Chiovaro, P.

Ciattaglia, S.

Cismondi, F.

Del Nevo, A.

Federici, G.

Moscato, I.

Spagnuolo, G.A.

Vallone, E.

English

Spagnuolo, G. A.

KITopen

Assessment of the Dose Rates due to Water Activation on an Isolation Valve of the DEMO WCLL Breeding Blanket Primary Heat Transfer SystemABSTRACTWithin the framework of the activities foreseen by the EUROfusion action on the cooling water activation assessment for a DEMO reactor equipped with a Water Cooled Lithium Lead Breeding Blanket (WCLL BB), theUniversity of Palermo is involved in the investigation of the absorbed dose induced by the decay of nitrogen radioisotopes produced by water activation, in the main components (e.g. isolation valves) of both First Wall(FW) and Breeder Zone (BZ) cooling circuits.The aim of this work is to assess the spatial distribution of the absorbed dose in the DEMO Upper Pipe Chase (UPC), focusing the attention on the space neighbouring a typical isolation valve of the Primary Heat TransferSystem (PHTS). To this end, a computational approach has been followed adopting MCNP5 Monte Carlo code. In particular, a totally heterogeneous neutronic model of a portion of the UPC has been set up, including thevalve and the main FW and BZ PHTS piping, and the spatial distribution of nitrogen isotopes concentrations, previously assessed, have been used to model the photonic and neutronic sources.The results obtained, herewith presented and critically discussed, provided some information on the nuclear issues of the WCLL BB PHTS, to be considered as hints for the blanket design optimization.P. Chiovaroa*, S. Ciattagliab, F. Cismondib, A. Del Nevoc P.A. Di Maioa, G. Federicib, I. Moscatoa, G.A. Spagnuolod, E. ValloneaaDepartment of Engineering, University of Palermo, ItalybEUROfusion Consortium, Boltzmannstr.2, Garching, 85748, Germanyc ENEA C.R. Brasimone, I-40032 Camugnano (BO), Italyd Karlsruhe Institute for Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, GermanyCONCLUSIONSWithin the framework of EUROfusion action, at the University of Palermo a research campaign has been performed in order to assess the dose absorbed in some key components of the WCLL BB PHTS in the DEMOreactor. The results obtained show, as expected, that the main contribution to the absorbed dose by matter in the UPC comes from the photons emitted by the 16N decay and that, on the other hand, the estimated 17N activityleads to consider specific analysis for the evaluation the extent of neutron activation in the pipes.Furthermore, these outcome lead to a further development of the present research activity aimed at developing PHTS design changes in order to lower the dose absorbed by the valve. In particular, the peculiarities of thespatial distribution of dose found suggest some simple modifications such as the use of bulkheads to shield the valve and/or change the lay-out of the pipes and/or develop more rad-resistant material for specific cases.RESULTSDetailed 3D photonic and neutronic analyses have been carried out for the assessment of the dose nearby FW and BZ cooling circuit key-points, due to γ radiation from 16N and neutron emission from 17N.A period of 7 FPY has been considered as it is assumed to be the expected life of the breeding blanket of DEMO taking into account an availability factor of ~33%. A steady state scenario has been taken into accountconsidering the plasma flat-top phase of the reactor.INTRODUCTIONWithin the framework of the activities foreseen by EUROfusion action on the“Cooling water activation assessment”, the University of Palermo is involved in thedose assessment around both First Wall (FW) and Breeder Zone (BZ) coolingcircuits (e.g. isolation valves, hot and cold legs) of the DEMO reactor equipped witha Water Cooled Lithium Lead Breeding Blanket (WCLL BB). The aim of thisresearch activity is to assess the spatial distribution of the absorbed dose, due to thedecay of nitrogen isotopes produced by coolant activation, around some keycomponents of WCLL BB cooling circuit, focusing the attention on the Primary HeatTransfer System (PHTS), in the Upper Pipe Chase (UPC) of the reactor.UPPER PIPE CHASESTEAM GENERATORFW AND BZ RINGSHEAT EXCHANGER ACTUATORNODE 16N 17NHot Feeding Pipe 4.893E+02 5.132E-02Hot Ring 2.089E+03 1.903E-01Hot Leg 9.368E+02 8.316E-02Cold Leg 1.683E+02 4.425E-03Cold Ring 3.488E+02 8.937E-03Cold Feeding Pipe 5.826E+01 1.466E-03Valve 6.973E+01 7.313E-03NODE 16N 17NHot Feeding Pipe 2.718E+02 3.093E-02Hot Ring 6.941E+02 6.781E-02Hot Leg 1.484E+02 1.163E-02Cold Leg 9.741E+01 5.664E-03Cold Ring 3.261E+02 1.845E-02Cold Feeding Pipe 8.526E+01 4.717E-03Table 1. Nitrogen activity in the FW circuit [GBq].Table 2. Nitrogen activity in the BW circuit [GBq].BZ HOT RINGBZ COLD RINGFW HOT RINGFW COLD RINGBZ COLD LEGFW HOT LEGFW COLD LEGFW & BZ FEEDING PIPESVALVEFig. 2. Isometric view of the UPC slice.Fig. 3. Sections of the MCNP model of the UPC: a)Toroidal-Radial section; b)Poloidal-Radial section.Fig. 1. View of DEMO PHTS in the UPC.INPUT DATA AND MODELThe WCLL BB PHTS foresees 2 parallel and distinct cooling circuits for FW and BZ. Attention has been focused on the PHTS pipingarranged in the UPC where important devices as isolation valves could be located. The study has considered a slice of 22.5°,corresponding to one blanket sector, where it is possible to notice the borated heavy concrete walls, the AISI 316 LN pipes in whichthe radioactive water flows and a simplified model of a DN 150 gate valve.• Energy distributions of both 16N photons and 17Nneutrons biased taking into account their discretespectra with the related branching from eachenergy level• super-imposed mesh:(500 ×500 × 500) • uniform voxel size of 2.52 × 5.56 × 1.86 cm3Photonic Dose [MGy] Photonic Dose [MGy] Photonic Dose [MGy]Neutronic Dose [MGy] Neutronic Dose [MGy]Fig. 4. Absorbed γ dose spatial distribution in the UPC slice (left) and an enlarged detail (right)Fig. 7. Absorbed neutron dose spatial distribution in a UPC slice detail (left) and in the valve (right). γ dose assessment:• 1011 histories for photon transport• The full-scale of 2 MGyrepresents the reference value forthe qualified valves in NPP.• Some design modifications of theBB and/or the PHTS must beforeseen.Neutron dose assessment:• 6·1010 histories for neutrontransport• Dose due to neutron radiation isseveral order of magnitude lower• 17N activity deserves furtherneutron transport studies toevaluate the inventory ofactivation productsFig. 5. Absorbed γ dose spatial distribution in a UPC slice detail (left) and in the valve (right).Fig. 6. Absorbed neutron dose spatial distribution in the UPC slice (left) and an enlarged detail (right).

Assessment of the Dose Rates due to Water Activation on an Isolation Valve of the DEMO WCLL Breeding Blanket Primary Heat Transfer System

https://publikationen.bibliothek.kit.edu/1000092113/40776892

Assessment of the Dose Rates due to Water Activation on an Isolation Valve of the DEMO WCLL Breeding Blanket Primary Heat Transfer System

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