# Presentation: 518526

*Target Hall Shielding Review*
- Radiation Safety Coordinator
*Nancy Grossman*
*FNAL*
- July 27, 2001

## Outline

- Review Process
- Access
- Prompt Radiation
- Groundwater Protection
- Air Activation
- Residual Dose Rates

## Review Process

- 1.	Presentations to NuMI Radiation Safety Advisory Committee (NRSAC)
- Beams Division and ES&H personnel
- Initial validation of calculation methods & Target Hall, Decay Region and Hadron Absorber “preliminary” shielding (7/99)
- Civil construction parameters addressed appropriately
- Final groundwater methodology presentation (7/00)
- Future presentations: Hadron Absorber shielding and the residual rate estimation methodology
- 2. “Preliminary Radiation Shielding Assessment” to Beams Division Radiation Safety for “Civil” review  (10/99)**
- Consensus to start civil construction in 1/00.
- 3. “Radiation Shielding Assessment” to Beams Division Radiation Safety for review and approval**
*Reiterate shielding calculations as necessary when engineering designs are nearly complete, *
*NuMI “Internal” Reviews*
*Include residual rate estimates, hot job procedures*
*Must do before going to the FNAL Senior Radiation Safety Officer (SRSO) for review and approval*
- 4. “Radiation Shielding Assessment” to SRSO for review and approval** (before operation commences)
- Sign as built drawings
- ** required

## Access

- _NuMI Beam, No Access_:
- Carrier Tunnel, Pre-Target, Target Hall, Decay Tunnel, Hadron Absorber Cavern, Muon Alcoves
- _NuMI Beam Access:_
- Base of Target Hall Shaft
- Power Supply & RAW Rooms
- RAW Room may have locked door.
- Bypass tunnel to some extent (determine final gate location when run and do measurements)
- MINOS Cavern
- _MI Beam NuMI Access_:
- Everywhere but the Carrier Tunnel (and upstream)
- Carrier Tunnel will have a Captured Key (or similar) door.

## Access

## Prompt Radiation

- Labyrinth and penetration exit dose rates :
- Labyrinth source terms where bulk shielding is present (dark blue text) are not well known (factor of ~10)
- MARS simulation of the Target Pile has at least 1 foot less steel on all sides than the present design (yellow shading)
*Preliminary MARS14 simulation of the present Target Pile shield design is nearly complete*
*MARS14 can more accurately determine the source terms outside of thick shielding (factor of 5)*

## Groundwater Protection

- Hired several groundwater consultants to determine water levels and flow rates around the _unlined_ regions of the NuMI tunnel.
- All water within 10’ of tunnel flows into the tunnel
- 	(within the aquifer region)
- Most water flows in rapidly through the fractures
- Determine an average inflow velocity based on groundwater consultant’s inflow estimates
- Use the Fermilab Concentration Model, modified to allow for water flow
- Fermilab Reports TM1851, TM2092, TM2009 (NuMI).
- Updated to include our latest understanding of groundwater contamination by 22Na and 3H, the only radionuclides of concern (NuMI-B-495)
- Flow dependent residency time of water in the region of the beamline (inflow or outflow) where applicable.
- Irradiation time = residency time of the water in the activation region (not 8 years, lifetime of experiment)
- Normal operation:  time water is in the activation region
- Accident condition: 1 pulse (1.9 sec repetition rate)

## Groundwater Protection

- Must be below the regulatory limit including uncertainties (FNAL, IEPA)
- Use uncertainties in _all_ parameters to determine overall uncertainty
- Determine effect on results and add in quadrature
- Conservative:
- Comparing concentrations in inflow water, which will be pumped to the surface to groundwater limits
- In “dry” regions, grout less to allow more inflow
- Model includes worst case conditions, most likely will not encounter
- Does not include decay during migration to a well
- Water along the unlined beamline tunnel can not get to any well other than the NuMI beamline “well”
- Does not include dilution & dispersion in transit to a well
- Monitoring well(s) will be used to monitor contamination (22Na and 3H concentrations)
- Update flow model to incorporate inflow measurements and geotechnical data obtained during construction
- Ready to start this process when grouting complete

## Groundwater Protection: Secondary Beam

- (Hadron Absorber values need to be updated for the present cavern and Hadron Absorber design.)

