Dose Equivalent Xenon replaces 100/E-bar

Steve Sandike, Entergy, Indian Point Energy Center June, 2008

History

100/Ebar was originally applied as a Technical Specifications source term limitation for reactor coolant, along with Dose Equiv Iodine.

With NUREG 1430-1432, Improved Tech Specs, included better definitions of Dose Equiv Iodine, and to some degree, 100/E-bar.

But there were still many issues with “Ebar”.

Original Purpose or 100/E-bar, PWR A Reactor Coolant source term limitation designed to

ensure the Site Boundary dose from a postulated SG Tube Rupture or Main Steam Line break accident remains

“a small fraction of the 10 CFR 100 limits”

DEI addressed the “critical organ”, CDE, or TODE concern, specifically, the Thyroid dose.

100/Ebar was supposed to address the whole body, CEDE or DDE concern (at first, with just noble gas)

Why Update to Alternate Source Term?

10CFR100 involved WB and Thyroid Dose (25 & 300 rem) from PRE-ICRP concepts of dose.

Part 100 was NOT updated with new part 20 (TEDE, CEDE, CDE) in early 1990s.

Tough to use new terms with Part 100.

A small portion of TEDE

10CFR50.67 just uses 25 rem TEDE.

“Operating a unit at the allowable limits could result in a 2-hour exclusion area boundary of a small fraction (i.e. 10%) of the 10CFR67 limits…”

10CFR50.67 and Control Room Dose

Along with the 25 rem requirement, 10CFR50.67 also involved control room dose considerations.

Size and flow rate through charcoal became a Tech Spec engineering function.

For Control Room Watchstanders, dose during an accident was limited to

5 REM TEDE.

NUREG 1430/1431/1432 (ITS)

B&W, CE, and Westinghouse Improved Technical Specifications (1998-2002)

Enhanced definitions of DEI and 100/Ebar in Stnd Tech Specs, including options for AST.

Included a short list of approved DEI coefficients

More detail and background data for E-bar, and unit-specific N/Ebar limitations.

New Tech Spec improvements for Dose Equivalent Iodine

Allowed source of coefficients were initially the same lists: TID 14844, RG 1.109, ICRP 30, etc.

The standard soon became Table 2.1 of EPA Federal Guidance Report (FGR) #11.

Either way, it was a clear requirement to be consistent with the applicable FSAR dose consequence analyses.

100/Ebar issues with NUREG 1431

Ebar is “the sum of avg beta & gamma energies of the isotopes in RCS…making up >95% …”

Tech Spec definition in NUREG 1431 does NOT stipulate that a gamma ray analysis is the source of this determination. So do we include H-3? Of course, it’s 99% of the activity!!!

Do we wait 6 weeks for Sr-90, Ni-63, Fe-55, and C-14 analyses? Why are we doing this???

The original USAGE of E-bar

Divide it in to a constant, yielding a uCi/gm Each licensee could change the constant (100)Establish this uCi/gm, obtained at the correct

time, for an RCS activity limit, good for 6 months.

Every week, compare Gross Specific Activity (GSA, one of the most enigmatic terms you will ever find), with the stored limit, N/Ebar.

Problem

If beta analyses are used for Ebar, then they need to be included in the resultant periodic surveillance for which 100/Ebar is to be applied!

Tech Spec BASES (NUREG 1431)

The basis section of the specs discussing the weekly surveillance clearly indicates that two combined gamma analyses are to be conducted to satisfy the requirement that Reactor Coolant “gross specific activity” is less than 100/Ebar.

This was NOT reflected in the definition section under EBAR, which does not stipulate WHICH isotopes are of concern. It DOES, however, say something about making up 95% of the total.

Two choices:

1) Use ALL (“greater than 95%”) isotopes for BOTH the Ebar and RCS surveillance test.

- or -

2) Use isotopes identified in the tandem gas and stripped-gas liquid sample identified in GAMMA RAY spectroscopy for BOTH the coolant Ebar determination AND the RCS surveillance test.

(A mixed combination of these cannot be correct,

DESPITE Tech Spec Instruction to do so!)

Temporary FixThe inclusion of H-3, with its low energy, will drive 100/Ebar very high (non-conservative).

To comply with current Tech Spec regulation, and to ensure a more accurate assessment of source term, you can employ a second limit for 100/Ebar, that uses gamma analyses only (still looking at both beta and gamma energies), but does NOT include isotopes that are NOT involved in determination of the weekly GSA.

It is a mistake to assume the inclusion of Beta emitters

in the EBAR calculation is a conservative move.

From 2001 slide:

100/Ebar Questions for Follow Up

Is it time to re-evaluate and determine a more valid source term limitation?

All BWRs seem to have deleted the 100/Ebar requirement (mostly from guidance from GE). It seems Noble Gas site boundary dose limits would still require a limited source term.

