documented in the next version of the PSAR.
Neutron absorbing material used to wrap instruments and internal parts of the bunker should be verified either combustible within the threshold or non-combustible.
The hazard of flooding of the bunker due to ruptures in the water cooling system should be addressed. This should also include a decision on whether or not there should be drain tanks present inside the bunker.
More information is needed about fire suppression methods inside the bunker. The documents at hand often do not identify the bunker or target specifically, which makes it difficult to assess the risk in that area. It is informed that the ESS level investigation is ongoing and decision is expected in mid-November 2018.
More information about the neutronic characteristics of the current design is needed to assess the hazard of radiation leaks from the bunker.
More information on air and water activation is needed for further analysis.
It is recommended to look at human actions and perform human reliability analysis in the further analysis.
The operating procedures should be defined to be able to analyse the risk from operator actions.
Finally, it is recommended to extend this hazard analysis to include the quantification of various safety and protection functions to conclude the event classifications.

17. Way forward
Bunker hazard analysis will be extended to include quantitative analysis.
Continue more investigation on the hazard analysis conclusions and more detailed analysis.

18. Thanks!
Questions?