## Airborne Activation

- Radioactive Air calculations are being revisited with the present detailed Target Hall design.
- Site-wide permit submitted including NuMI operations in 3/99
- Goal for NuMI is < 45 Ci/year:
- ~0.025 mrem/year (1/4 continuous monitoring limit)
- Previous NuMI estimates were ~40 Ci/year
- Majority of the air activation occurs inside the Target Pile
**Closed system (air recirculated within the target pile).**
**Preliminary calculations based on re-circulation: **
**@ 2250 cfm ventilation, leakage @1500 cfm-> ~20 Ci/year**
- Have a variable rate ventilation system from the Target Hall to the decay vent (2 speeds).
- _Measurements of air activation_ will be made early on and the ventilation rate can be adjusted (and the target pile can be better sealed if necessary)

## Residual Activation

**APO Residual rates (at most 20 mrem/hr on top of steel modules, below concrete)**
- Want similar rates in NuMI Target hall
- NuMI beam is an order 10X that at AP0, thus want about a factor of 10 more shielding
- 6’ of steel in the modules at AP0, want 7’ for NuMI
- Minimize crack sizes and line of sight to “beam” area
- Use sand/poly (10%) bead bags to fill in large cracks/holes where possible
- Make sure not compromise mechanical aspects of design in the process

## Residual Activation

**Irradiated samples above and below the steel modules at AP0 to investigate:**
- Residual rates versus MARS predictions (in and outside thick shielding).
- Isotope production in the materials we plan to use in the Target Pile ( Al, concrete and various kinds of steel) - especially short-lived.
- Cooling curves for the above samples.
- Neutron Fluxes above and below the modules and inside  2” and 6” thick poly cubes above the modules
- MARS predictions of neutron fluxes vs. measurements.
**Updated residual code was added to MARS13 -> MARS14**
- Can calculate residual activation levels for 3 different energy regimes (including thermal neutrons).
- Can calculate residual activation levels for wide range of irradiation and cool down times.

## Residual Activation

_**Preliminary Results:**_
- Residual rates versus MARS14 predictions (in and outside thick shielding).
- Inside and outside thick shielding agreement is within a factor of 2 to 5. (MARS overestimates in nearly all case)
- Agreement outside thick shielding was very good after 1 day cool down (MARS lacking in simulation of short-lived radionuclides).
- Isotope production in the materials we plan to use in the Target Pile ( Al, concrete and various kinds of steel) - especially short-lived.
- No unexpected isotopes were seen and no unusual levels were scene.
- Cooling curves for the above samples.
- Have cooling curves from the horn aluminum, structural steel, the 1018  steel and one type concrete.

## Residual Activation

_**Preliminary Results:**_
- Concrete activation levels can vary by up to a factor of 50, depending on the amount of sodium in the concrete.
- Residual dose rates varied from 0.03 mrem/hr to 1.7 mrem/hr (trace to 1.7% by weight 23Na, respectively).
- Neutron Fluxes above and below the modules
- Relatively good agreement
- 90% of neutrons below the steel had energy less than 10 MeV.
- Majority  of the neutron flux above the steel was from backscatter off the concrete cap.
- Plan to look at the effect of the cracks at AP0 on residual rates (run with and without cracks)

## MARS: Horn 1, Module, T-Blocks, Cracks

## MARS: Horn 1 Module with T Blocks & Cracks

## MARS: Horn 1

## MARS: Horn 1 Module Z Side Slice

## MARS: Horn 1 Module/T Blocks Cross Section

## MARS14: Target Chase & Residual Dose Rates

## Residual Rate Distributions

**Top Curve: inner side of bottom set of steel blocks in chase**
**Shaded Curve: bottom of T- Blocks**
**Bottom Curve: inner side of top steel blocks in chase**

## Residual Activation 

- MARS Residuals: 30 days irradiation, 1 day cool down (@2E13protons/sec)

## Summary/ Conclusions

- Prompt rates:
- Reasonable, but need to be revisited with updated with target hall shield design & MARS14.
- Groundwater Protection:
- Activation levels are ~2.5 below limit with present target hall shield design.
- Air Activation:
- Current estimates on how well need to seal target pile are reasonable.
- Need to revisit with update target hall shield design with cracks and penetrations (probably very little effect).
- Residual Dose Rates:
- So far so good.
- Need to complete updated numbers with stripline penetration,( air handling penetrations?)