HTR-PM Safety Requirement and Licensing Experience

Prof. Dr. LI Fu

INET, Tsinghua University, China

29 October 2014

7th International Topical Meeting on High Temperature Reactor Technology

- The modular HTR is advancing towards reality - 27-31 October 2014, Weihai, CHINA

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Contents

n  HTR-PM: High temperature reactor—pebble-bed module

n  1 Project background n  2 Safety requirement n  3 Licensing process n  4 Interested topics

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1 Project background

n  2001: Feasibility study was started n  2004: Standard design was started n  2006: Basic design was started n  April 2008: PSAR review was started n  Sept. 2009: PSAR review was finished n  Dec.9,2012: FCD of HTR-PM

n HTR-PM is scheduled to put into operation in the end of 2017

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1 Project background

n  HTR-PM: first commercial modular pebble bed HTR power plant, first of a kind n  Many challenges in system design and

component design n  Also many challenges for licensing

n  Current licensing requirement was developed mainly for/from LWR

n  Lack experience for licensee and licenser

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1 Project background

n  NNSA has many experiences on different type of plants n  LWR for Gen II n  VVER n  CANDU n  AP1000 n  EPR

n  HTR-10 experience

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2 Safety requirement

n  China have a systematic nuclear safety regulation system n  Laws, safety requirement (HAF), safety guide

(HAD) n  Most are based on IAEA safety series

n  Standards, norms n  Most are based on ASME, IEEE, IEC, …

n  China has most strict regulation system, combined newest requirements from different sources

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2 Safety requirement

n  Current requirement is generally applicable n  Especially in the level of laws, requirement,

guides n  This common understanding is reached between

licensing authority and designer n  Suitable standards and norms are selected

n  International ASME, IEEE, IEC, and equivalent national GB, EJ, NB …

n  Special: for helium property, pebble bed, ceramic internal, …, adopts KTA codes

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2 Safety requirement

n  Detailed requirement is specified in design criteria, 2004-2006 n  40 chapters , for different components and

systems n  Approved by NNSA

n  Guideline for review is developed, issued in 2008, including: n  probabilistic safety goal, PSA requirement,

VLPC, V&V, … n  The technical basis is …

Safety philosophy �

n  Technical basis for modular HTR n  High performance TRISO fuel n  High temperature core n  Self acting decay heat removal n  No severe accident

n  Possible weak points n  Less operation experience n  Some rumors/doubts for dust, metal fission

product, hot spot, … 9

Safety philosophy �

n  Safety function n  Same requirement as other types of NPP

n  Technically & Quantitatively n  Control of power, removal of decay heat, retain of

fission product

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Safety philosophy �

n  Safety function n  Philosophy in HTR-PM project is to reduce

licensing risk n  Same safety classification for pressure

boundary components n  Safety class for Engineered Safety

Features (RPS, isolation valves,…) n  Max fuel temperature criteria (nominal) vs.

mechanistic source term (behind) n Do no exceed the limit of 1620°C for

current design 11

Safety philosophy �

n  Safety function n  Philosophy in HTR-PM project is to reduce

licensing risk n  Early involvement of NNSA

n Design criteria n Review guidelines n Many review, dialogue, and

consultation activities n  HTR-10 licensing experiences in 1990s

n  & New requirement since then �12

Safety philosophy �

n  Safety goals n  Both deterministic goal & probabilistic goal n  Higher than before:

n  Gen IV ? n  Achievable

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3 Licensing process

n  Early involvement n  Design criteria, review guideline, …

n  Review of PSAR n  1.5 years, more than 100 reviewers involved

n  Dialogue & question sheet & answer sheet n  3 dialogue meetings, 8 topics reports and review

meetings, more than 2000 worksheets

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3 Licensing process

n  It was a hard work for designer and licensing authority

n  In Sep.2009, safety expert committee approved Preliminary Safety Evaluation Report

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4 Interested topics

n  Deterministic plus probability approach n  Quantitative safety goal

n  Realistic, achievable n  PSA: initiating events selection, design,

safety analysis, safety objective n  Function of VLPC n  V&V of safety software

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4 Interested topics

n  Deterministic plus probabilistic approach n  Deterministic requirement for DBA

n  Normal operation, AOO, DBA n  Special attention on LOFC, air ingress, water

ingress n  Criteria are given for NO, AOO, and DBA n  Analysis of ATWS are included in PSAR

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4 Interested topics

n  Deterministic plus probabilistic approach n  Probabilistic requirement:

n  PSA, reach the probabilistic safety goal n  Management of beyond design basis accident

n  BDBA, not Severe accident n  Additional report submitted, detailed analysis

of certain sequences n  Combined with PSA n  Mitigation measures were proposed

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4 Interested topics

n  Quantitative safety goal n  50mSv, 10-6/reactor year

n  Defined & required by NNSA n  Realistic, achievable

n  Technically no off-site emergency plan is needed: 50mSv, no need for evacuation

n  Verified by PSA n Result is much lower than 10-6

n  Within the scope of engineering judgment n  Instead of 10-8, 10-10,….

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4 Interested topics

n  PSA: n  Combined with initiating events selection,

design, safety analysis, safety objective n  Special chapter is SAR n  More analysis are required for external effect,

low power level and shutdown condition, for spent fuel storage

n  Directly gives out the probability of accident sequences and the release to environment

n  …

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4 Interested topics

n  Vented Low Pressure Containment (VLPC) n  Confinement? Containment? n  The term is not important, the function

requirement is key issue

n  Reality: reactor cavity, with discharging burst disc, with accident ventilation system

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4 Interested topics

n  Vented Low Pressure Containment (VLPC) n  According to function requirement

n  Supporting of safety System, Structure, Component (SSC), confinement of radioactive, reduction of radioactive release as low as reasonable achievable

n  Non-safety class of accident ventilation system n  According to dose result of primary circuit

break accident n  VLPC is defined, and accepted

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4 Interested topics

n  V&V of safety analysis software n  Widely used software n  V&V experience worldwide, including HTR-10 n  Check the code, check the manual n  Comparison calculation with other code systems n  More V&V calculation on HTR-10 data n  New experiment facilities

n  Pebble bed equivalent conductivity coefficient n  Graphite corrosion experiment n  Graphite dust n  …

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Conclusion remarks

n  Successful experience n  First Construct Permit for modular HTR n  Safety: Technically no off-site emergency plan is

needed n  Realistic experience

n  Same safety requirement n  Detailed design criteria in advance n  Guideline for review in advance n  Early involvement of licensing authority

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Conclusion remarks

n  Main issues addressed during licensing process, important issues: n  VLPC n  PSA plus quantitative safety goal n  Analysis and mitigation of BDBA, n  V&V, n  …

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Thanks for your attention !