CNRA Working Group on the Safety of Advanced Reactor (WGSAR) · - The systems and features involved in severe accident prevention and mitigation are expected to be reliable based

© 2015 Organisation for Economic Co-operation and Development

CNRA Working Group

on the Safety of Advanced Reactor

(WGSAR)

Marina Demeshko,

WGSAR Technical Secretariat

IAEA-GIF meeting

9 – 11 December 2019, Vienna

© 2015 Organisation for Economic Co-operation and Development© 2015 Organisation for Economic Co-operation and Development 2

WGSAR mandate

To exchange information and experience from licensing and oversight of past and current nuclear facilities. The WGSAR will plan its work to ensure improvements in nuclear safety through appropriate regulation for advanced reactors and associated installations.

To provide regulatory perspectives through the issuance of technical reports containing discussions of areas in which additional or revised regulatory framework and licensing approaches, including safety research, may be needed to facilitate effective regulation of advanced reactors and to develop common understanding and approaches.

To take into consideration the GIF safety design criteria and the development of the GIF safety design guidelines. The WGSAR will provide its feedback to GIF to establish effective and independent interactions with industry at early stages of advanced reactors development.


WGSAR Administration

• WGSAR Chair:

– Ms Amy Cubbage (NRC)

• WGSAR Vice-Chair:

– Mr Olivier Baudrand (IRSN)

• NEA Technical Secretariat:

– Ms Marina Demeshko

• Meetings:

– Last: 9-11 October 2019 (Paris)

– Next: 22-24 April 2020 (Paris)

• Membership: 10 countries + 2 international organisations


4th WGSAR Meeting

• 9-11 October 2019

• 7 countries participated

+ IAEA + EC +GIF delegation

• Discussion on the content of Technical report on Risk Informed Performance Based approach

• Presentation of (GIF SDC-TF) Second SDG report (S. Kubo)

• Presentation on GIF activities on safety design criteria and R&D for HTGR (Li Fu)

• Discussion on areas of GIF/WGSAR interactions focused to:

– Improve processes to identify critical issues related to safety relevant

phenomena and regulatory aspects for the different Gen IV concepts

– To enhance information exchange on new research results in more detail


Separate activity in the frame of cooperation with GIF:

Review of GIF SDC Phase 2 for SFR (limited in scope to regulatory aspects).

Next possible topics for WGSAR activities:

1

• GIF proposal for risk-informed and performance-based licensing basis event selection/bounding event selection; (critical safety functions; PRA for advanced non-LWRs;)

2 • Material selection, integrity and through life challenges, in-service inspection;

3

• Source term (graphite dust, activation of coolant impurities, migration of metal fission products);

4

• Identification of major physical phenomena (e.g. HTGR and air ingress topic; primary and secondary coolant interactions;)

5• Remote/autonomous operations for micro reactor;


Regulatory Perspectives on Safety Aspects Related

to Advanced SFRTechnical report on Severe accidents prevention and mitigation measures in SFRs (part 1)

• 14 “Common Positions” have been identified

- The safety goals for Generation IV SFRs are expected to be more demanding than those

for Generation III LWR reactors: Generation IV SFRs are expected to have lower core

damage frequency than Generation III LWR reactors, an enhanced robustness of the safety

case based on enhanced margins to safety, and less reliance on supporting systems (e.g.

electrical supply, cooling water supply, etc.) and operator actions.

- Consistent to Vienna Declaration, new Generation IV SFRs “are to be designed, sited, and

constructed, consistent with the objective of preventing accidents in the commissioning and

operation and, should an accident occur, mitigating possible releases of radionuclides

causing long-term off-site contamination and avoiding early radioactive releases or

radioactive releases large enough to require long-term protective measures and actions”.