Dose Equivalent Xenon has been suggested.

Tech Spec Task Force (TSTF-490): for B&W, Westinghouse, CW PWRs,

NUREGs 1430, 1431, 1432 Federal Register – described problem, solution

http://edocket.access.gpo.gov/2006/06-9330.htm

Consolidated Line Item Improvement Process (CLIIP) issued Mar, 2000.

TSTF-490 issued Sep, 2005.

The NRC Staff bases for DEX

Originally, used RG 1.195, assuming large release of COOLANT, not necessarily the typical PWR DBA, because fuel damage and coolant releases needed to be involved.

With alternate source term, used NUREG -0800, and RG 1.183, “Alternate Rad Source Terms or Evaluating DBA…”

New Dose Equiv Xenon (DEX)

Defined as:

“That concentration of Xe-133 (uCi/gm) that alone would produce the same acute dose to the whole body as the combined activities of noble gas nuclides Kr-85m, Kr-85, Kr-87, Kr-88, Xe-131m, Xe-133m, Xe-133, Xe-135m, Xe-135, and Xe-138 actually present.”

Requirements for DEX

Must use MDA if not present (just like the new requirement for DEI)

Notice Ar-41 is not listed.

Limited list of approved coefficients

DEX coefficients

Options are fewer and MUCH more clearNo confusion with regard to CDE / CEDEDEX is clearly CEDE.Coefficients from:

1) average gamma energies, (ICRP-38) or 2) dose factors from Table III.1 of EPA FGR #12, “External Exposure to Radionuclides in air, water, soil”

(AKA, ICRP #30)

Tech Spec Task Force verbiage

“The change incorporating the newly defined quantity DEX is acceptable from a radiological dose perspective since it will result in an LCO that more closely relates the non-iodine RCS activity limits to the dose consequence analyses which form their bases.”

Incumbent on the Licensee…

… to ensure that the dose conversion factors used in the determination of DEI and DEX are consistent with those of the applicable dose consequence analysis.

Since this is stated about 6 times, it’s probably something we should ensure!

Licensee Action

Send letter to NRC regarding proposed changes to Tech Specs to use DEX

Quote TSTF 490Include assessment of changes, technical

analysis, regulatory analysis, and references.Determine your site-specific DEX limit.

Calculate unit-specific DEX limit

FSARCEDE DCF per FGR 12 DE Xe-133

uCi / gm rem m3 / Ci sec Conc * DF uCi / gm

Kr-85m 1.85 2.768E-02 5.121E-08 8.872E+00

Kr-85 13.6 4.403E-04 5.988E-09 1.037E+00

Kr-87 1.22 1.524E-01 1.859E-07 3.221E+01

Kr-88 3.49 3.774E-01 1.317E-06 2.282E+02

Xe-131m 3.18 1.439E-03 4.576E-09 7.928E-01

Xe-133m 3.61 5.069E-03 1.830E-08 3.170E+00

Xe-133 257 5.772E-03 1.483E-06 2.570E+02

Xe-135m 0.555 7.548E-02 4.189E-08 7.258E+00

Xe-135 8.94 4.403E-02 3.936E-07 6.820E+01

Xe-138 0.694 2.135E-01 1.482E-07 2.567E+01

6.324E+02

Proceduralize Coefficients

FSARCEDE DCF per FGR 12 Coefficients

uCi / gm rem m3 / Ci sec For Procedure

Kr-85m 1.85 2.768E-02 4.796

Kr-85 13.6 4.403E-04 0.076

Kr-87 1.22 1.524E-01 26.403

Kr-88 3.49 3.774E-01 65.385

Xe-131m 3.18 1.439E-03 0.249

Xe-133m 3.61 5.069E-03 0.878

Xe-133 257 5.772E-03 1.000

Xe-135m 0.555 7.548E-02 13.077

Xe-135 8.94 4.403E-02 7.628

Xe-138 0.694 2.135E-01 36.989

Pushing through the Tech Spec update

Give a clean summary of derivation of the unit-specific limits to Licensing. Remember, these are UNIT specific, not necessarily site-specific.

Get Chem/Reactor Engineering/RP Senior Management on board for timely resolution.

Talk to those who have been hit with an LER or Tech Spec violation for Ebar.

New Tech Spec Conditions:A = Dose Equiv Iodine-131 not within limit, B = Dose Equiv Xenon-133 not within limitBOTH have a 48 hr LCO (much better!)

Condition C: DEI or DEX not within limits,

or DEI > 60 uCi/gm:

–Mode 3 in 6 hrs

–Mode 5 in 36 hrs

New Tech Spec Surveillances

NO MORE GROSS SPECIFIC ACTIVITY !NO MORE EBAR, or N/EBAR !Replaced with:

DEI Same as before, once per 14 days DEX Once per 7 days