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Nuclear cogeneration: advantages of the HTR safety concept
O. Baudrand – [email protected]
C. Pohl – TÜV [email protected]
NC2I-RNuclear Cogeneration Industrial Initiative Research and Development Coordination
1NC2I workshop - September 2015 - Brussels
Content
• Safety studies in the NC2I-R FP7 project• Lessons learnt from feedback on nuclear cogeneration• Advantages of the HTR safety concept for cogeneration• Foreseen cogeneration layouts• Recommendations for safety assessment and licensing• Recall of « generic » licensing steps• Pending options• Outline
2NC2I workshop - September 2015 - Brussels
Safety studies in the NC2I-R FP7 project
• Main questions: Which are the specific risks associated with nuclear cogeneration? Are the existing licensing procedures adapted? What could be the additional safety requirements induced by
cogeneration
• Main goals Analyse the feedback on nuclear cogeneration Identify the current status of licensing procedures in potentially
candidate countries and propose safety related milestones for the licensing of a prototype
List the specific issues and propose primary guidelines to support the licensing of a prototype cogeneration plant
3NC2I workshop - September 2015 - Brussels
Lessons learnt from feedback on nuclear cogeneration (1/5)
4
Typical layout for cogeneration with PWR reactor
NC2I workshop - September 2015 - Brussels
Barrier
Barrier
PRIMARYSECONDARY
TERTIARY
Limit of the nuclear site
Lessons learnt from feedback on nuclear cogeneration (2/5)• Review of past and existing
installations Switzerland (Beznau) Norway (Halden) Lithuania (Ignalina) Hungary (Paks) Slovakia (Bohunice) Czech Republic (Temelín) Germany (PNP project, Stade salt
works) China (project HTR-PM)
5NC2I workshop - September 2015 - BrusselsPaks
Beznau
Lessons learnt from feedback on nuclear cogeneration (3/5)• District heating, salt works, paper, pulp => production of hot
water or steam at low temp. (< 250°C) Steam bleeding from turbines + heat exchangers Primary circuit is separated from the heat grid by two « barriers » at
least (NPP steam generators & heat exchangers/boilers) Small amount of NPP thermal power diverted to cogen. (5~ 10%) No impact on NPP control
• Main safety concern: eliminate the risk of contamination of the delivered fluid Physical barriers => 3 at least (including fuel cladding) Pressure “barrier”=> Pheat grid > PNPP circuit
Control of the delivered fluid + isolation devices No specific licensing on existing installations (including recent safety
reassessments)
6NC2I workshop - September 2015 - Brussels
Lessons learnt from feedback on nuclear cogeneration (4/5)• Past projects with HTRs
Example of PNP-500 project for conversion of coal to syngas
7NC2I workshop - September 2015 - Brussels
Steam gasification of coalHydrogasification of lignite
Vessel
Powerproduction
Steam reformer inside nuclear island=> Process “integrated”into the plant
Lessons learnt from feedback on nuclear cogeneration (5/5)
• Past projects with HTRs (80’s) Paper projects Plant and process integration (take benefit of high temperature) Specific risks identified and studied:
Chemical reactions close to radiological barriers Risk of explosion Impact on plant standard parameters (pressure, coolant flow, power) Impact on plant control Potential for tritium contamination of the heat carrier fluid and the end
user product (ex. contamination of syngas.) R&D programs showed global feasibility (in the 80’s…) Licensing specificities have been discussed with safety authorities (ex.:
HTR-Modul in Germany)
8NC2I workshop - September 2015 - Brussels
Advantages of the HTR safety concept for cogeneration• Intrinsic resistance to external hazards
Naturally safe in case of loss of power supply Good mechanical stability of the core structure Confinement primarily ensured by the first barrier Simple heat removal circuit
• Low sensitivity to helium cooling transients High neutronic stability (favorable power feed-back coefficient) High thermal inertia of the core Helium properties limits the severity thermal shocks (compared with
water)
• Objective of limited releases in case of any hypothetic nuclear accident => reduced exclusion zone ( = plant site itself) safety distance imposed by the risks associated to the process
9NC2I workshop - September 2015 - Brussels
Foreseen cogeneration layouts
Heat (process steam) & electricity production for an industrial cluster
Energy storage (conversion to syngas)
G. Brinkmann –NED 1231 (1990)
Processsteam
Electricity
10NC2I workshop - September 2015 - Brussels
Condenser
Multipurpose installation: heat (steam, hot water) & electricity for an urban and industrial zone
