EFIT PB Design and Preliminary ULOFss Analysis

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• EFIT (PB) - Design and Preliminary ULOF(ss)
  Analysis
• M. Schikorr, D. Struwe (FzK)
• EUROTRANS DM1 WP1.5 Safety
• Lyon , 10-11 October 2006

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Topics

• Design Criteria for EFIT (Pb)
• 2. EFIT (Pb) design Data for Transient Analysis
• 3. Some EFIT (Pb) results to the ULOF transient

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1. Some important thermohydraulic EFIT Design
Criteria

• 1. Use MgO as fuel matrix for the MA-based fuel
• Assure an optimal MA burning rate
• Operate the system as a sub-critical system
  (k_eff 0.95 - 0.97)
• Account for the relatively low fuel temperatures
  allowable
• T_fuel_max lt 1600 C
• 5. Also use T91 as clad material (as of now).
• 6. Design core and primary system in such a
  manner to allow sufficient natural convection
  flow rate to survive a ULOF transient for at
  least 30 minutes without large number of pin
  failures (via gas blowout)

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EFIT ULOF Design Criteria requires
Assure a sufficiently large natural convection
flow rate ( gt 25 nominal flow) under ULOF
conditions. This implies 1. keep pressure drop
across the core low (lt 0.5 bar) by selecting
an appropriate fuel pin / subassembly
design 2. minimize pressure losses throughout
the primary / DHRS system such that total system
pressure loss lt 0.8 bar 3. assure a height
differential between the core midplane and the
heat sink midplane of 3.7 m
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Several EFIT design iterations were performed

• Option 1
• Assume a constant fuel matrix (i.e. 50 MgO) and
  vary the fuel pin / sub-assembly design in the
  two core zones in order to flatten the power
  profile.
• Several variations in pin diameters and
  sub-assembly sizes were tried but it was
  difficult to achieve a satisfactory radial power
  distribution without excessive radial form
  factors.
• Option 2
• Assume a uniform geometric pin / SA design for
  the two core zones but vary the fuel matrix
  composition.
• ENEA / ANSALDO decided for Option 2 with the
  following design

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EFIT (Pb) Design Data used Inner Core Zone CZ1,
Fuel 62.5 MgO
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EFIT (Pb) Design Data used Outer Core Zone CZ2,
Fuel 50 MgO
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EFIT (Pb) Fuel Design Inner and Outer Core
Zones
Source D1.6 Draft Sept.2006
Source D1.6 Draft Sept.2006
Source V. Sobolev Sep. 2006
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EFIT (Pb) Data Inner Core Zone CZ1
EFIT (Pb) Data Outer Core Zone CZ2
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Nominal Conditions Inner Core Zone at BOC EFIT
(Pb)
Source D1.6 Draft Sept.2006
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Nominal Conditions Outer Core Zone at BOC EFIT
(Pb)
Source D1.6 Draft Sept.2006
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Nominal Conditions Inner Core Zone at EOL EFIT
(Pb)
Note that peak clad temperatures exceed 500 C
requiring coating of the T91 clad material.
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Nominal Conditions Outer Core Zone at EOL EFIT
(Pb)
Note that peak clad temperatures exceed 500 C
requiring coating of the T91 clad
material. There is not much margin to the
temperature limit of coated T91 of 550 C !!
Note Hot spot analysis still pending
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• ULOF (ss) Inner / Outer Core Zone at BOC and EOL

• Natural Convection flow rate of EFIT under ULOFss
  conditions 43 !!
• (much higher than the 25 for XT-ADS)
• This leads to lower T91 cladding temperatures ( lt
  700 C ) for EFIT (Pb) in comparison to XT-ADS
  ULOFss temperatures ( 790 800 C )

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ULOF (ss) Inner / Outer Core Zone at BOC
Pgas 10 bar
Pgas 10 bar
Clad failure not an issue at these clad temps.
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ULOF (ss) Inner / Outer Core Zone at EOL
Pgas 178 bar tent.
Pgas 178 bar tent.
Clad failure not an issue at these clad temps.
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Conclusions on current EFIT (Pb) TH design
(1/2)

• 1.) From the TH point of view the current
  EFIT(PB) design as proposed by ENEA / ANSALDO is
  quite viable assuming the cladding is coated as
  clad temperatures exceed 500 C under nominal
  conditions.
• 2.) The calculations thus far have not assumed a
  form factor to account for the peak pin within
  the hottest subassembly (f_peak_pin should be
  1.04 instead of 1.0 as has been assumed). This
  will lead to even higher cladding temperatues of
  the peak pin, possibly in excess of 550 C.

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Conclusions on current EFIT (Pb) TH - design
(2/2)

• 3.) Under ULOF steady state conditions at EOL
  clad failure times are in excess of 1000 hrs as
  clad temperatures remain below 700 C
• MgO fuel temperatures also remain below 1430 C
  ( a limit of 1500 C was decided not to be
  exceeded )
• 4.) The design exhibits excellent natural
  convection characterisitics with w_nat 45
  under ULOF conditions ( low pressure losses lt 500
  mbar )
• 5.) The ULOF transient behavior of the design
  still needs to be analysed in detail