# Presentation: 274535

## Activation Issues for ANU

- Peter Kasper
- 17-Sep-2007

## Investigating the impact of tunnel activation at MI-14 and MI-39 on the ANU work

- Penetrations are planned to be installed during the 2008 shutdown
- The locations correspond to “hot spots” in the tunnel
- How do we deal with this?
- Lead blankets: Low impact but limited efficacy
- Removing magnets: High impact on cost, time, and operations

## First Step: Find out what we are dealing with

- Weekly radiation measurements in order to characterize cool down rates
- How much can we gain by waiting for things to cool down?
- Answer: Very little.
- Map the radiation fields in the relevant areas
- How local are the hotspots?
- Can lead blankets be usefully deployed?
- What is the average dose rate that a laborer might expect?

## Cooldown Measurements:

- Measurements taken with LSM at upstream end of all elements ...
- From 104-0 to 107-2
- From 400-0 to 405-2
- All readings are at 1 ft.
- Work areas are concentrated between ..
- 104-0 and 105-0
- 401-0 and 402-0
- These are the hottest parts of the tunnel
- Activated ion pump magnet RR 105-1 gave
- 0.18 mr  from Mn54 (312 days) and Co58 (71 days)

##  After 35 days most elements measured had cooled by ~2/3 (consistent with measurements on ion pump magnets)
 Larger reductions observed downstream of LAM-2 (downstream of the work area

-  Larger reductions observed downstream of LAM-2 (downstream of the work area

## Mapping the radiation:

- Measurements taken on a 1 ft-sq. grid
- 70 ft long section of tunnel at each work site
- 6 measurements between the inner wall and the beamline elements
- Measurements take ~2.5 hours (where is Tomlin’s robot when you need it?)
- Average dose rates obtained by averaging over all points within ~5 ft. of the major penetrations
- MI-14:  16.4 mrem/hr
- MI-39:    7.6 mrem/hr

## MI-14

**MI-14**

**MI-39**

- Location of big penetrations

- Location of big penetrations

**Max.**
**100 mr/hr**

**Max.**
**69 mr/hr**

## Work Steps:

- Excavation and installation of grillage
-  Drill pilot holes
- Cut penetration holes
- Install PVC penetrations
- Construct forms
- Pour and cure concrete
- Remove forms
- Clean up tunnel
- Backfill etc.

- Work Days
- 12
- 3*
- 8 (2*)
- 1 (1*)
- 2 (1*)
- 1
- 1
- 2*
- 40
- *In tunnel

## Tunnel occupancy:-

- 9 days spread over 18 work days ( = 3.6 weeks )
- Assume 1 tunnel day = 5 hours
- Assume time is evenly divided between the two sites
- Total dose
-  **539** mrem		(Quarterly limit: **300** mrem)
-  **150** mrem/week	(Weekly limit: **100** mrem)
-  **60** mrem/day	(Daily limit: **40** mrem)

## Repeat measurements in MI-10 with Pb blankets on 104-1 and 104-2, including gap between them

## New measurements :-

- Used the same 1 ft grid as the original
- Incomplete coverage
- 0 - 55 ft for new measurements (0 - 70 ft for original)
- Plots fill missing 15 ft with old measurements
- Taken ~10 days after the original
- New measurements scaled by 1/0.87 to account for extra cool down
- Factor chosen to obtain agreement over the last 5 ft
- Consistent  with measured cool down rate
- Thin point in the Pb coverage at the gap center

## Before

**Before**

**After**
**Cool down**
**corrected**

- Location of big penetrations

- Location of big penetrations

**Max.**
**100 mr/hr**

**35 mr/hr**
**Max.**
**44 mr/hr**

- Not remeasured

## Before - after

**Before - after**

- Location of big penetrations

- Location of big penetrations

**Max.**
**65 mr/hr**

- Not remeasured

- Not remeasured

**Before / after**

## Tunnel occupancy:-

- 9 days spread over 18 work days ( = 3.6 weeks )
- Assume 1 tunnel day = 5 hours
- Assume time is evenly divided between the two sites
- Total dose with Pb as installed
-  **357** mrem		(Quarterly limit: **300** mrem)
-  **99** mrem/week	(Weekly limit: **100** mrem)
-  **40** mrem/day	(Daily limit: **40** mrem)

## Comments

- Pb blankets gave significant dose reductions
- Implies that magnets are the dominant source
- A more extensive installation would easily provide the necessary dose reduction
- Already close to acceptable as installed
- Eliminate thin point at gap
- Cover the entire work area in both enclosures
- Increasing thickness gives marginal improvement

## Caveats

- Cool down correction
- Measurements were done after 35 days cool down
- Rates go up by 20% for a 12 day cool down
- Have assumed the same workers throughout
- Dividing the tasks among different individuals will reduce the totals even further
- Must not allow the tunnels to get significantly hotter