NGNP - D. Petti
Clearly separated process => may ease the licensing
Recommendations for safety assessment and licensing (1/4)
11NC2I workshop - September 2015 - Brussels
• Principle: risks induced by the vicinity of industrial facilities shall not lessen significantly the nuclear plant safety
• Limitation of the extension of exclusion and low population zones ex.: no protection measures needed for the industry operators in the
vicinity of the plant <=> if needed, operators of industrial sites could continue to monitor processes in case of accident on the NPP
• Mastering of the impact of heat demand variations on the core and reactor structures loading
Recommendations for safety assessment and licensing (2/4)
• Risks induced by cogeneration and specific industrial environment should clearly appear in the safety documents List of man induced hazards to be completed
Standard licensing procedures already provide a good frame to cope with cogeneration specific risks
Specific aspects of the standard licensing procedure need extended evaluation/documentation
12NC2I workshop - September 2015 - Brussels
Recommendations for safety assessment and licensing (3/4)
13NC2I workshop - September 2015 - Brussels
• Assessment of the minimum distance between nuclear island and industrial site Consideration of generic hazards induced by the chemicals on the NPP
(plume effects, explosion, fire, toxic and corrosive effects, etc.) For hydrogen production:
consideration of chemical hazards of end products (oxygen) and intermediate products (HI, H2SO4)
Use of existing knowledge base to define standard criteria for safety distance
Consideration of potential domino effects for determining scenarios (potential for accident worsening)
Recommendations for safety assessment and licensing (4/4)
14NC2I workshop - September 2015 - Brussels
• Elimination of the risk of noticeable contamination of the delivered fluid (water, steam or helium) Demonstration of the performance of the barriers Demonstration of the performance of the protection based on fluid
quality monitoring and isolation devices between nuclear circuits and circuits crossing the fence of the nuclear site
• Residual risk to be evaluated in the environmental impact study to take into account potential doses incurred by the public through the use or ingestion of process end products
Definition of contamination limits (approach depending on domestic regulations)
Recall of « generic » licensing steps (1/2)
1) Set up of the safety objectives Working groups with Safety Authorities / Commissions
of experts First review by TSO
2) PSAR Risk analysis Definitions of design options Design criteria
ValidationSafety approachFeasibility
PreliminarySafetydemonstration
Interface withindustrial risks
Cogen. 15NC2I workshop - September 2015 - Brussels
Main parameters impacted by the
cogen. applications
Recall of « generic » licensing steps (2/2)
1) Site selection2) Public inquiry: Environmental impact study, risk
analysis (extract from Preliminary Safety Report), summary of advantages for the local region Review by local Authorities / security authorities Review by independent associations, etc.
3) SAR4) Construction and operation license: Safety
Report + Emergency Planning Safety analysis of the SAR, EP report Feedback of commissioning tests
SafetydemonstrationSecurity
Definition of specific external
hazards
Specific safetystudies
Interface withindustry EPs
Cogen. 16NC2I workshop - September 2015 - Brussels
Legal aspectsPublic acceptanceSite validation
Pending safety options
• Mastering of tritium permeation to secondary circuit => foreseen technical solutions to be validated
Note : objective would be that the tritium concentration in process steam remains below an “approval free” limit.
• Definition of an envelope safety case involving radioactive releases (ex.: depressurisation accident) Already covered as part of the standard licensing procedures Depends on confinement strategy and design
17NC2I workshop - September 2015 - Brussels
Outline
• HTR safety concept would certainly ease the licensing of an HTR based cogeneration plant
• Depending on its design options, HTR has a potential for very low radioactive releases in case of accident no interference with safety distance (determined against external
hazards)
No significant increase of the risk in the industrial site area or local public (district heating)
• Current licensing procedures are convenient for nuclear cogeneration with HTR provided some adaptations: consistency of nuclear and conventional emergency planning Regulatory basis for assessment of delivered fluid safety
18NC2I workshop - September 2015 - Brussels