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Radiation Safety-4.15.2020 Workshop Final
	ML20105A002
Person / Time
Site:	Nuclear Energy Institute
Issue date:	04/15/2020
From:	; Nuclear Energy Institute
To:	; Office of Nuclear Material Safety and Safeguards
	Kallan P
References
	Download: ML20105A002 (15)
	v • d • e

Spent Fuel Performance Margins:

Radiation Safety NEI/NRC Workshop April 15 and 16, 2020 Washington DC

Agenda Goal Dose Rates and Safety Dose at Site Boundary (V-1)

Compliance with Safety Requirements

Regulation and Guidance

Comments on Guidance

Occupational Exposure

The Consequences

Proposed Change to Guidance Documents (V-1)

Guidance on Modeling Details (V-2)

Discussions

Goal Discuss Radiological Safety Discuss proposed reviews and revisions of guidance documents, for the purpose of ensuring activities that have no radiological safety significance are eliminated.

Dose Rates and Safety Radiological Safety Demonstration

Dose Rates can be measured, and are measured

Acceptance Criteria (Dose Limits) are clear Demonstrating compliance with the safety requirements is done with measurements, informed by analyses Vast amount of dose experience for dry storage of spent fuel

more than 3000 systems loaded with dose rates taken and compliance demonstrated Main safety criteria

Public: 25 mrem/year at the site boundary, including contribution from casks and from the plant

Occupational: 5 rem/year for each person

Dose at the Site Boundary (V-1)

Dose at the Site Boundary depends on

Number of loaded casks (Site specific)

Type of casks (cask vendor specific)

Distance to Site Boundary (Site Specific)

Fuel loaded into the casks (Site Specific)

Compliance with Dose at the site boundary is responsibility of the site (the licensee)

Demonstrated by measurements that are informed by calculations

Compliance with Safety Criteria Two criteria to be satisfied:

Site boundary dose limits

Occupational exposure ALARA

Compliance with Safety Criteria Site Boundary Dose Rates Typically accomplished in the following steps:

Step 1:

Offsite dose calculations performed (typically by cask vendor) to demonstrate compliance (in calculational space)

Level of detail and sophistication can vary significantly depending on site conditions Step 2:

Calculations of dose rates on transfer cask and storage cask at locations specified in the CoC, consistent with Step 1 Step 3:

Licensee develops cask loading plans/procedures consistent with Steps 1 and 2

Compliance with Safety Criteria (cont.)

Site Boundary Dose Rates (cont.)

Step 4 (for each cask):

Transfer cask is loaded, measurements are taken

If limits are met, process continues to next step Step 5 (for each cask):

Storage casks are loaded, measurements are taken

If limits are met, cask is placed on ISFSI Step 6:

After all casks of a campaign are loaded, dose rates at the site boundary are reviewed to again confirm limits are met (formal compliance demonstration).

Compliance with Safety Criteria (cont.)

Regulation and Guidance From 10CFR72.236 (d) Radiation shielding and confinement features must be provided sufficient to meet the requirements in

§§72.104 and 72.106.

From NUREG 1536/(2215) Section 6.4 (with sections highlighted)

In general, the DSS shielding evaluation should provide reasonable assurance that the proposed design fulfills the following acceptance criteria:

1. The radiation shielding features of the proposed DSS are sufficient for it to meet the radiation dose requirements in 10 CFR 72.104 and 72.106(b). The applicant demonstrates this with:

a. A shielding analysis of the surrounding dose rates that contribute to occupational exposure and off-site doses at large distances (for a single storage and transfer cask with bounding fuel source terms at various cask locations), and

b. A shielding analysis of a single cask and a generic array of casks at large distances.

Compliance with Safety Criteria (cont.)

Comments on Guidance Calculated dose rates in the FSAR, around a single cask or from a cask array, provide NO indication if 72.104 regulatory requirements can be met or not for an ISFSI site, since this depends on site specific parameters

For a small ISFSI far away from the site boundary, limits can be easily met even if dose rates around a cask are comparatively high

But for a large ISFSI close to the site boundary, even casks with very low dose rates can be a challenge, and may require additional shielding (e.g. a berm)

Additionally, using BOUNDING source terms in the FSAR further increases the discrepancy between FSAR calculations and site-specific dose rates, which may result in erroneous conclusions drawn from the FSAR.

Compliance with Safety Criteria (cont.)

Occupational Exposure Crew dose (dose to the loading crew for loading a single cask) are presented in the FSAR NRC still expects update and maintenance of the FSAR information, for changes to the designs and/or content Licensees have their established RP and ALARA processes, further informed by industry experience, to plan and perform loading operations.

FSAR crew dose information does not provide any relevant information in that context.

The Consequences Including information in the FSAR triggers a cascade of activities, on the part of the vendor, NRC and licensee:

The FSAR needs to maintained essentially indefinitely

May also inform limits specified in the Technical Specifications

Forever subject to 72.48 review

Reviewed by NRC, generating a Safety Evaluation Report

Used and maintained by the licensee as the licensing basis Any change to a cask design or content, even very small, triggers this cascade This should not be necessary for something that is not used or needed to demonstrate safety

Information for Licensees The licensee needs to know that the system is capable of meeting the regulatory requirements

This needs to be known before the casks are loaded, i.e. before measurements can be taken to demonstrate safety.

This is achieved through site-specific site boundary dose analyses, taking into account all previously discussed site specific and cask parameters For additional verification, licensees may consult general industry experience, from the 3000+ cask loaded Dose rates reported in the FSAR play no role here

Proposed Change to Guidance (V-1)

In the FSAR, provide dose rates for a typical cask design with representative content, showing values on the surface and at various distances for a single cask. The associated analyses establish the methodology to determine site boundary dose

Parameters for those calculations should be clearly specified

Additionally, present qualitative discussions of the impact of any possible variations of those parameters on the results

Cask type, content, ISFSI size, distance to side boundary

Impact on dose rates (small, factor 2, factor 5, factor 10, .)

Occupational exposure evaluations are provided to demonstrate that worker dose can be reasonably controlled ALARA

Licensee RP and ALARA programs, informed by industry experience control worker dose, not the SAR SAR presentation of off-site dose and occupational exposure are to demonstrate ability to meet site limits, and not for demonstration of compliance with the regulations.

Guidance on Modeling Details (V-2)

Guidance specifies lots of expectations on modeling approaches and the corresponding levels of details, often characterized as a need to be appropriate or bounding.

Without any appropriate concept on what is appropriate, the expectation often defaults to bounding.

Example: consider dimensional tolerances in shielding analyses Higher levels of details and/or bounding modeling approaches substantially increase the modeling effort

See the The Consequences slide for additional discussions on the consequences of this Over 3,000 loaded systems provide measured data for comparison - typically 50%

lower than calculated.

Recommendation

Review and revise the guidance on modeling, taking into consideration the industry experience on dose rates from the radiation protection programs.

ML20105A002

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