- For Generation IV SFRs, long term habitability restriction are not expected to be needed in

case of a severe accident. However, emergency planning zones and siting requirements

should be defined according to the national regulation.

https://www.oecd-nea.org/download/gsar/documents/NEA_CNRA_R_2018_1_V00.docx



to Advanced SFRTechnical report on Severe accidents prevention and mitigation measures in SFRs (part 1, cont)

- Credible conditions originating from multiple failures or conditions from extreme external

events should be determined based on specific design characteristics of SFRs and should

be considered as design extension conditions with the aim to prevent severe accidents.

- Provisions are expected to be implemented such that plant event sequences that could

result in high radiation doses or in a large or early radioactive release have to be

“practically eliminated” and plant event sequences with a significant frequency of

occurrence have to have no, or only minor, potential radiological consequences.

- In the safety case, the applicant is expected to demonstrate that provisions taken regarding

severe accident enable the plant to reach a safe and stable state, e.g. where the

confinement function is maintained or recovered and the corium is cooled and subcritical.

- Generation IV SFRs safety functions should be maintained consistent with the time needed

to recover off-site support, with a minimum of three days.





- The applicant is expected to demonstrate that the energy release from postulated severe

accidents does not challenge the structural integrity of the second and third barriers (e.g.

respectively the vessel and the containment). Additionally, the WGSAR considers that the

assessment of energy release in case of severe accident is a topic to be investigated. The

safety case should be supported by results of R&D works.

- The safety case should be based on deterministic and probabilistic approaches.

Probabilistic assessments (core damage and release frequencies) are expected to be done

early in the design. The WGSAR expects applicants to assess the sensitivity of reactor

state parameters in order to identify potential cliff-edge effects.

- The systems and features involved in severe accident prevention and mitigation are

expected to be reliable based on independence, diversity, and adequate system

classification and associated qualification. The systems involved in design extension

conditions (A and B) are expected to rely as little as possible on off-site power and cooling

water supply. The systems involved in severe accident mitigation are expected to be

designed with enhanced margins with regards to natural hazards and their plausible

combinations.





- Special attention should be given to neutronic parameters so that they do not compromise

the safety of SFRs.

- The WGSAR notices that the second barrier (e.g. the vessel(s) and the roof slab) can play

a major role to the confinement function in case of accident. Since potential leaks (e.g.

through the roof slab) can constitute a weak point of the confinement function, the second

barrier is expected to have appropriate quality and monitoring to ensure the leak rate is

limited as far as reasonably practicable.

- The licensee is expected to:

• implement I&C to diagnose severe accident conditions;

• address the information needs for accident management by obtaining information on

some key parameters; these parameters are expected to include at least

measurements of temperatures at critical locations, coolant levels, hydrogen

concentrations, and parameters indicating release kinetics and intensity;

• demonstrate with a reasonable assurance that the equipment and I&C will survive in

the ensuing harsh conditions through appropriate qualification.





- Due to high uncertainties in the SFRs severe accident domain, the WGSAR considers it

necessary to benchmark codes and models against adequate phenomena and

experiments. Sensitivity studies are expected with the objective of identifying the risk of

cliff-edge effect that should be avoided.




to Advanced SFRFinal report on Neutronics and criticality safety for SFRs (part 2)


- the existing regulatory framework for LWRs is general enough to be applicableto SFRs, but some specificities to be taken into account

- there is an agreement that neutron parameters of SFRs should meet certainrequirements (minimize the impact of sodium void reactivity effect, etc.)

- the use of inherent and passive safety with regards to core design of SFRsshould be encouraged

- the requirements for establishing and justifying neutron parameter safety limitsfor advanced SFRs are similar to conventional power reactors

- the uncertainty analysis is important and must address all important sources of code,nuclear data and input data uncertainty

- the experimental justification is required for v&v of computer codes and cross-sectionslibraries used in SFR design applications

• The report also identifies one topic for further discussion

- the reliability of shutdown mechanisms would include understanding the impact of phenomena such as sodium aerosol deposition, tribology issues etc. which could, for example, prevent control rod insertion systems



to Advanced SFRFinal report on Analytical codes and Methods (part 3)


- the existing guidance can be applied to SFR, no need identified for SFR specific guidance in this area at this time

- verification and validation of codes is necessary to provide confidence in results

