Severe accident management measures for a generic German PWR. Part II: Small-break loss-of-coolant accident. (December 2018)

• Record Type: Journal Article
• Authors: Jobst, M.; Wilhelm, P.; Kozmenkov, Y.; Kliem, S.
• Is Part Of: Annals of nuclear energy. Volume 122(2018)
• Page Start: 280
• Page End: 296
• Publication Date: 2018-12
• Subjects: Severe accident analysis -- SBLOCA -- PWR -- Accident management measures; ACCU Accumulator -- AMM Accident management measure -- ATHLET(-CD) Analyse der Thermohydraulik von Lecks und Transienten/Analysis of thermal-hydraulics of leak and transients (with core degradation) -- CET Core exit temperature -- CL Cold leg -- DG Diesel generator -- ECC Emergency core cooling -- ECCS Emergency core cooling system -- EOP Emergency operating procedure -- FP Fission product -- GRS Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH -- HL Hot leg -- HPIS High pressure injection system -- LH Lower head -- LPIS Low pressure injection system -- LOCA Loss-of-coolant accident -- MCP Main coolant pump -- MPI Mobile pump injection -- PSD Primary side depressurization -- PWR Pressurized water reactor -- RCS Reactor cooling system -- RPV Reactor pressure vessel -- SAMG Severe accident management guidelines -- SBLOCA Small-break loss-of-coolant accident -- TWCMAX Maximum temperature at wall centre -- WASA-BOSS Weiterentwicklung und Anwendung von Severe Accident Codes – Bewertung und Optimierung von Störfallmaßnahmen (Further Development and Application of Severe Accident Codes – Assessment and Optimization of Accident Management Measures; Nuclear energy -- Periodicals; Nuclear engineering -- Periodicals; 621.4805
• DOI: 10.1016/j.anucene.2018.08.017
• Languages: English
• ISSNs: 0306-4549

Abstract

Highlights: Investigation of SBLOCA severe accident transient with ATHLET-CD code. Mobile pump injection to reactor coolant system under various core conditions. Assessment of mobile pump injection combined with primary side depressurization. Quantification of releases of fission products and hydrogen. Proposal of a preferred mobile pump injection strategy based on simulation results. Abstract: This series of two papers focuses on the analysis of severe accident management measures for a generic German PWR of type Konvoi. A nuclear power plant model based on the severe accident code ATHLET-CD was developed in order to assess the code applicability for simulation of accident scenarios with core degradation. It was applied for investigation of two main groups of accident scenarios: station blackout and small-break loss-of-coolant accidents. Part I presented the analyses of a station blackout accident. Part II is focused on the analysis of the plant response in case of a hypothetical small-break loss-of-coolant accident (SBLOCA with 50 cm 2 leak in cold leg of pressurizer loop). Due to failure of components of the emergency core cooling system and assumed unavailability of several preventive and mitigative accident management measures (AMM), the accident develops into a severe accident scenario with core melt and reactor pressure vessel failure. An alternative AMM, which is not implemented in German PWRs, is investigated in the current paper: late coolant injection to the primary circuit with a mobile equipment (bleed and feed with low pressure pump). The analysis is performed on the basis of ATHLET-CD simulations (code version Mod 3.0 Cycle A). Two injection points are investigated: injection to cold leg and injection to hot leg. As in SBLOCA scenarios the primary pressure might remain high that injection by low pressure systems is not effective, the influence of primary side depressurization (PSD) as additional AMM is investigated. The simulations show, that mobile pump injection significantly reduces the amount of the released fission products and hydrogen, if it is started within 75 min after the core exit temperature (CET) exceeded 400 °C. Without PSD, melting of the fuel can be prevented if the mobile pump is started immediately when CET > 650 °C, but release of fission products can only be prevented if early pump injection is combined with PSD. Cases with a delay of mobile pump injection in combination with a delay of PSD (e.g. due to temporary malfunction) are also investigated: until 50 min after CET > 400 °C a lower release of fission products and longer grace times to prevent melt relocation to the lower head are observed (compared to immediate PSD at CET > 400 °C).