- uncertainties should be assessed, SFR analysis should be suitably conservative for DB, best estimate approaches are acceptable for DEC

- it should be confirmed that the legacy codes available are appropriately verified and validated for applicability to new designs

- the existing substantial body of SFR test data internationally to be made broadly available to support validation of codes

- it should be verified that any new important phenomena are identified for new designs andthat the relative importance of the phenomena is verified

• The report also identifies topics for further discussion

- it would be useful to develop additional standard international benchmarks that could be used to validate codes and assess uncertainties

- to establish a task group on analytical codes to discuss best practices for regulator use of analytical codes, to share experience with code development and validation, and to develop recommendations for additional research needs - done



to Advanced SFR

Final report on Fuel qualification for SFRs (part 4)


- term “fuel qualification” is defined as the process for verifying that fuel is acceptable for use

- failure mechanisms will need to be established for new innovative SFR fuel designs (e.g., fuelbowing and distortion should be evaluated)

- demonstration of fuel integrity at normal operation, transients and anticipated operating conditions should be supported by both analyses and experiments

- an irradiation testing program needs to be implemented covering at least the burnup limitsand fuel performance at NO and the range of AOCs

- testing data should be available to assess fuel performance for limiting DB events

- safety analysis of the SFR fuel assemblies should address the safety function of maintainingcore compactness and ensuring the core mechanical stability

- fuel testing and manufacturing should be conducted under a QA program with associatedrecordkeeping and reporting of operational events

• The report also identifies topic for further discussion

- a guidance in the area of fuel qualification to address regulatory requirements associated with fuel neutronic behaviour and thermal-mechanical performance


Current Activities (1/3)

Regulatory Approaches on Fuel Qualification for Advanced Reactors

• To share regulatory experience and to prepare a technical report on fuel qualification approaches related to advanced reactors. This report will identify safety criteria and additional research needs, if needed, to support the regulators’ safety review.

Objective

• Technical report describing the regulatory approaches on fuel qualification for advanced reactors with identification of safety criteria and additional research needs to support the safety findings by the regulators.

Outputs

• The WGSAR will interact with CSNI/WGFS, NI2050, and GIF, as needed.

Interaction with Others


Current Activities (2/3)

Regulatory approaches related to use of analytical codes and

methods in safety assessment of advanced reactors

• To share regulatory experience and to prepare a technical report on regulatory approaches related to use of analytical codes and methods in applicants safety assessment and regulatory confirmatory analysis of advanced reactors. This report will identify regulatory expectations for the development, validation and use of codes and methods, and highlight relevant knowledge gaps, to support the regulators’ assessment.

Objective

• Technical report describing the regulatory expectations on development, validation, qualification and use of analytical codes and methods in applicants safety assessment and regulatory confirmatory analysis of the advanced reactors with identification of commendable practices and knowledge gaps to support regulatory assessments.

Outputs

• The WGSAR will interact with CNRA/WGRNR and GIF, as needed.



Current Activities (3/3)International benchmark considering a core damage scenario in a lead cooled fast reactor (LFR) type to assess code capabilities and knowledge gaps relevant to regulators questions

• To conduct an international benchmark on a LFR plant application to assess capabilities from a regulators point of view of existing simulation codes to analyse a core damage scenario leading finally to fission product release into the environment. The benchmark results will be used to prepare a technical report on code capabilities for the purposes of regulatory studies of design margin and cliff edge effects. The report will identify regulators expectations for those codes and highlight possible knowledge gaps.

Objective

• Conduction of a step-wise international benchmark considering a core damage scenario in a LFR type reactor and a report describing, from the regulators point of view, the benchmark results, code capabilities, uncertainties and possible knowledge gaps.

Outputs

• The WGSAR will interact with CNRA, CSNI, WGAMA, IAEA, as needed.



Thank you for your attention!

Documents

CNRA Working Group on the Safety of Advanced Reactor (WGSAR) · - The systems and features involved in severe accident prevention and mitigation are expected to be reliable based